| Abstract: | Potential for regional climate engineering is gaining interest as a means of rainfall enhancement. In the hyper-arid United Arab Emirates (UAE), water scarcity is reaching crisis point due to high consumption, groundwater extraction, and global heating. To counteract this problem, the UAE has been successfully conducting cloud-seeding operations and research for many years. As well as cloud seeding there are now other means proposed for increasing water resources, as exemplified in the UAE Research Program for Rain Enhancement Science (UAEREP). We have proposed that very large areas covered with artificial black surfaces or photovoltaic solar panels will enhance rainfall via increased surface heating and vertical motion. Under the influence of the daily UAE sea breeze, this leads to convection initiation under the right atmospheric conditions. This study simulates the impacts of different sizes of black surfaces on convective processes and precipitation enhancement. Five square black surfaces of 10, 20, 30, 40, and 50 km sizes were simulated on several one-day cases, each for a period of 24 h. These were compared with a Control model run, with no black surfaces, to quantify the impacts. The surfaces were simulated by prescribing unique black surface characteristics like very low albedo and low surface roughness. Our results show that rainfall is enhanced by surfaces of 20 km or larger, primarily through increased wind convergence and buoyant updrafts, and a reduction in convection inhibition. The 10 km square ABS had very little impact. From 20 km upward, the volume of rainfall increased with the scale. The following increases were observed (as compared with the Control simulation): 20 km (571 616 m3 extra rainfall), 30 km (∼1 million m3), 40 km (∼1.5 million m3), and 50 km (∼2.3 million m3). If such enhancement occurred only 10 times a year, this would equate to an extra annual water supply for 31000, 50000, 79000, and 125000 people respectively, at current UAE water consumption rates. Thus, artificial heat islands offer an exciting means of enhancing rainfall in the UAE and should be made a high priority for further research.Oliver Branch, Lisa Jach, Thomas Schwitalla, Kirsten Warrach-Sagi, and Volker Wulfmeyer |
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