Characterization of annual and seasonal rainfall trend using innovative trend analysis (ITA) and classical methods: the case of Wadi Sebou basin (WSB) Morocco

The Mediterranean domain is one of the hot spots of climate change; drought and rainfall decline combined with the rise of temperatures and heat waves are the most impactful of these changes, which are well described in the recent studies. Morocco is one country where harmful effects on agricultural activities and water supply management have been observed. The aim of this work is to present the temporal and spatial patterns of annual and four seasonal rainfall series during the period of 1961-2018 at 15 stations within the Wadi Sebou basin of northern Morocco. Rainfall trends were investigated using classical Mann-Kendall (MK) and Theil Sen slope nonparametric tests and compared with the new innovative trend analysis (ITA) at 95% and 99% confidence levels. The spatial and temporal results of classical and ITA approaches are compared through maps of annual and seasonal trends. The results show a decreasing amount of -20% to -40% of the total annual precipitation over the study period. High values of rainfall show a clear trend to increase during autumn, and a general downward trend during winter and spring. With the sensitivity of the ITA method for trend detection, a high number of significant trends were detected by ITA method compared with the classical MK test. This finding highlights the capacity of the ITA method to detect hidden trends that cannot be detected by the MK test, with 70/75 or 93% of the cases found significant for ITA against only 27/75 or 36% of the significant cases for MK test. The other advantage of ITA stems from its capacity to show trends within three clusters of "high," "medium," and "low" rainfall values. The results of this study will help managers to understand the rainfall variability in the Sebou river basin, to improve their mitigation strategies and to have a prospective view on the impact of climate change on the river basins and water resources plans.