EVAPOTRANSPIRATION AND ENERGY BALANCE IN VARIOUS TYPES OF LAND USE

摘要

Evapotranspiration and energy balance in various types of land use. The objectives of this study are to study and compare the evapotranspiration and energy balance in various types of land use. The data was collected between Jan. 2002 - Sept. 2004 at paddy field, teak plantation and cassava field in Changwat Sukhothai, Lampang and Nakhonratchasima respectively. The results shown that the daily average solar radiation (Rs) in paddy field was 19.3 MJ m~(-2) day~(-1). The net radiation (R_n) was 13.2 MJ m~(-2) day~(-1) (70.4 percent of Rs) and used for latent heat (LE), sensible heat (H) and storage in soil (Gs) and in water (Gw) with the average value of 9.5, 3.0, 0.4 and 0.2 MJ m~(-2) day~(-1) or 72.3, 2.9, 3.1 and 1.7 percent of R respectively. While in teak plantation the daily average Rs was 19.0 MJ m~(-2) day~(-1). The average daily of R_n was 14.8 MJ m~(-2) day~(-1) or 78.2 percent of Rs. The R_n was used for LE, H and Gs about 71.6, 23.0 and 5.4 percent of R_n respectively. In cassava field the daily average Rs was 18.6 MJ m~(-2) day~(-1). The average daily of R_n was 14.3 MJ m~(-2) day~(-1) or 77.2 percent of Rs. The R was used for LE, H and Gs about 68.7, 27.5 and 3.8 percent of R_n respectively. The comparison of daily average solar radiation (Rs) among various types of land use were found that the Rs data of paddy field was very closed to teak plantation and higher than cassava field. It could be explained that paddy field and teak plantation were located in nearly same latitude. The radiant radiation was similar and less variation of Rs. While in cassava field Rs was a lot variation and located in lower latitude than the 2 other sites. The daily average ET _aof paddy field during planting season was 4.5 mm. while off planting season was 3.9 mm. In teak plantation ET_a in dry season was 3.7 mm. and 4.1 mm. in rainy season. While in cassava field ET_a during dry season was 3.9 mm. and 5.5 mm. in rainy season respectively. The average daily ET_a of the whole period study in cassava field was highest (4.7 mm.) follow by paddy field (4.1 mm.) and teak plantation (3.9 mm.). Due to planting period of cassava was longer (11 months) than paddy field (approximately 118 days) and teak plantation was falling leaf during dry period for 3 months respectively. ET_a in paddy field was higher than in teak plantation due to during planting season there was a water over the paddy field so there was always enough water for evapotranspiration process but in teak plantation water used for ET_a had come from soil moisture.