A global water cycle reanalysis (2003–2012) merging satellite gravimetry and altimetry observations with a hydrological multi-model ensemble

摘要

We present a global water cycle reanalysis that merges water balanceestimates derived from the Gravity Recovery And Climate Experiment (GRACE) satellite mission, satellite water levelaltimetry and off-line estimates from several hydrological models. Errorestimates for the sequential data assimilation scheme were derived fromavailable uncertainty information and the triple collocation technique.Errors in four GRACE storage products were estimated to be 11–12 mm overland areas, while errors in monthly storage changes derived from five globalhydrological models were estimated to be 17–28 mm. Prior and posterior water storageestimates were evaluated against independent observations of river waterlevel and discharge, snow water storage and glacier mass loss. Dataassimilation improved or maintained agreement overall, although resultsvaried regionally. Uncertainties were greatest in regions where glacier massloss and subsurface storage decline are both plausible but poorlyconstrained. We calculated a global water budget for 2003–2012. The mainchanges were a net loss of polar ice caps (?342 Gt yr−1) and mountainglaciers (?230 Gt yr−1), with an additional decrease in seasonal snowpack(?18 Gt yr−1). Storage increased due to new impoundments (+16 Gt yr−1),but this was compensated by decreases in other surface waterbodies (?10 Gt yr−1). If the effect of groundwater depletion (?92 Gt yr−1)is considered separately, subsurface water storage increased by+202 Gt yr?1 due particularly to increased wetness in northerntemperate regions and in the seasonally wet tropics of South America andsouthern Africa. The reanalysis results are publicly available via href="www.wenfo.org/wald/"target="_blank">www.wenfo.org/wald/.