Analysis of the BAU and Environmental Protection Scenario The Environmental protection policy scenario was used to demonstrate the utility of the WEAP model to explore the impact of various water management policies on the water supply and demand of the region and other water resource metrics, such as groundwater storage, water delivery by source, and reservoir storage. Fig.8 shows a select set of results for the BAU scenario both with and without climate change (BAU and BAU-RCP4.5) and the Environmental policy scenario (note: for this summary report, the RCP8.5 results are not shown but are available within the WEAP modeling framework). The RCP4.5 scenario represents the mid-range future climate change projection, with a global average increase in temperature of about 1.5oC between 2045 and 2065. The RCP4.5 scenario that we are using for this region of Thailand, shows a modest increase in temperature of 0.7oC by 2040 and is about 6.5% drier over the 20 year period of 2020 to 2040 when compared with the historic period of 1980 to 2000. Fig.8 shows a comparison among the scenarios for several water resource metrics. Comparing the BAU and BAU-RCP4.5 shows that diversions below the Phetchaburi diversion dam decrease under the climate change scenario for flows above about 10 cms or the 40th percentile ranking. For lower flows, the climate change impact is not large since these are managed flows, and thus maintained through releases from the Khangkachan Reservoir. Fig.8 shows the daily time series of storage in the reservoir, where it is evident that during periods of lower precipitation, greater reservoir releases are made in support of increasing demands and Phetchaburi diversion flows requirements. The Environmental policy scenario forces an increase in water delivery below the Petchaburi diversion, reflected in the increase flows from the about the 15th percentile level. Fig.8 includes the delivery of water to the eastern region including all uses (agriculture, municipal, and tourist) for the period 2020 to 2040 by surface water (Lower Left) and groundwater (Lower Right). Note that climate change, reflected within both the BAU- RCP4.5 and Environmental policy scenarios, increases both surface and groundwater delivery, with a total increase in water demand for the region of about 7% when compared to the BAU scenario that is based on the historic climate. This increase in demand places greater pressure on the Khangkachan Reservoir, which is drawn down further to serve both water use needs and meet environmental flows below the Petchaburi diversion dam. Fig.9 shows that in addition to increased pressure on surface water reflected in less storage in the Khangkachan reservoir, the climate change signal also manifests itself on the regional groundwater, creating a draw-down in stored water until 2035. After 2035, groundwater rebounds, as there is a wet period within the RCP4.5 climate scenario in 2034 and 2035 that are 10% and 20% greater than the long-term mean, which were preceded by two of the driest years in the sequence-2032 and 2033-with 20% and 5% less rainfall, respectively. Fig.9 also shows the monthly mean Khangkachan Reservoir storage and shows that the climate change signal reflected in the drying associated with the RCP4.5 climate scenario slightly reduces the mean monthly storage. The Environmental policy scenario reflects a greater reduction in reservoir storage to meet the increasing water demands and the increased environmental flow requirements below the Petchaburi diversion dam. In the Environmental policy scenario, 3 of the 20 years require supplemental groundwater be used to maintain levels of water use in the A3, A4, and A5 region, as there simply is not enough surface water to support both the environmental requirements and the growing demands. 250 Proceedings of the International Conference on Climate Change, Biodiversity and Ecosystem Services for the Sustainable Development Goals (SDGs): Policy and Practice 27-29 June 2016, Cha-am, Phetchaburi, Thailand
Proceedings of International Conference on Climate Change, Biodiversity and Ecosystem Services for the Sustainable Development Goals : Policy and Practice 27-29 June 2016 at the Sirindhorn International Environmental Park, Cha-am, Phetchaburi, Thailand
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