Enhancing UFS S2S Performance Through Land Model Development Using Hierarchical Testing

A collaborative effort is currently underway to develop NOAA’s next generation Unified Forecast System (UFS) framework. Within the UFS, there are multiple major earth system components, including atmosphere, oceans, and land. UFS applications span local to global domains and predictive time scales from sub-hourly to seasonal. These wide-ranging applications pose challenges and provide opportunities for the development and evaluation of UFS land components. This presentation will discuss on-going efforts in addressing and coordinating a land evaluation framework and land model physics advances. Models lacking proper coupled land-atmosphere behavior will underperform at all temporal and spatial scales, and will be prone to systematic biases in temperature, humidity and precipitation. A successful UFS Subseasonal-to-Seasonal (S2S) land effort will contribute to looking beyond the land surface model as an atmospheric boundary condition by providing land surface process-level information to expanding user communities.

In this presentation, a hierarchical testing approach is employed that involves a spectrum of LSM-only simulations, single-column coupled land-atmosphere modeling system, and coupled simulations. This approach is used to isolate and quantify the impacts of individual components on S2S prediction skill before systematically increasing complexity and inherently introducing non-linear, difficult to track interactions. Evaluation is extended beyond traditional meteorologic validation to land process metrics that focus on the interactions between land and the atmosphere. We especially focus on several elements of the global water cycle: diurnal-to-monthly evapotranspiration, runoff partitioning, surface heat flux partitioning and how these metrics influence traditional metrics such as precipitation and near-surface temperature and dewpoint.