That giant sucking sound you don’t hear is water being evaporated into an increasingly thirsty atmosphere, but also increasing groundwater withdrawals that ultimately end up adding to global sea level rise, to an eye popping degree.
Above, from PBS reporting, “This water loss is occurring in the mid latitude regions where most of the world’s population resides.”
Changes in terrestrial water storage (TWS) are a critical indicator of freshwater availability. We use NASA GRACE/GRACE-FO data to show that the continents have undergone unprecedented TWS loss since 2002. Areas experiencing drying increased by twice the size of California annually, creating “mega-drying” regions across the Northern Hemisphere. While most of the world’s dry/wet areas continue to get drier/wetter, dry areas are now drying faster than wet areas are wetting. Changes in TWS are driven by high-latitude water losses, intense Central American/European droughts, and groundwater depletion, which accounts for 68% of TWS loss over non-glaciated continental regions. “Continental drying” is having profound global impacts. Since 2002, 75% of the population lives in 101 countries that have been losing freshwater water. Furthermore, the continents now contribute more freshwater to sea level rise than the ice sheets, and drying regions now contribute more than land glaciers and ice caps. Urgent action is required to prepare for the major impacts of results presented.
As the dry areas of the world become drier (13, 16, 19) and surface water storage in rivers and lakes declines (12), society is becoming more reliant on groundwater (20). This increased reliance has led to its long-term depletion (21, 22), which is exacerbated by global shortcomings in groundwater management (20, 23) and which amplifies rates of TWS loss through a positive feedback. The consequences of global groundwater depletion include reduced irrigation water supply and threats to agricultural productivity, reduced capacity for climate adaptation, drought resilience and for growth in desert cities, reduced biodiversity (24) and damage to groundwater dependent ecosystems (25), decreasing access as water tables fall, and many others (21, 26, 27).
Global TWS changes also have major consequences for interannual variations in sea level and long-term global mean sea level (GMSL) rise (28–30). The loss of freshwater from the continents and the ice sheets eventually leads to a corresponding increase in ocean water mass. While the continental contribution drives GMSL variations at seasonal and interannual timescales (28), its long-term contribution at longer timescales has, until recently (8), been smaller than the ice sheets on human timescales. If the TWS trends identified here continue, then this may never again be the case.