Variability of rainfall regime in an agricultural region with a semi-arid climate: Case of Tadla irrigated perimeter (continental Morocco)

Abstract

The perimeter of Tadla, a strategic irrigated agricultural area in Morocco, but its rainwater resources are becoming scarcer. In fact, this work aims to study by relevant methods of rainfall variability in this perimeter, with a semi-arid climate, using 60 years (1958-2018) of data from the local network of 27 weather stations. Drought threshold is determined at 243 mm/year and the rainfall deviation index reaches -11%. Reduced centred indices provide information on equity in surplus, normal and deficit years of rainfall and that three successive periods corresponding in rainfall dominance to number: 13, 8 and 39 years; that Hanning's second order low-pass filter weighting maintains proportionalities but advances them by ten years. Mann-Kendall test also approves rainfall decrease; Sen's test gives a negative average trend slope. In addition, statistical tests for the detection of chronological rupture (Pettitt test, Lee and Heghinian bayesian method, Buishand U statistic, Hubert segmentation) detect the break in 1978 and lead to observations after rupture in reduction of 36 % in rainfall, increase in the frequency of deficit years at the expense of surplus years and mapping on a spatio-temporal distribution of precipitation of three homogeneous areas, including isohyets more displaced according to drying from west to east. Our results characterizing deep regional climate changes as rainfall are useful in programming resilience or adaptation to rainwater scarcity in such vulnerable agricultural biotopes.