Sub-seasonal reconstructions of Brahmaputra River discharge
Abstract
The Ganges-Brahmaputra-Meghna river system is the third largest in the world with an annual discharge of approximately 40,000m3/s with the Brahmaputra alone contributing nearly half of the total discharge. Climatic controls on streamflow in the lower Brahmaputra basin are complex and vary seasonally, with glacial and snow melt from the Himalaya and Tibetan Plateau dominating in the fall, winter and spring, and Indian monsoon precipitation acting as the major contributor to summer flow. Here we present a suite of seven sub-seasonal discharge reconstructions of past discharge at the Bahadurabad gauging station in Bangladesh based on a careful evaluation of streamflow clustering across different months and streamflow and tree-ring predictor relationships. Three wet season (May-June, July, and August-September) and two dry season (October and January-February) reconstructions are produced extending back approximately six centuries ( 1400-2014 C.E). The remaining two dry season reconstructions (November-December and March-April) are millennial length and span 500-2014 C.E. These resulting reconstructions have little predictor overlap allowing us compare low frequency variability and recent trends if any across different seasons and the entire year. The short instrumental data (1956-2014 C.E.) show increasing dry season flow and decreasing wet season flow, particularly since the 1990s. While these changes are likely associated with increased glacial melt and decreasing monsoon precipitation respectively, they lie within reconstructed paleo-discharge variability estimates. The deltaic flood plains of Bangladesh are extremely vulnerable to catastrophic seasonal floods particularly during summer months. Major flooding events occurred in 1871, 1966, 1987, 1988, and 1998. Our reconstruction indicates unusually high summer discharge in all of these years. The single year highest discharge value over the length of the six-century long reconstruction occurred in 1998. Using our reconstructions, we find on average five single-year high discharge events of comparable magnitude occur every century, but these events appear to more likely to occur during periods of decadal high flow. This suggests a potential to use our multi-centennial reconstruction for flood-hazard risk estimation.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H33L2239R
- Keywords:
-
- 1616 Climate variability;
- GLOBAL CHANGEDE: 1804 Catchment;
- HYDROLOGYDE: 1833 Hydroclimatology;
- HYDROLOGYDE: 1836 Hydrological cycles and budgets;
- HYDROLOGY