Analyzing the effect of earthquake correction on GRACE-derived drought indicators

For many years the satellite gravity mission Gravity Recovery And Climate Experiment (GRACE) provided important insights into a large number of hydrological processes on Earth. However, to derive observations that can be used for hydrological applications many different postprocessing steps, e.g. filtering, replacement of low-degree coefficients, correction for glacial isostatic adjustment, need to be applied. Therefore, the official analysis centers meanwhile also provide postprocessed total water storage anomalies on a grid. Unfortunately, the effect of large earthquakes is usually not reduced. The resulting biases and artefact trends then bias hydrological analysis such as the detection of droughts and their severity.

 

For the first time, we analyze the effect of large earthquake correction on GRACE-derived Drought Severity Index (DSI) over Peninsular Malaysia in the period 2003 to 2016. For this, we perform a time series analysis based on GRACE-derived total water storage anomalies, while estimating, among others, a co-seismic and post-seismic signal using a nonlinear Bayes estimator (Einarsson et al. 2010). Our results show that the earthquake correction has a significant impact on the detected drought severity, suggesting that the earthquake correction may become a standard tool in time series analysis of GRACE and GRACE-Follow-On level-3 data.