How Much Do We Know about the Storage Changes in the Major River Basins of the World? Analysis of Storage Change from GRACE

Abstract:

Change in storage is an important component of water cycle that is often ignored in large-scale hydrologic studies due to limited data and difficulty in measurement. For the first time, this study quantifies and inter-compares storage changes in major river basins of the world. Gravity Recovery and Climate Experiment (GRACE) monthly mass deviation in storage (MDS) data over 2003-2013 is used to compute monthly, annual and long-term change in storage (ΔS) for 51 major river basins of the world (> 200,000 km²). For each river basin, GRACE ΔS is analyzed to understand a) temporal variability in ΔS b) magnitude of ΔS at annual and decadal time scales and c) duration of storage cycle (time taken by a basin in months to return to initial storage condition). This study identified that 11, 33 and 7 out of 51 basins showed high, medium and low month to month variability in storage changes, respectively. Compared to basin precipitation, 48 out of 51 river basins showed storage to be considerable (5 – 35% of basin annual precipitation). Only 3 basins (Irrawaddy, St. Lawrence, and Brahmaputra) showed minimum variability in storage (< 5%). At long-term (decadal) time-scales, all the 51 river basins showed negligible storage changes (< 0.5%). This result emphasizes the fact that change in storage, ΔS is substantial at monthly and annual time scales but can be ignored over a decadal time scale. Analysis of storage cycle for each basin revealed that a basin can take anywhere from 5 to 12 months to restore itself. While, 14 out of 51 basins showed biannual storage cycle (≤ 6 months), six basins (Zambezi, Mekong, Orinoco, Tocantins, and Amazon) showed annual storage cycle of 12 months. Our results indicate that most basins within the tropics show positive correlation with precipitation indicating that precipitation is the main driver of storage. On the other hand, ΔS in the basins located in the higher latitudes mostly show negative correlation with precipitation. This study provides new insights into how basin storage changes in the major river basins. Future study would focus on the analysis of ΔS over large river basins within the United States. Such analysis and estimates of ΔS would help to (i) improve our knowledge of water availability and (ii) meet the goals of the WaterSMART (Sustain and Manage America’s Resources for Tomorrow) project.