Abstract
Abstract. To provide better and more robust estimates of evaporation and snowmelt in a changing climate, hydrological and ecological modeling practices are shifting towards solving the surface energy balance. In addition to precipitation and near-surface temperature (T2), which often are available at high resolution from national providers, high-quality estimates of 2 m humidity and surface incident shortwave (SW↓) and longwave (LW↓) radiation are also required. Novel, gridded estimates of humidity and incident radiation are constructed using a methodology similar to that used in the development of the WATCH forcing data; however, national 1 km×1 km gridded, observation-based T2 data are consulted in the downscaling rather than the 0.5∘×0.5∘ Climatic Research Unit (CRU) T2 data. The novel data set, HySN, covering 1979 to 2017, is archived in Zenodo (https://doi.org/10.5281/zenodo.1970170). The HySN estimates, existing estimates from reanalysis data, post-processed reanalysis data, and Variable Infiltration Capacity (VIC) type forcing data are compared with observations from the Norwegian mainland from 1982 through 1999. Humidity measurements from 84 stations are used, and, by employing quality control routines and including agricultural stations, SW↓ observations from 10 stations are made available. Meanwhile, only two stations have observations of LW↓. Vertical gradients, differences when compared at common altitudes, daily correlations, sensitivities to air mass type, and, where possible, trends and geographical gradients in seasonal means are assessed. At individual stations, differences in seasonal means from the observations are as large as 7 ∘C for dew point temperature, 62 W m−2 for SW↓, and 24 W m−2 for LW↓. Most models overestimate SW↓ and underestimate LW↓. Horizontal resolution is not a predictor of the model's efficiency. Daily correlation is better captured in the products based on newer reanalysis data. Certain model estimates show different dependencies on geographical features, diverging trends, or a different sensitivity to air mass type than the observations.
Highlights
IntroductionGeophysical modeling is advancing, and more and more hydrological, ecological, and land surface models (from here on referred to as land models) are estimating the surface energy balance (Mueller et al, 2013)
Geophysical modeling is advancing, and more and more hydrological, ecological, and land surface models are estimating the surface energy balance (Mueller et al, 2013)
This study addresses the aforementioned sources of uncertainty concerning commonly used estimates of humidity, either in the form of vapor pressure (VP) or converted to dew point temperature (Td), incident longwave radiation (LW↓), and incident shortwave radiation (SW↓) available for long-term land surface modeling in the region through the following processes
Summary
Geophysical modeling is advancing, and more and more hydrological, ecological, and land surface models (from here on referred to as land models) are estimating the surface energy balance (Mueller et al, 2013). Shortwave radiation is the exogenous energy provider to Earth. Estimating the surface energy balance provides a sensible heat flux, as well as a latent heat flux, which in turn can be converted to evaporation or snowmelt, key variables for estimating the surface water balance. Gridded data sets of high quality are needed to statistically bias-correct or downscale future climate scenarios (Abatzoglou, 2013), to spin up land surface models (e.g., Rodell et al, 2005; Koster et al, 2004; Kristiansen et al, 2012), and to assist model development
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