Evapotranspiration model

Dickinson, R. E. (1984). Modeling evapotranspiration for three-dimensional global climate models. Geo-physical Monographs Q. E. Hansen and T. Takahashi, eds.) 29,58-72. American Geophysical Union. 

If evapotranspiration of the system exceeds precipitation, it is possible to capture water that is moving vertically through soil. Areas that receive precipitation in the wintertime (the dormant season for deciduous trees) must be modeled to determine if the soil will be sufficiently dry to hold water for the next spring s growth period. 

Source Hauser, V.L. and Gimon, D.M., Evaluating Evapotranspiration (ET) Landfill Cover Performance Using Hydro-logic Models, Air Force Center for Environmental Excellence (AFCEE), Brooks City-Base, TX, January 2004. 

Evapotranspiration (ET) can occur from any of the storages. The model algorithms compute the amount of ET from each storage, based on potential ET data supplied by the user. 

Simple models are used to Identify the dominant fate or transport path of a material near the terrestrial-atmospheric Interface. The models are based on partitioning and fugacity concepts as well as first-order transformation kinetics and second-order transport kinetics. Along with a consideration of the chemical and biological transformations, this approach determines if the material is likely to volatilize rapidly, leach downward, or move up and down in the soil profile in response to precipitation and evapotranspiration. This determination can be useful for preliminary risk assessments or for choosing the appropriate more complete terrestrial and atmospheric models for a study of environmental fate. The models are illustrated using a set of pesticides with widely different behavior patterns. 

Input data for the most detailed soil model include parameters describing atmospheric deposition, precipitation, evapotranspiration, litterfall, foliar uptake, root uptake, weathering, adsorption and complexation of Pb, Cd, Cu, Zn, Ni, Cr and Hg. The input data mentioned above vary as a function of location (receptor area) and receptor (the combination of land and soil type) as shown in Table 6. 

These values are significantly different from those that have been earlier calculated by RAIN-ASIA model (World Bank, 1994). These differences might be related to the much more detailed and comprehensive national data sets on geological, soil, climate (precipitation, temperature, evapotranspiration, runoff, etc.) and vegetation mapping, physico-chemical properties of soils and geological rocks. This allows the authors to calculate more precise values of all constituents used for maximum sulfur critical load calculation and mapping. 

The models of general atmospheric circulation were thoroughly described by Nicolis and Nicolis (1995). The description of the atmospheric part of the hydro-logical cycle can be simplified by the equation dWA/dt + VQ = E-P, where WA is the vertically integrated specific air humidity in this column, and E and P are evapotranspiration and precipitation at the soil level, respectively. 

SVATs are simulated models that use parameters such as vegetation cover, soil texture, water-holding capacity of soils, surface roughness, and albedo, to make predictions on soil moisture, evapotranspiration, and runoff. 

Figure 8.7 Rates of fresh litter decomposition (y-1) in soils in the USA, using a simulation model based on evapotranspiration rates as a predictive variable. Contour lines represent loss rate (k) during an initial year of decay. (Modified from Meentemeyer, 1978.)...

Abramopoulos, F., Rosensweig, C., and Choudhury, B. (1988) Improved ground hydrology calculations for global climate models (GCMs) soil water movement and evapotranspiration. J. Climate 1, 921-941. 

A further estimate of evapotranspiration was made (Leopoldo et al., 1982b) for high forest on a model basin of 23.5 km, 60 km north of Manaus, which is drained by a large stream. This area has an average rainfall of 2000 mm. Measurements were made of precipitation, inter-... 

Water composition is also affected by concentration resulting from evaporation (and evapotranspiration). Example 15.1 will illustrate the principles, procedures, and calculations of the effect of concentrating natural waters by isothermal evaporation for a few simplified systems. These calculations illustrate how the reaction path of natural waters during evaporation depends on the Ca /UCO ratio. In a reaction progress model the effects of initial reactions on a reaction path, for example, on the appearance of a solid stable phase and on the redistribution of aqueous species, are described. Reaction progress models are usually based on the concept of partial equilibrium. Partial equilibrium describes a state in which a system is in equilibrium with respect to one reaction, but out of equilibrium with respect to others. 

Berthier, E., Dupont, S., Andrieu, H., and Mestayer, PG. (2001), Comparison of evapotranspiration in an urban area, as evaluated by both an atmospheric model and a hydrological model, International Symposium on Environmental Hydraulics, Tempe, Arizona, 5-8 Dec. 2001, Proceedings CD, 6 pp. 

Two box models are used for the parameterization of water as conservative material and salts, including sulfur, as non-conservative material. For example, the first estimates were made up for the wet season. For the coastal water body budget, the following fluxes were monitored and calculated precipitation, evapotranspiration, runoff, groundwater, and residual flow. These budget estimates give the fresh water residence time as 6.2 days with residual flow equal -822.34 x 10- For Klong... 

Because both the amount and distribution of rainfall and evapotranspiration change from year to year at a specific site, modeling can help generalize experimental results. One method for illustrating the effect of year-to-year weather variations is to perform a simulation with several consecutive years of rainfall. 

The altitude effecf and the continental effecf (Rozanski et al. 1993) refer to the tendencies for and 5D of precipitation to become progressively lower towards continental interiors and higher elevations. The altitude effect includes important control by temperature. Both may reflect a stochastic tendency for air masses moving away from moisture sources to encounter conditions (frontal/convective) that cause moisture extraction and so isotopic fractionation for °0 and D H it is possible that modeling of and 5D of precipitation could involve stochastic treatments. As reviewed by Rozanski et al. (1993), the continentality depletion for 5 0 of precipitation reaches 8 per mil over 4500 km into Europe from the Atlantic coast. This continental effect is more pronounced in winter than in summer, perhaps because evapotranspiration returns most summertime precipitation to the atmosphere, whereas runoff is more important in wintertime. 

FIGURE 10 The relationships between evapotranspiration and net primary production as they emerge from the Century model, applied globally. The near-linear realtionship between evaporation and NPP, very similar to those observed In semi-arid lands, is an emergent property. The differences in slope between biomes are largely due to differences in the C N ratio of different plant functional types. Indicating that ecosystem composition has direct effects on biogeochemistry (Scholes et al., 1999). 

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