Comparative evaluation of various drought indices (DIs) to monitor drought status: A case study of Moroccan Lower Sebou basin

Abstract

Due to the lack of studies on drought in the Lower Sebou basin (LSB), the complexity of drought phenomena and the difference in climatic conditions. Therefore, identifying the most appropriate drought indices (DIs) to assess drought conditions has become a priority. Therefore, evaluating the performance of different (DIs) was considered to identify the universal drought indices well adapted to the LSB. Based on data availability, five DIs were used: Standardized Precipitation Index (SPI), Standardized Precipitation and Evapotranspiration Index (SPEI), Reconnaissance Drought Index (RDI), self-calibrated Palmer Drought Severity Index (sc- PDSI) and Streamflow Drought Index (SDI). The DIs were calculated on an annual scale using monthly time series of precipitation, temperature, and river flow from 1984-2016. Thornthwaite's method was used to calculate potential evapotranspiration (PET). In addition, Pearson's correlation (r) was analyzed. In addition, data on the yield of durum wheat, soft wheat, and barley for the period 2000-2016 also contributed to the performance evaluation of these indices. The results proved that SPI is suitable for detecting the drought duration and intensity compared to other indices with high correlation coefficients, especially in sub-humid regions, knowing that it tends to give more humid results in stations with semi-arid climates. The multiscalar indices (SPI, SPEI, and RDI) follow the same trend during the period studied. However, sc-PDSI appears to be the most sensitive to temperature and precipitation by overestimating the drought conditions. In addition, yield/drought correlations tend to be higher for multi-scalar indices than for sc-PDSI. At the same time, slight differences were detected between SPI and SPEI in the performance of agricultural systems. Our results suggest that using multi-scalar indices in drought monitoring and assessment is necessary to have solid conclusions