On Estimating Crop Coefficients and Decoupling Factors of Forest Ecosystems in East Asia

For effective water management, the quantification of evapotranspiration (ET) is imperative. Considering the difficulty of measurement and adequate simulation of ET in large areas, the crop coefficients (Kc=ETc adj/ETo/Ks; where ETc adj is the adjusted evapotranspiration, ETo is the reference crop evapotranspiration estimated by the FAO56-PM method, and Ks is the water stress coefficient) and the decoupling factors (Ω=ETa/ETp; where ETa is the actual evapotranspiration, and ETp is the potential evapotranspiration estimated by the Penman-Monteith equation) are valuable information for the assessment of regional ET. In this study, we determined the Kc and Ω of seven forest ecosystems in East Asia (i.e., temperate and coniferous forests in Gwangneung, Korea, GDK and GCK, respectively; cool temperate forests in Changbaishan, China, CBS, in Takayama and Teshio, Japan, TKY and TSE, respectively; subtropical forest in Xishuangbanna, Southern China, BNS; tropical forest in Palangkaraya, Indonesia, PDF) using the multi-year observed ET by eddy covariance technique. Annual ETo ranged from 443 mm at the TKY site to 1368 mm at the PDF site. Annual ETp ranged from 835 mm at the TSE site to 2466 mm at the PDF site. The Kc and Ω for the (cool) temperate forests showed a clear seasonality with the minimum (~0.3 of Kc and ~0 of Ω) in winter and the maximum in summer or early autumn. The maxima of Kc were different among the sites and ranged from 0.6 at the TSE site to 1.2 at the BNS site. Unlike the maximum Kc, the maxima of Ω were similar among the temperate forests (0.4~0.5) and between the tropical forests (~0.6). Implications of the results are discussed in terms of usefulness and accuracy of using Kc and Ω. Acknowledgement - This study was supported by the Korea Meteorological Administration Research and Development Program under Grant CATER 2012-3030. The flux database was provided by CarboEastAsia - A3 Foresight Program and KoFlux.