ffp-1p-229Effects of Climate change Almaz

BALWOIS 2004 Ohrid, FY Republic of Macedonia, 25-29 May 2004

Effects Of Climate Change On Agriculture Particularly In Semi-Arid Tropics Of The World With Some Examples Of Ethiopian Condition

Almaz Demessie

National Meteorological Services Agency Addis Babab, Ethiopia

Abstract Today climate change is a burning issue all over the world because of its global nature. Fears have arisen that, climate may be changing for the worse and its impact may be felt on agricultural production, which will reduce the supply of food to growing population, especially in developing countries. Climate change would affect various human activities. Agriculture is one of the activities, which can be seriously affected by climate change. Due to high inter-annual variability and uneven distribution of rainfall during the rainy season, recurrent droughts have been observed in semi-arid tropics of the world over the last three decades. As White, (cited in Climate Variability and Agriculture by Y.P Abrol, S. Gadgil and G. B.Pant 1996) pointed out rain fed agriculture in the semi-arid tropics is limited mostly by high climatic variability with principal limiting factor being rainfall. The main crops of traditional rain fed agriculture are sorghum, millet, maize, cowpea, pulses and sesame. Adverse climatic conditions are the bottleneck of Ethiopia’s rain fed agriculture development. As a result, Particularly in drought prone regions of Ethiopia agriculture production is determined by climate variability. There is a suggestion that increased CO2 will benefit temperate and humid tropical agriculture more than that in the semi-arid tropics. During the process of photosynthesis plant species with the C3 photosynthetic pathway tend to respond positively to increased CO2 while the C4 have a poor response. Since C4 plants are mostly tropical crops, the situation will be worst over the areas (Parry, 1990). Besides, agricultural production suffers from periodic outbreak of pests and deceases, both pre- and post harvests, in most parts of Ethiopia. The factors involved here are principally wind, precipitation and temperature. Some pests are becoming a serious problem in some areas where the rainfall condition is erratic. For instance, Sorghum Chafer becomes a chronic problem since 1993 over northeastern highlands of Ethiopia including Afar regions. Climate change will alter the nature of occurrence of agricultural pests in terms of area. Warmer temperatures shorten the generation time; increase the development rate of epidemic.

The objective of the research study is to identify and characterize the effect of climate change on agriculture by assessing the climatic condition of the selected areas and its effect on agriculture.

Introduction Climate is the average weather parameters, usually 30 years of a given locality. The measures of climate include mainly the estimates of average values of weather parameters and measures of variability near to the average value. As Biswas, (cited in Climate Variability and Agriculture by Y.P Abrol, S. Gadgil and G. B.Pant 1996) has stated in most cases, some deviation of average values between two reference periods in mainly due to large weather variability. There may be real shifts of the average or changes in variability between two periods. These deviations from the mean value constitute climate variation or change. Adverse climatic conditions are the bottleneck of Ethiopia’s rain fed agriculture development. As a result, Particularly in drought prone regions of Ethiopia agriculture production is determined by climate variability. The rainfall variability in the rainy seasons is the most serious problem encountered by Ethiopian farmers. Therefore, it is very important to clearly understand the characteristics of weather parameters together with the triggering factors that exert significant impacts. The main crops of traditional rain fed agriculture are sorghum, millet, maize, cowpea, pulses and sesame. There is a suggestion that increased CO2 will benefit temperate and humid tropical agriculture more than that in the semi-arid tropics. During the process of photosynthesis plant species with the C3 photosynthetic pathway tend to respond positively to increased CO2 while the C4 have a poor response. Since C4 plants are mostly tropical crops, the situation will be worst over the areas (Parry, 1990). Besides, agricultural production suffers from periodic outbreak of pests and diseases, both pre- and post harvests, in most parts of Ethiopia. The factors involved here are principally wind, precipitation and temperature. Some pests are becoming a serious problem in some areas of Ethiopia where the rainfall condition is erratic. For instance, Sorghum Chafer becomes a chronic problem since 1993 over northeastern highlands of Ethiopia including Afar regions. Climate

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change will alter the nature of occurrence of agricultural pests in terms of area. Warmer temperatures shorten the generation time; increase the development rate of epidemic.

Drought recurrence has been a serious problem in the history of Ethiopia. Improvement of existing techniques and development of an effective operational method of early warning system is the only alternative to mitigate the effect of recurrent drought on the society. Analyzing of long-term average of different meteorological parameters is one of the important tools of this system. Therefore, in this study long term records of meteorological data such as rainfall, maximum and minimum temperature, Relative Humidity, wind speed and sunshine hours of two stations from the northeastern Ethiopia taken as an example to analyze the climatic situation and its effect on agriculture. Long term mean monthly rainfall and mean monthly ETo were computed in order to determine the Length of Growing Period (LGP) and Agricultural Rainfall Index (ARI) which are the major indictor of moisture condition in a given area.

LGP is describing the period during which crop growth is not affected by climatic constraints, i.e. the period of the year when water availability allows crop growth and when the temperature is not limiting crop growth. As many studies have indicated, the duration of the period in which rainfall exceeds selected levels of evapotranspiration is the most useful index of agricultural potential. This period refers to the length of time during which water and temperature permit crop growth. As FAO (1991) stated, three specific values are identified for climatic classification, namely: arid, with LGP of less than 75 days; Seasonally dry, with LGP of between 75 and 270 days; and humid with LGP of more than 270 days. Annual or seasonal rainfall is traditionally used to describe the supply of water to crops, because it is the primary measurement particularly for rain fed agriculture. Nevertheless they should be supplemented by the information in which the availability of water, now more easily obtainable by the concept of reference evapotranspiration (ETo). Where sufficient water is available, crops need specific periods to accumulate the energy necessary to complete their growth and development. In this study, in addition to the above methodology, Nieuwolt’s (1981) approach of an agricultural rainfall index (ARI) will apply. In this approach instead of mean monthly rainfall 80% probability of exceedance (dependable rainfall) is important to determine LGP in which periods with ARI value greater than 100 considered as growing season. Many researchers agree that 80% probability of rainfall is dependable for the continuation of vegetative growth if the rainfall amount at that level of probability is sufficient for plant growth. Consideration of 80% probability level is important to identify a specific area in terms of moisture availability, because it covers a longer period (i.e. 8 out of 10 years). In this study, both approaches will test. From the analysis, I try to figure out the shift in mean values, LGP and ARI for the selected stations, which is the major indicator of climate change.

Materials and Methods

Materials

Meteorological Data More than 30 years data used for the analysis of climate change. All elements are used which are important for the calculation of ETo such as maximum temperature, minimum temperature, Relative Humidity, Sunshine hours and wind speed mm/sec.

Crop Data

FAO Crop Calendar Fig. 2.1 indicate the general crop calendar of major crops of the country. However, the crop calendar varies area-to-area (nature of the soil), variety-to-variety and depends up on the climatic feature of the area. The availability of rainfall is the major factor together with air temperature, soil temperature and the water holding capacity of the soil. The importance of this figure in this study is to determine the initial and end of the cropping season. The on-set, distribution and cession of rainfall is very important in the process of crop growth and development. In case of Ethiopia land preparation and sowing is following the rainfall pattern in most places.

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Figure 2.1 Crop Calendar of Ethiopia. Meher is the main season, and Belg the secondary one. Source

FAO 1997 www.fao.org/WAICENT/faoinfo/

Crop yield data Yield data taken from different Ethiopian Central Statistics Authority year Books. Cumulative yield amount of major cereal crops like maize, sorghum, teff, barley, wheat and millet was taken to assess the change in crop yield. Thirty years data was available, however there is a gap in some years.

Methods The purpose of this study is to analyse the effect of climate change on agriculture by using different meteorological parameters and different types of crop models and statistical analysis in order to investigate the influence of climatic variability on crop performance in terms of crop production and protection aspect of Ethiopia.

Statistical Methods Excel used for simple statistical analysis like for the calculation of mean and mean deviation. The percent probability analysis was done for the cropping season.

In order to indicate year-to-year variability of rainfall selected stations have been analyzed. The statistical analysis used to indicate variability is percent deviation from the mean:

((Actual-Mean)/Mean)*100) (2.1)

and to indicate percent probability of rainfall the methodology that was developed by Dorenbos and Pruitt (1977: cited in Technical Note 179) was used. It is the ranking order method; each record is assigned a ranking number (m). The ranking numbers are then given probability levels Fa (m), which is calculated as follows:

Fa (m)=100m/(n+1) (2.2)

FAO CROPWAT (Version 4.3) Model The FAO Penman Monteith as modified by FAO (1994), which is described in http://www.FAO.ORG/AG/AGLW/WCROP.HTM for the calculation of reference evapotranspiration (ETo). The definition of reference evapotranspiration is “the rate of water loss from a short green crop fully covering the ground and fully supplied with water”. As FAO in many studies has pointed out Penman Monteith method overcomes shortcomings of the previous FAO Penman method and provides values more consistent with actual crop water use.

The data used for the calculation of ETo is on a monthly basis i.e. monthly maximum and minimum temperature (oC), mean relative humidity (RH%), wind speed (m/s), sunshine hours. Other data like elevation, latitude, longitude and Julian day i.e. day of the year from January.

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http://www.fao.org/WAICENT/faoinfo/


FAO Methodology to calculate Length of Growing Period (LGP) LGP is expressing the period during which crop growth is not affected by climatic constraints or it characterizes the period of the year when water availability allows crop growth and when the temperature is not limiting crop growth. The method to calculate LGP is FAO methodology by Frere and Popov (1979). “The growing period (GP) is defined as the time (days) during a year when precipitation exceeds half the potential evapotranspiration (PET) plus the time (days) necessary to evapotranspire 100mm of water (or less if 100 mm is not available) from excess precipitation stored in the soil profile. The period during which the daily mean temperature value is less than 6.5oC is subtracted from the length of the period during which water is available”. However, in this study, daily values of temperature were not available. As a result, ten-day mean temperature is considered in place of daily mean. Besides, Nieuwolt (1981, cited in Technical Note 179) methodology that was introduced as an Agricultural Rainfall Index:

ARI = 100* P/ETo (2.3)

where P is 80% probability of exceedance of rainfall.

In this case, 80% probability of exceedance for the rainfall season will be applied instead of mean annual rainfall. According to his concept-growing period is considered when ARI is over 100.

Methodology to analyze rainfall and temperature variability In order to see the year-to-year variability of rainfall, % deviation from the mean annual rainfall will calculated as follows:

%Deviation = [(Annual rainfall – Mean annual rainfall)/Mean] * 100 (2.4)

Climate change Climate is the average weather parameters, usually 30 years of s given locality. The measures of climate include mainly the estimates of average values of weather parameters and measures of variability near to the average value. As Biswas, (cited in Climate Variability and Agriculture by Y.P Abrol, S. Gadgil and G. B.Pant 1996) has stated in most cases, some devotion of average values between two reference periods in mainly due to large weather variability. There may be real shifts of the average or changes in variability between two periods. These deviations from mean value constitute climate variation or change.

Causes of climate change The effect of Greenhouse gases [Carbon dioxide (CO2), Chlorofluorocarbons CFCs), Methane (CH4) and Nitrous Oxide (N2O)] is the main cause for climate change. Increases in concentration of greenhouse gases negatively affect the Earth’s radiation balance, with more of the long wave radiation being absorbed in the lower atmosphere and some of this being re-emitted back to the Earth’s surface. Among factors that may be contributing to global warming are the burning of coal and petroleum products (sources of carbon dioxide, methane, nitrous oxide, ozone); deforestation, which increases the amount of carbon dioxide in the atmosphere; methane gas released in animal waste; and increased cattle production, which contributes to deforestation, methane production, and use of fossil fuels.

According to IPCC report (1990), CO2 has increased by about 25% over the two centuries largely because of the burning of fossil fuels but also due to clearance of forests for agriculture. In Ethiopia, mismanagement of natural resources is the main constraint in the process of crop production and one of the constraints is deforestation. At present CO2 concentration is growing at the rate of about 0.5% per year. Nitrous Oxide is increasing in atmospheric concentration at an annual rate of about 0.33% largely due to an increased use of nitrogen fertilizers. Until agreement was achieved through the Montreal Protocol in 1989, which focused on control of CFCs use, the rate of CFCs concentration was growing at an annual rate of 4.0% largely due to the expansion of their use as propellants, solvents and blowing agents for foam packaging. Agriculture is also an important source of greenhouse gases. It contributes about 35% of all current methane emissions, and a significant but unspecified amount of all N2O emissions. From the total GHG it contributes about 15%. These days’ uses of pesticide are increasing due to high pest infestation particularly over drought prone areas of Ethiopia.

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The effect of climate change on agriculture Climate affects agriculture in many ways. Effects due to increased atmospheric CO2 concentration, CO2 induced changes of climate and rises in sea level are the major ones. Many research studies have stated that meteorological parameters like rainfall, temperature and wind play an important role in changing agricultural production more than other parameters. Rising emission of carbon-dioxide, methane, nitrous oxide and other radioactive gases (Greenhouse Gases) will lead not only to an increase of surface temperature of the earth but also a change of precipitation (Parry et al, 1990). Thus, this condition could have a significant negative impact on agriculture.

Any deviation from the mean climatic condition would affect agricultural activities negatively. Agriculture can show little sensitivity to moderate variations around those means. If the condition persisted a bit longer it could affect the overall physiological activities of the plants and result in crop damage and final yield reduction. As a result agriculture becomes particularly sensitive to climate change. For example, weak monsoon rain in 1987 caused significant decreases in crop production in India, Bangladesh, and Pakistan (World Food Institute, 1988).

If we take Ethiopian rainfall condition from the period 1962 to 2001 in case of Bahir Dar and from 1957 – 2001 in case of Debre Tabor (meteorological stations from the northwestern parts of Ethiopia) the following percent deviation from the mean monthly rainfall was observed. As can be seen from the figures below there is clear pattern of difference between two periods (the periods from 1962 – 1977 and 1978 – 2001 in case of Bahir Dar, from 1957 – 1982 and 1983 – 2001 in case of Debre Tabor)

% Dev from the mean for Bahir Dar from 1962-2001

-60

-40

-20

0

20

40

60

1962

1964

1966

1968

1970

1972

1974

1976

1978

1980

1982

1984

1986

1988

1990

1992

1994

1996

1998

2000

years

%D

ev

Figure 1 shows percent deviation from the long years mean rainfall for Bahir Dar

% Dev from the mean for Debre Tabor from 1957-2001

-80-60-40-20

0204060

1957

1959

1961

1969

1975

1977

1979

1981

1983

1985

1987

1989

1993

1995

1997

1999

2001

Month

%D

ev

%Dev

Figure 2 Shows percent deviation from the long years mean rainfall for Debre Tabor

As Fig. 3 indicates there is a shift in mean values and decease in mean amount of rainfall during the second period. Thus, this condition can clearly shown the effect of climate change in the area.

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Mean monthly rainfall difference between two periods(1957-1982 and 1983-2001)

0

200

400

600

1 2 3 4 5 6 7 8 9 10 11 12

MM rainfallM

onth

Mmean1 Mmean2

Figure 3 Shows difference in monthly mean rainfall between two periods (1957-1982 and 1983 –

2001) for Debre Tabor

Crop yield from 1953/4 - 2001/2 for major cereal crops of Ethiopia 000ton

0

2000

4000

6000

8000

10000

12000

year s

Figure 4 Shows crop yield for major cereal crops of Ethiopia

% Deviation from the mean yield from 1953/4- 2001/2 for mejor cereal crops of Ethiopia

-100

-50

0

50

1953

/4

1955

/6

1962

/3

1964

/5

1967

/8

1969

/70

1971

/72

1985

/86

1988

/89

1990

/91

1993

/94

1995

/96

1997

/98

1999

/00

2001

/02

Years

% D

ev

Figure 5 Shows % deviation from the mean yield from 1953/4-2001/02

Average April-September precipitation in the western long cycle crop-growing region (shaded region on map)

Figure 6 A decrease in rainfall amount over long cycle crop growing region(Source FEWS.net October

6, 2003)

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As the FEWS NET report (October 6, 2003) indicates, the precipitation in the long cycle region (areas mainly grown long cycle crops like maize and sorghum) pointed out the rainfall amount shows a negative trend by 5.4 mm per year. Thus, this situation can have negative impact on agriculture, thereby decreasing yield production year to year significantly, since the Ethiopian agriculture mainly depend on rainfall amount and distribution.

If we see the overall rainfall condition allover the country, it shows a decreasing trend (Fig 6), thereby the crop yield showing decreasing trend year to year (Fig. 4).

The process of photosynthesis CO2 has an important role in the process of photosynthesis. Increases in CO2 concentration would increase the rate of plant growth. As recent findings indicate a doubling of CO2 may increase the photosynthetic rate by 30-100%, depending on other environmental conditions such as temperature and availability of moisture.

As Parry (1990) pointed out, different species of plants have different levels of response to increased CO2. Plants species with the C3 photosynthetic pathway tend to respond positively to increased CO2. Thus, this condition could favour C3 crop growing areas of the world. On the other hand, C4 are less responsive to increased CO2. The major C4 plants are maize, sorghum, sugarcane and millet, which are mainly grown in Ethiopia as major crops like other tropical regions. Recent research studies have stated that CO2 enrichment will favour temperate and humid tropical agriculture more than that in the semi-arid tropics. Moreover, C3 crops in temperate and sub tropical regions could also benefit from reduced weed infestation due to the difference in response to increased CO2. According to the research findings, fourteen of the world’s 17 most troublesome terrestrial weed species are C4 plants in C3 crops. On the other hand, C3 weeds in C4 crops, will suppress the growth of C4 plants in the tropics.

Crop water requirements of plants Climate variability can have significant affect on the availability of water to semi-arid ecosystems. As Parry (1990) pointed out a doubling of ambient CO2 concentration causes about 40% decrease in stomata openings in both C3 and C4 plants, which may reduce transpiration by 23-46%. This condition would favour areas where water is a limiting factor, such as in semi-arid regions. Nevertheless, there are many uncertainties, like how much the greater leaf area of plants as a result of increased CO2 will balance the reduced transpiration of each plant will increase in case of irrigated crops. Besides, increased CO2 can induce abnormal and erratic rainfall distribution, which would affect the normal process of water requirements of crops, and this situation leads to poor crop performance.

Some research pointed out that a doubling of atmospheric CO2 concentrations from 330 to 660 ppmv cause 10 to 50% increase in growth and yield of C3 crops (such as wheat, soybean and rice) and a 0 to 10% increase for C4 crops (ibid).

Crop growth rates Temperature is the dominant climatic factor in the development of plants and animal growth. Any variation beyond the optimum level has a negative impact on the normal development of plant. As Parry (1990) pointed out recent studies indicated that an increase in temperature resulted in lower yields in cereals and the reverse was true for root crops and grassland. However, due to higher rate of evaporation and reduced moisture availability, which could be created by the global warming, the overall yield will be less.

Dekadal Average Temperature for Bahir Dar(May - Nov) from 1962 - 2000

22.523

23.524

24.525

25.526

26.527

27.5

1 10 19 28 37 46 55 64 73 82 91 100

109

Dekads

T °C

Figure. 7 Dekadal mean maximum temperature for Bahir Dar from 1962 – 2000 during the cropping

season (May – November)

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% Deviat ion fro m the mean dekadal maximum temp erature fo r Bahir Dar from 19 62 - 200 0

-6-4-202468

Dekads(t en days)

% D

ev

Figure 8 Shows % deviation from the mean dekadal maximum temperature for Bahir Dar (1962-2001)

As can be seen from figure 7 there is a rise in mean maximum temperature continuously and from figure 8 we can figure out there was a positive deviation from the mean maximum temperature mostly as of dekade 57. This is obvious that the increased temperature amount has a great contribution for the rise of reference evapotranspiration (ETo). Thus, a rise of ETo together with a decrease in rainfall amount over the area would have negative impact on LGP; thereby decreasing crop yield is inevitable since the agricultural activities mainly dependent on rainfall in Ethiopia.

Growing seasons As Parry (1990) has stated, the effect of warming on length of growing season and growing period will vary from region to region and from crop to crop. In tropical climates, in which there is less seasonal temperature changes, the amount of available moisture often determines the periods of plant growth; in the rainy season growth is luxuriant and in the dry season many plants become dormant. As a result in this case the variation in temperature amount is more serious in mid and high latitude regions. For instance it is estimated that the growing season of wheat will extend by ten days per oC in Europe and in central Japan by about 8 days pre oC. In general the conclusion is that increased mean annual temperatures, if limited to two or three degrees, could generally be expected to extend growing seasons in mid-latitude and high-latitude regions. Increases of more than this could increase evaporation rate, which leads to reduced soil moisture and limit the growing season.

LGP for B Dar 1962-1977 (According to FAO method 1979)

0100200300400500600

J AN FE B MAR AP R MAY J UN J UL AUG SE P OC T NOV DE C

months

wat

er in

mm

M mean EToM M 1/2 ETo 1/4 ETo 1/10ETo

Figure 9 Shows LGP for Bahir Dar from 1962 – 1977

LGP for Bahir Dar from 1978-2001

0

200

400

600

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Month

wat

er in

MM

M mean EToM M 1/2 ETo 1/4 ETo 1/10ET

Figure 10 Shows LGP for Bahir Dar from 1978 – 2001

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Difference in LGP between two periods(1962-1977 and 1978- 2001)

0100200300400500600

JAN

FEBMAR

APRMAY

JUN

JUL

AUGSEP

OCTNOV

DEC

Months

MM

rain

fall

M mean 1 EToM M 1/2 ETo M mean 2 EToM M

Figure 11 Shows difference in Length of Growing Season between two periods (from 1962 – 1977 and 1978 - 2001)

From the above figures (Fig. 9 and Fig. 10), we can understand easily that the effect of mean deviation of rainfall on Length of Growing Period (LGP). The effect is not only on LGP there is also a decrease in rainfall amount through out the growing season in case of second period (Fig. 11).

ARI Difference for the periods 1962 - 1977 and 1978 -2001

0100200300400500600

MAY JUN JUL AUG SEP OCT NOV

Grow ing season

AR

I

ARI-1 ARI-2

Figure 12 Agricultural Rainfall difference of the two periods (from 1962 – 1977 and 1978 - 2001)

As the ARI analysis shows there is a shift in LGP in case of ARI 1 the duration is July – October while it is June – September in case of ARI 2.

Various phenological models have predicted that generally the length of growing period of the crop plants would be reduced as a result of higher temperature caused by GHG (Alocilja and Ritchie, 1991; Roberts et al, 1993; Gangadhar Rao and Sinha, 1994 cited in Climate Variability and Agriculture by Y.P Abrol, S. Gadgil and G. B.Pant 1996). Due to this condition, the total dry matter accumulation period also will be reduced. Moreover, as Kroff et al (cited in Climate Variability and Agriculture by Y.P Abrol, S. Gadgil and G. B.Pant 1996) have pointed out that, an increase in temperature will reduce not only the total duration, but the dry matter production also.

Livestock production Increased CO2 concentration has a great effect on animal feed. Most forage crops are C4 crops and C4 crops have a poor response to increased CO2. As a result the availability of pasture would limit livestock production. A rise in temperature could also have a significant effect on the performance of farm animals.

Effects of changes in soil moisture Water is the most limiting factor in semi-arid regions of the world. Due to the deficient rainfall situation the soil moisture reserved in the soil is minimal. An increase in temperature over tropical areas could exacerbate the existing moisture stress over the semi-arid areas. Over most parts of the tropical and equatorial regions of the world the yield of agricultural crops is negatively affected more by the amount of water received by and stored in the soil than by the air temperature, particularly in areas where rain fed agriculture is the dominant activity. Reliability of rainfall, particularly at critical phases of crop

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development, has a great importance in terms of yield. An increase in atmospheric temperature can result in a higher reference Evapotranspiration (ETo) and a shortage of soil water reserves. The amount and availability of water stored in the soil, a crucial input to crop growth, will be affected by changes in both the precipitation and seasonal and annual evapotranspiration regimes. As Rind et al., (cited in Climate Change and World Agriculture, 1990) pointed out some Global Climate Model (GCM) predictions have interpreted that the rise in potential evapotranspiration will exceed that of rainfall resulting in drier regimes throughout the tropics and low to mid-latitudes. Because the soil moisture processes are represented so crudely in the current GCMs, however, it is difficult to associate much certainty with these projections (IPCCa, 1990).

Pest and diseases Global warming leads to a change in the nature, habit and distribution of pests. Studies suggest that temperature increases may extend the geographic range of some insect pests currently limited by temperature.

The effect of climate warming plays an important role on the distribution of pests. In Ethiopia, the most susceptible areas for insect out breaks are apparently the highland regions below 2000 meters and parts of lowlands. However, plant pests occur everywhere during the rainy season particularly at the time of drought when erratic rainfall is a common phenomenon over drought prone areas of the country. Pests at present limited to tropical countries may spread into the temperate regions causing serious economic losses. For instance, Sorghum Chafer becomes a chronic problem since 1993 over northeastern highlands of Ethiopia including Afar regions. Climate change will alter the nature of occurrence of agricultural pests in terms of area. Warmer temperatures shorten the generation time; increase the development rate of epidemic. Most agricultural diseases have greater potential to reach severe levels under warmer conditions. Higher precipitation and warmer air temperature would increase the spread of fungal and bacterial pathogens in given areas. Cereal crops are more susceptible to pest and diseases under warmer and humid conditions.

Available cultivable agricultural land As IPCC points out, due to global warming, sea level rises will be the major problem. This condition results in thermal expansion of the oceans and partial melting of glaciers and ice caps. As a result, the amount of cultivable land will decrease, mainly through the inundation of low-lying farmland but also through the increased salinity of coastal ground water.

International actions In order to tackle the problems and mitigate the effect of climate change many conventions were ratified like the Kyoto international conventions, Climate Change convention, United Nations Framework Convention (UNFCCC), Malaysia and the U.N convention, etc. Besides, the Intergovernmental Panel on Climate Change has been set up under the auspices of the World Meteorological Organization (WMO) and the United Nation Environmental Programme (UNEP), to examine the problems, which are related to climate change. Many studies have been made on climate change in terms of impact, adaptation and vulnerability. Thus, these studies would be helpful to prepare action plans in order to mitigate the effect of climate change. In addition to that, these days countries are focusing on producing CFC free products to minimize the emission of GHG. Many studies have examined the likely impacts of climate change on agriculture and inventories have been made through different country study programs. For example through the U.S. Country Studies Program, the U.S. Government has been providing technical and financial support to 56 developing countries and countries with economies in transition to assist them in conducting climate change studies (http://www.gcrio.org/CSP/webpage.html). So that many climatic inventories have been made in different countries by using this financial support. In 1992, at the United Nations Conference on Environment and Development, over 150 nations signed a binding declaration on the need to reduce global warming. A UN Conference on Climate Change, held in Kyoto, Japan, in 1997 resulted in an international agreement to fight global warming, which called for sharp reductions in emission of industrial gases (http://www.climatenetwork.org/).

Adaptation Adaptation has the potential to reduce adverse impacts of climate change and to enhance beneficial impacts. The capacity of human nature to adapt to and cope with climate change depends on such factors as wealth, technology, education, information skills, infrastructure, access to resources, and management capabilities. Thus, the adaptation capacity of developing countries will be limited due to

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their low level of technological advancement. Therefore, intergovernmental activities are important in order to perform sound adaptation measures.

Possible adaptation measures Applying improved knowledge to develop better techniques and to resist the effect of climate change in a given locality. Cultural practices that can precondition for the plant need to be further explored and implemented to mitigate the effect of stress factors. Change in land use by using deferent techniques such as changing farm area, change to crops with higher thermal requirements and drought-tolerant crop, a switch to crops with lower moisture requirements and changes in crop location. Change in management in terms of the use of irrigation, fertilizer, in the control of pests, in soil drainage, in farm infrastructure. Create awareness among people about the causes of climate changes so that farmers could change their wrong management practices such as deforestation, over grazing, etc. which are the main causes for desertification and climate change at large.

Conclusion Climate change induced by increasing greenhouse gases is likely to affect crop yields differently from region to region across the globe. Decreases in potential crop yields are likely to be caused by shortening of the crop-growing period (Fig. 11), decrease in water availability due to higher rates of evaporation. As many studies suggested, the tropical regions appear to be more vulnerable to climate change than the temperate regions for several reasons. Temperate C3 cops are likely to be more responsive to increasing levels of CO2 than C4 cops. Besides, insects and diseases, already much more prevalent in warmer and more humid regions, may become even more widespread. Tropical regions may also be more vulnerable to climate change because of economic and social constraints. Greater economic and individual dependence on agriculture, widespread poverty, and inadequate technologies are likely to exacerbate the impacts of climate change in tropical regions. Thus, plant breeders should give more emphasis on development of heat and drought-resistance crops. Research is needed to define the current limits to these resistances and the feasibility of manipulation through modern genetic techniques. In some regions, it may be appropriate to take a second look at traditional technologies and crops as ways of coping with climate change. Better management techniques in crop and livestock production should be developed in order to mitigate the effect of climate change. In order to avoid mismanagement of natural resources like deforestation, overgrazing, cleaning farmland by using fire, etc creating awareness among farmers has great importance.

As can be mentioned in the above statement, those with the least resources have least capacity to adapt and are the most vulnerable. Thus, since the effect of Global Worming affects both developing and developed countries intergovernmental economic support is very important to tackle the problem and to achieve sound solution for climate change. In many cases, reducing vulnerability to current climate variability should also serve to mitigate the impact of global warming.

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