Earth Sciences Division
Research
Climate Variability and Carbon Management Program
Objectives
Regional Climate Simulation For the Western United States Using the RCSM
Annual Report 1998-1999
features. The Soil-Plant-Snow (SPS) model The main objectives of this calculates land-surface processes in regional climate simulation are to Jinwon Kim and Norman L. Miller the RCSM. The RCSM predicts soil evaluate the Regional Climate System moisture content, soil temperature, Contact: Model (RCSM) and to investigate the wa t e r - e q u i valent snow cover and Jinwon Kim (510) 495-2375, jinwon_kim@lbl.gov hydroclimate and its variability within canopy water content. It also calcuthe we s t e rn United States. Results lates skin temperature and surface from this study will be used to compute the effects of future wetness, and drainage of soil water into deep ground. It needs global climate variation in the western United States. In addition, data for soil texture, vegetation characteristics and initial guesses evaluation of this multi-year simulation (also known as a hindfor soil moisture and temperature. The initial guesses for soil cast) will be used to identify the strengths and weaknesses of the moisture and temperature were obtained from the NCEP global RCSM for future improvements. In parallel with the simulation analysis data. The land-surface and vegetation characteristics experiment, development of a high performance version of the were obtained from satellite-based monthly-mean data for leafRCSM (RCSM.hp) is under way in collab o ration with the area index and green-leaf fraction data.This recent monthly vegNational Energy Research and Scientific Computing Center etation data from the NCEP/NASA has eliminated much uncer(NERSC) at LBNL. tainty and resulted in a significant improvement in the RCSMThe focus of this hydroclimate simulation experiment is to simulated surface energy and water budget. study precipitation, snow budget and soil moisture variations Precipitation and atmospheric forcing simulated by the MAS that significantly affect human activities and natural environand SPS are processed to compute the area-averaged forcing data ment in the western United States. for the RCSM hy d ro l o gic models (spatially - d i s t ributed TO PMODEL and the spatially-lumped Sacramento model) using an Approach are a - m a t ching method. This method pre s e rves the total water/energy between the MAS model and hydrologic models in a way consistent with the basic assumptions of the models. To generate the western U.S. hydroclimate, we downscaled Accurate area-matching is important for quantitative precipitathe global analysis data from the National Center fo r tion simulations in the western United States, where steep terEnvironmental Prediction (NCEP) at 2.5o x 2.5o resolution to a 36 x 36 km2 resolution (Figure 1). This intermediate-resolution rain generates a large spatial gradient in precipitation. climate data will be further downscaled to a 12 x 12 km2 resoThe western U.S. climate simulation starts in 1979 and covers lution for a California-Nevada domain when the RCSM.hp is comthe next 10-15 year period to capture several wet/dry periods in pleted. The NCEP global analysis data, together with the global recent years. Due to an extensive requirement for computational analysis data from the European Center for Medium-Range resources, the actual period of this simulation will be deterWeather Forecasts (ECMWF), is regarded as the most accurate mined by the available computational resources. large-scale data ava i l able. This pre l i m i n a ry study Howeve r, spatial resolution examined the atmospheric of both analysis data is too physics fo rmulations for a coarse for detailed regional long-term climate simu l aimpact assessments. tion. Different schemes for The Mesoscale Atmospheric atmospheric phy s i c s , most Simulation (MAS) model is importantly for cumulus conthe limited-area atmospheric ve c t i o n , in the MAS can model of the RCSM.The MAS cause a significant difference has an accurate adve c t i o n in the simulated regional clischeme and comprehensive mate. The MAS is equipped physics including short- and with two convection longwave r adiation, convecschemes: the simple Anthes tion, cloud microphysics and scheme and the Simplified cloud-radiation intera c t i o n . A ra k awa - S ch u b e rt Scheme The MAS is being used to (SAS). The SAS scheme, even s i mulate re gional hy d ro cl ithough it is more physically mates of the western United based than the Anthes States and eastern Asia. It is scheme, includes many tuncontinu o u s ly improved fo r Figure 1. Domain and orography (height of terrain above mean sea level) of the ing para m e t e rs. Most of better physics and numerical western U.S. domain at 36x36 km2. The color contour intervals are at 250 m. these parameters are empiri147