ENSO IMPACTS ON COASTAL RESOURCES AND ENVIRONMENT AT BAN DON, SURAT THANI, SOUTHERN THAILAND BY LANDSAT DATA

摘要

The Landsat data in 3 periods: which are during the El Nino years (1993, 1994, 1997 and 2002); the La Nina years (1988,1998 and 2000); and Normal year (1989, 1996 and 1999), are classified for landuse types and by NDVI (Normalised Difference Vegetation Index). We found that during El Nino years, the rainfall anomalies are minus (less than normal), the air temperature anomalies are plus (hotter than normal), Tapi river discharge anomalies are minus, and NDVI's are lower than normal (less growing vegetations). During La Nina years, the rainfall anomalies are plus (higher than normal), the air temperature anomalies are minus (colder than normal), the Tapi river discharge anomalies are plus, and NDVI's are higher than normal (much growing vegetations). In 1998, first half of the year was El Nino, and last half of the year was La Nina. However, we used the data on 27 April 1998, which is in the El Nino period, so it received the impact of El Nino. For fisheries statistics at Surat Thani during El Ni?o years, the quantity of fish catch and the yields of aquacultures (shrimp and fish) were higher than average. During the La Ni?a years the same parameters were lower than average The areas of shrimp ponds have been increased with the increasing population. The population of Surat Thani has been increased every year. During the El Ni?o years, the areas of natural and mangroves were decreased, while during the La Ni?a years, the areas were increased. El Ni?o caused higher frequency of tropical cyclone. La Ni?a also caused tropical cyclone but lesser than El Ni?o linkage. The linkage of ENSO on MSL is not very clear owing to the small quantity of data. During La Ni?a years, MSLs show plus and minus anomalies for one of each year. However, we may conclude that El Ni?o causes higher MSL than mean value. El Ni?o caused lower river runoff than normal. La Ni?a caused higher runoff than normal. STUDY AREA Bandon Bay (9.20 0 N and 99.67 0 E) is located in Surat Thani Province, southern Thailand. The watershed of the bay is 12,220 km 2, of which an important part consists of agricultural lands and aquaculture. The population living within the watershed numbers approximately 830,000 with fisheries, aquaculture and tourism as their main activities. Ban Don Bay is an inlet of the biggest river on the east coast of the Southern Peninsula, which is the Tapi-Phumduang river to the Gulf of Thailand, which lies to the east of Surat Thani province. Mangrove forest plays an important role in the economies of Ban Don Bay, particularly as a source of energy and food protein. However, population and economic development pressures have been responsible in part for the conversion mangroves to various land uses in the past years, I.e., agricultural, residential and industrial sites, salt ponds, ports and harbors, and aquaculture.