There can be severe frost generally and even weeks of snow in the mountains. The western and eastern regions are hot and humid in the summer months, with maximum temperatures around 42 C, while the winters are warm. In the north, annual rainfall varies between 100 and 200 mm. Further in the south, except near the coast, annual rainfall drops below 100 mm. Water resources Heavy rainfall sometimes results in flash floods of short duration.
River beds are dry for the rest of the time.
Part of the surface runoff percolates through the sedimentary layers in the valleys and recharges the groundwater, some is lost by evaporation. About 1 km3 recharges the usable aquifers. Dams In 1993, approximately 185 dams of various sizes had been constructed for flood control and groundwater recharge with a combined storage capacity of 475 million m3. About 45 new dams were planned to be built. A major dam, the Bisha dam in the south-west with a capacity of 325 million m3, was under construction in 1993.