Seasonal Variations of Evapotranspiration Observed in a Mixed forest in the Seolmacheon Catchment
2009
Kwon, H.J., Yonsei University, Seoul, Republic of Korea | Lee, J.H., Hydrological Survey Center, Goyang, Republic of Korea | Lee, Y.K., Hydrological Survey Center, Goyang, Republic of Korea | Lee, J.W., Hydrological Survey Center, Goyang, Republic of Korea | Jung, S.W., Hydrological Survey Center, Goyang, Republic of Korea | Kim, J., Yonsei University, Seoul, Republic of Korea
The importance of securing water resources and their efficient management has attracted more attention recently due to water deficit. In water budget analysis, however, evapotranspiration (λE) has been approximated as the residual in the water balance equation or estimated from empirical equations and assumptions. To minimize the uncertainties in these estimates, it is necessary to directly measure λE. In this study, using the eddy covariance technique, we have measured λE in a mixed forest in the Seolmacheon catchment in Korea from September 2007 to December 2008. During the growing season (May-July), λE in this mixed forest averaged about 2.2 mm d-¹, whereas it was on average 0.5 mm d-¹ during the non-growing season in winter. The annual total λE in 2008 was 581 mm y-¹, which is about 1/3 of the annual precipitation of 1997 mm. Despite the differences in the amount and frequency of precipitation, the accumulated λE during the overlapping period (i.e., September to December) for 2007 and 2008 was both ~110 mm, showing virtually no difference. The omega factor, which is a measure of decoupling between forest and the atmosphere, was on average 0.5, indicating that the contributions of equilibrium λE and imposed λE to the total λE were about the same. The results suggest that λE in this mixed forest was controlled by various factors such as net radiation, vapor pressure deficit, and canopy conductance. In this study, based on the direct measurements of λE, we have quantified the relative contribution of λE in the water balance of a mixed forest in the Seolmacheon catchment. In combination with runoff data, the information on λE would greatly enhance the reliability of water budget analysis in this catchment.
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