Scaling artificial heat islands to enhance precipitation in the United Arab Emirates

Abstract

Potential for regional climate engineering is gaining interest as a means of solving regional environmental problems like water scarcity and high temperatures. In the hyper-Arid United Arab Emirates (UAE), water scarcity is reaching a crisis point due to high consumption and over-extraction and is being exacerbated by climate change. To counteract this problem, the UAE has conducted cloud-seeding operations and intensive desalination for many years but is now considering other means of increasing water resources. Very large "artificial black surfaces"(ABSs), made of black mesh, black-painted, or solar photovoltaic (PV) panels have been proposed as a means of enhancing convective precipitation via surface heating and amplification of vertical motion. Under the influence of the daily UAE sea breeze, this can lead to convection initiation under the right conditions. Currently it is not known how strong this rainfall enhancement would be or what scale of black surface would need to be employed. This study simulates the impacts at different ABS scales using the WRF-Noah-MP model chain and investigates impacts on precipitation quantities and underlying convective processes. Simulations of five square ABSs of 10, 20, 30, 40, and 50gkm sizes were made on four 1gd cases, each for a period of 24gh. These were compared with a Control model run, with no land use change, to quantify impacts. The ABSs themselves were simulated by altering land cover static data and prescribing a unique set of land surface parameters like albedo and roughness length. On all 4gd, rainfall is enhanced by low-Albedo surfaces of 20gkm or larger, primarily through a reduction of convection inhibition and production of convergence lines and buoyant updrafts. The 10gkm square ABS had very little impact. From 20gkm upwards there is a strong scale dependency, with ABS size influencing the strength of convective processes and volume of rainfall. In terms of rainfall increases, 20gkm produces a mean rainfall increase over the Control simulation of 571g616gm3gd-1, with the other sizes as follows: 30gkm (∼1/4g1 milliongm3gd-1), 40gkm (∼1/4g1.5 milliongm3gd-1), and 50gkm (∼1/4g2.3 milliongm3gd-1). If we assume that such rainfall events happen only on 10gd in a year, this would equate to respective annual water supplies for >g31g000, >g50g000, >g79g000, and >g125g000 extra peoplegyr-1 at UAE per capita consumption rates. Thus, artificial heat islands made from black panels or solar PV offer a means of enhancing rainfall in arid regions like the UAE and should be made a high priority for further research.