The climate is arid with very high summer temperatures. Spate irrigation area - ha 3. Mean annual rainfall is about 100 mm, ranging from less than 40 mm around Liwa in the southern desert to 160 mm in the north-eastern mountains. Spring and summer witness only occasional concentrated heavy rainfall. The rainfall distribution is highly variable over space and time.
Rainfall tends to be more reliable in the north-eastern mountain region.
The total annual surface runoff produced from rain is about 150 million m , but there are no perennial streams. The average annual groundwater recharge is about 120 million m, most of which comes from infiltration from the river beds. The total groundwater abstraction during the year 1995 is estimated at l 615 million m . In any case, the over-extraction of groundwater resources has led to a lowering of the water table by more than one metre on average during the last two decades, while sea water intrusion is increasing in the coastal areas. Dams To increase the groundwater recharge a number of dams have been built at various locations in the country.