Hydrological Modeling Where No Meteorological Stations Exist

Introduction Hydrologic modeling at daily or sub daily resolution requires accurate precipitation and temperature data, which is particularly important when planning land use changes and live management operations such as irrigation allocation. Weather gage data pose a variety of challenges, including the fact that they are nonexistent in many watersheds of interest. We show that by integrating global forecast products and reanalysis datasets from the atmospheric modeling community into the hydrologic models commonly used, we can circumvent some of the issues with point-of-measure weather gauges. Traditionally in hydrologic forecasting, a precipitation forecast is used from a nearby precipitation station on which the hydrologic model has been calibrated. Here we present the results of two studies. First, we compare calibrating a watershed model (SWAT) using weather forecasts from ensembles of raw gridded atmospheric models interpolated to the center of subbasins against using the closest weather gage measurements. Second, we perform a similar study using global reanalysis datasets. In addition, we look at what scales and radii using direct gridded model output may introduce equal or less error to watershed modeling projects than using the closest station. We demostrate: -There is validity to using reanalysis datasets in place of weather station data to force hydrologic modeling systems when nearby weather stations are not available or have inconsistent records -There is validity to using short term forecast archives in place of weather station data to force hydrologic modeling systems. -The distance to the where the model skill produces the same accuracy as the weather stations is closer than we thought. -Variables from the atmospheric models are physically linked, and we should likely keep them that way. Conclusion This study found that weather forecast archives and CFSR reanalysis data provide a potentially valuable alternative to “nearest weather station” data for hydrological modelers. Indeed, this study found that the CFSR data may actually be a better representation of the weather than point observations, at the scale of small watersheds (Presented Nov. 2011. Third International Forum on Water and Food (IFWF3). Tshwane, South Africa http://waterandfood.org/2012/04/22/third-international-forum-on-water-and-food/