Abstract
At present, Para rubber is an economical crop which provides a high priced product and is in demand by global markets. Consequently, the government of Thailand is promoting the expansion of Para rubber plantations throughout the country. Traditionally, Para rubber was planted and grown only in the southern areas of the country. However, due to the Government’s support and promotion as well as economic reasons, the expansion of Para rubber plantations in the northeast has increased rapidly. This support has occurred without accounting for suitable cultivation of Para rubber conditions, particularly in areas with steep slopes and other factors which have significant impacts on hydrology and water quality. This study presents the impacts of Para rubber expansion by applying the Soil and Water Assessment Tool (SWAT) hydrological model on the hydrology and water balance of the Nam Loei River Basin, Loei Province. The results showed that the displacement of original local field crops and disturbed forest land by Para rubber production resulted in an overall increase of evapotranspiration (ET) of roughly 3%. The major factors are the rubber canopy and precipitation. Moreover, the water balance results showed an annual reduction of about 3% in the basin average water yield, especially during the dry season.
Highlights
Zeigler et al [1] estimated that over 500,000 ha of upland areas in southeast Asia had been converted to Para rubber (Heveabrasiliensis) production in southeast Asia by 2009 and that the land area devoted in the region to Para rubber production could double or triple by the year 2050 [1].Updated estimates for the same timeframe indicate that the expansion of total rubber production area in non-traditional Southeast Asia growing regions at >1,000,000 ha and that the production area could increase by a factor of four by 2050 [2]
Eight major groups comprise the spatial extent of soils in the Nam Loei River Basin (NLRB), with the most dominant being the following three soil types: (1) the Slope complex (Sc) soil group which covers 44.3% of the basin, and represents a soil mixture in steep areas with >30% slopes that are generally characterized by forest, low permeability, and high risk of soil erosion; (2) the Wang hi (Wh) soil group, which covers 16.5% of the basin, represents soils derived from decay of various materials, and are characterized by fine-grain textures and high permeability; and (3) the Chiang Khan (Ch) soil group, which cover 14.4% of the basin, is derived from river sediments, and reflect sedimentary rock weathering and high permeability
The choice of ALPHA_BF, CN2, ESCO and other parameters varied (Table 4) between the two (Table 4) between the two subbasins that drain to gauges Kh.28A and Kh.58A, respectively
Summary
Zeigler et al [1] estimated that over 500,000 ha of upland areas in southeast Asia had been converted to Para rubber (Heveabrasiliensis) production in southeast Asia by 2009 and that the land area devoted in the region to Para rubber production could double or triple by the year 2050 [1]. Updated estimates for the same timeframe indicate that the expansion of total rubber production area in non-traditional Southeast Asia growing regions at >1,000,000 ha and that the production area could increase by a factor of four by 2050 [2]. Para rubber has become one of the most important economic crops in Thailand, which is the largest exporter of Para rubber by volume worldwide [4].
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