Regional and global teleconnections patterns governing rainfall in the Western Mediterranean: case of the Lower Sebou Basin, North-West Morocco

Rainfall in north-western Morocco has shown significant monthly fluctuations with dramatic socio-economic impacts over the past decades. Several studies have suggested that variability is related to fluctuations in large-scale circulation patterns. In recent years, several promising centennial reanalysis datasets have become available, paving the way for new dynamic studies that facilitate an understanding of observed rainfall variability. Here, a statistical analysis of the rainfall time series of three stations in the Lower Sebou Basin (LSB) covering the period 1948-2017, as well as other global reanalysis datasets is used to explore teleconnections based on extensive statistical analysis and empirical orthogonal functions (EOFs). The Mann-Kendall test (MK) was conducted to identify significant monthly rainfall trends. The notable trend among significant trends is selected using the Theil Sen's slope (TS) where downward trends were identified in early winter (December) and early spring (March) with rainfall decreases of 0.5 mm/year and 0.42 mm/year, respectively. Changes in significant trends found under the influence of different teleconnection patterns using their indices such as the North Atlantic Oscillation Index (NAOI), the Mediterranean Oscillation Index (MOI) and the Southern Oscillation Index (SOI) are determined by the partial Mann-Kendall test (P-MK). Overall, the results obtained in this study suggest that teleconnections affect the amounts of rainfall in the LSB. Negative and statistically significant correlations are observed between the NAOI and MOI and the amounts of rainfall falling in the LSB. Spring rainfall shows significantly negative (positive) correlations in the Eastern (Western) Pacific with sea surface temperature (SST), again highlighting the negative impact of El Nino (negative phase of SOI) on rainfall in Northwestern Morocco. These results are useful for monthly rainfall forecasting and water resource planning.

Automated summary

Rainfall variability in north-western Morocco is significantly influenced by large-scale circulation patterns. Negative correlations between rainfall and North Atlantic Oscillation Index (NAOI) and Mediterranean Oscillation Index (MOI) are observed, while El Nino and the negative phase of Southern Oscillation Index (SOI) have a negative impact on rainfall.