Abstract
Abstract. Noah (version 2.7.1), the community land-surface model (LSM) of National Centers for Environmental Predictions-National Center for Atmospheric Research (NCEP-NCAR), which is widely used to describe the land-surface processes either in stand-alone or in coupled land-atmospheric model systems, is recognized to underestimate snow–water equivalent (SWE). Noah's SWE bias can be attributed to its simple snow sub-model, which does not effectively describe the physical processes during snow accumulation and melt period. To improve SWE simulation in the Noah LSM, the Utah Energy Balance (UEB) snow model is implemented in Noah to test alternate snow surface temperature and snowmelt outflow schemes. Snow surface temperature was estimated using the force-restore method and snowmelt event is regulated by accounting for the internal energy of the snowpack. The modified Noah's SWE simulations are compared with the SWE observed at California's NRCS SNOTEL stations for 7 water years: 2002–2008, while the model's snow surface temperature is verified with observed surface-temperature data at an observation site in Utah. The experiments show that modification in Noah's snow process substantially reduced SWE estimation bias while keeping the simplicity of the Noah LSM. The results suggest that the model did not benefit from the alternate temperature representation but primary improvement can be attributed to the substituted snowmelt process.
Highlights
The Noah landsurface model (LSM), a moderately complex community model, is widely used in weather and regional-climate models and is the operational land-surface scheme for National Centers for Environmental Predictions-National Center for Atmospheric Research (NCEP-NCAR) (Chen et al, 1996; Chen and Dudhia, 2001; Ek et al, 2003; Leung et al, 2005, 2006; Jin and Miller, 2007; Jiang et al, 2008)
The model has been noted for substantially underestimating snow water equivalent (SWE) (Jin et al, 1999a; Pan et al, 2003; Sheffield et al, 2003; Mitchell et al, 2004; Jin and Miller, 2007; Slater et al, 2001; Livneh et al, 2009; Wang et al, 2010; Barlage et al, 2010; Niu et al, 2011; Yang et al, 2011) by simulating less amounts of snow during peak winter season as well as melting the snow earlier in the spring
We address the problem of Noah’s SWE bias and early snowmelt by implementing the snow surface temperatures and snowmelt processes of the Utah Energy Balance (UEB) model (Tarboton et al, 1994; Tarboton, 1994; Tarboton and Luce, 1996; Luce and Tarboton, 2001) in the Noah LSM
Summary
The Noah LSM, a moderately complex community model, is widely used in weather and regional-climate models and is the operational land-surface scheme for National Centers for Environmental Predictions-National Center for Atmospheric Research (NCEP-NCAR) (Chen et al, 1996; Chen and Dudhia, 2001; Ek et al, 2003; Leung et al, 2005, 2006; Jin and Miller, 2007; Jiang et al, 2008) It is used in land-data assimilation systems such as the North America Land Data Assimilation System (Mitchell et al, 2004), the Land Information System (Peters-Lidard et al, 2007), and HRLDAS (Chen et al, 2007).
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