Environmental Science
Impact of Deforestation on Regional Hydrological Cycles
Quick fact
The Amazon rainforest generates about half of its own rainfall through evapotranspiration—a 'biotic pump' that recycles moisture.
Why this is interesting
You might think cutting down trees only harms wildlife, but it can also change the weather. How can a forest, miles away, influence the rain that falls on your city?
Read the full explanation
Understanding Impact of Deforestation on Regional Hydrological Cycles
Forests act as natural water pumps. Trees draw water from the soil and release it into the air as vapor through their leaves, a process called evapotranspiration. This moisture rises, cools, and forms clouds, leading to rainfall. When forests are cleared, this moisture source disappears. The air becomes drier, and the region receives less rainfall. Meanwhile, without tree roots to hold soil and slow down water, rain runs off the land quickly, carrying away topsoil and reducing the amount of water that seeps into the ground to recharge aquifers. This leads to a drier landscape, decreased river flow during dry seasons, and a higher risk of both floods and droughts.
A deeper explanation
The mechanism is rooted in energy and water balance. Forests absorb solar radiation and use it to evaporate water, which cools the surface and humidifies the air. This creates a low-pressure area that draws in moist ocean air, promoting rainfall (precipitation recycling). Deforestation lowers evapotranspiration, causing a decline in atmospheric moisture. The surface albedo increases (bare ground reflects more sunlight), which can further alter temperature and atmospheric circulation. In the tropics, large-scale deforestation has been shown to reduce regional rainfall by up to 30%. Additionally, deforestation reduces soil infiltration capacity and water storage, so more water becomes surface runoff, leading to soil erosion and reduced baseflow in rivers. This creates a feedback loop: less forest leads to less rain, which makes it harder for forests to regrow, and so on.