A modelling exploration of the sensitivity of the India’s climate to irrigation

The Indian subcontinent is one of the most highly irrigated regions of the world where water use has intensified since the second half of the twentieth century. This agricultural intensification has resulted in changes in the water and energy balance between land surface and atmosphere is affected by these changes, which further influences climatic parameters that directly affect us. Over India, the practice of irrigation has changed in recent years resulting in an increased agricultural productivity as well as a depletion of groundwater. In this study, we use the Community Earth System Model CESM1.2 (Community Land Model (CLM4.5) with an active crop model coupled to the Community Atmospheric Model and a slab ocean) to examine the sensitivity of India’s climate to the amount of irrigation. We vary the amount of irrigation water by varying the irrigation factor in the CLM4.5 to produce a range of conditions from a bare minimum of no water stress in the crop to saturated soil. By holding all other forcings constant at year 2000 levels, we are able to examine the changes in temperature and precipitation over India due to varying amounts of irrigation. We find that irrigation decreases the maximum and minimum temperatures by nearly 3 °C and 4 °C respectively over the most heavily irrigated parts of the Indian subcontinent as a result of increased latent heat partitioning of energy. The resultant cooling (about 4% in annual mean temperature across India) impacts the monsoon circulation and reduces the moisture transport resulting in a statistically significant decrease of 1.46–4.17% in the all India summer monsoon rainfall with a decrease over the eastern part of the Gangetic basin and an increase over the Punjab region of Pakistan and India. While the large effect on temperature and precipitation may be a result of the model simulations having an irrigation seasonality that peaks in the pre-monsoon months, there is significant disagreement across different model based irrigation estimates on the timing and amount of the peak irrigation water added. This uncertainty in irrigation needs to be resolved to better understand its effects on India’s climate.