Abstract
Spatiotemporal variations of water volume over inundated areas located in a large river basin have been determined using combined observations from a multisatellite inundation data set, the TOPEX/POSEIDON (T/P) altimetry satellite, and in situ hydrographic stations for the water levels over rivers and floodplains. We computed maps of monthly surface water volume change over the period of common availability of T/P and the multisatellite data (1993–2000). The basin of the Negro River, the largest tributary in terms of discharge to the Amazon River, was selected as a test site. A strong seasonal signal is observed with minima in October and maxima in June. A strong interannual component is also present, particularly important during ENSO years. The surface water change was estimated to be 167 ± 39 km3 between October 1995 (low water) and June 1996 (high water). This result is consistent with previous estimates obtained for the 1995–1996 hydrological cycle over the same area using the JERS mosaic data. The surface water volume change is then compared to the total water volume change inferred from the GRACE satellite for an average annual cycle. The difference between the surface storage change and the total storage change derived from GRACE was computed to estimate the contribution of the soil moisture and groundwater to the total storage change. Our study supports the hypothesis that total water storage is almost equally partitioned between surface water and the combination of soil moisture and groundwater for the Negro River basin. The water volume changes are also evaluated using in situ discharge measurements and the GPCP precipitation product (correlation of 0.61). The results show the high potential for the new technique to provide valuable information to improve our understanding of large river basin hydrologic processes.
Highlights
AND BACKGROUNDthey have crucial impact on terrestrial life and human needs, and play a major role in climate variability [Cosandey and Robinson, 2000; Perrier and Tuzet, 2005].Among the various reservoirs in which fresh water on land is stored, surface waters play a crucial role in the global biochemical and the hydrological cycles [de Marsily et al, 2005]
We propose a new approach to estimate river volume changes in a large drainage basin that combines estimates of spatial and temporal surface water extent from a multi-satellite technique [Prigent et al, 2007] with water level measurements from satellite altimetry
Their seasonal and inter-annual variability has been evaluated over different environments and over different large river basins with respect to rain rate and snow estimates, altimeter river height levels, and were found consistent with other related hydrological variables such as in situ river discharge
Summary
Among the various reservoirs in which fresh water on land is stored (ice caps, glaciers, snow pack, soil moisture, groundwater, etc.), surface waters (rivers, lakes, reservoirs, wetlands and inundated areas) play a crucial role in the global biochemical and the hydrological cycles [de Marsily et al, 2005]. Even if wetlands and floodplains cover about 6 % of the Earth surface [OECD, 1996], they have a substantial impact on flood flow alteration, sediment stabilization, water quality, groundwater recharge and discharge [Maltby, 1991; Bullock and Acreman, 2003]. Extensive floodplains along large South American rivers, such as Amazon, Paraná or Orinoco, have a significant role in the hydrological cycle of fluvial basins. The water storage in these wetlands and its outflow represent a significant part of the water balance in the basin [Richey et al, 1989; Alsdorf et al, 2001]
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