The central objective of the proposed project is to objectively determine the utility of satellite-estimated precipitation (at an hourly time scale), from the current TRMM mission, in providing spatially distributed precipitation data to support conventional hydrologic modeling at the watershed scale. At present, a major problem with satellite-estimated precipitation is the lack of continuous coverage over any given 24-hour period. Future missions (GPM) are currently planned and will provide complete temporal coverage using a variety of satellite platforms. However, at present there is limited information about the effectiveness of satellite-estimated precipitation data in terms of providing primary input for surface hydrological models. This study will develop methodologies for converting TRMM precipitation estimates (3B42) to support hydrologic modeling. The hydrologic model we have chosen is the Soil and Water Assessment Tool (SWAT), which has been developed into a versatile watershed management tool. A definite advantage of this TRMM validation study is the semi-arid climate regime of the South Texas and Mexican borderland region in which base flow, surface discharge contributed from the subsurface, is essentially zero in this region. Consequently, discrete discharge events that correspond with periods of TRMM coverage can be analyzed without the complicating affects of prior discharge events that may not have corresponded with periods of TRMM coverage. In this manner we can objectively determine the utility of future satellite-based radar platforms in terms of providing data to support future hydrologic modeling efforts.
Our study area is the Middle Rio Grande and Nueces River Basins region around Laredo, TX. Spatial variation in precipitation is highly marked in this area; a region located in a semi-arid climatic regime. Official ground measurements of precipitation are limited with a total of three active NWS cooperative stations scattered over Webb County (Laredo is the county seat); a county with dimensions similar to several northeastern states. Additionally, a significant fraction of the study area is located at the edge of the coverage envelopes of the NWS NEXRAD weather radars present in the region limiting the accuracy of these systems to provide reliable spatially distributed precipitation data to support hydrologic modeling. Therefore, TRMM estimated precipitation could provide a critical accounting of potential water resources for the South Texas and Mexican Borderlands region. Additionally, an ArcIMS-based web visualization and publication system facilitating dissemination of model results to the widest possible audience will be developed. The methodologies developed in this project have obvious potential for adoption in other regions of the world that have limited ground-based precipitation measurements and could benefit from TRMM data.
