Total Land Water Storage Change over 2003-2013 Estimated from a Global Mass Budget Approach

Abstract:

We estimate the total land water storage change over 2003-2013 using a global water mass budget approach. It consists of comparing the ocean mass change from GRACE space gravimetry to the sum of the main water mass components of the climate system : glaciers, Greenland and Antarctica ice sheets, atmospheric water vapour and land water storage (the latter being the unknown quantity to be estimated). We first compute a mean trend over the study period. Then, we account for the change in rates (acceleration) seen in several terms of the mass budget equation (e.g., GRACE-based ocean mass, Greenland, Antarctica and glaciers mass balances). For the glaciers and ice sheets, we use published estimates of ice mass trends based on various types of observations covering different sub-periods of the 2003-2013 decade. For each component, we compute a changing rate through time. We also consider time series of mass balance rates and associated accelerations. From the global water mass budget approach, we derive a time series of land water storage rate over the study period. The computed changing rate in global land water storage mainly represents direct anthropogenic effects on land hydrology, i.e. the net effect of ground water depletion and impoundment of water in man-made reservoirs (estimates from hydrological models driven by meteorological forcing show that natural climate variability essentially cause interannual fluctuations in the net land water storage but negligible long term trend). Our results are compared with independent estimates of human-induced changes in global land hydrology, in particular ground water depletion.