The impact of climate change on the quantity and quality of the surface runoff of the three reservoir upper watersheds: Dokgray, Nong Pla-Lai and Klong-Yai
Assit. Prof. Booncherd Nu-Im
Ph.D. Candidate in Environmental Science,
Faculty of Science, Burapha University, Thailand
This research aimed to assess the quantity and quality of the surface runoff affected by climate change in the watershed areas in the eastern part of Thailand. The three reservoirs studied were: Dokgray, Nong Pla-Lai and Klong-Yai. The researcher employed many methods such as Comformal Cubic Atmospheric Model (CCAM), Soil and Water Assessment Tool (SWAT), and Digital Elevation Model (DEM). It was found that the rain quantity increased. The delineation of the protected environment areas and the land use in 2003 in case of the carbon dioxide increased from the present level 1.5 times (540) and two times (720 ppm) was different significantly between the underground water quantity and the total water quantity. Also, the delineation of the protected environment areas, which made land use of the water resources, forest, industry, and community increased, whereas the agricultural area decreased, causing the reduction of the underground water quantity and total water quantity. For the surface water quality, it was found that they were different significantly. The land use as the delineation of the protected environment area had effect on the surface runoff quality in the future.
Keyword: climate change, SWAT model, hydrology
There are main water reservoirs in the eastern coast of Thailand, Dokgray, Nong Pla-Lai and Klong Yai. Raw water from these reservoirs has been used for consumption, industry and agriculture. The upper watershed areas of these three reservoirs have been specified as the middle area of the master plan of the land use and community of the eastern coastal areas stage 2, which still remains as the semi-agricultural countryside area. The special characteristics of those areas are that there are potentials for setting up new cities. There are many industrial estates in the southern area near the port of Laemchabang, including the convenient transportation network that enables the area to have the potential of the industrial investment. However, since these areas are the upper watershed areas and are nearby the preservation areas, there is environmental sensitivity on the occurring changes. There will be the expansion of the development areas for the industry and the city community in the future, which will have impact on the quantity and quality of the surface runoff.
This study is concerned with future land use that has the government policy for the delineation of the protected environmental areas and the climate changes from the CCAM (The Conformal Cubic Atmospheric Model) in case of the carbon dioxide increased from present level 1.5 times (540 ppm) during the years 2024 to 2033 and two times (720 ppm) during 2052 to 2061.
Objectives of the research
To study the impact of climate change on the quantity and quality of the ground surface water in the upper water area, namely the Dokgray Reservoir, the Nong Pla-Lai Reservoir and the Klong Yai Reservoir.
Land use has important roles which induce different hydrologic watershed systems for each area (Heuvelmans, Muys, & Feyen, 2005). Land use has effects on the vanished quantity of the surface water due to the confinement on surface, evaporation emission and permeability. The absolute forest area will cause less surface flow but will induce more vanished rain due to confinement, more permeability and more water restraining around the plant roots. On the other hand, in the city community area mainly covering with the impervious area, there will be much quantity of the surface flow and rapid flow rate.
Tan, Melesse, and Yeh (2000) has applied remote sensor images and the geologic information technology to the estimation of the runoff quantity by using the methodology of SCS-CN Curve Number. They found that during 1990, 1995 and 2000, land use in the town area increased, whereas agricultural areas reduced causing the incline of the runoff quantity. Moreover, the increase of the forest areas reduced of the flow rate and the surface water quantity (Weber, Fohrer, & Moller, 2001), but the baseflow increased relatively (Fohrer, Eckhardt, Haverkamp, & Frede, 2001). The increasing land use change for the agriculture influence the raised quantity of the surface water, including the increased transmission of the sediments and nutrients into water resources (Lenhart, Fohrer, & Frede, 2003). Whereas, the watershed area that mainly has the land use for the agriculture and for the pasture land or empty land has the small impact on the surface water quantity (Huisman, Breuer, & Frede, 2004). However, the important thing is to have the regulation for the soil and water preservation in order to provide the watershed management and to preserve the water balance as well (Behara & Panda, 2005)
Climate changes induce the change of the natural balance and have the impact on the global resources and the global food production. The increased heat would cause the variation on the temperature and climate, drought and heavy rain causing more floods. In Thailand there is a study of the climate change, which found that the trend of the temperature is inclined approximately 2.5 to 4 degree Celsius. Furthermore, Norman, Bery, Brown, Lzauralde and Thomson (2003) studied the impact of the climate change on agriculture by using the General Circulation Model (GCM: Had CM2) to study the climate change during two periods, in 2030 and 2095. The study has applied the SWAT model on the study of the hydrologic change and found that the water balance increased 35 % in 2003 and will increase 38% in 2095 induced by the increase of the carbon dioxide from 365 ppm to 560 ppm. The raised rain would cause the increase of the surface water quantity, which affected the transmission of the nutrients and sediment within the watershed area (Boorman, 2003)
Neitsch, Arnold, Kiniry, Williams and King (2002) have generated the Soil and Water Assessment Tool (SWAT), which is copyright-free and can be applied to several studies. The SWAT has the ability to simulate the complicated models in terms of hydrology, DDT, the nutrient chain, the erosion and displacement of the sediment. The SWAT has been developed in the study of the quantitative effect of the management of large watershed area or large rivers. This tool will consume mainly the physical data and will enable the study of the effect in long term.
The studied areas are the watershed areas of three reservoirs, namely the Dokgray, the Nong Pla-Lai and the Klong Yai. The location of the studies area was between Chonburi Province and Rayong Province.(Fig. 1)
Data Sources and Data Collection
The data was obtained from sources of many Thai government’s units, digital data of remote sensor images, map and the land use data during years 2003, the contour map data, soil group map data at the scale 1: 50,000, water route data at the scale 1: 50,000, climate data composed of the daily rain data, the maximum and minimum daily temperatures since 1989 to 2003, the runoff measurement data since 1989 to 2003, the map of the environmental preservation area at the watershed area of the Nong Pla-Lai, Dokgray and Klong-Yai reservoirs, the climate change data retrieved from the Conformal Cubic Atmospheric Model (CCAM) in case of the carbon dioxide level increase from the present 1.5 times (540 ppm) during years 2024 to 2033 and increased twice (720 ppm) during 2052 to 2061, retrieved data from the Network Center for the Analysis, Research and Training of the Global Change at the South East Asia region, Chulalongkorn University, water quality data from the analysis report of the industrial park about the environmental impact on the studied areas, and Field data, which examined the land use and the coordination of the involved in local administration offices.
- The data on land use from the DEM using the SWAT model and the Arc view program, enabling the collection of the coordinated data in the area and the level within each grid cell that has the same size in order to analyze the topography surface of the data of each grid cell that continuously jointed together as the same panel.
- The SWAT model was employed to get the soil data and characteristic in Thailand.
- Data from the CCAM was to analyze the atmospheric condition in three main cases: firstly, the carbon dioxide in normal condition during years 1980 to 1989 (350 ppm), secondly in case of the increase of the carbon dioxide level 1.5 times compare to present level (540 ppm) during years 2024 to 2033, and finally two times of the carbon dioxide level which will occur during years 2052 to 2061.
- The runoff quantity was determined by using the SWAT model in conjunction with the Arc view program to assist the analysis.
Fig. 1 The study areas