A farmer plants rice saplings in a field against the backdrop of pre-monsoon clouds in Amritsar, June 2013. Photo: Reuters/Munish Sharma/Files
Estimates of water use by the agriculture sector typically range between 80-90% over India. This is largely consistent with the rest of the world’s agricultural sector. India however leads the world in groundwater mining for irrigation application as well; especially in the breadbasket of India in the northwest. This is highly unsustainable and a serious jeopardy to the nation’s food, water and energy security.
Seasonal monsoon rainfall has trended down for over 60 years now and despite the conjectures of a recovering monsoon, widespread extreme rainfall events are here to stay interspersed with regional and local droughts. Some of the subsidies such as electricity for pumping water for irrigation are counterproductive to the goal of using groundwater sustainably. It is evident that irrigation water use has become independent of whether the monsoon rainfall is normal surplus, or deficit.
The need for reducing water for irrigation can hardly be overstated. A new study from the Indian Institute of Technology, Bombay, led by graduate student Adrija Roy under the guidance of Subimal Ghosh, professor of Civil Engineering and the convened of Climate Studies at IIT Bombay, shows the way forward. An irrigation decision tool has been co-developed with Sahyadri Farms of Nashik, Maharashtra (this author is part of the team that published the study). The results have just been reported in a paper in the journal Water Resources Research.
As can be expected, farmers do not simply dump water on their farms to hedge against the vagaries of the monsoon. They use a tank model where they consider soil properties such as porosity, and root zone depths, rainfall, irrigation water input, and leakage of water. They try to maintain the soil moisture above a threshold to prevent stressing the crops and yield loss. Sahyadri Farms is a cooperative of over 8,000 farmers which has invested in monitoring weather and soil moisture over its farms.
The IITB study exploited the farmers’ irrigation tank model and their data to develop a sophisticated ecohydrological model which balances the water in the tank that farmers define. The additional key advance is to use the weather forecasts at short (days 1-3), medium (days 3-10) and extended (weeks 2-4) range from the India Meteorological Department (IMD), to produce reliable rainfall information at farm level. Forecasts issued by forecast centres across the world are not directly usable by farmers. It is critical to bring the forecasts down to the farm level.
Using past rainfall data and past forecasts from IMD, the team generates a probabilistic rainfall information over the farm to plan irrigation and avoid excess water use. The trust of the farmers in this farm level forecast is ensured by giving them the option of choosing the risk of how much crop stress they are willing tolerate. The farmers want to reduce water use without losing yields because they want to reduce input costs and also are aware of the ills of over irrigation – such as water logging and soil salinisation.
Crop stress is monitored via soil moisture threshold and evapotranspiration (evaporation mediated by the crops which is an indication of crop growth), and soil properties. This ensures that crop yield loss is avoided or kept within prescribed tolerances. The study focuses on three years, 2015-2018, for both Kharif and Rabi seasons. Such decisions on irrigation are crop dependent in addition to the local weather and soil properties. The present study focused on grapes, the main crop at Sahyadri. But the tool is transferable to any other crop and other weather regimes across the country.
The results clearly show that a saving of 10-30% in irrigation water use can be accomplished by using the farm-scale weather forecast information in conjunction with this ecohydrological model, instead of following fixed irrigation schedules. The success of the study is clearly attributable to the data and the details of their irrigation approach brought to the table by the farmers. The fact that the decision tool was co-developed with the farmers from the get go greatly enhances the use and usability of the irrigation decision tool.
This approach can include soil nutrients as well to manage fertiliser applications and crop choices to deliver an end-to-end dashboard for agricultural management.
Needless to say that this study is a pilot implementation. The network of farmers to participate in this approach has to be expanded across the nation. Soil moisture data is critical for the success of monitoring crop stress and for ensuring that crop yield losses are avoided. This requires that some investments be made in building a soil moisture network. The co-benefits of such a soil moisture network include potential improvements in weather and climate forecasts, synergy with increasing soil carbon and thus crop yields.
Increased soil carbon also helps modify soil structure to retain more nutrients and soil moisture. Enhanced soil carbon will also allow India to make progress on its commitments to the Paris Agreement in terms of developing additional carbon sinks.
A normal monsoon has been forecast for the upcoming season. Considering the impending extremes, ‘normal’ is an oxymoron now. Early warning systems and decisions tools are the best climate adaptation tools for India in managing these these unavoidables.
Raghu Murtugudde is a professor of atmospheric and oceanic science and Earth system science at the University of Maryland. He is currently focusing on developing climate courses as an open source for his Climate Academy.