Hydrological extremes in hyperarid regions: A diagnostic characterization of intense precipitation over the Central Arabian Peninsula

Aridity is typically associated with deep and dry daytime boundary layers, stable nighttime stratification, divergent flows, and limited large-scale moisture advection. All these factors are paramount in regulating the hydroclimatology of hyperarid regions, resulting in extremely intermittentand often intenselocal precipitation patterns. However, the link between synoptic-scale forcing and intense precipitation over arid regions has been scarcely investigated in the literature and still remains exceedingly unexplored. We present here a diagnostic study of intense precipitation in the Central Arabian Peninsula, based on the analysis of local extreme signatures embedded in synoptic patterns. Special emphasis is given to the genesis of winter extremes over the Peninsula, and to possible effects of synchronization between the atmospheric circulation over the Mediterranean and the Indian Ocean. Based on composites of the tropospheric circulation for a large ensemble of intense events, we show that moisture necessary to trigger winter extremes over the Peninsula starts to build up in average 8 days before heavy rainfall occurrence, mainly as a consequence of the interplay between the Mediterranean and the Monsoonal circulation. Moisture advection is in turn associated with an upper troposphere cyclonic circulation and pronounced potential vorticity intrusions. Overall, our results demonstrate how large-scale precursors can be effectively used to improve the predictability of rainfall extremes in hyperarid regions.