Simple Hydroecological Models: Is Root Zone Average Soil Moisture An Adequate Driver In The Functions For Evapotranspiration And Assimilation?
Kurc, Shirley A 1 ; Small, Eric E 2
1 University of Colorado, Geological Sciences
2 University of Colorado, Geological Sciences
In water-limited semiarid and arid areas, the ecosystem scale exchanges of water and carbon between the land surface and the atmosphere are complex. Both the water and carbon fluxes are the sum of 2 components (i.e. evapotranspiration = evaporation + transpiration; net ecosystem exchange = respiration – assimilation). All 4 of these components depend on soil moisture in different ways and also depend on soil moisture in different parts of the soil profile. How these fluxes are controlled by soil moisture and rainfall is fundamental to studying their interactions. A main simplification in many hydroecological models used to study these interactions is the dependence of water and carbon fluxes on root zone averaged soil moisture. Clearly, this simplification ignores important characteristics of the ecosystem, including how fluxes depend on soil moisture in different parts of the soil profile or how small rainfall events only wet the surface soil. Here, we compare 3 years of water and carbon flux measurements made within a semiarid grassland and shrubland in central New Mexico to results from (1) a simple model based on vertically averaged root zone soil moisture, and (2) a simple two-layer model. We find that although the root zone model resolves the general trend of the observed time series of evapotranspiration and assimilation, the two-layer model is able to better resolve the dynamic nature of the time series, including the magnitude and overall frequency of peaks.
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