Table 1 Status of Sargassum distribu on of Ly Son island, Quang Ngai province
Research communica ons - NF-POGO alumni Suriyan Saramul Department of Marine Science, Faculty of Science, Chulalongkorn University, Thailand Wikipage: h p://www.nf-pogo-alumni.org/~Suriyan+Saramul
Impact of climate change on salt intrusion in Songkhla Lake, Thailand: a numerical study Introduc on ocated in the south of Thailand, Songkhla Lake, is considered the largest lake and the only natural freshwater lake in Thailand (Fig. 1a). It covers approximately 20 km wide and 80 km long with an average depth of 2 m. There is only one entrance which connects to the Gulf of Thailand at the south westernmost point. Salinity in Songkhla Lake is variable depending on geographic loca on. Based on field observa on, the lower, central, and upper lake water are rela vely salty, brackish, and fresh, respec vely (Pornpinatepong, 2005, 2006). Apart from the rain precipita on, water from distributaries (Fig. 1c) is an important source of freshwater that dilutes seawater in Songkhla Lake system. However, these two parameters change seasonally. The peak of precipita on and water discharge occur between November and December (wet season). And dry season is around April to June which causes smaller discharge. Consequently, salt intrusion at the upper lake, Thale Luang, frequently appears. The circula on in Songkhla Lake is mainly dally-driven. Tidal range during spring de at Lampho sta on is approximately 9.5 - 23 cm, while at Pak Ro it is about 6 - 14 cm (see Figure 1 for loca on). Near the central lake, Thale Sap, dal range decreases to 4 - 8.5 cm (Ponpinatepong, 2005). Hence, de in the upper lake, Thale Luang, is small. Strong dal current tends to appear in the deeper area, Klong Luang and at the lake’s entrance, for instance (Figure 1c). The northern area of the lake is mostly used as paddy field. Farmers in the area grow rice twice a year, first, during the rainy season, and second, during the dry season. As a result, it is necessary to use a lot of freshwater. The sources of freshwater that the farmers can use are from irriga on canals and from the northern part of the lake (sta on W1 and W2, pumping sta ons; Fig. 1c). Therefore, the problem of salt intrusion up to the salinity threshold level (1.5 ppt) usually occurs during the second rice crop. This study will use a mathema cal model to predict the salt water intrusion in the northern part of Songkhla Lake due to the influence of climate change and water u liza on in the area. Methods The hydrodynamic model of the Songkhla Lake has been successfully calibrated, so it is with confidence that this can be used to simulate the water quality (as determined by salinity) in this lake. The model is forced by des and salts at the open boundary (Fig. 1b). It is also forced by the freshwater discharges from tributaries (Fig. 1c). At the surface, the model allows the loss/gain of water due to evapora on/precipita on. Figure 2 shows evapora on rate for present (blue) and future (green) cases and the precipita on rate (assume both cases have the same rate). The evapora on process causes the increase of salinity in some area where discharge is small. In order to see the impact of climate change, a 20-year present case (P0; 1990 - 2010) and future case (F0; 2030 - 2050) are simulated and compared. Note that evapora on rate is computed
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Contact us: Suriyan.S@chula.ac.th, info@nf-pogo-alumni.org, lilian.krug@nf-pogo-alumni.org NANO website: www.nf-pogo-alumni.org
