Potential Impacts of Climate Change Using Long-Term Historical Climate Data on Evapotranspiration (ET) and Groundwater Contribution to Wheat and Cotton Crop

Assessing the potential impacts of climate change on crop evapotranspiration (ET), groundwater contribution (GWC) towards meeting ET and yield is crucial in allocating water resources particularly in the areas where shallow water-table depths (WTDs) are expanding on larger area. The impact of climate change on crop ET and yield has been evaluated in the past by indirect methods using simulation models. However, those models are lacking the function of GWC which is one of the most important parameters while determining ET at different water-table depths (WTDs) and its impact on yield. Direct methods (without simulation models) using long term historical weather data (observed data) provide more accurate results of climate change impact on ET, GWC towards meeting ET and yield at different WTDs. In this study, long-term historical weather data for the last 34 years (1987-2020) and data obtained through lysimeteric studies were analyzed to examine the trends of climatic parameters, their relationship and impact on wheat and cotton ET, GWC to ET, yield and water use efficiency (WUE). These studies were carried out during 1986-1987 and 2017-2021 periods at 1.50 m, 2.25 m, and 2.75 m WTDs in Sultanpur soil series (silt loam textured) and Miani soil series (silty clay loam textured). The mean daily temperature has increased 0.45 oC and rainfall 75.5 mm/year over a period from 1987 to 2020 which is witnessing the climate change. Wheat ET is increased, GWC contribution to ET is decreased and, yield and WUE is highest during the cropping periods of 2017-2021 as compared to 1986-1987. Climate change has decreased cotton ET and GWC towards meeting ET. It has also reduced the wheat and cotton cropping cycles by 8 days and 21 days, respectively. Higher magnitude of rainfall (during July-September) in 2019 and 2020 resulted in reducing cotton average yield of 2017-2020 compared to 1987. The study demonstrates that irrigation allocation should be increased for wheat and decreased for cotton particularly in the shallow water-table areas under Sultanpur soil type where water-table remains at 1.50 m – 2.25 m depths. Moreover, cotton crop should be cultivated by the 1st week of April, so that highest yield of cotton could be harvested before onset of monsoon.