What to Expect
Climate change poses a serious threat to global freshwater and agricultural systems, with rising deficits in surface and groundwater availability. This is particularly of concern for India, which is simultaneously facing severe groundwater depletion and where the feedbacks between crop water stress, groundwater depletion, and climate change are understudied. In this seminar, I will present my approach to developing a better understanding of these feedbacks in two parts. In the first part of my talk, I will present how I developed a new automated Ensemble-mean of surface energy balance (SEB) framework (EnSEB) based on global remote sensing and reanalysis data to derive a pixel-based (1 km2) estimate of seasonal evapotranspiration (ET) across India from 2001 until 2016. In the second half, I will share how these ET maps when combined with field and climate data were able to answer pressing agricultural water sustainability questions in India. I find that EnSEB was more accurate than commonly used ET models, and its pixel to watershed scale validations suggest that EnSEB produces ET maps with reliable accuracies in regions with little or no ground data for calibration. Furthermore, using these ET maps in panel fixed effect regressions, I find that warming temperatures increase crop water stress, but this effect is small in magnitude. This indicates that farmers pursue effective short-term adaptations by withdrawing groundwater to offset increased evaporative demand and suggests that warming temperatures likely accelerate groundwater depletion due to farmer behavior. Projected estimates of net groundwater loss in 2050 and 2070 under different warming scenarios are up to five times current depletion rates even after considering the effects of projected increases in monsoon precipitation. Our study reveals the previously unrecognized impacts of warming temperatures on groundwater depletion in India, which has serious implications for the country’s future food and water security.
Nishan is a postdoctoral research fellow in the School for Environment and Sustainability at the University of Michigan and a trained physical/remote sensing scientist with expertise in hydrological remote sensing, geospatial data science, image processing, and vegetation mapping. He is currently studying the impacts of warming temperatures on crop water stress, groundwater depletion, and agricultural sustainability in India. Through his research, he seeks to answer what kind of adaptation strategies are most effective to cope with reduced water availability. He has also focused on advancing the use of remote sensing for modeling evapotranspiration through which he developed automated and multi-model remote sensing tools that appear in several high-impact papers in journals like Remote Sensing of Environment and Hydrology & Earth System Sciences. Nishan is actively engaged in interdisciplinary collaboration with researchers in physical and social sciences – exploring the linkages between changes in vegetation cover and environmental policy, climate change, hydrological responses, and socio-economic outcomes. Nishan is an editorial board member of the journal GIScience and Remote Sensing and currently serves as a guest editor for a special issue on Remote Sensing of Evapotranspiration for the journal Remote Sensing. Nishan received his Ph.D. in Environmental Resources Engineering from SUNY College of Environmental Science & Forestry, NY, in 2015, MS in Forestry (Hydrology) from Auburn University, AL, in 2010, and BS in Forestry from Tribhuvan University, Nepal, in 2006. From 2015-2016, he was a postdoctoral fellow at Tufts University, MA. As a scientist, Nishan hopes to advance the application of remote sensing tools to develop a better understanding of key ecohydrological processes and their interactions within the Earth’s system and help solve real-world sustainability issues related to food and water security. Finally, Nishan values research, scholarship, and service that promotes diversity, equity, and inclusion.
Note: Contact Haruko Wainwright for Zoom meeting details.