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United States Department of Agriculture

Agricultural Research Service

Research Project: GLOBAL CHANGE: RESPONSES AND MANAGEMENT STRATEGIES FOR SEMI-ARID RANGELANDS

Location: Rangeland Resources Research

Title: Simulating energy, water and carbon fluxes at the Shortgrass Steppe Long Term Ecological Research (LTER) site

Authors
item Beltran-Przekurat, Adriana - COLORADO UNIVERSITY
item Pielke, Roger - COLORADO UNIVERSITY
item Morgan, Jack
item Burke, Ingrid - COLORADO STATE UNIVERSITY

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 21, 2005
Publication Date: December 5, 2005
Citation: Beltran-Przekurat, A., Pielke, R.A., Morgan, J.A., Burke, I.C. 2005. Simulating energy, water and carbon fluxes at the Shortgrass Steppe Long Term Ecological Research (LTER) site. In: Proceedings of the Bi-Annual mtng of the American Geophysical Union, EOS Tran. AGU 86(52), Fall meeting supplement, Abs B34A-03.

Technical Abstract: Coupled atmospheric-biospheric models are a particularly valuable tool for studying the potential effects of land-use and land-cover changes on the near-surface atmosphere since the atmosphere and biosphere are allowed to dynamically interact through the surface and canopy energy balance. GEMRAMS is a coupled atmospheric-biospheric model comprised of an atmospheric model, RAMS, and an ecophysiological process-based model, GEMTM. In the first part of this study, the soil-vegetation-atmosphere-transfer (SVAT) scheme, LEAF2, from RAMS, coupled with GEMTM, are used to simulate energy, water and carbon fluxes over different cropping systems (winter wheat and irrigated corn) and over a mixed C3/C4 shortgrass prairie located at the USDA-ARS Central Plains Experimental Range near Nunn, CO, the LTER Shortgrass Steppe site. The new SVAT scheme, GEMLEAF, is forced with air temperature and humidity, wind speed and photosynthetic active radiation (PAR). Calculated canopy temperature and relative humidity, soil moisture and temperature and PAR are used to compute sunlit/shaded leaf photosynthesis (for C3 and C4 plant types) and respiration. Photosynthate is allocated to leaves, shoots, roots and reproductive organs with variable partition coefficients, which are functions of soil water conditions. As water stress increases, the fraction of photosynthate allocated to root growth increases. Leaf area index (LAI) is estimated from daily leaf biomass growth, using the vegetation-prescribed specific leaf area. Canopy conductance, computed and based on photosynthesis and relative humidity, is used to calculate latent heat flux. Simulated energy and CO2 fluxes are compared to observations collected using Bowen ratio flux towers during two growing seasons. Seasonality of the fluxes reflecting different plant phenologies agrees well with the observed patterns. In the second part of this study, simulations for two clear days are performed with GEMRAMS over a model domain centered at the SGS site. Simulated spatial differences in the energy fluxes can be associated with the highly heterogeneous landscape in this area.

Last Modified: 8/19/2014
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