Assessment of Drought Characteristics and Climatic Interactions in a Tropical Region using the Palmer Drought Severity Index with Multiple Evapotranspiration Models

Drought remains a critical hydroclimatic hazard in Nigeria, affecting agriculture, water resources, and livelihoods across its different ecological zones. This study aimed to assess drought characteristics and their climatic interactions across Nigeria using the Palmer Drought Severity Index (PDSI) with three potential evapotranspiration (PET) models: Penman-Monteith (PM), Hargreaves (HG), and Thornthwaite (TW). Monthly climatic variables spanning 1979–2021 at a 0.5 ^o by 0.625 ^o latitude and longitude resolution were sourced from the Modern-Era Retrospective Analysis for Research and Applications, Version 2 (MERRA-2) reanalysis data and aggregated to annual and decadal scales. Using the PDSI technique, drought duration, intensity, frequency, severity, trends, change points, and climate sensitivity were analyzed. The Sahel region showed the highest drought frequency under PDSI-TW (77%) and maximum intensity of -1.40, with a 2013 change point and peak cross-correlation with precipitation (R = 0.62). The Guinea Savannah experienced peak drought intensity of -1.55 (PDSI-TW), maximum frequency of 75% (PDSI-PM), and a significant decreasing trend (slope = -0.018, p  < 0.01), with strong climatic sensitivity (R = 0.78 with precipitation). In the Rainforest, maximum drought intensity reached − 1.69 (PDSI-HG), frequency peaked at 92% (PDSI-HG), and decreasing trends were most pronounced under PDSI-TW (slope = -0.026, p  < 0.001), with significant precipitation sensitivity (R = 0.62). The Coastal region experienced the most extreme intensity values (PDSI-HG: -3.78) and critical frequencies (up to 67%), with a 2016 change point and high precipitation correlation (R = 0.76). The study concludes that drought patterns are region- and method-specific, with PDSI-TW better capturing thermal-driven stress in arid zones, while PDSI-HG and PDSI-PM effectively detect droughts in coastal and humid environments. These results enhance localized drought risk assessment and inform region-specific adaptation strategies.