Assessment and monitoring of meteorological and hydrological drought in semiarid regions: The Wadi Ouahrane basin case study (Algeria)

The aim of this study is to use the Standardized Precipitation Index (SPI) and the Standardized Runoff Index (SRI) to investigate meteorological and hydrological drought in the Wadi Ouahrane basin of north Algeria. Indeed, in recent years, the Wadi Ouahrane basin has suffered from persistent and recurrent meteorological and hydrological droughts, which caused large economic losses and extreme difficulties for the local population, resulting in widespread out-migration and poverty throughout the country. In order to evaluate the SPI, 6 monthly rainfall series for the period 1972-2018 have been considered. Moreover, with the aim to evaluate the SRI, monthly runoff data from 1972 to 2018 were also collected in one station. Both the SPI and the SRI have been evaluated at 1-, 3-, 6-, 9-, 12- and 24-month timescales. Although a similar percentage of positive and negative values of both the indices has been detected for the different timescales, the temporal distribution of these values allowed us to identify the periods characterized by severe or extreme drought conditions such as 1982, the end of 1983, 1987-1990, 1992-1995 and, recently, 2014-2016. Finally, in order to detect drought temporal evolution in the period 1972-2018, the SPI and SRI series at the different multi-times scales were tested for trends through the Theil-Sen estimator (SS), the Mann-Kendall test (MK), the Modified Mann-Kendall test (MMK) and the Innovative Trend Method (ITA). As a result, although the SS evidenced negative values, the MK test did not show significant trends thus indicating stable drought conditions.