Analysis of satellite observed rain fall amounts and discharge measurements at the Datong Hydrologic Station

The Datong hydrologic station at Changjiang (or Yangtze River) is about 450 km upstream from the river mouth. The average annual discharge measured at the station is 29,000m3/sec according to Chen et al. (2003), which is equivalent to 914km3/year. This study uses satellite observations to estimate the rainfall amounts over the entire Changjiang basin and for the upstream to the Datong station. The difference between these two rainfall amounts is small due to the small downstream area coverage. The correlation between the rainfall amounts and the discharge measurements are higher than 88% with a 40-days phase delay of the discharge for daily means based on 2003-2007 data.

Furthermore, the discharge at Datong is compared well with the satellite estimated difference between precipitation and evaporation although the absolute values are different due to land surface water storage. The satellite precipitation data are from the Global Precipitation Climatology Project (GPCP), and the evaporation is estimated from the constraint of the satellite surface net radiation flux of SRB (Surface Radiation Budget) project on land surface energy budget with a separation of latent and sensible heat fluxes using the Bowen ratio from the land model CLM (Community Land model). Base on 1990-2005 data, the average annual discharge are 934 and 910 km3/year from Datong and satellite measurements, respectively. These values are close to the reports of climatologic annual means of 907 and 914km3 by Dai et al. (2008) and Chen et al. (2003), respectively.

The advantage of using satellite data is that the estimations of precipitation, evaporation and discharge can be obtained over wide spectra spatio-temporal scales, and be used for the rivers with stations being far away from river mouths and having malfunctioned measurements or even without stations. The observed phase shifts among different hydrological components can be further investigated for individual sub-regions within the river basin for flood warning and water resource management.