This Annual Mekong Flood Report for 2007 follows the structure, format and content that was agreed during the preparation of the 2006 report. The regional flood hydrology and meteorological conditions form the nucleus of the material that is presented complimented by an overview of the four National Flood Reports for 2007. Appendices provide the relevant reference data.
Having contributed significantly to the understanding of Mekong mainstream floods and flooding in the Annual Mekong Flood Report 2006, this document has made the logical progression and taken the flood hydrology of the tributaries as its theme.
As with the 2006 report, the 2007 report is laid out with the theme material presented first in Chapter 2. Here the tributary flood hydrology is considered within three mainstream reaches: Chiang Saen to Vientiane, Vientiane to Pakse and Pakse to Kratie, which reflects some important geographical distinctions. The theme is introduced with a short note upon the impacts of land-use change and deforestation upon the flood hydrology of the tributaries, of which there is no significant evidence. This is followed by an overview of the geography of the major tributary contributions to the Mekong mainstream. In considering the nature of the tributary flood regimes, flash flooding has been given particular attention. Losses from flash floods, including related hazards such as landslides and debris flows, appear to be increasing due to pressure on land resources. There is also widespread agreement that under global warming storm rainfall intensities will increase. The point is made that the location, type, and value of human activities that appear to be expanding into more hazardous areas needs to be reassessed on the basis of a better understanding of the flash flood phenomenon, which regionally is not confined to small, steep, river basins.
A particular effort has been made to present reference schematics that reveal the location of 'functional' tributary data, that is data that of sufficient length and reliability for meaningful analysis. In the past this has not been a straightforward task. Amongst the analyses undertaken here using these data is the provision of a methodology for estimating flood risk at un-gauged sites. Such estimates are required increasingly, as regional water resources development accelerates. For example, they are required for the estimation of design spillway floods for hydropower schemes.
Chapter 3 reviews regional flood conditions during 2007 and the major storm events of the year. A number of standard diagrams that were developed during 2006 are once again employed and some new ones presented.
Chapters 4 to 7 contain overviews of the four National Flood Reports, the aim being to be concise and emphasise the major flood and storm events that occurred over the year, the types of damage caused, and the principal lessons that have been learnt.
Chapter 8 presents the conclusions of the 2007 report and some recommendations. The document closes with selected data appendices.