Effects of climate variability on green gram yield in Tharaka North Sub-County, Tharaka Nithi County, Kenya

Abstract

This study evaluated the effects of climate variability on green gram ( Vigna radiata L.) yield in Tharaka North Sub-County, Tharaka Nithi County, from 2004 to 2024. Climate data on precipitation and temperature were sourced from the European Center for Medium-Range Weather Forecasts Re-Analysis (ERA5-Land) reanalysis dataset, while drought conditions were assessed using the Standardized Precipitation Evapotranspiration Index (SPEI). Long-term climate trends were evaluated using the non-parametric Mann–Kendall test and Sen’s slope estimator. Results revealed a statistically significant warming trend over the 21-year period with a Sen’s slope of +0.035°C per year. Annual rainfall exhibited pronounced interannual variability, ranging from a low of 235.21 mm in 2022 to a high of 1088.06 mm in 2018. SPEI analysis indicated frequent and prolonged drought episodes, within the study period including several severe and extreme drought events. Green gram yields varied substantially, ranging from 0.23 to 0.68 t ha⁻¹, with a mean of 0.41 t ha⁻¹. Regression analysis confirmed rainfall as the dominant climatic driver of green gram productivity (β = 5.97 × 10⁻⁴, p < 0.001), while temperature exerted a marginally significant negative effect on green gram yield (β = −0.14, p = 0.091). This study contributes to the limited empirical evidence on climate–yield relationships for legumes in Kenya’s ASALs and provides a basis for developing targeted, climate-resilient agricultural strategies to enhance food security and farmer livelihoods.