An examination of Sudan's ecological zones indicates that the majority of its land is quite vulnerable to change in temperature and precipitation. The country's inherent vulnerability may best be captured by the fact that food security is mainly determined by rainfall, particularly in the rural areas where more than 65% of the population lives.
Mean annual temperature lies between 26º to 32º but in some places it reaches 47º C causing a lot of stresses and heat related diseases. Rainfall is erratic and varies significantly from the North to the South. The unreliable nature of rainfall together with its concentration during the short growing season increases the vulnerability of the rain-fed agricultural system. A trend of decreasing annual rainfall in the last 60 years (0.5%) and increased rainfall variability is contributing to drought conditions in many parts of the country. This pattern has led to serious and prolonged drought episodes. For example, Sudan experienced a succession of dry years from 1978 to 1987 resulting in severe social and economical impacts including many human and livestock fatalities and migration and displacement of several million people. Drought problems such as these will increase if trends continue.
Sudan also experienced many devastating floods, of two specific types, during the past several decades. The first type occurs during torrential rain when high levels of water overflow the River Nile and its tributaries, usually due to above normal rainy seasons in the Ethiopian Plateau. Severe floods were reported in 1946, 1988, 1994, 1998 and 2001. The other type of flood occurs as a result of heavy localized rainfall during the rainy summer season and such incidents were reported in 1952, 1962, 1965, 1978-1979, 1988 and 1997. In addition to drought and floods there are other climate extreme events such as dust storms, thunderstorms and heat waves whose occurrence though less frequent, still pose serious threat to local livelihood.
Beside the adverse economic impacts of these climate changes related phenomena there are also associated social impacts. For example during drought events conflicts occur due to competition over diminished natural resources. Also - as has happened many times - food shortages lead to famine, followed by displacement and refugees which in turn leads to misuse of the natural resources that remain. During floods and droughts people typically move to cities where their arrival causes stress and shortages of already limited services. The displaced also live in very acute conditions that can lead to disturbances that undermine stability and security.