Application of satellite nadir altimetry for forecasting river flow in transboundary rivers S. Biancamaria 1 F. Hossain 2, D.P. Lettenmaier 1, E.A. Clark 1 1 Civil and Environmental Engineering, University of Washington, Seattle WA 2 Civil and Environmental Engineering, Tennessee Technological University, Cookeville TN H11F-0885 AGU Fall Meeting Introduction Figure 1. In-situ gages (magenta dots), Topex/Poseidon’s virtual stations (red dots) and ground tracks (red lines) -Ganges and Brahmaputra basins shared between India (upstream) and Bangladesh (downstream). -Issue: no information on rivers’ state shared between the 2 nations. the farthest upstream point of water level measurement for Bangladesh is at the border. -Consequence: Bangladesh can forecast water level only 3 days in advance (inadequate for risk managements). 2. Purpose of the study and methodology Purpose: Use water level anomalies from Topex/Poseidon (T/P) satellite nadir altimeter (from LEGOS-HYDROWEB, Fig. 1 and Table 1) in India and water level anomalies from two gages in Bangladesh (from BWDB/IWM, Fig. 1) to extend forecast lead time. Methodology: I.Compute correlation between in-situ and upstream T/P water level anomalies occurring k days earlier (k=time lag). II.For high correlations, compute in-situ versus time lagged T/P water level anomalies rating curve. III.Use the rating curve to forecast water level anomalies at the gage location from upstream T/P measurements. T/P Virtual station RiverDistance from gage Numb of obs. Mean time between obs. 166_1Brahmaputra250 km5816 days 053_1Brahmaputra540 km3825 days 242_1Brahmaputra550 km7114 days 155_1Ganges320 km1345 days 014_1Ganges530 km2522 days 079_1Ganges680 km2129 days 116_2Ganges1560 km4912 days 116_1Ganges1800 km4613 days Table 1. Topex/Poseidon measurements from HYDROWEB 3. Data used -Water level in-situ measurements on the Brahmaputra River at Bahadurabad (Fig. 1) are available from January 2000 to September Measurements on the Ganges River at Hardinge Bridge are available from January 2001 to September T/P measurements available from January 1993 to August T/P repeat period is equal to 10 days, but mean times between 2 obs. in the HYDROWEB time series are higher (Table 1). -Studied time period: Jan to Aug (Brahmaputra) and Jan to Aug (Ganges) + focus on monsoon (June to September) and dry season (October to May). -Brahmaputra: year 2000 = high discharge, floods in August; year 2001 = lower discharge, no floods; Ganges: year 2001 = “normal” discharge year, no floods (Fig. 2). Figure 2. In-situ water level and discharge at the gage locations (Fig. 1) Water level (m, ref. PWD)Discharge (10 4 m 3.s -1 ) v v v.. 4. Results -5-day forecast at Bahadurabad (Brahmaputra) using T/P virtual station 166_1: -5-day forecast at Bahadurabad (Brahmaputra) using T/P virtual station 242_1: -5-day forecast at Hardinge Bridge (Ganges) using T/P virtual station 014_1: -10-day forecast at Hardinge Bridge (Ganges) using T/P virtual station 116_2: 5. Conclusions and perspectives -Nadir altimetry can forecast water level anomalies on the Brahmaputra and Ganges rivers with RMSE~0.4m for 5-day lead time and with RMSE~ m for 10-day lead time. -Temporal resolution of the forecast could be improved by using data from several nadir altimeters (like ERS-2, GFO, ENVISAT, JASON-2). -Future wide swath altimetry (like SWOT) should improve detection of floods, which might be currently missed when using only 1D measurements from nadir altimeters. -Future work: coupling with hydrodynamic model to do some forecasts inside Bangladesh. -Acknowledgements: HYDROWEB ( for T/P data; BWDB/IWM for in-situ data. 5-day time lag 10-day time lag I. 5-day time lag I Correlation in-situ/alti Time lag (days) Correlation in-situ/alti Time lag (days) Correlation in-situ/alti Time lag (days) Correlation in-situ/alti Time lag (days) In-situ water lvl anom. (m) II day lag alti water lvl anom. (m) In-situ water lvl anom. (m) day lag alti water lvl anom. (m) In-situ water lvl anom. (m) day lag alti water lvl anom. (m) In-situ water lvl anom. (m) day lag alti water lvl anom. (m) day time lag 5-day time lag Forecast RMSE Time lag (days) RMSE in-situ/alti (m) Time lag (days) RMSE in-situ/alti (m) Time lag (days) RMSE in-situ/alti (m) Time lag (days) RMSE in-situ/alti (m) Feb Apr Jun Aug Oct Dec Feb Apr Jun Aug Oct Dec Danger level 2001 Lowest year (2002) Highest year (2003) Flood level Danger level Flood level Lowest year (2002) Highest year (2004) Ganges at Hardinge Bridge Brahmaputra at Bahadurabad Monsoon+Dry Dry Monsoon Monsoon+Dry Dry Monsoon Monsoon+Dry Monsoon Dry Wat. lvl gage (m) Time (years) III Wat. lvl gage (m) Time (years) Wat. lvl gage (m) Time (years) Wat. lvl gage (m) Time (years) In-situ 5-day forecast In-situ 5-day forecast In-situ 5-day forecast In-situ 10-day forecast Monsoon+Dry Dry Monsoon Bangladesh Ganges Brahmaputra India