Few attempts have been made to determine the ecological, economic and cultural importance of rivers before they have been dammed. Even fewer before-and-after studies exist. This is especially the case in regard to environmental and social impacts below dams. What is known is that such impacts will be more serious in the future than in the past, which adds an additional burden to late-industrializing countries in which the majority of future dams will be built. Impacts on people will be more serious for two major reasons. One is that downstream populations are larger as a result of population increase. The other is that, in comparison to downstream populations in North America, Europe and Japan, their livelihoods are more dependent on natural flood regimes because of the greater importance of flood recession agriculture, floodplain grazing, fishing, foraging and aquifer recharge for domestic water supplies and reforestation.