Abstract
The most significant large-scale environmental challenge that many countries, especially in the arid and semi-arid regions of the world, will face in the middle and long-term are water scarcity problems, which are attributed to climate change impacts such as temperature increase, abundance of high solar radiation, and aridity in addition to population pressure. In many countries, current water resources use already exceeds sustainable and renewable supply. Various methodologies are suggested to increase the sources of water supply, among which one of the alternatives is rainwater and runoff harvesting (ROH). Water scarcity and additional stress are among the most specific problems in arid and semi-arid regions, where vegetation cover is very weak under extensive solar irradiation effects with high evaporation rates. Present global warming, climate change impacts, and their future patterns are expected to cause increase in the evapotranspiration rates and hence reduction in the groundwater recharges. Under such circumstances, any simple but effective water storage augmentation facility as the artificial groundwater recharge gains vital importance for sustainability of water supply and survivals in desert ecosystems. Although intensive and frequent rainfall events are rare they generate significant surface water flow during occasional floods and especially flash floods with huge amounts of surface water. It is, therefore, necessary to enhance artificial groundwater recharge from consequent frequent runoffs through suitable hydraulic structures. This paper aims at assessing the importance of ROH systems for domestic supply in arid regions with specific reference to the Kingdom of Saudi Arabia. For this purpose, it presents ROH from the surface flows in depressions of Quaternary wadi deposits in arid and semi-arid regions.