UC Irvine

Groundwater is a crucial natural resource that supports large portions of the world's population and ecosystems. Traditional methods to assess the state of large groundwater systems are difficult to implement over large scales. I present a methodology to increase the state of knowledge for both groundwater use and availability in the world's largest aquifer systems. First, a Renewable Groundwater Stress (RGS) ratio is defined to quantify the extent to which water use exceeds renewable water availability in the study aquifers. Groundwater use is estimated with observations from the Gravity Recovery and Climate Experiment (GRACE) satellite mission. Aquifer systems that have diverse anthropogenic biome types, especially systems that are dominated by irrigated agriculture, were found to have the highest levels of renewable groundwater stress. Second, a Total Groundwater Stress (TGS) ratio is defined to quantify the impact of GRACE-based groundwater depletion estimates on the resilience and lifespan of the study aquifers as a function of total aquifer storage. The results highlight a significant lack of knowledge on the total volume of groundwater in storage globally. The uncertainty in storage estimates limits the quantification of TGS in the study aquifers. Therefore, a methodology to reduce uncertainty in total storage estimates with GRACE is presented. Ultimately, scientific findings on the state of groundwater should be used to support science-based decision making. The Scientist-Stakeholder Iterative (S2I) Method is presented as a framework for using research to implement sustainable policies to govern natural resources.