Evaluation of Hydrological Models in Low Runoff Ratio Regions: Next Generation Water Resources Modeling Framework vs National Water Model v3.0

The diverse hydroclimatic regions across the United States present a significant challenge for any single hydrologic model to accurately forecast stream flows and represent soil moisture dynamics at scales ranging from local to continental. This is due to the lack of a comprehensive theory of stormflow generation, which means that no single hydrologic model can be formulated to capture all dominant hydrologic processes at such a range of scales. To address this challenge, NOAA’s Office of Water Prediction is developing the Next Generation Water Resources Modeling Framework (NextGen) – a model and language-agnostic modeling framework that enables execution of different model formulations in different hydroclimatic conditions. We leverage the NextGen capabilities to evaluate the performance of models within the NextGen framework compared to the WRF-Hydro based NWM 3.0, focusing on regions with a low runoff ratio. Analyses show that in these regions, the current NWM 3.0 either over- or underpredicts annual runoff volumes, depending on the specific location. Thus, this work aims to determine whether hydrologic models running in the NextGen framework have the potential to enhance the performance of future NWM versions in these regions. We focus on two hydrologic models: the Conceptual Functional Equivalent (CFE2.0), with a newly incorporated Nash Cascade-based surface runoff scheme with parameters estimated from a geomorphic instantaneous unit hydrograph, and the Lumped Arid Semi-Arid Model (LASAM) which employs the continuous Layered Green-Ampt with Redistribution (LGAR) precipitation partitioning method. Here, we present results of these hydrologic models coupled with a land surface model and a channel routing model, assessing their performance against hourly observed streamflow and NWM 3.0 over 516 CAMELS basins spanning the years 2010-2015. Additionally, we examine simulated soil moisture against observations recorded by the USDA SCAN network at a few selected regions. These preliminary findings suggest that the heterogeneous approach enabled by the NextGen Framework is highly likely to improve forecast skill, in particular streamflow and soil moisture in regions with low runoff ratios.