Land reservoirs helped offset sea level rise, study says
Recent increases in the storage of excess groundwater may be helping to offset sea level rise by as much as 15%, a new study finds. While the capacity of land to store water is known to be an important factor affecting sea level rise, the magnitude of its storage contributions are not fully understood. Land masses store water in numerous ways, though some human-induced changes — including to groundwater extraction, irrigation, impoundment in reservoirs, wetland drainage, and deforestation – are affecting this process, as are climate-driven changes in rainfall, evaporation, and runoff. To gain more insights into how the land storage capacity may have changed over recent years, John Reager and colleagues analyzed satellite data from 2002 to 2014 that measure changes in gravity, and thus underlying changes in water storage. They combined this satellite data with estimates of mass loss of glaciers to determine what impact land water storage might have had on sea level change. Their analysis suggests that during this timeframe, climate variability resulted in an increase of approximately 3,200 gigatons of water being stored in land. This gain partially offset water losses from ice sheets, glaciers, and groundwater pumping, slowing the rate of sea level rise by 0.71 ± 0.20 millimeters per year, the authors say. While a small portion of the increase in land water storage can be directly attributed to human activities – primarily, the filling of reservoirs – the authors note that climate is the key driver. The greatest changes in land water storage were associated with regional climate-driven variations in precipitation.