HYDROLOGIC APPLICATIONS OF SATELLITE DATA .2. FLOW SIMULATION AND SOIL-WATER ESTIMATES

The uncertainty in streamflow simulations and soil water estimates ass ociated with satellite rainfall forcing is investigated for the Upper Des Moines River basin in the midwestern United States. Synthetic seri es of satellite rainfall estimates were produced with a rain gauge-sat ellite stochastic model and 10 years of daily rain gauge data (1979-19 88) for three basins with drainage areas ranging from 2,000 km(2) to 1 4,000 km(2). The synthetic satellite rainfall series was based on obse rved satellite visible and infrared data which provided estimates of s atellite rainfall for 180 randomly selected days in the period 1980-19 87. Streamflow and soil water estimates were obtained with a rainfall- runoff-routing model (3R), based on soil water balance and accounting for snowmelt and frozen ground effects. Sensitivity of flow prediction with respect to rainfall was examined for three different conditions: (1) 3R calibrated and forced with rain gauge data, (2) 3R calibrated with rain gauge data and forced with satellite rainfall, and (3) 3R ca librated and forced with satellite rainfall. The most important result s regarding the effect of satellite rainfall on flow simulation and so il water estimation for climate studies are as follows: (1) Flow simul ation accuracy is sensitive to the basin scale, yielding higher correl ation of simulated with observed streamflow for larger scales, (2) the hydrologic model forced with satellite data possesses skill during th e period May-July for the midwestern United States, (3) derived upper soil water estimates are similar to the ones obtained using rain gauge forcing, and derived lower soil water estimates are lower than those obtained from rain gauge forcing.