Remote Sensing Monitoring Of Coastal Change In The Gulf Of Thailand And The Coastal Zone Assessment Of Vulnerability

The coastal zone is an interaction of land and sea,which is the combination of land and sea area on the surface of the Earth.The high density of coastal residents and the high speed of coastal zone development make the coastal zone under increasing pressure,at the same time,global climate change and under the influence of external forces such as sea level rise,the coastal zone is seriously affected by environmental vulnerability.The coastal countries of the Gulf of Thailand are the node countries of"Belt and Road",and the coastal zone of the Gulf is vulnerable to erosion of external forces.Traditional methods of monitoring shoreline and mangroves are time-consuming and costly,and the measurement process is also susceptible to climate and weather,so it is difficult to achieve large-scale and long time series change monitoring and vulnerability assessment of the coastal zone.Based on the Landsat series images of 1988,1996,2006 and 2016 and the GF-2PMS-1 remote sensing image of 2016,this paper extracts the coastline and mangrove information of the Gulf of Thailand from 1988 to 2016,analyzes the changes in the remote sensing of coastline and mangroves.Combined with natural factors and human activities,an index system for evaluating vulnerability of coastal zone in the Gulf of Thailand is constructed.This paper proposes a method combining the analytic hierarchy process and the variation coefficient method to determine the index weights,and developed the vulnerability assessment of the Gulf of Thailand,based on the CVI model(Coastal Vulnerability Index),the large-scale vulnerability assessment of the coast of the Gulf of Thailand is carried out.The main research results and conclusions are as follows:Through the coastline extraction analysis,it is concluded that:1)The total length of the coastline in the Gulf of Thailand in last 30 years has been growing,and the rate of growth has changed from fast to slow.The total length of the coastline increased from 4256.8km in 1988 to 4504.9km in 2016.The coastal section nearly the port of Phetchaburi and Chon Buri was selected as the focus study on the rate of shoreline transition from 1988 to 2016.From 1988 to 2016,the average EPR of the shoreline was-5.72 m/a(negative value means erosion).The location of the maximum erosion was near the Ta Chalom in Samut Sakhon,the erosion rate was-68.88m/a,and the largest deposition position was near Samrong in the Samut Prakan,with the deposition rate was 26.65m/a.2)The area of the coastal zone in the Gulf of Thailand has decreased during the past 30 years,with a net decrease of924.88 hm~2 in the coastal zone,and the annual reduction rate of 31.89 hm~2/a.The overall coastal line of the Gulf of Thailand is mainly the mariculture embankment and muddy shoreline landward retreat,advancing to the sea port construction.Major erosion occurs in the areas south of Bangkok and the vicinity of Pattani.Using the SVM(support vector machine)classification combined with the shoreline extraction model for the 2016 mangrove spatial distribution range,the application of GF-2 PMS1 data validation shows that the overall classification accuracy is better than 81.1%.Statistics on mangrove forests in the Gulf of Thailand for the past 30 years revealed that:1)In terms of time series,the mangrove area in the last 30 years has shown a trend of decreasing–increasing–decreasing.The total area has changed from 92,866.66 hm~2 in 1988 and the area was reduced by497.86hm~2 in 2016.2)In the spatial distribution,the overall change in the central Cambodian area was relatively small,decreasing 1309.09 hm~2.The area of mangroves in the eastern part of Vietnam has been reduced,with a decrease of2,374.37 hm~2.The area of mangroves in Thailand has the largest change,with an increase of 3185.59 hm~2 as a whole.3)The dynamic change drivers of mangrove area are divided into natural and human activities.Among them,natural factors include coastal erosion,sea level rise,storm surge,pests and diseases,etc.Human factors mainly include over-exploitation activities such as deforestation,aquaculture,and land reclamation.Based on the results of remote sensing monitoring of coastal shoreline and mangrove,this paper proposes a method of determining the index weights combined with the analytic hierarchy process and the coefficient of variation method,constructs a vulnerability evaluation system for the Gulf of Thailand,and develops Coastal vulnerability assessment index CVI model in the Gulf of Thailand,carries out the large-scale vulnerability assessment of the coast.The following conclusions are drawn:From the CVI model of the coastal zone vulnerability index,the vulnerability index of the Gulf is calculated between 1.37 with 4.43,an average value is 2.49.Most of the coastal zone in the Gulf of Thailand is of low and moderate vulnerability,with an area ratio of 63.73%.The area of the low-vulnerable area is 4881.87km~2,accounting for 18.87%of the total area of the study area.It is mainly distributed in parts of the province of Ca Mau,Kien Giang,southwest coast of Chanthaburi,and part of the Pattani and Songkhla.The area of high-vulnerable area is 1,152.18km~2,accounting for 4.45%of the total area of the study area.It is mainly distributed in the Samut Prakan,Bangkok,and in Samut Songkhram.The vulnerability of the Gulf of Thailand is caused by natural factors and human activities.The natural factors are the rise of sea level and the impact of seawater intrusion and the construction of shrimp farms in human activities and the destruction of mangrove forests are the main reason of the coast to be highly vulnerable.