Assessing Global Water Storage Variability from GRACE: Trends, Seasonal Cycle, Subseasonal Anomalies and Extremes

Abstract

Throughout the past decade, the Gravity Recovery and Climate Experiment (GRACE) has given an unprecedented view on global variations in terrestrial water storage. While an increasing number of case studies have provided a rich overview on regional analyses, a global assessment on the dominant features of GRACE variability is still lacking. To address this, we survey key features of temporal variability in the GRACE record by decomposing gridded time series of monthly equivalent water height into linear trends, inter-annual, seasonal, and subseasonal (intra-annual) components. We provide an overview of the relative importance and spatial distribution of these components globally. A correlation analysis with precipitation and temperature reveals that both the inter-annual and subseasonal anomalies are tightly related to fluctuations in the atmospheric forcing. As a novelty, we show that for large regions of the world high-frequency anomalies in the monthly GRACE signal, which have been partly interpreted as noise, can be statistically reconstructed from daily precipitation once an adequate averaging filter is applied. This filter integrates the temporally decaying contribution of precipitation to the storage changes in any given month, including earlier precipitation. Finally, we also survey extreme dry anomalies in the GRACE record and relate them to documented drought events. This global assessment sets regional studies in a broader context and reveals phenomena that had not been documented so far.

Understanding terrestrial water storage variations in northern latitudes across scales

“…Additionally, our model shows a weaker performance in subarctic and arctic wetlands, and in central North America and east- ern Eurasia. The latter are both relatively dry regions that are rather dominated by inter-annual TWS variations (Humphrey et al, 2016). Discrepancies between TWS obs and TWS mod thus relate to a low signal-to-noise ratio in TWS obs due to small seasonal TWS variations.…”

Groundwater Depletion in the West Liaohe River Basin, China and Its Implications Revealed by GRACE and In Situ Measurements

“…The details on the reconstruction method of climate-driven sub-decadal water storage variability can be found in [48,49]. In brief, first, the effect of one day's precipitation flux to later days can be expressed by an exponential decay filter:…”

“…Then, filtered daily time series was averaged to the monthly resolution using an arithmetic mean. As the exponential decay filtered daily precipitation is highly correlated with interannual and subseasonal TWSA [49], the precipitation-driven TWSA was formulated as following:…”

“…Because the precipitation data from CMDC with daily resolution are available until 2013, we reconstructed the TWSA time series from 1980 to 2013. In the original TWSA reconstruction by Humphrey et al [49], temperature change was also considered in addition to precipitation. In this study, however, we only used precipitation data because temperature has less effect on TWSA (Vincent Humphrey, personal communication).…”

Basin-scale water-balance dataset (BSWB): an update

“…However, penetration depth is limited to the top few centimetres of the soil (Owe and Van de Griend, 1998). On the other hand, remotesensing-based measurements of TWS from the Gravity Recovery and Climate Experiment (GRACE; Tapley et al, 2004;Ramillien et al, 2008;Humphrey et al, 2016) only go back to 2002. Thus, for further retrospective evaluation of TWS, alternative approaches are required.…”