1. Jfuas No.2 December 2013
1
Trends of rainfall and Temperature in North Darfur State
Salih Ahmedai Abdalla, Faculty of Environmental Sciences and Natural
Resources
University of Al-Fashir, Sudan
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Abstract
Precipitation in arid and semi-arid zones results from convective
cloud mechanisms producing storms of short duration, relatively high
intensity and limited areas extent. The climate of Al- Fashir is semi-
desert (a typical Sahel). The mean annual rainfall for Al- Fashir
meteorological station for the period 1917-2012 (96 years) is 249.6
mm. The return period for p 67% is 197.2 mm or higher can be
expected in 2 years out of 3 years. The return period for p 33% is 285
mm or higher can be expected in 1 year out of 3 years. There was
considerable short-term variability in annual rainfall totals and
drought conditions are integral part of the climate in North Darfur
State.
In North Darfur State there was an increase of the annual
temperature since 1950 to2009 which is about 0.5 o C. Climate
change induced loss of livelihood in crop and pastoral and drives
farmers to fall back on more Intensive exploitation of forest resources
3. Jfuas No.2 December 2013
3
with consequences for biodiversity. Studies reported that increasing
temperatures due to climate change will increase rainfall by 5-20%
from December to February, and decrease rainfall by 5-10% from
June to August by 2050. On regional variations it was concluded that
warming is likely to be greatest over the interior of the semi- arid
margins of the Sahara and central Southern Africa. Droughts have
become more common, especially in the tropics, since 1970.Droughts
are becoming longer and more severe and affecting wider area. This is
consistent with decreased precipitation in some areas and higher
temperatures causing drying conditions. Increasing sea surface
temperatures and loss of snow are direct contributors to drought.
1-Introduction
North Darfur State lies between latitudes 12º N and 20º N and
longitudes 21º 52′ E and 27º 54′ E. It had a population of 2.1 million
according to 2008 census. The state located on the southern edge of
the Sahara desert and falls within the Sahel zone. The boundaries of
the Sahel are demarcated by the 100 mm and 600 mm isohyets
average annual rainfall. The numerous definitions of the Sahel locate
it between10º N, with an average rainfall of 600 mm and 17º N, with
average 100 mm rainfall. The rainy season extends from May to
October with a peak in August. The dominant characteristic of this
region is that the rains fall in summer over a 2- 4 month period, with
extreme dryness during the rest of the year (Abdalla, 2008).
The landscapes consist of repeating patterns of sand dunes and
sandy loamy clay depressions separated by gentle slopes. The sand
4. اﻟﻔﺎﴍ ﺟﺎﻣﻌﺔ–ﻣﺠﻠﺔاﻟﻌﻠﻮماﻟﺘﻄﺒﻴﻘﻴﺔ-اﻟﺜﺎين اﻟﻌﺪد–دﻳﺴﻤﱪ2013م
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dunes have good infiltration but low water holding capacity. Due to
large pore spaces in the soil heavy showers of rain can rapidly
penetrate the depth. As a result losses through runoff and evaporation
are much lower on the loamy sand soils. This makes the dunes the
favored environment for cultivation and growing millet. Areas where
infiltration is less than rainfall, surface water gathers to form pools
which are used as watering places. In the depressions water can
infiltrate deeply contributing to the formation of groundwater. This
enable trees and herbaceous perennials to survive and provide browse
for livestock. Natural and manmade wells in such sites supply
drinking water for man and animals (Abdalla, 2008).
People practice rain-fed shifting cultivation on sandy and clay
soils. They cultivate sorghum, millet, sesame and groundnuts during
the rainy season and they keep livestock. Farmers practice a type of
rotating agriculture which left portion of the land as fallow. Rainwater
harvesting techniques were used for cultivation of crops. Land tenure
was held either by tribe or group. Agriculture is adversely affected by
low and erratic rainfall. Areas of low annual rainfall may receive
heavy thunder storms causing flood and erosion. Three months appear
to be of importance for crop growth and production. July rainfall
determines the beginning of the cultivation, the growing days and
production. When July is dry, the number of growing days is reduced
and growth is consequently limited. When August is wet, water can be
stored in the soil and used by plants for growth during September.
September rainfall can influence the plants maturation period. Apart
5. Jfuas No.2 December 2013
5
from these three months, rainfall has little bearing on production; it
can trigger early germination and influence species composition. Late
rains in October can be disastrous causing the dry vegetation to rot.
Hundred years ago, the average temperature of the earth was
about 13.7 o C (56.5 o F); today, it is closer to14.4 o C (57.9 o F).
During the past 150 years, the earth has slowly become warmer,
mostly between the years 1910 and 1940. From 1940 to 1975, there
was a slight cooling trend beginning with the 1970s, the pace picked
up. Intergovernmental Panel on Climate Change (IPCC, 2007)
reported that the average global temperature increased more rapidly at
a rate of 0.2 oC (0.36 o F) per decade. The warmest years on record
are the most recent. Studies in East Africa suggest that increasing
temperatures due to climate change will increase rainfall by 5-20%
from December to February, and decrease rainfall by 5-10% from
June to August by 2050. It is reported that the average global
temperature has increased by 0.74 °C (1.3°F) over the past century
and the warmest years on record have occurred during the recent 12
years 1995-2006.The warming trend for the last 25 years is more than
double of the past century (IPCC,2007). The purpose of this paper was
to assess the significant trends of rainfall and temperature on the state.
Droughts have become more common, especially in the tropics,
since 1970. Droughts are becoming longer and more severe and
affecting wider area (Jerry, 2008).
6. اﻟﻔﺎﴍ ﺟﺎﻣﻌﺔ–ﻣﺠﻠﺔاﻟﻌﻠﻮماﻟﺘﻄﺒﻴﻘﻴﺔ-اﻟﺜﺎين اﻟﻌﺪد–دﻳﺴﻤﱪ2013م
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2-Data and methods
The study was carried out in Al-Fashir meteorological station
which was established in 1917 for the measurements of rainfall,
temperature, evaporation, radiation and other climatic parameters. The
data was collected for rainfall and temperature for the periods1917-
2012, 1959-2009; respectively. Al- Fashir town (Meteorological
Station) lies on latitude 13o 38′ N, longitude 25o20′ E with elevation
of 730 meter. The climate of the state is semi-desert (a typical Sahel).
In the Sahel zone three divisions are recognized. The sub-desert
rainfall is less than 200 mm, the typical Sahel 200-400 mm with a
rainy season of 2 to 2.5 months, and the Sahel of Sudanese border
400-600 mm with a growing season of 3 months. The main features of
the climate are the short rainy season, highly variable with
unpredicted droughts and 90% of the rainfall falls between July and
September (Tables I, 2, 3, 4 and Fig.1)
10. اﻟﻔﺎﴍ ﺟﺎﻣﻌﺔ–ﻣﺠﻠﺔاﻟﻌﻠﻮماﻟﺘﻄﺒﻴﻘﻴﺔ-اﻟﺜﺎين اﻟﻌﺪد–دﻳﺴﻤﱪ2013م
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Probability rainfall analysis is a graphical method to determine
the probability or frequency of occurrence of yearly or seasonal
rainfall. The probability of occurrence p (%) can be calculated from
the equation (FAO, 1991).
W й с ;ŵ Ͳ Ϭ͘ϯϳϱͿͬ ;EнϬ͘ϮϱͿ džϭϬϬ
Where: P = probability in % of observation of the rank m, m =
the rank of the observation, N = total number of observations used.
The above equation is recommended for N equal 10 to 100. From the
curve the probability of occurrence or exceedance of a rainfall value
of a specific magnitude can be obtained. Inversely, it is also possible
to obtain the magnitude of the rain corresponding to a given
probability (Fig4).The return period T can be derived once the
exceedance probability P (%) is known from the equations:
d сϭϬϬͬW ;LJĞĂƌƐͿ
3- Results
3-1 Rainfall
The annual rainfall for AL-Fashir meteorological station for the
period 1917-2012 is 249.6 mm (Table 1, 2 and Fig 1). In the area
between latitudes 12o N- 15o N about 85% of the annual rainfall
occurs during July and September and over 60% of the total
precipitation occurs in July and August and most of the rains fall in
the form of heavy thunder storms of short duration. The long-term
annual rainfall for the periods1951-1980, 1961-1990, 1971-2000 were
263,212.6 and 193.4 mm, respectively (Table 2). The mean annual
11. Jfuas No.2 December 2013
11
rainfall for the periods 1917-1946,1947-1976 and1977-2006 were
288.8, 274.9 and194.5 mm, respectively (Fig2). ILO(1997) reported
that the ten-yearly mean annual rainfall for the periods 1946-1955,
1956-1965, 1966-1975 and 1976-1985 were 327.1, 286.1, 224.9 and
161.8 mm, respectively(Fig3). .
Ϭ
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ŵŵ
ŝŐϮ͘dŚĞ ϯϬ LJĞĂƌƐ ŵĞĂŶƐ ĂŶŶƵĂů ƌĂŝŶĨĂůů ĨŽƌ ƚŚĞ ƉĞƌŝŽĚ ϭϵϭϳͲϮϬϬϲ
12. اﻟﻔﺎﴍ ﺟﺎﻣﻌﺔ–ﻣﺠﻠﺔاﻟﻌﻠﻮماﻟﺘﻄﺒﻴﻘﻴﺔ-اﻟﺜﺎين اﻟﻌﺪد–دﻳﺴﻤﱪ2013م
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ŝŐϯ͘dŚĞ ƚĞŶͲLJĞĂƌůLJ ŵĞĂŶ ĂŶŶƵĂů ƌĂŝŶĨĂůů ĨŽƌ ƚŚĞ ƉĞƌŝŽĚ ϭϵϰϲͲϭϵϴϱ
GFZ/GTZ (1988) reported that the mean annual rainfall showed
a decline of 51% since 1950’s(Table3).The figures indicate that the
proportion of seasonal rainfall expected in July, a critical month for
millet production has fallen from around 30% down to 17%. A
considerable proportion of annual rainfall can fall in one or two
storms and the period 1937-1986 (50 years) the isohyets moved about
200 km to the south. The average amount of annual rainfall became
considerably less. In 1985 almost 20% of annual rainfall occurred in
April and May, while in May 1989 about 21% of the year’s rain fell in
one 38.8 mm storm. Most of this rain would have been used up by
weeds before the millet could be planted. The average annual rainfall
for 1987 and 1988 almost the same but the difference in rainfall
13. Jfuas No.2 December 2013
13
distribution caused failure of the millet crop in1987 and very good
harvest in 1988.
ϯͲϮ ZĂŝŶĨĂůů ƉƌŽďĂďŝůŝƚLJ
Table (1) was ranked in descending order and the rainfall
probability and return period were calculated to the following
equations. The mean annual rainfall for Al- Fashir meteorological
station for the period 1917-2012 (96 years) is 249.6 mm. The return
period for p 67% is 197.2 mm or higher can be expected in 2 years out
of 3 years. The return period for p 33% is 285 mm or higher can be
expected in 1 year out of 3 years. There was considerable short-term
variability in annual rainfall totals and drought conditions are integral
part of the climate in North Darfur State. Droughts have become more
common, especially in the tropics, since 1970.Droughts are becoming
longer and more severe and affecting wider area. This is consistent
with decreased precipitation in some areas and higher temperatures
causing drying conditions. Increasing sea surface temperatures and
loss of snow are direct contributors to drought.
14. اﻟﻔﺎﴍ ﺟﺎﻣﻌﺔ–ﻣﺠﻠﺔاﻟﻌﻠﻮماﻟﺘﻄﺒﻴﻘﻴﺔ-اﻟﺜﺎين اﻟﻌﺪد–دﻳﺴﻤﱪ2013م
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0
100
200
300
400
500
600
700
020406080100
Series1
ŝŐ ϰ͘dŚĞ ĂŶŶƵĂů ƌĂŝŶĨĂůů ƉƌŽďĂďŝůŝƚLJ ĚŝĂŐƌĂŵ ĨŽƌ ƚŚĞ ƉĞƌŝŽĚϭϵϭϳͲ ϮϬϭϮ
͵Ǧ͵‡’‡”ƒ–—”‡
The mean annual temperature increases from north to south and
it is high throughout the year. The drop in temperature by summer
rains is greater than that caused by sun in winter. For the comparison
of the climatologically factors between the long –term 1951-1980
and1971-2000, in the former the wind speed and relative humidity
were higher where in the lateral the temperatures were high (Table
2).This indicated that the region became more arid (El Sheikh, 2009).
Solar radiation average over 200 watts / m2 in most places and in
Sahara 275 watt/m2. Evaporation exceeds 3300 mm / year and the wet
15. Jfuas No.2 December 2013
15
periods extend from the second week of June to the third week of
September. The hot dry winds reduce the effectiveness of rainfall by
evaporation from the soil surfaces. Potential evapotranspiration (ETP)
in the southern Sahel is 4.2 mm/day during the growing season and in
the north it is 5.2 mm/ day. During the cooling winter months
December to February evapotranspiration falls to over 3 mm/day
(ILO, 1997).There was an increasing of the annual temperatures since
1950 to2009 which about 0.5 oC (Table 4,5 andFig.4). IPCC (2007)
reported that the average global temperature has increased by 0.74 °C
(1.3°F) over the past century and the warmest years on record have
occurred during the recent 12 years 1995-2006.The warming trend for
the last 25 years is more than double of the past century.
Surface temperatures have been observed in East Africa for
more than 100 years and results indicate that since 1905, and even
recently, the trend of TM ax. is not significant and T Min results
suggest an accelerating temperature rise.
dĂďůĞ͘ϱ ů ͲĂƐŚŝƌ ŵĞƚĞŽƌŽůŽŐŝĐĂů ƐƚĂƚŝŽŶ ŵĞĂŶ ĂŶŶƵĂů ƚĞŵƉĞƌĂƚƵƌĞƐ ;Ž
Ϳ
ĚƵƌŝŶŐ ƚŚĞ ƉĞƌŝŽĚ ϭϵϱϬͲϮϬϬϵ
WĞƌŝŽĚ DĂdž͘ DŝŶ͘ DĞĂŶ
ϭϵϱϬ Ͳϭϵϲϵ ϯϰ͘ϱ ϭϲ͘ϴ Ϯϱ͘ϲ
ϭϵϳϬ Ͳϭϵϴϵ ϯϰ͘ϴ ϭϳ͘ϱ Ϯϲ͘ϭ
ϭϵϵϬͲϮϬϬϵ ϯϰ͘ϵ ϭϴ͘ϵ Ϯϲ͘ϵ
16. اﻟﻔﺎﴍ ﺟﺎﻣﻌﺔ–ﻣﺠﻠﺔاﻟﻌﻠﻮماﻟﺘﻄﺒﻴﻘﻴﺔ-اﻟﺜﺎين اﻟﻌﺪد–دﻳﺴﻤﱪ2013م
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4-Discussion
Al-Fashir meteorological station mean annual rainfall for the
period 1917-2012 is249.6 mm. The return period for 67% is 197.2 mm
or higher can be expected in 2 years out of 3years. The return period
for 33 % is 285 mm or higher can be expected in 1 year out of 3 years.
There was considerable short-term variability in annual rainfall totals
and the poor rains to drought conditions are integral part of the climate
in North Darfur and should not be considered as an expected event.
The normal rainfall for the following successive periods, 1941-
1970, 1961-1990 and1971-2000 shows declining trend. The
coefficient of variation of rainfall for the same periods shows a rising
trend. In the central part of the country, the coefficient of variation
ŝŐϰ͘ ů ͲĂƐŚŝƌ ŵĞƚĞŽƌŽůŽŐŝĐĂů ƐƚĂƚŝŽŶ ŵĞĂŶ ĂŶŶƵĂů ƚĞŵƉĞƌĂƚƵƌĞƐ
ĚƵƌŝŶŐ ƚŚĞ ƉĞƌŝŽĚ ϭϵϱϬͲϮϬϬϵ
Ϭ
ϱ
ϭϬ
ϭϱ
ϮϬ
Ϯϱ
ϯϬ
ϯϱ
EĂdž DŝŶ DĞĂŶ
ϭϵϱϬ Ͳ ϭϵϲϵ
ϭϵϳϬ Ͳϭϵϴϵ
ϭϵϵϬ ͲϮϬϬϵ
17. Jfuas No.2 December 2013
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varies between 20 and 60%.The trend lines of the mean annual rainfall
indicate a long wet period during 1960-1970 and a relative dry period
during1971-2006. Comparison of the two mean annual normal rainfall
isohyets: namely, the 200 mm and the500 mm, for 1941-1970 and
1971-2000, shows remarkable shift in the rainfall belt in the Western
Sudan.
There was an increasing of the annual temperatures since 1950
to2009 which about 0.5 o C (Table 4, Fig.5). . Boko ( 2007). reported
that in the low latitudes of the tropics, many wet areas will get wetter
and dry areas, drier, aggravating drought and food tendencies. In
addition the frequency and magnitude of extreme weather events will
increase, creating more variability in water supplies that drive
agricultural and hydrological systems.
5-Conclusion
FAO (1994) defines food security as access by all people at all
times to the food needed for a healthy and active life. FAO (2008)
gives the four main components of food security as food availability,
food accessibility, food utilization and system stability which implies
affordability. The impact of climate change on Africa’s agricultural
systems related from increased intra- annual and inter-annual climate
variability followed by rapid depletion of Sub- Saharan Africa’s
natural resources and increasing of the soil erosion which further
threatens the sustainability of the peasant farmer (Padgham, 2009 ). In
arid and semi-arid climates the standard deviation ratio of maximum
to minimum annual amounts is greater. With mean annual rainfalls of
18. اﻟﻔﺎﴍ ﺟﺎﻣﻌﺔ–ﻣﺠﻠﺔاﻟﻌﻠﻮماﻟﺘﻄﺒﻴﻘﻴﺔ-اﻟﺜﺎين اﻟﻌﺪد–دﻳﺴﻤﱪ2013م
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200-300 mm the rainfall in 19 years out of 20 ranges from 40-200% of
the mean and for 100 mm/year from 30-350% of the mean(
FAO,1991). Warming in Africa may be higher than the global average
and that it may persist throughout all seasons. Further, annual mean
surface air temperatures are expected to increase between 3oC and
4oC by 2009, roughly1.5 times the average global temperatures rises
.On regional variations it was concluded that warming is likely to be
greatest over the interior of the semi- arid margins of the Sahara and
central Southern Africa. It was reported that in oceans rising water
temperatures may reduce the food supplies that fish in upper water
layers depend on, and increased carbon dioxide in the atmosphere will
increase the acidity of water bodies (IPCC, 2007).
African dry lands are affected by temperature increases for most
of Africa, while expected rainfall trends vary (Christensen et al.,
2007).There is a general consensus that climatic variability will
increase, leading to an increase in drought and floods and to grow
uncertainty about the onset of the rainy season. Annual rainfall
fluctuations affects the hydrological cycle, water resources, agriculture
and ecosystem performance and services.
Water is essential for all life and is used for food production,
drinking and domestic and industrial uses. It is also part of the large
ecosystem on which biodiversity depends. Precipitation, converted to
soil and groundwater and thus accessible to vegetation and people, is
the dominant pre-condition for biomass production and social
development in the dry lands. Lack of water is caused by low water
19. Jfuas No.2 December 2013
19
storage capacity, low infiltration, large inter-annual and annual
fluctuations of precipitation and high evaporation demand.
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