Assessing the Water Budget of the Arabian Peninsula and Its Internal Recycling Potential

Abstract The Arabian Peninsula, a predominantly hyperarid region, is facing increasing demands for freshwater driven by its growing population. The pressure on the resource would be reduced if local evaporation led to more rainfall within the domain. This study assesses moisture recycling in the region by evaluating moisture transport, precipitation, and evaporation in four state-of-the-art reanalyses against in situ and remote sensing data. The reanalyses reliably capture the main spatial and temporal features of the transport, in particular its two-layered structure. The upper layer, above 900 hPa, is marked by an anticyclonic circulation which has moisture enter in the northwest and exit in the southwest with little net effect. The lower layer is shaped by an influx of moisture from sea breezes during the day and an outflux during the night. However, the reanalyses underestimate daytime sea-breeze imports compared to radiosonde data, leading to a net average outward flow of moisture from the domain. This diurnal imbalance is likely not due to desert agriculture because the reanalyses do not explicitly consider irrigated cropland. Certain reanalyses also report nonphysical residual evaporation across the region, contradicting remote sensing data. Agreement between reanalyses and observations is better regarding precipitation because it is controlled in part through synoptic conditions. Despite the uncertainties, the magnitude of incoming transport relative to evaporation suggests that internal moisture recycling is negligible. As a consequence, increased evaporation due to incremental land-use changes and irrigation is unlikely to enhance regional rainfall. Significance Statement The societal demand for water is high in the Arabian Peninsula, but rainfall is scant. The locally sourced precipitation, originating from past rains or human usage rather than transport from remote regions, is expected to increase in response to additional irrigation. The regional hydrological budget in four reanalyses was established and tested against observations. The main features were consistent, including a recycling ratio in the mere single-digit percentages. Thus, irrigation losses are unlikely to be recouped as extra rainfall.