Meteorological Drought Assessment in the Middle Moulouya Basin, Morocco, Using Meteorological Drought Indices

Abstract

Drought is a phenomenon that threatens Morocco generally and the Middle Moulouya in the country's northeast specifically. In fact, the basin's climate is arid to semi-arid, with additional factors that intensify the phenomenon. The latter has enormous negative consequences affecting various vital areas, including water availability and food security in this region which suffers from unfavorable socio-economic conditions. Surveillance and monitoring of this phenomenon is crucial for a region like Middle Moulouya. This paper aims to examine meteorological drought in this arid to semi-arid region between 1980 and 2021, based on three relevant and frequently used indices: Standardized Precipitation Index (SPI), the Standardized Precipitation Evapotranspiration Index (SPEI) and the Reconnaissance Drought Index (RDI). This study is carried out at four distinct time scales (3, 6, 9, and 12 months). The different indices were calculated using temperature and precipitation data from five weather stations. To examine the similarities between the indices, we used Pearson correlation, while the Mann-Kendall test and Sen's slope were used to identify trends. Frequency, duration, intensity, and severity were the distinguishing characteristics of the drought episodes. The review revealed notable differences in drought frequency and severity depending on station location. The Outat El Haj (center) and Tendit (downstream) stations exhibit particularly critical conditions, with a drought frequency of 87% at Tendit, a maximum period of 10 years, and extreme severities (reaching up to -128.88 with the SPI-6 and -127.63 with the SPEI-3). In contrast, the Laarichat and Missour (upstream) stations exhibit more beneficial conditions, with frequencies of 65% and less severe severities. Analysis of correlations between indices revealed a close link between the SPI and the RDI, particularly over the long term, while the SPEI is characterized by greater responsiveness to the impacts of temperature. Mann-Kendall analysis demonstrated notable positive trends for SPI and RDI at various stations, while SPEI showed a negative trend at Outat El Haj station, highlighting the increasing effect of increased evapotranspiration. The use of a multi-index strategy proved effective in capturing the complexity of hydrometeorological dynamics at the basin scale.The results constitute a valuable basis for the development of adaptation strategies and sustainable management of water resources in this basin suffering from poverty and unfavorable socio-economic conditions. SPI, SPEI and RDI indices, for the time scales of 3, 6, 9 and 12 months, were used for the first time for the assessment of meteorological drought in the Middle Moulouya basin (Morocco). Precipitation and temperature data were used for the calculation of the three indices. The results highlight the characteristics of drought at the basin level and show that the basin suffered, during the period 1980-2021, from several drought sequences of significant intensity, duration, severity and frequency. These results provide a basis for policymakers and decision-makers to establish action plans to mitigate the consequences of the phenomenon on local populations, who mainly suffer from precarious living conditions.