Investigating Scaling Effects and Runoff Behavior Using Remote Sensed Data and Modeling in the Mississippi River Basin

Abstract:

The hydrologic community has made significant advancements in our predictive understanding of the hydrologic cycle at continental to global scales. Still, there is need for improving model realism at the local scale (i.e., individual river reaches) to evaluate potential impacts of climate variability or landscape disturbances on water availability, ecosystem services and flood/drought risk. It is also well known that scaling issues has large effects on different hydrological processes. The assessment of local water resources and related systems (e.g., ecological and biogeochemical cycles) requires predictive capabilities for flood events not achievable in many current Earth System models. Here, we use an event-focused hydrologic modeling approach applicable at continental to global scales to study hydrologic scaling effects by systematically varying model scales. A case study in the Mississippi River Basin (3.0 M sqkm) is presented. Driven by TRMM precipitation (3B42v7), MODIS evapotranspiration (MOD16A2), MODIS land cover (MCD12C1), AMSR-E snow water equivalent (SWE), LandSat based river widths, and SRTM digital elevation data (v4.1), the Hillslope River Routing (HRR) hydrologic model is used to estimate daily streamflow throughout the Mississippi River Basin for the period 2004-2012. To generate runoff, a coefficient (α) based is used approach, where runoff is α times precipitation and α varies with soil moisture. The generated runoff is routed with HRR to simulate event hydrographs. In our approach, the runoff coefficient varies in space and time with the maximum value based on land cover, soil type and slope, and the time varying values are based on a relationship with relative soil moisture. Results are presented to illustrate how initial soil moisture conditions impact runoff generation and event hydrograph behavior. Simulated hydrographs are analyzed over a range of model resolutions (i.e., sub-catchment areas ranging from about 10 to 10,000 sqkm) to investigate hydrologic scaling behavior. We also explore model behavior related to individual hydrologic characteristics by systematically averaging over different spatial scales individual model parameters and forcings (rainfall, soil depth, and slope, etc).