Forest change detection A study of the flooded area in king amphoe phipunProvince of Nakhon SI Thammarat, Thailand
Ake Rosenqvist,Shunji Murai
Institute of Industrial Science University of Tokyo
7-22 Roppongi, Minato-Ku, Tokyo 106, Japan
Suvit Vibulsresth
National Research Council
Bangkok 10900, Thailand
Abstract
In November last year (188) the area of king Amphoe Phipun, in the province of Nalhon Si Thammarat in Southern Thailand, suffered seriously from flood and landslides (earthslides) after three consecutive days of heavy rain. One cause f the landslides is believed to be the change of the landuse in the region, were large areas of the natural forest, also on steep mountain sides, have been cut and changed into orchards and rubber plantation's
multitemporal satellite data was used in order to monitor the forest change for the period of the last 4 years. Principal component analysis on images recorded in April 1984 (MSS) and March 1988(TM) as applied to detect areas that had changed from vegetation to non-vegetation and vice versa. The mages were also classified using maximum data available and an on-site investigation not yet had been performed the classified images were used as preliminary reference.
To an effort to find out the relationships the landslides, the landuse ad the slope inclination, a SPOT image recorded in February 1989 (2.5 months after the flood0 was used as well as a DTM of the area.
Background
Due to the catastrophy, the area around King Amphoe Phipun has received very much attention lately ad a lot of research is now being carried out to find the causes of the disaster. If this can be done it may then be possible to predict where future disasters may strike and also, in a long term to prevent this from happening again.
Although forest change probably not is the single reason for what happened it is most likely that it played an important role. Concerning this area, the change is to a great extent natural forest that has been converted into rubber plantations. Problems occur when this is made not only on flat land but also on mountainsides. Since the roots of rubber tress are very shallow compared to those of natural forest, it make rubber tress less capable to hold the soil, for instance in case of heavy rain. This is also one theory of what actually happened in Phipun last November. Smaller landslides occurred as rubber dams of mud and logs. As the rainfall continued these occurred and propogated as fallen tree trunks, water and mud tore up fore tress downhill. Many people were killed as masses of logs, debris and mud reached the village on the plain downstream.
Fig.1 Landslides on the mountains near Ban Kathun Village
