Climate Variability and Gully Erosion Development in Abia State, Nigeria: Trends in Rainfall, Runoff, and Temperature (1994–2024)

Climate variability and gully erosion represent major environmental challenges threatening agricultural productivity, infrastructure, and ecosystem stability in southeastern Nigeria. In Abia State, increasing rainfall irregularity, runoff intensification, and rising temperatures have heightened erosion susceptibility, yet integrated hydro-climatic assessments linking these variables to gully development remain limited. This study therefore examined the influence of rainfall, runoff, and temperature variability on gully erosion dynamics in Abia State between 1994 and 2024. Monthly rainfall and temperature data obtained from the Nigerian Meteorological Agency were analyzed using linear regression and the Mann–Kendall trend test, while runoff was estimated using the Soil Conservation Service Curve Number (SCS-CN) model. Rainfall concentration was evaluated using the Modified Fournier Index (MFI), and a Composite Gully Erosion Forcing Index (GEFI) was developed to assess combined climatic forcing on erosion processes. Results revealed that annual rainfall exhibited only a weak increasing trend (+7.6 mm decade⁻¹), but rainfall concentration and runoff variability were substantially high. Peak erosion-risk years, notably 1995, 1999, 2008, and 2019, were characterized by intense wet-season rainfall concentration and elevated runoff generation. Maximum and minimum temperatures also increased by approximately +0.11°C decade⁻¹ and +0.04°C decade⁻¹, respectively, contributing indirectly to erosion through enhanced evapotranspiration and reduced vegetation stability. The persistence of high GEFI values between 2018 and 2021 indicates sustained climatic pressure on vulnerable landscapes. The study demonstrates that rainfall concentration and runoff intensity, rather than total annual rainfall alone, are the dominant climatic drivers of gully erosion in Abia State. The findings provide critical insights for climate adaptation, sustainable watershed management, erosion control planning, and resilient infrastructure development in southeastern Nigeria.