Application of Modis 250m Images without in Situ Observations for Mapping Mekong River Basin Land Cover

Mekong River runs from Hengduan Mountains in central-west China to Vietnam covering 805,604 sq km of land by its basin. The Lower Mekong Basin (LMB), the region mapped in this study, covers nearly 3/4 of the entire basin. About 90% of the population and agricultural activities of the Mekong River basin is located in this fertile LMB which faces disastrous floods almost annually. Mapping LMB at moderate resolution gives number of advantages for studies of flood mitigation and land utilization. However, compiling a cloud free mosaic and collecting ground truth data for training samples and map validation make map production process a challenging task. This study utilized MODIS 250m image data of the region obtained in 2005 February. Dry weather in Jan-Apr makes the sky relatively free of clouds and 2005 February also had fewer disturbances coming from smoke of biomass burning. The methodology of the study substantially relied on high resolution images in Google Earth for collection of training sample for supervised classification and accuracy assessment. Arc GIS generated KMZ file of unclassified and classified maps used to overlay image and map on Google Earth for identifying training site and field information extraction for accuracy assessment. Also ground information collected by a different research projects in 2008 were combined with information gathers from Google Earth images. The classified map showed 29.2% of the LMB under forest, 36.5% under Scrubland, when combined its Highland and Lowland subcategories. Three subcategories of paddy cultivated area covered 27.9% of LMB. Accuracy assessment conducted with randomly selected 200 points against high resolution images gave an overall accuracy of 80.7% in major land cover classes. According to the 250m resolution, urban features have not clearly separated though large urban areas like Phnom Penh and Can Tao have accurately classified. The methodology of this study produced a noteworthy success in classifying land cover of large areas like LMB, without expensive data sources and difficult and costly field investigations. 1. THE LOWER MEKONG BASIN (LMB) The Mekong River basin is one of the few river basins of the world that has an immense social and economic impact on the regional and the global economy. Starting at 4,500m high Tibet Plateau, Mekong runs southward passing 4,800km, before it enters into South China Sea. The massive river system which covers parts of China, Myanmar, Lao PDR, Thailand, Cambodia and Viet Nam, is one of the 10 greatest rivers of the world, by the volume of water discharge to the sea. The total area under Mekong River, 795,000 square kilometers was divided into two major parts as upper and lower basin (see Figure 1). The upper Mekong consists of steep mountain slopes and only contributes about 15-20% of total volume of water (Mekong River Commission, 2005). The Lower Mekong basin covers nearly 75% of the land area of the total river basin. About 90% of the population and agricultural activities of the total river basin are located in this lower part. The total contribution from agriculture (farming, fishing and forestry) provides living for 85% of people in the Lower Mekong Basin (LMB), making the river an integral part of domestic life. About 60 million people in the region annually produce enough rice to feed 300 million people (Mekong River Commission, 2005). In production of rice, Vietnam farmers alone produce over 3.5 million tones, annually, while Laos became self sufficient with rice in 1999. The LMB also enjoys a healthy consumption of fish and fish products annually. The per capita consumption of fish within the region in 2002 was 36 kg/person/year. This is a significantly larger volume compared to average consumption in EU countries, which was 26 kg/person/year in 2003 (Kent and Simon, 2003). With the growing population which is estimated to increase up to between 75 to 90 million people by 2025 (Mekong Figure 1. The Mekong River Basin River Commission, 2005), LMB is facing many challenges to maintain its biodiversity while feeding the huge population. The construction of new dams in upper Mekong Basin is affecting the biodiversity of LMB (WWF, 2009), while annual occurrences of floods are threatening the life and physical environment. Although, there is no significant change in annual flood levels in recent decades (Flood situation report, 2008), ever increasing human interaction with the river has caused extensive damage from flood in recent years. International Archives of the Photogrammetry, Remote Sensing and Spatial Information Science, Volume XXXVIII, Part 8, Kyoto Japan 2010