Reply on RC2 After Revision

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.