RESEARCH ON RELATIONSHIP BETWEEN AVERAGE EVAPOTRANSPIRATION WITH FOREST COVER CHANGE: CASE STUDY AT THE CENTRAL HIGHLANDS IN VIETNAM

摘要

The Central Highlands is one of the regions of Vietnam. It contains Gia Lai, Kon Turn, Dak Lak, Dak Nong and Lam Dong provinces. The impact of forest cover change on average evapotranspiration (ET) of mountainous tropical rain forest areas in the Central Highlands was quantified using average ET products and forest cover and change data. The average ET considered in this study are the annual average ET products for two years; 2000 and 2010. The key controls on ET are rainfall interception, net radiation, advection, turbulent transport, leaf area and plant-available water capacity. Forest cover data was obtained for 2000 and 2010 from the Forest Inventory and Planning Institute, Vietnam (FIPI) and the data was classified into 15 classes. The results from the statistic of annual average ET with each forest cover class showed that there is a good relationship between long-term average ET and forest cover. The average ET correlated quite strongly with each forest cover class from 2000 and 2010. The highest average ET values occurred in the mixed and deciduous forest class (excluding the open water class) with an average ET of more than 1300 mm/year. The lowest average ET occurred in the agriculture and residential areas with less than 700 mm/year. The medium evergreen forest has an average ET between 1100 to 1200 mm/year, and the mixed bamboo forest has a higher average ET of 1200 to 1300 mm/year. The average ET also changed based on the forest cover change between 2000 and 2010. From these results, the forests-non forest area can be controlled based on annual average ET. For some forest cover classes are more difficult to manage by annual averages ET excepted some classes: the deciduous forest covered by the highest ET area, medium evergreen forest and mixed bamboo forest. The value of annual average ET plays an important role in the forest control system. Some areas where there is an abnormal change of ET can be checked and managed. The present analysis provides a theoretical basis to evaluate the relationship between average ET and forest cover change for forest management systems.