Hydroclimatic variability and drought characterisation in Northern and North-Central Togo, 1981–2025

Abstract

Climate change is increasingly intensifying drought conditions across West Africa, with northern and north-central Togo emerging as one of the most drought-vulnerable sub-regions of the continent yet lacking locally adapted tools for effective drought monitoring and moisture deficit assessment. This study analyses rainfall variability, drought frequency and moisture deficit across its three agroecological zones from 1981 to 2025. Three synoptic stations were combined with NASA POWER reanalysis and CHIRPS with satellite data. The Hamed-Rao modified Mann-Kendall test, Sen’s slope estimator and three change-point tests (Pettitt, Buishand, Standard Normal Homogeneity Test) were applied at annual, seasonal and monthly timescales, alongside the Standardised Precipitation Index (SPI), Standardised Precipitation-Evapotranspiration Index (SPEI) and Willmott-Feddema Moisture Index (MI). No statistically significant precipitation trends were detected at any station, while a significant warming of + 0.27 to + 0.34 °C per decade coincided with a post-2000 divergence between SPI and SPEI, strongest at Sokodé; a common change point at exactly 2003 was not statistically clear-cut. This divergence persisted under an independent Penman-Monteith PET formulation, even though Penman-Monteith PET itself showed no comparable warming-driven increase, suggesting the divergence reflects a broader shift in the surface energy and moisture balance rather than temperature alone. All stations recorded predominantly negative MI values, indicating a persistent climatic moisture deficit, whereas spatial trend analysis revealed predominantly positive (wetting) trends, with significant drying confined to fewer than 8% of grid cells. These findings highlight the value of temperature-sensitive drought indices for early-warning systems and provide climate information relevant to rain-fed cereal production and water-resource management in one of West Africa’s most climate-exposed regions.