Inter-annual Water Storage Changes in Asia from GRACE Data

Abstract

Time-varying gravity field solutions from the Gravity Recovery and Climate Experiment (GRACE) satellite mission have been used to investigate the inter-annual changes of hydrologic water storage (∆ S) within Asia, focusing on the India–China–South Asia region. Instead of computing GRACE monthly ∆ S from geopotential coefficients, we choose to compute the annually averaged ∆ S before data smoothing, which improved the accuracy for the resulting inter-annual water storage changes. We then applied a novel method of decorrelation, filtering and land signal leakage reduction to the data, which yielded more accurate and higher spatial resolution (200 km or longer, half-wavelength) GRACE storage change observables over the study region. The technique provides a tool for future more in-depth studies of terrestrial hydrology in this region or globally. GRACE inter-annual variations in water storage change (2002–2007) exhibit large extremes over the region: droughts in Eastern China in 2004 and Indo-China and Bangladesh in 2005; and flooding in Indo-China and India in 2006. In general, GRACE inter-annual ∆ S variations have significantly larger amplitudes (increase or decrease of water storage change) than the values predicted by the Global Land Data Assimilation System (GLDAS) hydrologic model, and than the total precipitation observed by the Topical Rainfall Measurement Mission (TRMM).