The advent of satellite-based quasi-global, real-time precipitation analyses at high temporal resolution has lead to the reality of running global hydrological models for the estimation of the occurrence of floods (see trmm.gsfc.nasa.gov). These calculations provide information useful to national and international agencies in understanding the intensity, timeline and impact on populations of these significant hazard events. The current quality and timeliness of the composite rainfall products (e.g., TRMM Multi-satellite Precipitation Analysis [TMPA]) has allowed for production of useful real-time flood products. The status of these flood calculations will be shown by case study examples and statistics against a global flood event database. The statistics indicate that results improve with longer duration (> 3 days) floods and that the statistics are impacted by the presence of dams, which are not accounted for in the model calculations. Limitations in the flood calculations that are related to the satellite rainfall estimates include space and time resolution limitations, biases in over-land passive microwave retrievals, underestimation of shallow orographic and monsoon system rainfall, and poor accuracy in cold-season precipitation (including snow).

The quality of hydrological estimations should improve, however, due to continuation and improvement of multi-satellite precipitation observations through the Global Precipitation Measurement (GPM) program and the further development of the hydrological models. This talk will summarize the results from the current real-time flood nowcasts and forecasts and describe directions for improving results going into the GPM era. The expected positive impact of the GPM products will be described as well as directions in global flood models and how their improvements will impact the need for improved precipitation information. Improvements over the next few years should focus on 1) better precipitation analyses utilizing space-time interpolations that maintain accurate intensity distributions along with methods to disaggregate the rain information, 2) improved rain estimation for shallow, orographic rainfall systems and some types of monsoon rainfall, 3) higher resolution flood models with accurate routing and regional calibration, and 4) use of satellite soil moisture retrievals along with use of precipitation information for more accurate pre-conditions. Examples of some of these advances will be shown, including the use of higher resolution hydrologic models and the use of forecast precipitation to augment the satellite-observed rainfall estimates and extend the flood estimates for 1-5 day forecasts.