ADEQUACY OF SELECTED EVAPOTRANSPIRATION APPROXIMATIONS FOR HYDROLOGIC SIMULATION¹

Abstract

Evapotranspiration (ET) approximations, usually based on computed potential ET (PET) and diverse PET‐to‐ET conceptualizations, are routinely used in hydrologic analyses. This study presents an approach to incorporate measured (actual) ET data, increasingly available using micrometeorological methods, to define the adequacy of ET approximations for hydrologic simulation. The approach is demonstrated at a site where eddy correlation‐measured ET values were available. A baseline hydrologic model incorporating measured ET values was used to evaluate the sensitivity of simulated water levels, subsurface recharge, and surface runoff to error in four ET approximations. An annually invariant pattern of mean monthly vegetation coefficients was shown to be most effective, despite the substantial year‐to‐year variation in measured vegetation coefficients. The temporal variability of available water (precipitation minus ET) at the humid, subtropical site was largely controlled by the relatively high temporal variability of precipitation, benefiting the effectiveness of coarse ET approximations, a result that is likely to prevail at other humid sites.

Estimation of Evapotranspiration and Water Budget Components Using Concurrent Soil Moisture and Water Table Monitoring

“…PET data are more readily available and can be computed from either pan evaporation or from energy budget methods (e.g., [8][9][10][11], etc.). The above methodologies, though simple, suffer from the fact that meteorological data collected in the field for PET are mostly under nonpotential conditions, rendering ET estimates as erroneous [1,12].…”

“…For upland and wetland settings water budgets are driven principally by precipitation (P) and evapotranspiration (ET). Given the magnitude of ET relative to other processes, for example, infiltration and runoff, quantification of ET for different land cover types is critical to transient hydrologic analysis [1]. Understanding of the contribution of ET from different sources, for example, interception, shallow and deep soil is very valuable for simulation modeling [2].…”

Using Soil Moisture Data to Estimate Evapotranspiration and Development of a Physically Based Root Water Uptake Model

“…PET data are more readily available and can be computed from either pan evaporation or from energy budget methods (Penman 1948;Thornthwaite 1948;Monteith 1965;Priestly and Taylor 1972, etc.). The above methodology though simple, suffer from the fact that meteorological data collected in the field for PET are mostly under non-potential conditions, rendering ET estimates as erroneous (Brutsaert 1982;Sumner 2006). Lysimeters can be used to determine ET from mass balance, however, for shallow water table environments, they are found to give erroneous readings due to air entrapment (Fayer and Hillel 1986), as well as fluctuating water table (Yang et al 2000).…”

Factors that influence the hydrologic recovery of wetlands in the Northern Tampa Bay area, Florida

“…Although rainfall and evaporation can vary among wetlands and rainfall dominates wetland water-budgets over short time periods (Sumner, 2006;Lee and others, 2009), atmospheric factors are assumed to affect all wetlands in this region equally over long time periods. All Northern Tampa Bay area wetlands are more likely to be dry during droughts and to flood during wet years, but how individual wetlands respond to reductions in groundwater withdrawals is more a function of differences in their physical and hydrogeologic settings than differences in climate.…”