Meteorological drought variability and its characterization in sub humid mediterranean region, the Wadi Isser basin of Algeria from 1970 to 2017

Abstract In this study, the trend and the persistence in Standardized Precipitation Index (SPI) time series, derived from monthly rainfall data obtained from 26 gauging stations in the Wadi Isser basin (Algeria), have been analyzed using a suite of complementary methods to address the spatial trend behavior, the trend dynamics and the persistence. First, the SPI was calculated for 1-, 3-, 6-, 9-, 12- and 24-month time scales from 1970 to 2017. Then, the Mann–Kendall (MK) test and the modified MK (MMK) test were used to determine the direction of the trend in the precipitation and SPI series. These methods evidenced decreasing trends in short- and long-term droughts in the northern and southern regions of the study area and increasing trends in the stations in the central regions of the basin. Finally, the temporal changes in the SPI trend were analyzed by the Sequential Mann–Kendall test (SQMK) showing a change point in 2000s in most of the series, implying the role of the global climatic shift of 1997–1998 on modulating drought conditions in the basin. The persistence estimates showed that the Eastern part of the basin is highly drought-persistent, irrespective of the time scale. The persistence and predictability increase with the increase of the drought time scale, reinforcing the complex behavior of short term drought of the basin.