Extreme rainfall events in Morocco: Spatial dependence and climate drivers

Abstract

The history of Morocco is replete with tragic natural disasters related to floods that led to numerous casualties and significant material losses. An important driver of these floods is extreme precipitation. Understanding the spatial characteristics of extreme precipitation events is critical to accurately predicting, assessing, and mitigating the risks they pose. Yet, the physical drivers of extreme precipitation events (EPEs) in Morocco remain poorly known. To address this gap, we apply a clustering method to divide Morocco into regions that are spatially consistent in terms of extreme precipitation. We then determine the drivers of extreme precipitation by analyzing atmospheric circulation anomalies during the occurrence of some well chosen EPEs in each region. Our findings suggest that Morocco can be subdivided into 5 spatially coherent regions. Extreme precipitation in the northwestern regions is associated with patterns similar to the negative phase of the North Atlantic Oscillation (NAO) with strong upper-level flow anomalies enhanced by Greenland blocking and/or Rossby wave breaking (RWB) episodes. By contrast, the southern regions are associated with relatively weak upper air troughs but strong water vapor transport anomalies from the tropics.