ABSTRACT

Gravity Recovery and Climate Experiment (GRACE) data have a relatively short time span (since its launch in 2002), making most analyses of GRACE data subjected to the recent decade. A longer time series of total water storage (TWS) changes, for example, 30 years, should be more helpful in examining TWS variations on a climatic timescale. This section elaborates an approach to quantify how climate change impacts TWS in the long term, and how climate extremes (e.g., droughts and floods) impact TWS in the short term. Droughts and floods alternately occur over a large karst plateau (Yun-Gui Plateau) in Southwest China. Here we show that both the frequency and severity of droughts and floods over the plateau are intensified during the recent decade from three-decade total water storage anomalies (TWSA) generated by GRACE satellite data and artificial neural network (ANN) models. The developed ANN models performed well in hindcasting TWSA for the plateau and its three subregions (i.e., the upper Mekong River, Pearl River, and Wujiang River basins), showing coefficients of determination (R2) of 0.91, 0.83, 0.76, and 0.57, respectively. The intensified climate extremes are indicative of large changes in the hydrologic cycle and brought great challenges in water resources management there. The TWSA of the plateau remained fairly stable during the 1980s, and featured an increasing trend at a rate of 5.9 ± 0.5 mm/a in the 1990s interspersed extreme flooding in 1991 and during the second half of the 1990s. Since 2000, the TWSA fluctuated drastically, featuring severe spring droughts from 2003 to 2006, the most extreme spring drought on record in 2010, and severe flooding in 2008. The TWSA of the upper Mekong has decreased by ~100 mm (~15 km3) compared with that at the end of the 1990s. In addition to hindcasting TWSA, the developed approach could be effective in generating future TWSA and potentially bridging the gap between the current GRACE satellites and the GRACE Follow-On Mission expected to launch in 2017.