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

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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

Results and Discussion

The Delineation for Sub-watershed Area

The delineation for sub-watershed area was conducted by using the automated watershed delineation tool under SWAT/GIS Interface by using the DEM map, grid size of 50x 50 m., to evaluate the threshold area, which was approximately 200 square kilometer. The watershed of the Dokgray Reservoir has the water reserved area at 321.71 square kilometers. The watershed of the Nong Pla-Lai Reservoir has the area of 410.93 square kilometers. The watershed of the Klong Yai Reservoir has the area 322.54 square kilometers. All the reservoirs cover some parts of both Chonburi and Rayong, Besides, the rainfall analysis in the three reservoirs above found that there was much rain in the watershed area of the Dokgray Reservoir, average quantity at 1,400 millimetre, followed by the watershed of the Nong Pla-Lai and Klong Yai at 1,300 millimetre.

The Model Calibration

1. Calibration areas Data was collected from the water measurement station, used for the calibration in the studied areas and covers the data during 1989 to 2003. The data above retrieved from station named Z15 located in the watershed area of the Klong Yai Reservoir. The calibration was done with the Web-Based Hydrograph Analysis Tool on the flow quantity analysis of the water from the runoff measurement station and from the SWAT model. 2. The calibration result. The surface runoff quantity has the decision coefficient at 0.51 and the efficiency coefficient at 0.34, whereas the baseflow has the decision coefficient at 0.52 and the efficiency coefficient at 0.40. And the total water quantity has the decision coefficient at 0.61 and the efficiency coefficient at 0.55 (Table 1). Therefore, the model calibration has the acceptable statistics value on the data analysis of the surface flow, baseflow and the total water quantity. The data from the SWAT model can be efficiently applied to studied area within the watersheds of the Dokgray, the Nong Pla-Lai and the Klong Yai reservoirs.

Table 1. The decision coefficient, efficiency coefficient and the regression equation.

Water flow quantity	Decision coefficient	Efficiency coefficient	Regression equation
Surface water	0.51	0.34	8.47+1.51X
Baseflow	0.52	0.40	-15.5+0.97X
Total water quantity	0.61	0.55	-31.75+1.48X

Remark: X represented the analysis value gained from the model.

The Impact of the Climate Change on the Quantity and Quality of the Surface Runoff

Climate change has impact on the quantity and quality of the surface runoff. The CCAM data, in case of the carbon dioxide increased 1.5 times (540 ppm) compared to the present level during years 2024 to 2033 and two times (720 ppm) occurred during 2052 to 2061, revealed that the rain quantity in the upper watershed of the three reservoir, Dokgray, Nong Pla-Lai, and Klong Yai has the significant difference. For the two-time increase (720 ppm), there is the average rain quantity at 1,105 millimeter, more than the case of 1.5 times (540 ppm), which has the average rain quantity at 1,069.34 millimeter. The increase of the carbon dioxide at 1.5 times (540 ppm) and two times (720 ppm) has no effect on the hydrologic conditions such as the flow out rate, the surface runoff quantity, the baseflow quantity and the total quantity of the water. The planning for the land use as the allocation of the environment protected area and the land use in 2003 in case of the carbon dioxide increased 1.5 times (540 ppm) and two times (720 ppm) compared to the present amount showed that the Dokgray Reservoir watershed has different quantity of the surface runoff, while the Nong Pla-Lai reservoir watershed has the different flow rate, and the Klong Yai reservoir has the different flow rate, the quantity of the surface runoff, and the baseflow. The allocation of the environment protected area allowed the increasing land use for the water resources, forestry, industry and community. In contrast, the agricultural areas were reduced as the regulation that will affect the hydrologic condition, causing the reduction of the baseflow quantity and the total water quantity.

The surface runoff quality consisted of nitrogen in the organic form, phosphorus in the organic form, ammonia nitrite, nitrite that passed through the area. From the format of the land use as the allocation of the environment protected area and the land use in 2003 in case of the carbon dioxide raised 1.5 times (540 ppm) and two times (720 ppm) from the present level, it was found that within the area of the Dokgray reservoir watershed the quantity of nitrite and the oxygen dissolved into water has some differences. The Nong Pla-Lai reservoir watershed has different ammonia quantity, nitrate and the oxygen dissolved into the water, whereas the Klong Yai reservoir watershed has the differences of the nitrogen in the organic form, the quantity of the phosphorus in the organic form, the ammonia quantity and the quantity of the oxygen dissolved into the water. The environment protected area induced the nutrient corrosion into the water resources rather than the land use format in 2003, which showed that the allocation according to the regulation of the environment protected area would cause the effect on the surface runoff quality.

The following are suggestions for land use planning from the land use analysis in 2003 and the allocation of the environment protected areas in to be in accordance with the climate change in the future.

The area of the Dokgray, the Nong Pla-Lai and the Klong Yai watersheds must have the control of the community and industry expansions. Forest should be planted in the upper watershed areas in order to slow down the runoff flow and to increase the baseflow quantity.
The land use for agriculture is needed for the soil and water preservation. Therefore, the preservation will enable the soil to retain the moisture content. Also, there must be the plantation adjustment to match the climate changes.
Climate changes reduce annual rainfall, but the water demands of the community and industry increased. These demands would reflect the water shortage in the future. Therefore, there must be a plan for the integral water supply management.

Conclusion

Climate change has impact on the quantity and quality of the surface runoff. When the carbon dioxide increased, rain increase as well. Increasing of carbon dioxide has no effect on the hydrologic conditions. Different watershed has different organic forms. The regulation of the environment protected area would cause the effect on the surface runoff quality. The allocation of the environment protected area allowed the increasing land use for the water resources, forestry, industry and community. In contrast, the agricultural areas were reduced. To improve the condition of runoff quality, the control of the community and industry expansion that would obstruct the water ways is suggested, and expanding forest area is encouraged to prevent water shortage in the future.

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