Characterization of drought using four drought indices under climate change in the Sahel region of Nigeria: 1981–2015

Drought is a natural hazard that has affected agriculture which is the main livelihood of the people in the Sahel region of Nigeria (SRN) in the last few decades. Continental and regional drought monitoring is very essential for the development of an early warning system especially in the context of global warming. The severity of drought was simulated to evaluate climate change impacts on drought conditions in the SRN using the standardized precipitation evapotranspiration index (SPEI), the standardized precipitation index (SPI), the original and self-calibrated Palmer drought severity indices (PDSI and scPDSI). The difference between the Hargreaves (Har) and Penman-Monteith (PM) potential evapotranspiration (PET) models used for the computation of the SPEI were also studied. The Mann-Kendall test was used to analyze the trends and significance of the climatic data. The time series of four drought indices were compared at six synoptic stations within the SRN. The influences of climate change on drought conditions were examined with a hypothetical gradual precipitation changes (+ 10%) and 2 °C increase in temperature. The findings showed that there was a significant correlation between Har and PM models, and between the SPEIs estimated from the two PET models. However, a major drought episode (1982–1983) indicated by SPEI-PM was not captured under SPEI-Har. Considering climate change conditions, the severity and intensity of drought increases as the twenty-first century progresses under both the scPDSI and SPEI mainly due to more demand for moisture based on a temperature rise of 2 °C. Either a slight (10%) increase or decrease in the monthly accumulation of rainfall depth will not have a significant impact on drought, if there is a slight increase in temperature as it is being currently observed in the SRN. Thus, it is pertinent for stakeholders to critically consider establishing policies that can ameliorate this phenomenon as the twenty-first century progresses.