Projected Shifts in Potential Evapotranspiration under the Impact of Climate Change for India and Karnataka: A Jensen-Haise Approach

Abstract

Climate change, driven by long-term shifts in weather patterns caused by greenhouse gas emissions, has profound effects on agriculture, particularly crop production, which is highly dependent on weather conditions. Changes in rainfall patterns and rising temperatures can significantly reduce crop yields, especially in subtropical regions like India. Elevated levels of CO2 and temperature influence key biological processes such as respiration, photosynthesis, plant growth, reproduction, and water use. One crucial aspect of crop management affected by climate change is evapotranspiration, which plays a central role in the soil-plant-atmosphere water balance and determines irrigation frequency. Potential Evapotranspiration (PET) refers to the total water loss through the combined processes of transpiration and evaporation, both of which are governed by weather factors such as temperature, humidity, solar radiation, and wind. PET is an important indicator of the water that needs to be replenished through rainfall or irrigation, and its estimation is critical for calculating crop water requirements and adjusting irrigation schedules to maximize water efficiency. As climate change intensifies, it is essential to estimate PET for various crops, cropping systems, and agro-ecosystems over the coming decades to ensure effective crop and resource management. This study estimates PET for India, including Karnataka, from 2021 to 2070 using the Jensen-Haise method. The results show a mix of increasing and decreasing trends in annual PET, but an overall slight upward trend is projected over the 50-year period. The average annual PET for Karnataka is estimated at 2,516 mm/year, with an increasing trend expected in the next five decades. The highest monthly PET values are predicted for April (279.30 mm), May (307.46 mm), and June (319.36 mm). These projected increases in PET must be factored into crop selection, cropping systems, and water management plans to ensure sustainable crop yields and improved water use efficiency in the face of climate change.