3 - Destroying the Rains, c. 1500–1830

Summary

Another long-standing convention links forests with rainfall. The plentiful rainfall in the Americas was associated with the thick forests, and deforestation was thought to reduce rain. A similar belief unfolded elsewhere in the world, and conservationists reframed the forest-climate question from one of deforesting the land to make a more temperate climate to one of preserving forests and planting trees to protect the supply of water. In rainfall, conservationists found a way to convey the environmental destruction wrought by deforestation. The scientific basis for forest influences on rain was found in new knowledge of stomata, transpiration, and photosynthesis. Eighteenth- and nineteenth-century naturalists sought further evidence for changes in rainfall in the flow of water in streams and rivers. Interception of rainwater by the leaves in forest canopies, infiltration into the soil, runoff over the ground, and evaporation from the soil were identified as key determinants of streamflow. A backlash arose, however, as the nineteenth century lengthened and the advocacy of forests galvanized into a worldwide campaign for forest conservation and tree planting to enhance rainfall.