Assessment of flood risk in Hat Yai Municipality, Southern Thailand, using GIS

Abstract

This article assesses the risk of flooding and identifies efficient measures to reduce flood risk in Hat Yai Municipality, southern Thailand using GIS and satellite imagery. The center of commercial trade and administration in southern Thailand, Hat Yai is located in the downstream area of the Khlong U-Taphao Basin. From 1982 to 2002, forest resources in the basin's upstream were decreased from 48,281 to 26,781 hectares, equivalent to a reduction of 44.5 %. This was largely attributable to the expansion of rubber cultivation. Further analysis revealed that 17,116 ha, 42.7 % of the forest resources in the basin's headwater source areas mainly had been replaced by rubber plantations. As a consequence of extensive deforestation, particularly in headwater source areas, the municipality has become vulnerable to natural disasters; primarily floods. Hat Yai Municipality experienced two flood events of catastrophic magnitudes in 1988 and 2000. These destructive floods were detrimental to its vulnerable social and economic development due to the loss of life and destruction of property. Since the 2000 flood, considerable structural mitigation measures have been undertaken to prevent and alleviate future flooding of the municipality. Recent flooding on 10 December 2003, caused by a storm like that experienced in 2000, indicates that structural mitigation efforts undertaken so far are inadequate to withstand natural threats. Hat Yai Municipality will continue to be extremely vulnerable to future flood disasters. This shows the compelling need to increase the municipality's resilience against flooding through adoption in the coming year of non-structural disaster reduction schemes to supplement existing efforts. Risk assessment based on hazard and vulnerability analysis is needed to identify and implement adequate and successful non-structural alternatives. Analyses showed that 99.0, 400.0, 1110.0, 346.0, and 100.0 ha of the municipality's total land areas were subjected respectively to very low, low, moderate, high, and very high flood hazards. Further analysis revealed that 39.6, 654.6, 152.7, 664.5, and 543.6 ha of the land areas respectively faced very low, low, moderate, high, and very high flood risks. Analyses also showed that all the residential, commercial, industrial, and the public utilities and facilities areas, equivalent to 1,188.0 ha (57.8 %) of the municipality's total land area, faced high and very high flood risks. Measures to reduce the risk of flooding in Hat Yai Municipality are discussed.