Changes in Regional Circulation Weather Type in Morocco During the Period 1980–2019

Abstract

Morocco is among the regions in the Mediterranean basin most exposed to the impacts of climate variability and change. This increasing exposure requires a detailed and rigorous analysis of regional atmospheric dynamics to better understand the mechanisms behind recent climate trends. This study aims to examine the variability of circulation weather types (CWTs) at a regional scale over the period 1980–2019, within a geographical area bounded by latitudes 20° to 40° N and longitudes 10° to 22.5° W. The analysis is based on data from the NCEP-DOE Reanalysis 2, including mean sea level pressure (MSLP) and geopotential height at 500 hPa (Z500), with a spatial resolution of 2.5° in both latitude and longitude. The adopted methodology identifies daily CWT using a principal component analysis (PCA) in S-mode with Varimax rotation (PCAV), followed by the evaluation of their monthly distributions and temporal trends. The analysis highlights a marked trend toward increased atmospheric configurations conducive to hot conditions during the dry season, associated with the intensification and northward shift in the Saharan thermal low. This dynamic is reinforced by the increased frequency of ridges or high geopotential heights at 500 hPa, which transport warm tropical air toward the region. Moreover, the study reveals a notable decrease in the frequency of upper-level troughs at 500 hPa during the wet season. These upper-level troughs play a crucial role in cyclogenesis and the delivery of precipitation. These findings indicate a shift toward a regional atmospheric dynamic unfavorable to Morocco’s hydric balance, characterized by more frequent and intense summer heat and worsening winter drought.