Characterization of Climatic Drought Sequences in the Upper Moulouya Watershed, Morocco

Abstract

Like most of the countries of the African continent and the MENA, Morocco has experienced alternating wet and dry periods for several decades and is still confronted with the effects of unstable climate change due to the specificities conferred by its geographical position and the diversity of its ecosystems. It is one of the countries most affected by desertification, with an arid and semi-arid climate covering more than 93% of its territory. Indeed, the Upper Moulouya watershed has been exposed to severe droughts several times in recent decades. The spatial and temporal distribution of drought episodes in this watershed is studied over a 91-year period between 1931 and 2022. In order to characterize and evaluate the severity and sustainability of drought in this watershed, four indices were used and applied in this study, as they have advantages in terms of statistical consistency and have the capacity to describe, through different time scales (short, medium and long) the impacts of the climatic drought in question. These are the Standardized Precipitation Index SPI, RDI, RI and DI. The annual rainfall series at the eight meteorological stations of the said watershed show irregularities and very marked spatial and temporal variability with a generally decreasing trend. The SPI calculation results obtained show a heterogeneous distribution of SPI values throughout the watershed area. The analysis of the graphical illustrations of this index allowed to highlight an important fluctuation of the dry and wet periods with a strong dominance and tendency to drought with the order of 51% in the stations of Midelt, and Ansegmir, 52% in the station of Zaida, 59% in the stations of Tabouazant, Barrage (Dam) Enjil and El Aouia, 58% in the station of Louggagh, 47% in the station of Anzar Oufounes. The analysis of the results of the of the drought indices RDI, RI and DI at the level of this watershed also made it possible to highlight the existence of numerous drought sequences alternating with other wet sequences and indicates a dominance of dry years, perfectly remarkable during the period 1976-93. The most important dry episode, in number of successive years, was recorded at the Ansegmir station from 1976-89 and the most important rainy episode was recorded at the Midelt station from 1966-76. The years of the 2015-2022 series show an overall persistent decrease in rainfall, thus allowing the installation of a severe drought episode. The trend in the entire watershed is a decrease in rainfall and the installation of mild, moderate and severe drought episodes of varying length and duration.

Climate Change and Water Resources Management in Ghis-Nekor Watershed (North of Morocco) – A Comprehensive Analysis Using SPI, RDI and DI Indices

“…To evaluate drought severity and sustainability, three indices were applied: standardized precipitation index (SPI), rainfall deficit index (RDI), and drought index (DI) (Bhalme and Mooley, 1979;McKee et al, 1993;Hachem et al, 2023).…”

“…Its adaptability across time frames allows comprehensive evaluations of short-to long-term water reserves. Adopted globally by the World Meteorological Organization (WMO) in 2009 as a global instrument for measuring meteorological droughts (Jouilil et al, 2013;Hachem et al, 2023), SPI efficiently quantifies precipitation deficit, enabling analysis of wet and dry periods. SPI is calculated following the equation ( 1):…”

“…Climate change profoundly influences critical elements, such as rainfall, river and groundwater levels, temperature, and soil moisture (Aimar, 2019). The recurrence of drought emerges as a pressing concern, impacting Climate Change and Water Resources Management in the Ghis-Nekor Watershed (North of Morocco) -A Comprehensive Analysis Using SPI, RDI and DI Indices socio-economic activities and ecosystems (Hachem et al, 2023). This is especially alarming in Morocco, where water scarcity is exacerbated by climate change, particularly in semiarid areas (Bouchaou et al, 2011).…”

“…Various indices, each with its strengths and limitations, have been developed for this purpose. Notable indices include the Palmer drought severity index (PDSI) (Palmer, 1965), rainfall deficit index (RDI) (Bhalme and Mooley, 1979), surface water supply index (SWSI) (Shafer and Dezman, 1982), standardized precipitation index (SPI) (McKee et al, 1993), effective drought index (EDI) (Byun and Wilhite, 1999), reconnaissance drought index (ReDI) (Tsakiris et al, 2007), drought index of effective drought index (IDE) (Nalbantis and Tsakiris, 2009), standardized maximum soil moisture index (IMSM) (Vicente-Serrano et al, 2010), regional agricultural drought index (RAI) (Fleig et al, 2011), and agricultural drought reference index (ADRI) (Woli et al, 2012), the rainfall index (RI) and the drought index (DI) (Hachem et al, 2023). Despite the simplicity of calculating the Standardized Precipitation Index (SPI), its drawback lies in neglecting crucial factors like temperature, potential evapotranspiration (PET), wind velocity, and soil moisture, making it less reliable in a warming climate (Vicente-Serrano et al, 2010).…”