During the second half of the 20th Century, Asia South-East was the arena of a series of armed conflicts, direct consequences of the Second World War, decolonization and the Cold War, followed by political instability which continued up to the 1990s. The region’s history has left its scars: extensive forests razed from the map by bombing, populations displaced or obliged to emigrate, entire areas abandoned although vegetation is steadily taking over again . Research scientists from the IRD and its partners( 1) recently showed the discharge rate of the Mekong has oscillated in close correlation with the major events that had taken place. Runoff increased by over 50% in southern Laos between 1972 and 1975, at the height of the Vietnam War. Conversely, the north of the country saw it decrease by 30% between 1995 and 2004, following people’s exodus from the area to escape from the communist forces’ advance. Only the extensive changes in land-use and vegetation pattern can explain such variations in discharge of the Mekong.