Land-atmosphere interactions affect the monsoon system, but the role that specific land and water management practices play has remained unclear. A team of researchers at the Pacific Northwest National Laboratory (PNNL), Oak Ridge National Laboratory (ORNL), and Indian Institute of Technology (IIT) used a climate model to study how irrigation in South Asia affects the Indian Summer Monsoon. When realistic representation of unmanaged irrigation and paddy cultivation over north-northwest India was included in the simulation, the model showed an increase in the late-season terrestrial monsoon precipitation and an increase in extreme rainfall events over central India, which was consistent with observations. The findings stressed the need for an accurate representation of irrigation practices to improve the simulations of monsoon precipitation and its extremes over South Asia.
This study confirmed that excess irrigation over northern India causes a northwestward shift in monsoon rainfall and intensifies extreme precipitation over Central India. The study demonstrated that it is important to represent land management and irrigation practices accurately in earth system and weather models for improved predictions.
South Asia is one of the most heavily irrigated regions of the world, and a large proportion of the water for irrigation is extracted through groundwater pumping. The major summer crop of the region is paddy, which is cultivated in fields flooded with water. To understand the effects land and water management practices have on monsoon circulation and precipitation, researchers at PNNL, ORNL, and IIT implemented modules to represent irrigation, groundwater pumping and flooded paddy fields into the Community Land Model version 4 coupled to the Weather Research and Forecasting model (WRF-CLM4). They found that the excess irrigation over northern India shifted the September monsoon rainfall towards the northwestern part of the subcontinent, consistent with observations. This pattern of change was also visible in recorded rainfall over the region in the recent past. Another major impact they saw was on the intensity of extreme rainfall events over the central part of the country. Central India has witnessed an increase in extreme rainfall in recent decades and through this study, the researchers found that irrigation increases the rainfall intensity over Central India during these events. These findings indicate that it is important to represent irrigation practices more accurately in weather and climate models.
The released codes and scripts can be found here: https://github.com/IMMM-SFA/WRF_CLM4_Irrigation.