Trend analysis of reference evapotranspiration and identification of responsible factors in the Jhelum River Basin, Western Himalayas

Evapotranspiration (ET) is a crucial agrometeorological parameter and is of significant importance for irrigation planning and management. Any change in reference evapotranspiration (ETO) and the consequent change in actual ET can cause a significant change in the water demand, thereby affecting the water balance adversely. This study analyzes the trends in the ETO time series using non-parametric Mann–Kendall and Sen's Slope estimator at six stations for 102 years (1901–2002) in the Kashmir valley. Results indicate statistically insignificant trends at the annual timescale at a 95% confidence level. However, at the seasonal timescale, a significant trend was observed. Winter ETO time series showed an increasing trend while summer ETO showed a decreasing trend at a 95% confidence level. The trend analysis of the governing meteorological variables revealed increasing trends in winter temperature and cloudiness in summers in the study area. The water deficit calculated in terms of the difference of precipitation and ETO showed an increasing trend for all the stations at the annual timescale. At the seasonal timescale, four out of the six stations showed an increasing deficit for the spring season.