GLOBAL FLOOD ESTIMATION USING SATELLITE RAINFALL INFORMATION AND HYDROLOGICAL MODELS: STATUS AND FUTURE

Flood detection and intensity estimates are being made in real-time using satellite precipitation information (e.g., TRMM Multi-satellite Precipitation Analysis [TMPA]) and a hydrological model. This experimental system, the Global Flood Monitoring System (GFMS) uses the 3-hr resolution composite rainfall analyses as input into a hydrological model that calculates water depth at each grid (at 0.25° latitudelongitude) over the tropics and mid-latitudes with real-time results displayed at http://oas.gsfc.nasa.gov/globalflood/. These calculations can provide information useful to national and international agencies in understanding the location, intensity, timeline and impact on populations of these significant hazard events. A validation of the systems ability to detect floods compared to a global flood event data base indicate results improve with longer duration (> 3 days) floods and that the statistics are impacted by the negatively by the presence of dams, which are not accounted for in the model calculations. The current quality of these flood estimations is at the level of being useful, but there is a potential for significant improvement, mainly through improved and more timely satellite precipitation information and improvement in the hydrological models. Limitations in the flood calculations that are related to the satellite rainfall estimates include space and time resolution limitations, false-precipitation artifacts (often over mountainous regions) and underestimation of shallow orographic and monsoon system rainfall. Examples of these precipitation-based impacts will be discussed. NASA’s Global Precipitation Measurement (GPM) program should lead to improved precipitation analyses utilizing space-time interpolations that maintain accurate intensity distributions along with methods to disaggregate the rain information. But, the testing of improved precipitation products in flood detection and intensity determination will continue to be important for understanding limitations in the precipitation information. Higher resolution flood models with accurate routing and regional calibration, and the use of satellite soil moisture retrievals should also advance the state-of-the-art.