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Annual Mekong Flood Report 2014

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MRC (2015) Annual Mekong Flood Report 2014, Mekong River Commission, 70 pages.

I. SYNOPSIS

As is now the established format the Annual Flood Report is made up of three major sections:

• The annual theme, which for 2014 is the impact of flash floods

• A review of the flood season over the year, and

• A summary overview of the four National Flood Reports

Every year intense rainfall, often generated by tropical storms sweeping in over the Lower Mekong Basin (LMB) cause the sudden rise of water level in tributary catchments, resulting in what is known as flash floods. Because this often takes place in mountainous and steep areas the water flows with high speed, causing erosion, uprooting of trees, landslides and local flooding. This in turn results in damage to houses, roads, bridges and other infrastructure, and sometimes leads to loss of human life. Flash floods are the main cause of damage in Thailand’s Mekong part, and in Lao PDR. In Cambodia and Viet Nam inundation of the flood plains cause the most damage, but flash floods occur every year, especially in the Central Highlands of Viet Nam.

An attempt is made to look at the performance of the Flash Flood Guidance System (FFGS) installed at Regional Flood Management and Mitigation Centre (RFFMC) of the Mekong River Commission (MRC). The FFGS has been in operation since 2010, and provided warnings for flash floods based on satellite imagery.

The year 2014 was more or less normal concerning rainfall, and did not experience any serious inundation floods along the Mekong River. Water levels stayed mostly below alarm level, and also the flash floods were less damaging than during many previous years.

The influence of the Chinese hydropower cascade on the mainstream Mekong in Yunnan had a distinct effect on the downstream flow regime. The dry season flows were highest on record, but flood season flow volume especially at Chiang Saen was very low, indicating that filling of upstream reservoirs was cutting flood peaks downstream. The ratio between dry season and wet season flows was record high at Chiang Saen, but the effect dissipates somewhat when going downstream.