Increasing potential evapotranspiration despite non-significant rainfall trends: a 35-year hydroclimatic analysis and assessment of farmer perceptions in Southern Ethiopia

Abstract

Rainfed smallholder agriculture in sub-Saharan Africa is increasingly exposed to rising atmospheric evaporative demand and hydroclimatic variability, even where long-term annual precipitation totals show no significant directional change. This study examines 35-year hydroclimatic variability and farmer-reported climate conditions in the Boricha and Bilate Zuria districts of Sidama Regional State, Ethiopia. We integrated instrumental observations from the Ethiopian Meteorological Institute and ERA5 reanalysis data (1990–2024) using non-parametric trend analysis, the Standardized Precipitation-Evapotranspiration Index (SPEI), and a household survey (n = 204, conducted September–December 2024). Annual precipitation exhibited no statistically significant long-term trend, showing only minor, non-significant positive tendencies (Mann–Kendall tau: 0.059–0.082; Sen’s slope: +1.14 to + 1.80 mm yr⁻¹), whereas mean annual temperature increased significantly (Sen’s slope: +0.0167 to + 0.0171 °C yr⁻¹). Potential evapotranspiration (PET) also exhibited a significant upward trend, reflecting increased atmospheric evaporative demand under regional warming and indicating greater potential for water loss as temperatures rise. Multi-scalar SPEI series revealed pronounced interannual variability ranging from extreme drought to severe wet conditions, but no statistically significant long-term drying trends. Despite the absence of a long-term downward trend in annual rainfall totals, 89.7% of surveyed households reported perceiving shifts in rainfall patterns, 76.5% perceived an increase in drought frequency, and 72.5% observed a shortened rainy season. Leading household-reported climate-related impacts included flooding (68.1%), land degradation (48.5%), and resource-based conflict (43.5%), with cumulative shock exposure significantly determined by district and household wealth status (p = 0.001–0.003). These results demonstrate that reliance on annual rainfall totals alone may obscure important dimensions of climate exposure linked to rising evaporative demand. They underscore the importance of integrating temperature-driven water-balance metrics, intra-seasonal rainfall characteristics, and crop-specific climate sensitivities into climate-risk management in smallholder systems.