Feifei Cao, Elie Gerges, Claudia Ruz Vargas, Andrew R Pearson, Elisabeth Lictevout
Abstract Groundwater, as the largest storage of liquid freshwater on Earth and a major component of the water cycle, is critical for supporting surface water flow, ecosystems as well as water and food security. Human dependence on groundwater has increased sharply over recent decades, contributing to wealth creation and poverty alleviation. However, anthropogenic activities, including groundwater abstraction and climate change, have modified groundwater dynamics, leading to groundwater level (GWL) changes. We analysed 20 year time series of GWLs in 47 countries distributed across a range of climatic, geographic, hydrogeological and socioeconomic contexts worldwide. Using different indicators based on three time series analysis methods, we show that almost one third of the GWLs trends are declining—thus reflecting overexploitation of groundwater—while GWLs are rising in 18% of wells—not always indicating a recovery but also the consequence of human impact on the environment. Globally, GWLs show a mix of declining and rising trends, however, at regional scale, patterns and hotspots are evident. We also explored the associated impacts of GWL change on humans and ecosystems, by reviewing 28 case study examples. We show that both rising and falling GWLs have substantial impacts on water and food security, ecosystems, infrastructure and socioeconomic wellbeing. Our findings underscore an urgent need for expanding monitoring programmes, protecting groundwater, and defining acceptable impacts to determine sustainable groundwater usage and minimise impacts of GWL change.