Multi-year atmospheric forcing datasets for hydrologic modeling in regions of complex terrain – Methodology and evaluation over the Integrated Precipitation and Hydrology Experiment 2014 domain

Abstract

A framework to derive high-resolution long-term meteorological forcing for hydrologic models from mesoscale atmospheric reanalysis products is presented, including topographic and cloud corrections, and a new physical parameterization of near-surface wind fields. The methodology is applied to downscale 3-hourly North American Regional Reanalysis (NARR) fields originally at 32km spacing to 1km and hourly resolution for a seven-year period (2007–2013) over the Integrated Precipitation and Hydrology Experiment 2014 (IPHEx2014) domain with the focus on the Southern Appalachian Mountains (SAM) in the SE US. Evaluation of the adjusted downscaled products was conducted against flux tower observations in the IPHEx domain. At high elevations, the Root Mean Squared Errors (RMSEs) of atmospheric pressure decreased from 44.71 to 2.78hPa, and the RMSEs of near-surface temperature improved by 1K (up to 5K in winter). In addition, RMSEs decreased by as much as 100% for near-surface winds (10m above ground) at all tower locations and by 25–30W/m2 for shortwave radiation at low elevations. Using the uncalibrated Duke Coupled surface-groundwater Hydrology Model (DCHM), the value and utility of the downscaled products for hydrologic offline simulations are demonstrated through comparative analysis of the sensitivity of water and energy budgets in mountain watersheds for four water-years (2007/10–2011/09) including a severe drought and several flood events. Cloud and topographic corrections applied to incoming solar radiation result in hourly net radiation changes ranging from 200 to 500Wm−2 at mid-day for clear-sky and cloudy conditions, respectively. Improvements in shortwave radiation and near-surface wind speed estimates have the highest impact on evapotranspiration and soil surface temperature. Wind speed differences of 2–10m/s translate into basin-averaged differences mid-day surface fluxes up to 300Wm−2 and 100Wm−2 in the inner SAM, for sensible and latent heat respectively.