Evaluating the National Water Model Soil Moisture's Response to Precipitation Forcing

National Water Model (NWM) is a new hydrologic prediction model that NOAA is developing to address the needs from the water resources stakeholders for consistent, high space- and time-resolution, integrated water analysis, predictions, and data to address critical unmet information and service gaps related to floods, droughts, water quality, water availability, and climate change. The NWM simulates and forecasts land surface runoffs and river discharges using model estimated land surface soil moisture. Because of the uncertainties in model physics and input parameters, and potential errors in forcing data such as precipitation, the soil moisture estimates used to initialize the model at each time step may be erroneous, resulting uncertainties in the output of the NWM.

Soil moisture is the key variable for the partitioning of rainfall into infiltration and runoff, thus playing a fundamental role in runoff modelling and flood forecasting. This study evaluates the NWM soil moisture simulations with in situ and satellite SM observations in conjunction with precipitation information from rain gauges and ground radars. We are interested in the rainfall impact on soil moisture field variability and contributions toward understanding the impact of the rainfall as a forcing to the soil moisture field. We’ll examine the time response and rate of soil drying after significant rainfall events from in situ, satellite, and modeled soil moistures. Correlation analysis to quantify the spatial correlation between NWM SM simulations (which uses precipitation as a forcing input) and satellite SM retrievals (which does not use precipitation information) with precipitation data from rain gauges and ground radars such as Multi-Radar/Multi-Sensor (MRMS, Zhang et al., 2016) will also be investigated.