Abstract: Intense condensation associated with high evaporation from natural forest cover maintains regions of low atmospheric pressure on land. This causes moist air to flow from ocean to land, which compensates the river runoff. Deforestation induces large-scale desiccation by disrupting this flow. Here we overview this theory and quantify the horizontal pressure gradients that govern the continental moisture supply. High evaporation and extensive natural forests guarantee both a stable and high throughput hydrological cycle. Forests protect a continent against devastating floods, droughts, hurricanes, and tornadoes. Sustaining natural forests is a sound strategy for water security and climate stabilisation.