Regional Geoengineering to Increase Rainfall over the Red Sea Arabian Coastal Plains by Utilizing Sea Breezes

The Red Sea (RS), which is squeezed between Africa and Arabian Peninsula, has a high evaporation rate, exceeding 2 m of water per year. The water vapor is transported from the shorelines by breezes as far as 200 km landward. Relative humidity in the vicinity of the RS exceeds 80% in summer. Nevertheless, precipitation is scarce in most of the Arabian RS coastal plain except its Southern part, where mountain ridges reach 3 km height. The coastal mountains in the central part of the RS (18N-24N) are 1 km high and therefore cannot trigger orographic precipitation in the same way as the southern part of 5 the RS coastal plain. In this work we assess how deliberate changes (geoengineering) in land-surface characteristics affect precipitation over the Arabian RS coast. For these purposes we use the Weather Research and Forecasting (WRF) regional model to test whether altering the surface albedo or converting bare lands to wide leaf forests over an extended coastal plain region could trigger precipitation from the vast amount of water vapor transported by see breezes to the land. The calculations are performed using 10 a cloud-resolving model configuration with 3 km grid spacing for the Summer season of 2013, 2015, and 2016, with boundary conditions derived from ECMWF 9 km operational analysis. Our simulations show that geoengineering of land surface characteristics perturbs the coastal circulation. This includes the heat, moisture, and momentum exchange between land surface and atmosphere, as well as the breezes, the structure of the planetary boundary layer, cloud coverage, and eventually the amount of precipitation. We found that extended afforestation 15 and increase in surface albedo are not effective in triggering precipitation over the RS coastal plains. Conversely, decreasing surface albedo over the coastal plains intensifies breezes, enhances vertical mixing within the Planetary Boundary Layer, and triggers more coastal precipitation. Such a decrease of surface albedo could be achieved by distributing solar panels over the coastal area, which will not only provide clean energy but also increase fresh water supply. This form of regional land-surface geoengineering, along with advanced methods of collection and underground storage of fresh water, provides a feasible solution 20 to the mitigation of the Water Crisis in the Desert Coastal Regions.