Model estimates of sea-level change due to anthropogenic impacts on terrestrial water storage

Global sea level has been rising over the past half century, according to tide-gauge data1,2. Thermal expansion of oceans, melting of glaciers and loss of the ice masses in Greenland and Antarctica are commonly considered as the largest contributors, but these contributions do not entirely explain the observed sea-level rise1. Changes in terrestrial water storage are also likely to affect sea level3–6, but comprehensive and reliable estimates of this contribution, particularly through human water use, are scarce1. Here, we estimate sea-level change in response to human impacts on terrestrial water storage by using an integrated model that simulates global terrestrial water stocks and flows (exclusive to Greenland and Antarctica) and especially accounts for human activities such as reservoir operation and irrigation. We find that, together, unsustainable groundwater use, artificial reservoir water impoundment, climate-driven changes in terrestrial water storage and the loss of water from closed basins have contributed a sea-level rise of about 0.77 mm yr−1 between 1961 and 2003, about 42% of the observed sea-level rise. We note that, of these components, the unsustainable use of groundwater represents the largest contribution. Global sea-level change (SLC) is widely debated3–10 because it is affected by numerous natural and anthropogenic factors such as thermal expansion of the oceans, melting of glaciers associated with global warming and change in terrestrial water storage (TWS) including soil water, groundwater, snow and surface water in natural lakes and artificial reservoirs. Tide-gaugebased observations indicate that the global sea level rose by ∼ 1.8mmyr−1 over the second half of the twentieth century1,2. The total contribution of climate-related factors (thermal expansion of oceans, glaciers and ice caps melting, and loss of ice masses in Greenland and Antarctica) has been estimated to be ∼1.1mmyr−1 (refs 1,11–14), which leaves an unaccounted SLC of∼0.7mmyr−1. The Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC) concluded that the budget of sealevel rise has not yet been closed satisfactorily, primarily owing to the large uncertainties in the contributions of anthropogenic TWS variations1 (for example, artificial reservoir water impoundment, groundwater depletion). More recent literature has affirmed the significance of these anthropogenic impacts3,5,15. Among the two most significant anthropogenic impacts, artificial reservoirs have caused a drop in the sea level by impounding a