Agrometeorological adaptation strategies to increasing climate variability and climate change

Agrometeorological adaptation strategies to increasing climate variability and climate change

Agricultural and Forest Meteorology 103 (2000) 167–184 Agrometeorological adaptation strategies to increasing climate variability and climate change ...

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Agricultural and Forest Meteorology 103 (2000) 167–184

Agrometeorological adaptation strategies to increasing climate variability and climate change M.J. Salinger a,∗ , C.J. Stigter b , H.P. Das c b

a National Institute of Water and Atmospheric Research, Auckland, New Zealand TTMI-Project, Department of Environmental Sciences, Wageningen University, Wageningen, Netherlands c Meteorological Office, Pune, India

Abstract This paper starts with summarizing the indications for climate change as they are reviewed in the most recent WMO global climate system reviews. There are indications in the paper for increasing climate variability in certain areas. Some of the principal causes of increasing climate variability and climate change (ICV & CC) are a mixture of external and internal factors to the climate system. Of changes over the past century, increases in greenhouse gases have probably been the most important cause of climate change. Continued warming of global climate is expected to occur if atmospheric greenhouse gases keep increasing, with global climate models projecting an increase in mean temperature by 1–3◦ C by 2100 a.d. Upon these general background trends interannual climate variability has operated. Volcanic eruptions that inject significant amounts of sulphate aerosols into the stratosphere cause a cooling of global climate in the order of 0.5◦ C for a period of 12–24 months. The ENSO (El Niño/Southern Osciallation) is the major cause of climate variability on seasonal to interannual time scales. Since 1976 El Niño episodes of the Southern Oscillation have increased in frequency, and become more extreme. There has yet been little analysis of short-term extreme events, such as high intensity rainfall, tropical storms, tornadoes, high winds, extreme temperatures and droughts to show if the frequency and intensity of these have changed. However, for some of these events in some areas an increase is occurring while in other areas no changes have currently occurred. Changes in extremes cause significant impacts on agriculture. Strategies to fight slower variations have already been widely proposed and require application. Agrometeorologists can assist the agricultural community in developing strategies to adapt to ICV & CC that should be validated on-farm for improved extension advisories, together with farmers. To enhance adaptation and promote sustainable development, strategic planning studies for assessment of natural resources, technological change and innovation are required to increase productivity, with sustainable economic growth that preserves finite natural resources. The ten most essential agricultural umbrella projects with agrometeorological priority components in the literature that either modify the consequences of ICV & CC and/or mitigate their causes have been selected. The Commission for Agricultural Meteorology has pledged to guide the implementation of projects that assist adaptation strategies to ICV & CC within the WMO Agrometeorological Programme. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Agrometeorological adaptation strategies; Agrometeorological advisories; Climate change; Climate variability; ENSO; Extreme events

1. Introduction



Corresponding author. Fax: +64-9-375-2051. E-mail address: [email protected] (M.J. Salinger)

Several years ago, from evidence summarized in WMO (1995) it could only be concluded that trends and anomalies could still largely be explained from

0168-1923/00/$ – see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S 0 1 6 8 - 1 9 2 3 ( 0 0 ) 0 0 1 1 0 - 6

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relatively short term fluctuations to the general circulation dynamics rather than from longer term trends. Parameters like snow cover variation or massive ice sheet surfaces gave no conclusive indications for departures from the range of natural variability. However, increases were observed in surface global temperatures during the 20th century, and significant interannual climate variability was observed in many regions of the globe (Salinger, 1994; Salinger et al., 1997). These were confirmed especially in tropical latitudes; from such events as the 1982/1983 and 1997/1998 El Niño events and the 1991 Mt. Pinatubo volcanic eruption (WMO, 1995, 1998). Recently WMO (1998) reported on warming trends, with proof for climate change and its continuation observed from Arctic and Antarctic sea ice, from later ice appearance days and earlier ice breakup days particularly in European Russia, the Ukraine and Baltic countries. Shrinking of mountain glaciers during the 20th century and the increase of permafrost temperatures in many areas also occurred. Agrometeorology provides significant methods and technologies to allow adaptation of food and fibre production to cope with increasing climate variability and climate change (ICV & CC). There is now better understanding of the climate system, and the natural and anthropogenic factors that have caused climate variability and change over the past century, and likely changes in climate and its variability during the 21st century (Salinger, 1994; Salinger et al., 1997, 1999). Although ICV & CC have significant impacts on agriculture, extreme climatic events can have dramatic effects on agriculture. It is changes in these, such as the hypothesized increase in high intensity rainfall (IPCC, 1996) that food and fibre producers will have to adapt to. Agrometeorological strategies are available to allow the ‘climate proofing’ of agriculture to ICV & CC. These methodologies are both traditional and new. It is these methodologies, promoted within the WMO Agrometeorological Programme, that will allow food and fibre producers to cope with current and adapt to future ICV & CC. This discussion paper summarizes knowledge on current ICV & CC, and examines regions vulnerable to climate extremes. Possible adaptation strategies are outlined for developed and developing nations as well as the challenges faced in different regions for the ‘climate-proofing’ of farming. The Commission for Agricultural Meteorology

(CAgM) wants to play a crucial role in assisting farmers, particularly in developing countries, through national meteorological and hydrological services with adaptation strategies.

2. Current understanding of increasing climate variability and climate change (ICV & CC) 2.1. Definitions In the context of this Workshop, observations of climate change or trends that point to climate change were reported by Dagvadorj (1999a) for Mongolia, Hyera (1999) for Tanzania and Rivero Vega with Rivero Jaspe et al. (1999) for Cuba. Often a distinction is made between factors, which cause natural variation of the climate system, and those due to human activities. The latter include agricultural and forestry operations, industrial processes, urbanization and transport. This section wants to briefly review the main known processes that have caused past and present ICV & CC. Climate change referred to here is taken from the Intergovernmental Panel on Climate Change (IPCC) usage (IPCC, 1996). This is a movement in the climate system because of internal changes within the climate system or in the interaction of its components, or because of changes in external forcing either by natural factors or anthropogenic activities. Climate variability refers to variability observed in the climate record in periods when the state of the climate system is not showing changes. If the climate state changes, usually characterized by a shift in means, then the frequency of formerly rare events on the side the mean has shifted might occur more frequently with increasing climate variability (Salinger, 1994). 2.2. External causes The main known external causes of ICV & CC are changes in solar output. These effect both the amount and seasonal distribution of solar radiation received by the climate system. Much attention has been placed on short-term variations in the solar constant because of the 11-year sunspot cycle. Space-borne satellite measurements

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since 1978 show that the solar irradiance varies by 0.2 W m−2 , or about 0.1% of the incoming solar radiation at the top of the atmosphere (IPCC, 1994). Mean annual numbers of sunspots have been recorded for many years by astronomers, and these show the relative absence of sunspots from 1650 to 1700 a.d., the ‘Maunder Minimum’, with a slight decrease in solar output (Eddy, 1976). This minimum has been linked by some to explain the Little Ice Age (1430–1850) cold period in Europe. Estimates place the increase in solar irradiance between the Maunder Minimum and now between 0.5 and 1.4 W m−2 , or an increase of 0.3% of the solar irradiance (IPCC, 1996). The variation of the Earth’s orbit around the sun and the position of the earth rotational axis with respect to the plane of the orbit also affect the seasonal and geographical distribution of solar radiation received on the Earth’s surface, but integrated annual totals remain constant. This variability occurs on time scales of tens of thousands of years, from astronomical variations, and will not be discussed here. 2.3. Internal causes 2.3.1. The enhanced natural greenhouse effect Within the climate system there are many mechanisms that can lead to climate variability, some well understood, and some only poorly described. There are, as well, factors that have yet to be discovered. Of the myriad of causes internal to the climate system, the main emphasis will be placed on those arising from atmospheric causes which are best understood, and are responsible for climate variation and change on time scales of tens to hundreds of years. Within the atmosphere there are naturally occurring greenhouse gases, which trap some of the outgoing infrared radiation emitted by the earth and the atmosphere. The principal greenhouse gas is water vapour, but also carbon dioxide (CO2 ), ozone (O3 ), methane (CH4 ) and nitrous oxides (N2 O), together with clouds, keeps the Earth’s surface and troposphere 33◦ C warmer than it would otherwise be. This is the natural greenhouse effect. Changes in the concentrations of these greenhouse gases will change the efficiency with which the earth cools to space. The atmosphere absorbs more of the outgoing terrestrial radiation from the surface when concentrations of greenhouse gases increase. This is emitted at higher altitudes and

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colder temperatures and results in a positive radiative forcing which tends to warm the lower atmosphere and Earth’s surface. This is the enhanced greenhouse effect — an enhancement of an effect which has operated in the Earth’s atmosphere for billions of years due to naturally occurring greenhouse gases (IPCC, 1996). The natural concentration ranged from about 190 to 280 parts per million (ppm). When CO2 concentrations were low, so too were temperatures, and when CO2 concentrations were high, it was warmer. 2.3.2. Volcanic aerosols Volcanic activity can inject large amounts of sulphur containing gases (primarily sulphur dioxide) into the stratosphere. Once reaching the stratosphere, some gases rapidly oxidise to sulphuric acid and condense with water to form an aerosol haze. The volcanic aerosols increase the planetary albedo and the dominant radiative effect is an increase in scattering of solar radiation, which reduces the net radiation available to the surface/troposphere, thereby leading to a cooling. This can produce a large, but transitory negative radiative forcing, tending to cool the Earth’s surface and lower atmosphere for periods of up to 2–3 years. The eruption of Mt Pinatubo in the Philippines stands out from the climatic point of view as the most important eruption this century. A cooling of global surface temperature observed following the eruption reached a maximum of 0.3–0.5◦ C during 1992, which then diminished over the following 2 years. Clearly, then individual volcanic eruptions can produce large radiative cooling on climate. To have global effects though, the latitude of eruption must lie between 30◦ N and 30◦ S. Eruptions poleward of these latitudes will only effect the hemisphere where the eruption occurs (IPCC, 1996). Because the impacts of volcanic aerosols only last a few seasons they increase the variability due to other effects. 2.3.3. Clouds Any changes in the radiative balance of the earth will tend to alter atmospheric and oceanic temperatures and the associated circulation and weather patterns. These will be accompanied by changes in the hydrological cycle, for example cloud distributions. Clouds can both absorb and reflect solar radiation (which cools the surface) and absorb and

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emit long-wave radiation (which warms the surface) depending on cloud height, thickness and cloud radiative properties. In the global and annual mean, clouds have a cooling effect on the present climate as evaluated from the Earth Radiation Budget Experiment (ERBE). A 31 W m−2 enhancement of the thermal greenhouse effect is exceeded by a 48 W m−2 increase in the reflection of short wave radiation to space (Ramanatham et al., 1989). But there are large variations in net cloud forcing with geography and cloud type. For low clouds, the reflected short-wave dominates so that an increase would cool the climate, but an increase in thin tropical cirrus clouds acts as a positive energy feedback to the climate system. The radiative properties of clouds depend on the evolution of atmospheric water in its vapour, liquid and ice phases and upon atmospheric aerosols (IPCC, 1996). The process is complex and the sensitivity of climate to changes in cloud types and amounts are yet to be quantified accurately. Current climate models are highly sensitive to cloud parameterizations, and these have not yet provided definitive evaluations of effects of the future role of clouds on climate (IPCC, 1996). The determination of cloud-dependent surface radiation and precipitation fluxes is a significant source of uncertainty for both land-surface and ocean climate modeling. 2.3.4. Hydrosphere The hydrosphere comprises the liquid water on the Earth’s surface. There is evidence of rapid warming about 11 500 years ago, with increases in central Greenland temperatures of up to 7◦ C, and 5◦ C in the Norwegian Sea, in a few decades as changes occurred in the path of the Gulf Stream, which switched its flow from the Bay of Biscay to the Norwegian Sea in the North Atlantic (IPCC, 1996). This is a field of active investigation. 2.3.5. The Cryosphere The changes in the global snow and ice cover, other than in clouds, operate on long time scales except for seasonal snow cover. Monitoring of seasonal snow cover since 1972 shows that the extent of Northern Hemisphere snow cover has been less since 1987, particularly in spring (e.g. WMO, 1998). This will decrease the regional surface albedo

with a consequent temperature increase in the winter period for high latitude areas of the Northern Hemisphere, which will have the largest impacts on agriculture in these regions (e.g. Sirotenko, 1999). Thinning of the mountain glaciers since the midand late-19th century has been occurring in many parts of the world, and continues (e.g. WMO, 1998). This provides a source of water for sea level rise (IPCC, 1996). 2.3.6. Land surface changes Land surface changes, particularly large-scale afforestation or deforestation of areas will affect the regional albedo and aerodynamic roughness. These will effect the transfer of energy, water and other materials with the climate system. These effects often are more regional in their impacts on climate in the planetary boundary layer (e.g. Oke, 1987). Recent studies of the sensitivity of the Amazon Basin climate to a change from forest to grassland in general circulation model studies (Henderson-Sellers et al., 1993) are very sensitive to the specification of surface properties such as albedo. Reductions in absorbed solar radiation due to higher surface albedos reduce evapotranspiration but it is uncertain how the change in precipitation relates to changes in evapotranspiration. 2.3.7. Internal dynamics of the climate system Changes in the climate system components described earlier can cause the climate to vary or change. As well, climate can vary because of internal dynamics of the climate system. These arise from natural coupled interactions between the atmosphere and ocean, and lead to large important systematic fluctuations of climate on time scales from seasons, and year to year. The most important source of this shorter time scale variability is from the El Niño/Southern Oscillation (ENSO) phenomenon (Allan et al., 1996). The North Atlantic Oscillation (NAO) is important for modulating European climate (Hurrell, 1995). Changes in sea surface temperature (SST), associated with sudden changes in oceanic circulation as observed in the North Atlantic 11 500 years ago (Lehman and Keigwin, 1992) could dramatically influence European agriculture.

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2.3.8. The Southern Oscillation Most of the internal variability of climate in the tropics and a substantial part of mid latitudes are related to ENSO. Internal variations in short-term climate occur as a consequence of this natural coupling in which the tropical winds drive the ocean currents and determine the SSTs, affecting the location of tropical convection and ultimately changes in the global atmospheric circulation. ENSO is a natural phenomenon, and atmospheric and oceanic conditions in the tropical Pacific vary considerably, fluctuating somewhat irregularly between the El Niño phase and the opposite La Niña phase. In the former, warm waters from the western tropical Pacific migrate eastwards, and in the latter cooling of the tropical Pacific occurs. The whole cycle can last normally from 3–5 years. As the El Niño develops, the trade winds weaken as the warmer waters in the central and eastern Pacific occur, shifting the pattern of tropical rainstorms east. Higher than normal air pressures develop over northern Australia and Indonesia with drier conditions or drought. At the same time lower than normal air pressures develop in the central and eastern Pacific with excessive rains in these areas, and along the west coast of South America. Approximately reverse patterns occur during the La Niña phase of the phenomenon. The primary source of the ENSO phenomenon is in the tropical Pacific. The observed global influences occur from teleconnections as the atmosphere transmits the anomalous heating in the tropics to large-scale convection and thus to anomalous winds in the atmosphere. Details on the main impacts of climate variability of ENSO regionally are described in Salinger et al. (1997). The main global impacts are that El Niño events cause above average global temperature anomalies. Since the mid-1970s El Niño events have been more frequent, and in each subsequent event global temperature anomalies have been higher. Fig. 1 shows the Southern Oscillation Index since 1950; the Tahiti minus Darwin normalised pressure index, which measures whether the climate system is in the El Niño or La Niña state. An index of –1 or lower indicates the El Niño state, and +1 or higher the La Niña state. 2.3.9. The North Atlantic Oscillation This large-scale alternation of atmospheric pressure between the North Atlantic regions of the subtropical high (near the Azores) and subpolar low pressure

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Fig. 1. Time series of smoothed averages of the Southern Oscillation Index (SOI), 1950–1997. The SOI, which is the normalized Tahiti minus Darwin pressure difference, measures the atmospheric state of the ENSO system. A positive index indicates that the ENSO system is in the La Niña state, and a negative index the El Niño state.

(extending south and east of Greenland) determines the strength and orientation of the poleward pressure gradient over the North Atlantic, and the mid-latitude westerlies in this area. One extreme of the NAO occurs in winter when the westerlies are stronger than normal, bringing cold winters in western Greenland and warm winters to northern Europe. In the other phase the westerlies are weaker than normal which reverses the temperature anomalies. In addition, European precipitation is related to the NAO (Hurrell, 1995). When this is positive, as it has been for winters in the last decade, drier than normal conditions occur over southern Europe and the Mediterranean, and above normal precipitation from Iceland to Scandinavia. 2.3.10. Anthropogenic causes of climate variation Any human-induced changes in climate are superimposed on a background of natural climatic variations by mechanisms, some of which have been discussed. Human activities are changing the concentrations and distributions of greenhouse gases and aerosols in the atmosphere. These changes can produce a radiative forcing by changing either the reflection or absorption of solar radiation, or emission of terrestrial radiation. The main human activities causing these are the combustion of fossil fuels, and deforestation by forest burning. The 1990 level is estimated to be already 0.5◦ C higher due to these effects. The IPCC (1996) assessed that global mean surface temperatures had

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increased by between 0.3 and 0.6◦ C since the late 19th century. If the Mt. Pinatubo eruption had not occurred it seems quite likely from our current understanding of its effects on temperature that the six warmest years of the entire record would have occurred in the last 6 years (WMO, 1998). Moreover, 1997 and 1998 were the warmest in the instrumental period. Future climate for next century is projected using general circulation models (GCMs) of the atmosphere and oceans. These represent the complex land-surface processes, sea ice processes and many other complex processes in the climate system. Detailed projections of future climate rely heavily on coupled atmosphere–ocean models. Many uncertainties currently limit the ability to project future climate change. Uncertainties in GCM simulations arise from uncertainties in estimations of future anthropogenic greenhouse gas emissions as well as feedback’s associated with clouds, oceans, sea-ice and vegetation (IPCC, 1996). Despite these uncertainties, GCMs provide a reasonable estimate of the important large-scale features of the climate system including seasonal variations and ENSO-like features. Many climate changes are consistently projected by different models in response to greenhouse gases and aerosols and are explainable in terms of physical processes. The models also produce with reasonable accuracy other variations due to climate forcing such as interannual variability due to ENSO, and the cause of temperature change because of stratospheric aerosols from the Mt. Pinatubo volcanic eruption. The GCMs project the equilibrium response of global surface temperature to a doubling of equivalent carbon dioxide in the range 1.5–4.5◦ C with a ‘best estimate’ of 2.5◦ C. From these the IPCC (1996) has projected an increase of global warming of 1–3◦ C above 1990 levels by 2100 a.d. with a ‘best estimate’ of 2◦ C. The increases in surface temperature, and other associated changes are expected to increase climate variability. Average sea level is expected to rise as a result of thermal expansion of the oceans, and melting of glaciers and ice-sheets. The IPCC (1996) estimates sea-level rise in the range of 15–95 cm from 1995 to 2100 a.d., with a ‘best-estimate’ of 50 cm. Such increases will have very significant effects on coastal agriculture in areas little above sea level such as the Nile Delta, or Bangladesh, and in combination with

(most likely even increased) storm surges, areas as the Atlantic east coast (Aakjaer et al., 1994; Purnell, 1994). Further details of the regional impacts are found in Salinger (1994).

3. Vulnerable regions and extreme events in relation to ICV & CC 3.1. General introduction Extreme weather events are important aspects of climate. They generally occur at synoptic scale and are of shorter duration than global climate change. Since changes in extremes have immediate impacts on nature and human society, such changes are more credible than global changes averaged over time and space. Changes in variability affect the occurrence of extreme events. Katz and Brown (1992) have shown that changes in the variance can have a larger impact on the exceedance frequencies for monthly maxima than a change in the mean. Nevertheless, enhanced greenhouse simulations indicate that the effect of changes in mean temperature are usually much larger than the effect of changes in variance (Cao et al., 1992; Hennessey and Pittock, 1995). Current climate models lack the accuracy at smaller scales and the integration is often too short to permit analysis of local weather extremes. Except for high intensity rainfalls, there is currently not much agreement between models on changes in extreme events. Climatologically extreme events are associated with anomalous weather. Many of the deleterious impacts of a global climate change often result from extreme and severe weather events such as tropical cyclones (TC), storms, heavy rainfall, wind, extreme temperatures and wildfires, rather than from changes in mean values of the atmospheric variables such as temperature. Numerical model simulations of the climatic effects for an enhanced greenhouse effect suggest that the frequency and intensity of some extreme events may change (Nicholls, 1995). Trends in intense rainfalls are not globally consistent, although in some areas (Japan, USA, and tropical Australia) there is evidence of increase in the intensity of extreme events. There has been a clear trend to fewer low temperatures and frosts in several widely separated areas in recent decades. Widespread

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significant changes in extreme high temperature events have not been observed, even in areas where the mean temperatures have increased. Although reports on TC trends are conflicting (see Section 3.3), there is evidence that intense TC activity has decreased in North Atlantic, the one TC region with apparently consistent data over a long period (Landsea et al., 1996). Bruce (1994) claims that more recent atmospheric-ocean coupled transient climate models suggest increases in extremes, high intensity rainfall in some areas, droughts in others, and severe storms with increasing greenhouse gases. To date global trends in extreme weather events have not been thoroughly analyzed for the 20th century. This is one of the tasks that the IPCC Third Assessment Report on climate change will be examining. On regional scale there is clear evidence of changes in some extremes and climate variability, with changes both toward greater and lower variability. Increased frequency and magnitude of extreme events has been frequently mentioned as a potential characteristic of future global climate (e.g. Easterling, 1990). Even small changes in the frequency of extreme events have a disproportionate effect. For instance the life cycle of perennial plants changes drastically if the frequency of extremes increases, because seedling establishment and mortality of these plants are highly sensitive to extremes (Graetz et al., 1988). Both the stability or forage supply and the balance between temperature and subtropical species are largely controlled by the frequency of extreme climatic events and thus are easily subject to change in a CO2 warmed climatic change scenario. One important aspect of short-term extreme events is the apparent randomness and abruptness with which they arrive. In the following short term extreme events are discussed with reference to ICV & CC and agriculture.

3.2. High intensity rainfall and floods Vulnerable regions prone to floods are some small islands, regions affected by TC, and the lower reaches of big rivers. Delta regions in south and southeast Asia are particularly vulnerable to frequent floods. Floods in the USA in 1993 strongly support the view that it was a significant climatic variation and could not be visualised as an expected natural event (WMO, 1995). It

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is very difficult to define credible scenarios for changes in flood producing climatic events (Beran and Arnell, 1995; Weijers and Vellinga, 1995). Although humans possesses considerable adaptive management capability to deal with floods; yet flooding could become a more common problem with ICV & CC even if average precipitation decreases. Global warming can be expected to produce changes in the frequency of intense rainfall in a catchment for two reasons (1) There may be a change in the paths and intensities of depressions/storms, and (2) There may be an increase in convective activity (Whetton et al., 1993). High SSTs can be expected to increase the intensity of TC and to expand the area over which they may develop. They may also strengthen other anomalies. Abu-Taleb and Dawod (1999) report that the rainfall event during the 1994 flood over eastern Egypt was caused by entraining of moist and warm air from the Indian Ocean into a low level jet stream. This showed a temporary change in direction, bringing the water vapour into unstable conditions over the east of Egypt. Heavy rains and floods have several combined destructive effects on crops, particularly rice and sorghum. Local-scale floods show various effects on rice yield, as shown by Yoshino (1993) for tropical Asia. Erosion and sedimentation are the physical effects caused by flooding while waterlogging causes damage to the plants by cutting of the oxygen supply to the roots. A few studies have attempted to quantify changes in flood occurrence. Geflens (1991) used a daily rainfall-runoff model to stimulate river flows in three Belgian catchments. More frequent floods were found, with flows remaining above high thresholds for longer periods. The mean annual flood peak increased between 2 and 10% under the scenario used. Bultot et al. (1992) used the same model and scenario to estimate possible changes in flood frequency in a small Swiss catchment and found identical results. Kwadijk and Middelkoop (1994) investigated potential changes in flood risk in the Rhine basin, using both hypothetical change scenarios and GCM simulations, and found an increase in precipitation and a rise in temperature leading to major increase both in flood frequencies and in the risk of inundation. Schreider et al. (1996) estimated the impact of climate change on the probability of flood occurrence and found that flood frequency may increase with 50% at 2030 and 100% at 2070.

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3.3. Tropical storms, tornadoes and strong wind Regions susceptible to TC (hurricanes and typhoons) are south, southeast, and east, Asia and Oceania as well as Central America, the Caribbean, parts of Mexico and the United States. The impact of climate change on tropical storm is still unclear (Ryan et al., 1992). Some authors suggest that storm tracks may change, or that severe TC may become more severe with ICV & CC (Okamoto, 1991). However, there is little agreement among climate models on TC and the evidence inferred from models based on relationship between SST and formation of TC is often conflicting (Stein and Hense, 1994), and such is other information. Houghton (1994) estimates an increase in both the frequency and severity of tropical and other storms. In the northeast and southwest Pacific, the number of observed TC has increased following Thompson et al. (1992), because of improved observation systems over this period. Landsea et al. (1996) note a downward trend in intense hurricances in the North Atlantic. Maunder (1995) therefore concluded that there appears to be no significant change in the number of TC during the last 20 years. From the Third International Workshop on Tropical Cyclones he concludes that present evidence suggests that the effects of global warming on either the frequency or severity of TC will be minor. WMO (1995) shows the regional variability in increased or decreased numbers of tropical storms, in which it is difficult to detect any trends. On the other hand, intense Atlantic hurricane activity over the period 1970–1987 was less than half that in the period 1947–1969 (Gray et al., 1992). WMO (1995) indicates a significant increase in intense extra-tropical storms over the North Atlantic during the winter season related to strengthened temperature and pressure gradients between the subtropics and the polar regions. Other extra-tropical storminess appears also on the increase. Tropical storms are associated with strong winds that cause the bigger part of the damage and storm surges. These tidal waves inundate vast areas of cultivable lands destroying standing crops. The saline water makes the land unfit for agriculture purpose for years to come. The traditional small-scale fisheries and livestock are also hit by the cyclones. Strong gusty winds are associated with the downdrafts of tornado. Though countries most affected by

tornadoes are the United States, Canada and Russia, they do occur in many other parts of the world (Grazulis, 1991) and even occasionally in Bangladesh and India. 3.4. Extreme temperature including heat waves and cold waves Decreases over the past few decades in the frequency of extreme low minimum temperatures or the length of the frost season have been reported for several widely separated locations (Salinger et al., 1990; Stone et al., 1996). Stone et al. (1996) examined daily temperature series for several stations in eastern Australia and found a significant decrease in the number of days with minimum temperatures below 0◦ C, and the dates of last frost, over the 20th century. Similar decreases in frequency for other low temperature thresholds have also been found. Changes in frequency of extreme maximum temperatures were less consistent than for minimum temperatures. Heat waves are likely to become more common and severe if the climate warms. Similarly, cold waves are expected to be less common or severe due to global warming. Climatologically, in the Northern Hemisphere, the southern part of the temperate zone and northern part of the subtropical zone in summer are the most vulnerable. In the Southern Hemisphere, sub-Saharan Africa and Australia are both vulnerable, especially when heat is combined with drought. Episodes of extreme cold and blizzards are major climate concerns for the circumpolar countries like Russia and Canada (Phillips, 1993). In both hemispheres, severe snow or ice storms can adversely affect most economic sectors. In Asia cold waves can penetrate to 15–20◦ N latitude (Yoshino and Kawamura, 1989). Extreme maximum temperature can directly lead to unhealthy development of plant organs, which results in lower yield or poorer quality of plants. Low but above freezing temperatures besides curtailing the crop growth period may severely damage or inhibit the productivity of many tropical or sub-tropical horticulture and agriculture plants, although varieties have been developed which thrive under low temperature conditions. Obviously damage due to low temperatures is the joint effect of the low temperature and the length of time such temperature persists.

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3.5. Droughts Droughts can be broadly classified as meteorological, hydrological, and agricultural droughts. An illustration of the difference between meteorological and agricultural drought is provided by Dagvadorj (1999b). Climate change scenarios with warming and increase of precipitation (decrease of meteorological drought) indicated generally declining steer production because of decreasing water availability and plant nutrient quality (increase of agricultural drought). Agricultural drought in a particular growing season in Africa may apply to maize but not to millet and/or sorghum because of their higher drought tolerance (e.g. Hyera, 1999). In the south Asian latitudes, they are intensified by prolonged dry seasons caused by anomalous monsoon circulation. The most vulnerable areas are those under the influence of subtropical anticyclones. Because of the quasi-cyclic nature of drought over large sections of the globe, it is unclear whether climatic warming will decrease their intensity or frequency. Agricultural settlements in regions such as sub-Saharan Africa, Australia, China, southern Europe and midcontinental North America are also sensitive to drought conditions. The increased sensitivity of crops to drought during the period from rooting to heading stage is well known. Particularly adverse is the combination of drought and high temperature that enhances evapotranspiration, and reducing soil moisture. These conditions also reduce number of heads which at this time as well as occasionally the number of seeds per head leading to the reduction of yield (e.g. Onyewotu et al., 1998). Drought is only in certain areas found significantly correlated with ENSO phenomenon. Whetton et al. (1993) examined changes in drought occurrence in terms of seasonal soil water deficits in Australia. Results indicate that significant drying may be limited to the south of Australia. No current GCM simulates ENSO effects well so changes in ENSO events due to global warming are unclear. The observed interannual variability of rainfall in north and east Australia is strongly influenced by ENSO. The intensity (although not necessarily the frequency) of ENSO linked dry periods has also been increasing over the past two or three decades in the Indonesia-New Guinea region, because of recent shifts in Pacific climate (Harger, 1992; Salafsky, 1994; Power et al., 1999). By far the

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most pronounced change in precipitation levels in any of the dryland areas is seen in the Sahelian region. Here, precipitation levels have dropped sharply since the mid 1950s, and the decrease in precipitation has contributed to enormous human and economic loss in the region (Glantz, 1987; Le Houerou, 1989). Interrelated changes in SSTs (including linkages to ENSO events), land-surface conditions, general atmospheric circulation patterns and atmospheric concentration of various greenhouse gases have all been proposed to explain some of the variance in the observed regional precipitation levels (Ayoade, 1977; Druyan, 1989; Nicholson, 1989; Lamb and Peppler, 1991). Models with elevated atmospheric concentrations of various greenhouse gases predict less precipitation in this area, and the observational record is broadly consistent with projection. Climate models indicate that temperatures will rise in all dryland regions in all seasons. There is some evidence that the warming will be more rapid in the middle to higher latitudes. For precipitation, models are inconsistent regionally, and the confidence limits or the predictions of precipitation changes in dryland areas are lower than those are for temperature (WMO, 1997). 3.6. Wildfires and bushfires Regions in Asia like Indonesia, Malaysia, and Borneo etc. having equatorial green forests are at the most risk during the dry summer period when summer thunderstorms may spawn lightning strikes. These may become more common with ICV & CC (Price and Rind, 1993). Recent fire frequencies and intensities in these countries and also in Australia, California and southern Europe conform to a globally warming climate (Bryant Edward, 1997). The dominant factor contributing to the occurrence of bush fires/wild fires is the existence of meteorological conditions conducive to combustion and spread of fire low relative humidity and high wind speed play a key role in determining the likelihood of a bush fire and its severity. These two factors are likely to be affected by global warming. Frequent fires are also related to inappropriate environmental management, wasteful logging practices, swidden agriculture and poor fire prevention and fire-fighting systems. ICV & CC could exacerbate

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them if it also results in drying or intensification of El Niño conditions.

5. Possible adaptation strategies 5.1. General

4. Need for adaptation strategies to ICV & CC Even when it would leave the many debates on imminent climate change to the scientific specialists and those on the consequences to global policy makers, the agricultural sector has two obligations as to the phenomena of (possible where not yet detected) ICV & CC: (i) react to the demands of reducing its contributions to possible global warming, which asks for changes in production methods, and (ii) be better prepared to react to the (increasing) variabilities and extremes and prepare scenarios for possible lasting change. On (i), the present authors feel that for the time being only industrialized countries with a high degree of organization of agricultural production and markets can be asked to contribute unconditionally. The other countries should for the time being be left out unless substantial additional financial and technological assistance, to combat environmental degradation directly, and help with structural economic problems are granted (French, 1992; Flavin and Dunn, 1997), while trading of emissions should be abandoned. This is fair for at least two reasons: developing countries were not and are not yet the main sources of global warming, not in total (25% only) and even much less so per person (e.g. Flavin and Dunn, 1997) or in carbon dioxide equivalent greenhouse gas emissions that agricultural activities account for (which activities were summarized by Salinger et al., 1997). Their agricultural production strategies have already enough problems (e.g. Brown, 1997), although all forms of afforestation and appropriate forest management should be encouraged. However, all countries can be asked to act on (ii), as soon as this need has been established. There are many ways to do this, as we will see later. The character of this need to adapt is determined initially by worsening limiting factors of agricultural production and the vulnerability of farming systems. International initiatives as developed in the context of the UNCED, the World Food Summit Plan of Action etc. have to be taken seriously and scientists have a guiding role to play in this getting prepared.

A wide range of views exists on the potential of agricultural systems to adapt to ICV & CC. From historic time, farming systems have adapted to changing economic conditions, technologies, resource availabilities and population pressures. Even with the last mentioned factor under control, resource availability remains the most important factor. This determines much of the strategies to be adapted for sustained development of agriculture. Uncertainty remains whether the rate of required adaptation to ICV & CC would add significantly to the disruptions resulting from other socioeconomic or environmental changes. Easy access to developed and well tested technology is important for many countries but so are local innovations. An effective ICV & CC response strategy should pay adequate attention to the possibilities of linking response options with responses to socioeconomic transition phenomena. In many Asian countries, agriculture is at present highly dependent on energy use, and farmers have to depend on external sources, mostly government, for much of their energy supply. An adequate and timely process of efficient use of environment friendly energy seems imperative, specially in developing countries. In addition, many of these agricultural systems are based on monocultures, e.g. high yielding varieties of wheat or rice, which increase soil exhaustion and are more vulnerable to massive infestations of pests and diseases (e.g. Baldy and Stigter, 1997; Bonte-Friedheim and Sheridan, 1997). Options for dealing with the possible impacts of ICV & CC on increased uncertainty about future supply and demand of water resources include (a) efficient management of existing supplies and infrastructure; (b) institutional arrangements (e.g. markets and regulatory measures) to limit future demands of water; (c) improved forecasting techniques and establishment of early warning systems for floods/drought and (d) construction of new reservoir capacity to capture and store excess flows produced by altered patterns of rainfall regimes and storms. Dawod (1999) provides an example of successful correlative forecasting of rainfall in two periods for four stations on the north coast of Egypt from a combination of various monthly SSTs.

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Replies to scarcities are often made by increases in efficiencies. For example changes in water availability to agriculture, because of demands by other sectors of society, have already led to improved water use efficiencies, a subject in which agrometeorologists have a large role to play (e.g. Hatfield, 1994). However, this process has to continue because projected irrigated area per person for the entire world falls before 2010 below its level in the late 1940s, when it was increasing (Brown, 1997). 5.2. Industrialized world ICV & CC are therefore not the only problems asking for agrometeorological adaptation strategies and some strategies can handle more than one problem. For example for water use efficiency in irrigated agriculture one may propose what Flavin and Dunn (1997) indicate as successful in stimulating energy use efficiency: set minimum efficiency standards that producers must follow. If supported by higher water prices and combined with incentives that motivate producers and inform consumers, such standards can be raised in the course of time, whatever the cause. To obtain these ever increasing water use efficiencies will partly be an agrometeorological adaptation strategy. A comparable reasoning can be made for land use efficiency and sustainable land mangement in the industrialized world. As soon as the soil is seen as a natural resource base, land use diversification — necessary because it is a safeguard for effects of ICV & CC — may or may not run counter to other reasons for changes in land use planning. Stimulating increased land use efficiency for different agricultural purposes will again be partly an agrometeorological adaptation strategy. All multiple cropping systems are examples of such increased land use efficiencies (e.g. Stigter and Baldy, 1995; Baldy and Stigter, 1997). When efficiency of the use of other external inputs (such as commercial energy), in what is now called precision farming, and changes in such efficiencies due to ICV & CC, have agrometeorological components, the same reasonings apply. 5.3. Developing world It is of interest in the context of this paper to read a most recent collection of modern planning approaches

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to sustainable land management (Beek et al., 1997) and ask oneself the question what role agrometeorology has to play there, particularly in developing countries, as far as adaptation strategies to conditions of ICV & CC are concerned. It looks as if scale and detail of GIS data sets are presently not adequate at farm level in developing countries and that at best they can support advisory services and contribute to setting agricultural research agendas (Bie, in Beek et al., 1997). Another example is the recent collection by Rijks et al. (1998) of agrometeorological applications for regional crop monitoring and protection assessment. These have been developed for European conditions but only few can at present easily be used in developing countries, due to lack of data, skilled personnel and proper equipment infrastructure. However, Röling (Beek et al., 1997) nicely exemplifies the important role that science has played in developing, testing, and consolidating a low external input alternative to conventional farming, which is profitable to farmers, for example in Indonesia and Africa. Agroforestry plays an important role as do other afforestation techniques, with an additional role as CO2 sink. There are numerous drought adaptation measures that can be taken and have been taken: these range from time of planting, practising water conservation techniques, using crops with very extensive and deep rooting systems to planting drought resistant varieties (e.g. Salinger et al., 1997). Among many others Baldy and Stigter (1997) and Zhaozhan and Jubao (1998) mention simple agrometeorological ways in which water use efficiency of crops in drylands can be improved: e.g. tillage in the fallow period, mulching, soil moisture management with adapted fertilization, crop rotation and mutiple copping. Such measures and ways can be validated accordingly (Mungai et al., 1996; Olufayo et al., 1998). 5.4. Challenges for applications in different regions For support to third world farmers and farmers in countries in transition, three principle ways are open: (i) assistance in access to proper amounts of inputs, be it physically by increasing availability at local markets at the required time and providing advice on amounts to be applied, or economically by regulation of prizes (for inputs and products) or

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conditioned subsidies etc.; (ii) extension through permanent (weather) advisories on farming, production and cropping systems, in accordance with the possibilities for change in the different farming communities. This applies to techniques of using inputs, soil conditions and planting densities, choices of cropping systems and varieties, applications of (improved) protection strategies in crop/tree space and applications of other multiple cropping microclimate management and manipulation techniques; (iii) extension through on-line current advisories, on time scales and in spatial scales as required. Examples are weather and climate forecasts; proposals for sowing dates and timely advice on other farm operations such as weeding, fertilizing, spraying, integrated pest management, harvesting and drying. These three possible approaches for support to third world farmers also apply for adaptation strategies when ICV & CC cause changes in kind and severity of production limiting factors. However, because of the changing dynamics of the environment, the alertness needs to be larger, the rate of reaction will need to be increased, and the knowledge on local suitability for future cropping and farming systems improved. Regions with more resources have more adaptation possibilities, but extreme weather causes damage everywhere. Insurances are an approach in such areas. Absorption of new technologies is fastest here. Investments are available for improvements. The main challenge is to minimize the vulnerability of farmers. Sivakumar (1997) has recently given some examples of catagory (iii) to approach consequences of climate variability that will also be of use in cases of increasing variabilities. He optimistically believes that modern technologies and modern communication techniques will assist in meeting these challenges everywhere. Examples in Hyera (1999) confirm the feasibility of some of these attempts but also remaining needs. Dmitrenko (1999) believes that the base of the general concept of ‘Agrometeorological Adaptation Strategies to Climate Variability and Climate Change’ can be caught by defining a ‘Fruitfulness of Climate’ (in which ‘fruitfulness’ means ‘productivity’). Sirotenko (1999) provides an example of the complexity of category (ii). Using several GCM scenarios, he shows that versus 2030 the cereal crop productivity for entire Russia

will drop by in the order of 25% unless soil conditions are actually optimized by present-day levels of technology. However, the arable zone of Russia may be expected to increase by 50% from global warming alone, which means that successful adaptations to the new potential would give a very positive outlook. Olufayo et al. (1998) have recently exemplified what is successfully going on in problem oriented participatory agrometeorology in tropical Africa, illustrating a vision on priority directions and needs in research, education and services. They show that there is various progress in African agrometeorology, be it that successes in research and education are strongly related to external support (see also Bonte-Friedheim and Sheridan, 1997). Olufayo et al. (1998) show increasing needs for operational agrometeorology in Africa, because the environment is endangered in many places in many ways. They conclude that on-farm validations of new approaches and technologies, that take traditional and more recent local expertise into account, are needed most of all. These are in first instance not fully new farming or cropping technologies but existing technologies adapted to new problems caused by ICV & CC. Baldy and Stigter (1997) have for this purpose given an account of agrometeorology of multiple cropping in warm climates. Stigter and Baldy (1995) holds additional examples. The vulnerability of African agriculture remains high (e.g. Hyera, 1999) and only by using all possible human resources and other capacities to increase countervailing power, local famine will continue to strike, like at present. The situation in Asia and Latin America is again particularly resources related. Recent climatic catastrophies show serious shortcomings in preparedness of governments, particularly where also an economic malaise has simultaneously occurred and more so in economically backward areas. The interaction of traditional agricultural technologies as well as unlicensed habits in commercial forestry with climatic catastrophy have shown for example in Indonesia and Brazil that the consequences are becoming transboundary phenomena. The challenge is here to develop or get into use safer technologies of exploitation. From slash and burn to slash and bury in Brazil. From intensive pesticide use to Integrated Pest Management in Indonesia.

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6. Resources, structures and strategies required for sustained efforts The last mentioned cases are examples of serious governmental failures to keep emergency situations under control. Laws should be made and/or applied, alternatives should be researched as priorities and resources should be made available to assist farmers that cannot easily change their farming systems to alter some of their methods or apply them harmlessly. Development oriented agrometeorology can certainly play a role here (e.g. Stigter, 1995; Olufayo et al., 1998; Zhaozhan and Jubao, 1998). Dagvadorj (1999a) concludes from different climate change scenarios using GCMs that although standing biomass would increase, plant quality and livestock production would decline in the scenarios with warming for Mongolia. He brings forward as adaptation strategies: (i) improving vegetation cover artificially in the south; (ii) changing the management of current grazing systems throughout Mongolia; (iii) intensifying the breeding in the north; (iv) strengthening feed reserves and supplying fodder during critical periods throughout the country; (v) changing pasturage technology in desert areas. Nguyen Van Viet (1999) provides an example of a strategy to cope with expected warmer winters in production of winter/spring rice that have a tendency for decreased yields under such conditions. An early-maturing variety should be used to be sown and planted in such a way that flowering occurs between the last decade of April and the first decade of May. Rivero Vega with Rivero Jaspe et al. (1999), using a GCM in combination with a biophysical model or with a climatic index together with a life zone model, were able to distinguish cowpea as an attractive crop for warming not exceeding 2◦ , in their area in eastern Cuba. Forestry appears only feasible there in the long run when degraded from dry forestry to savannas (Rivero Vega with Rivero Jaspe et al., 1999). Extension habits and structures will have to be changed and strengthened. External support for large scale validation of alternatives would be very meaningful here. In summary, the following three interrelated strategies may be brought forward for enhancing adaptation and promoting sustainable development: 1. Technological change and innovation to ensure greater productivity and efficiency in the sustain-

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able exploitation, use and development of natural resources; 2. Sustainable economic growth while conserving fragile finite natural resources; and 3. Intensified research efforts and an enhanced training infrastructure. These strategies could be worked out within the following three principles (selected from Goklany, 1995; Reilly, 1996; Bonte-Friedheim and Sheridan, 1997): 1. Local communities and individuals should be provided with economic incentives in the resources they manage; 2. Decision-making on resource (including water) use and management should be decentralized, wherever practicable, but decision-making on food security should be regionally more centalized; 3. Research and development of new, innovative, cheaper, more efficient and productive technologies and practices should be increased. There should be interactive communication that brings research results to farmers and also farmers’ problems, perspectives, successes, to researchers. Provision should be made for a two-way training process between researchers and farmers, particularly in developing countries where education of rural workers is rather limited. Meagre resources of local funding and of human and other capacity, as well as external support to capacity building in local research systems have to be harnessed. A policy to particularly use available senior expertise in developing countries to co-supervise externally financed Ph.D. and M.Sc. research education at local universities has shown to yield very positive results (Stigter et al., 1998). Such problem oriented participatory research on agrometeorological adaptation strategies should be full circle, from problem identification to validation of proposed solutions (Mungai et al., 1996). For sustained efforts, such examples should be multiplied. What kind of agrometeorological projects we could think of? It should first be realized that at present already the principal cause of undernutrition and malnutrition is poverty. Poverty alleviation can best be achieved by lowering production costs and increasing poor famers’ entitlements, assets, incomes and empowerment (Bonte-Friedheim and Sheridan, 1997). Poverty alleviation should therefore be a boundary condition for any project, just like not increasing and

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Fig. 2. Schematic representation of a proposed support structure for the WMO Agricultural Meteorology Programme.

preferably relieving the threats due to ICV & CC. Agrometeorological priority projects that can be selected for any funding should themselves be part of global agricultural umbrella projects. CAgM and other global, national and local agrometeorological projects should be part of such priority projects. The present authors have selected the 10 most essential agricultural umbrella projects with agrometeorological priority components that they found proposed in the literature. These either modify the consequences of ICV & CC and/or improve the preparedness for ICV & CC and/or mitigate their causes. They include examples already detailed earlier, and propose work on: (i) methodological research at the ecoregional level (ISNAR, 1998), (ii) geo-information for sustainable land management (Beek et al., 1997), including a global terrestrial observing system (GTOS) (ICSU/UNEP/FAO/UNESCO/WMO, 1996), (iii) participatory on-farm validation of new approaches and (environmentally sound or eco-) technologies in agricultural production (Reijntjes et al., 1992; ILEIA, 1995; Olufayo et al., 1998), (iv) efficiencies of use

of resources and their protection, including those of use and protection of germplasm, soil, water and energy in agricultural production (see earlier in this paper), (v) (environmentally sound) impact reduction (from sources to targets and from forecasting to preparedness) of natural disasters, including pests and diseases, reducing agricultural production (e.g. Jager and Ferguson, 1991), (vi) reduction of contributions of agro-ecosystems to global warming (Salinger et al., 1997), (vii) protection and use of tropical forests and large scale afforestation (Bonte-Friedheim and Sheridan, 1997), (viii) convincing decision makers to support research and validation exercises in any of the earlier described fields by presenting proper examples of successes, that is of sustainable economic and social benefits, in particular for the most vulnerable people, countries and regions and for the planet as a whole (Bonte-Friedheim and Sheridan, 1997), (ix) important aspects not yet mentioned that should be taken care of as other boundary conditions for projects to be appropriately met. They have to do with macroeconomic policies, gender aspects,

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agreements in global conventions and public policies (Bonte-Friedheim and Sheridan, 1997), (x) any educational and teaching exercises that assist in promoting work on the earlier mentioned priority umbrella projects (Stigter et al., 1998). The CAgM of WMO should act in a guiding role in the agrometeorological projects described earlier. The links along which this should take place are given in Fig. 2. A CAgM Working Group or Joint Rapporteurs on a global project ‘Agrometeorological adaptation strategies to increased climate variability and (possible) climate change’, as a follow up to earlier Groups on such subjects, could be a component in such efforts. The Advisory Working Group of CAgM has recently pledged to guide the implementation of such global projects within the WMO Agrometeorological Programme (Fig. 2). National Meteorological and Hydrological Services should be supported to strengthen agrometeorology and to work out approaches in their services to farmers with respect to adaptation strategies. In line with the descussion here, research and research education in agrometeorology should get prioritized, focussed and proposed for funding in relation to such strategies.

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