Sensitivities of subgrid-scale physics schemes, meteorological forcing, and topographic radiation in atmosphere-through-bedrock integrated process models: A case study in the Upper Colorado River Basin

Abstract

Abstract. Mountain hydrology is controlled by interacting processes extending from the atmosphere through the bedrock. Integrated process models (IPM), one of the main tools needed to interpret observations and refine conceptual models of the mountainous water cycle, require meteorological forcing that simulates the atmospheric process to predict hydroclimate then subsequently impacts surface-subsurface hydrology. Complex terrain and extreme spatial heterogeneity in mountainous environments drive uncertainty in several key considerations in IPM configurations, and require further quantification and sensitivity analyses. Here, we present an IPM using the Weather Research and Forecasting (WRF) model coupled with an integrated hydrologic model, ParFlow-CLM, implemented over a domain centered over the East River Watershed (ERW), located in the Upper Colorado River Basin (UCRB). The ERW is a heavily-instrumented 300 km2 region in the headwaters of the UCRB near Crested Butte, CO, with a growing atmosphere-through-bedrock observation network. Through a series of experiments in water year 2019 (WY19), we use four meteorological forcings derived from commonly used reanalysis datasets, three subgrid-scale physics scheme configurations, and two terrain shading options within WRF to test the relative importance of these experimental design choices on key hydrometeorological metrics including precipitation, snowpack, as well as evapotranspiration, groundwater storage, and discharge simulated by the ParFlow-CLM. Results reveal that sub-grid scale physics configuration contributes to larger spatiotemporal variance in simulated hydrometeorological conditions, whereas variance across meteorological forcing with common sub-grid scale physics configurations is more spatiotemporally constrained. For example, simulated discharge shows greater variance in response to the WRF simulations across subgrid-scale physics schemes (26 %) rather than meteorological forcing (6 %). Topographic radiation option has minor effects on the watershed-average hydrometeorological processes, but adds profound spatial heterogeneity to local energy budgets (+/-30 W/m2 in shortwave radiation and 1 K air temperature differences in late summer). The findings from this study provide guidance on an IPM setup that most accurately represents atmospheric-through-bedrock hydrometeorological processes and can be used to guide future modeling and fieldwork in mountainous watersheds.

Impact of Seasonal Snow‐Cover Change on the Observed and Simulated State of the Atmospheric Boundary Layer in a High‐Altitude Mountain Valley

“…The study area is the East River Valley, which is embedded in the East River Watershed and located near Crested Butte and Gunnison in Colorado's Rocky Mountains (Figures 1a and 1b). The land cover type is a mix of evergreen and deciduous forest, grasslands, and barren land (Xu et al., 2022). The distance along the valley axis from the measurement site furthest down the valley (Roaring Judy) to the site furthest up the valley (Avery Picnic) is around 35 km (Figure 1).…”

Sensitivities of subgrid-scale physics schemes, meteorological forcing, and topographic radiation in atmosphere-through-bedrock integrated process models: a case study in the Upper Colorado River basin

“…An improved predictive understanding of watershed dynamics and response to perturbations is particularly important for mountainous watersheds due to the multitude of natural services they provide even while those services are highly vulnerable to anthropogenic and natural environmental change (Hubbard et al, 2018;Siirila-Woodburn et al, Z. Xu et al: Sensitivities of subgrid-scale physics schemes 2021). The Upper Colorado River basin (UCRB), which supports 40 million people and ecosystems, has experienced major hydrological change in recent decades (James et al, 2014).…”

“…Data availability. All WRF model output files can be found at https://portal.nersc.gov/archive/home/z/zexuanxu/Shared/www/ IPM (Xu et al, 2023).…”