Assessing reference evapotranspiration trends in the Amaravathi river basin

Evapotranspiration (ET) is a key component of the hydrological cycle and climate change has impacted its patterns, potentially leading to abnormal weather conditions. This study investigates the trends in reference evapotranspiration (ET0) over the Amaravathi river basin using monthly ET0 of AgERA5 dataset from 1979 to 2022. The result revealed that the mean annual ET0 was 1909.79 mm with a low coefficient of variation (CV) of 3.14 %, indicating stability despite seasonal fluctuations. The Southwest Monsoon (SWM) accounted for the largest share (36.20 %) of annual ETo, followed by summer (30.30 %), Northeast Monsoon (NEM) (18.48 %) and winter (15.02 %). Trend analysis using the Mann-Kendall test and Sen's slope estimation showed a significant decreasing trend in annual ET0 at a rate of 2.35 mm per year (p < 0.05), suggesting a long-term decline in evapotranspiration potential. Pettitt’s test identified a significant change point in the ET0 series, with a shift around 2003, indicating a change in the climatic regime. Principal Component Analysis (PCA) further corroborated these trends, with the first principal component (PC1) explaining 63.24 % of the variance, strongly correlating with ET0, solar radiation and mean temperature. The significant drop in ET0 over the previous few decades is highlighted in this study, highlighting the necessity of adaptive water management techniques considering shifting climatic conditions.