Making it Rain in the Desert: Fantasy or Future
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Regreening initiatives are being undertaken as climate change mitigation strategies, to improve water and food security, and to increase biodiversity. Because of positive feedback loops between vegetation and precipitation, regreening has the potential to lead to the restoration of local and regional water cycles. However, in arid and hyper-arid regions, the amount of available rainwater is not sufficient to sustain the initial stages of regreening. A technology that uses solar energy to evaporate seawater may be able to enhance convective rainfall. The main research question is: Can evaporation through technology potentially be used for water cycle restoration in arid and hyper-arid regions? Using atmospheric boundary layer theories as described by Stull (1988), a simple atmospheric column model was developed and coupled to a surface model with a dynamic vegetation component. Results of sensitivity analyses with this numerical model show the importance of atmospheric conditions and it is found that evaporation through technology has the potential to be effective in regions with a relatively moist and cold atmosphere. Regions that satisfy these conditions and also have a dry soil are mostly found 25-35°N near coasts and/or in mountainous areas. One such area is the Sinai Peninsula. Numerical simulations using ERA5 reanalysis data as boundary conditions show that the evaporation technology can increase precipitation locally, but this increase is small. However, because of the wind directed southward and up the mountain range of South Sinai, the technology has the potential to cause precipitation non-locally as well as is shown by simulations where the atmospheric column is moved along a streamline. In conclusion, enhanced evaporation through technology has the potential to be used for regreening projects if atmospheric conditions are favorable. However, more research is needed and the potential adverse effects, such as warming, need to be taken into consideration.