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Title: Evapotranspiration model of different complexity for multiple land cover types

Author
item CHOI, M - Hanyang University
item Kustas, William - Bill
item RAY, R - San Diego State University

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2011
Publication Date: 12/29/2011
Citation: Choi, M., Kustas, W.P., Ray, R. 2011. Evapotranspiration model of different complexity for multiple land cover types. Hydrological Processes. 26:2962-2972.

Interpretive Summary: An accurate estimation of actual evapotranspiration (ET) is essential for understanding the hydrological cycle and the interactions/feedbacks with/to climate as well as assessing water resources and the impact of drought on agriculture. There is no routine observational network available to quantify ET at large scales (watershed, basin and regional scales) necessitating modeling approaches, some of which make use of remote sensing data. Estimates of ET using three models of different complexity, namely the Priestley-Taylor (P-T), reference Penman-Monteith (P-M), and Common Land Model (CLM) was conducted at three AmeriFlux sites having very different land cover and climate conditions (i.e., arid grassland, temperate forest, and sub-humid cropland). Using the reference P-M model with a semi-empirical soil moisture function to adjust for water-limiting conditions yielded ET estimates in reasonable agreement with the observations (root-mean-square errors (RMSE) of 0.5-1.9 mm/day) and similar to the much more complex CLM scheme with an RMSE of 0.4-2.1 mm/day at the grassland and cropland sites. However, the semi-empirical soil moisture function with the P-M approach was not applicable at the forest site suggesting that more physically-based approaches are required for these vegetation types. On the other hand, the use of the soil moisture product derived from microwave remote sensing information was found to be a reliable metric of regional moisture conditions to adjust the simple ET models for water-limited conditions. Further studies are needed to evaluate the utility of simplified remote sensing-based ET methods for different landscapes and climatic conditions.

Technical Abstract: A comparison between half-hourly and daily measured and computed evapotranspiration (ET) using three models of different complexity, namely the Priestley-Taylor (P-T), reference Penman-Monteith (P-M), and Common Land Model (CLM) was conducted using three AmeriFlux sites under different land cover and climate conditions (i.e., arid grassland, temperate forest, and sub-humid cropland). Using the reference P-M model with a semi-empirical soil moisture function to adjust for water-limiting conditions yielded ET estimates in reasonable agreement with the observations (root-mean-square errors (RMSE) of 0.5-1.9 mm/day) and similar to the complex CLM with an RMSE of 0.4-2.1 mm/day at the grassland and cropland sites. However, the semi-empirical soil moisture function was not applicable at the forest site suggesting that more physically-based approaches are required. On the other hand, under certain land cover/environmental conditions, use of microwave-derived soil moisture information was found to be a reliable metric of regional moisture conditions to adjust simple ET models for water-limited conditions. Further studies are needed to evaluate the utility of the simplified methods for different landscapes.