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

Abstract

Abstract. We present a global water cycle reanalysis that merges water balance estimates derived from the Gravity Recovery And Climate Experiment (GRACE) satellite mission, satellite water level altimetry and off-line estimates from several hydrological models. Error estimates for the sequential data assimilation scheme were derived from available uncertainty information and the triple collocation technique. Errors in four GRACE storage products were estimated to be 11-12 mm over land areas, while errors in monthly storage changes derived from five global hydrological models were estimated to be 17-28 mm. Prior and posterior water storage estimates were evaluated against independent observations of river water level and discharge, snow water storage and glacier mass loss. Data assimilation improved or maintained agreement overall, although results varied regionally. Uncertainties were greatest in regions where glacier mass loss and subsurface storage decline are both plausible but poorly constrained. We calculated a global water budget for [2003][2004][2005][2006][2007][2008][2009][2010][2011][2012]. The main changes were a net loss of polar ice caps (−342 Gt yr −1 ) and mountain glaciers (−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 water bodies (−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 northern temperate regions and in the seasonally wet tropics of South America and southern Africa. The reanalysis results are publicly available via www.wenfo.org/wald/.

Recent Changes in Land Water Storage and its Contribution to Sea Level Variations

“…Coarse spatial resolution and noise contamination inherent in GRACE data hinder global application of estimating GWD (satellite-based method). Van Dijk et al (2014) used a data assimilation framework to integrate water balance estimates derived from GRACE satellite observations and several hydrological models, which improved the estimate of global GWD derived from a hydrological model from 168 to 92 km 3 year -1 (averaged over the 2003-2012 period). Earlier estimates of GWD contribution to SLR ranges from 0.075 to 0.30 mm year -1 (Sahagian et al 1994;Gornitz 1995Gornitz , 2001; Foster and Loucks 2006; see also Table 1).…”

Rivers and Floodplains as Key Components of Global Terrestrial Water Storage Variability

“…The contribution of reservoir operation to global TWS change was evaluated by Zhou et al (2016) but then neglected the contribution of river channel and floodplain storage. Among the GRACE data assimilation (DA) initiatives, a few studies have considered SWS, mostly using relatively simplistic approaches (Eicker et al, 2014;Tian et al, 2017;van Dijk et al, 2014). However, the majority of GRACE DA studies assume that TWS is the sum of land surface model (LSM) water storage (LWS) components, for example, groundwater storage (GWS), soil moisture (SM), snow water equivalent (SWE), and total canopy interception water storage (e.g., Girotto et al, 2016Girotto et al, , 2017Houborg et al, 2012;Kumar et al, 2016;Zaitchik et al, 2008).…”

High‐resolution modeling of human and climate impacts on global water resources

“…Excessive groundwater pumping, however, often leads to overexploitation, causing groundwater depletion [Konikow and Kendy, 2005;Rodell et al, 2009;Tiwari et al, 2009;Famiglietti et al, 2011;Konikow, 2011;D€ oll et al, 2012;Scanlon et al, 2007Scanlon et al, , 2012aScanlon et al, , 2012bWada et al, 2012aWada et al, , 2012bTaylor et al, 2013] that may have devastating effects on environmental streamflow, groundwater-fed wetlands and related ecosystems [Gleeson et al, 2012;Gleeson and Wada, 2013;Wada and Heinrich, 2013] As a result, terrestrial water fluxes have been affected by humans at an unprecedented scale and the fingerprints that humans have left on Earth's water resources are turning up in a diverse range of records and can be seen in surface freshwater (water in rivers, lakes, reservoirs and wetlands) and groundwater resources alike [Van Dijk et al, 2014].…”