Deforestation and the multiple functions of tropical watersheds: are tropical forests indispensable for regulating rainfall and ensuring clean and reliable water supplies?

Old-growth TROPICAL FORESTS provide several major ‘watershed functions’ essential to human survival and local livelihoods. They hold soil in place and help maintain the productivity of the land. They also regulate the quantity and timing of water flows control sediment loads and so protect water quality. Cutting down tropical forests undermines these valued functions. But hydrological patterns on the land vary widely from one catchment area to another and between sites or plots within the same catchment. They depend not only on the extent of natural tree cover but also on a host of other factors. These include rainfall topography (especially slope) geology soil type the area and distribution of food and forage crops leaf litter over soil the extent of compaction from livestock and machinery and the presence of impervious surfaces such as roads and buildings. Some non- forested landscapes have no major problems with watershed functions – so strictly speaking they don’t need ‘forest’ to maintain their water flows. Thus a web of human and other factors determines how land will process rainfall and whether the net result will present hazards for local and downstream people. To blame local water-related hazards solely on ‘deforestation’ while ignoring other key parameters influenced by post- forest land management is to severely limit one’s options in the search for balanced solutions

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