Environmental Science
How Deforestation Affects Local Rainfall Patterns
Quick fact
In the Amazon, about half of all rainfall is generated by the forest itself through transpiration—so removing trees can cut rainfall by up to 30% locally.
Why this is interesting
You might think deforestation only removes trees, but what if it also robs the sky of rain? Why do some deforested regions become drier even far away from the cleared area?
Read the full explanation
Understanding How Deforestation Affects Local Rainfall Patterns
Forests act as natural water pumps. Trees draw water from the soil and release it as vapor through their leaves (transpiration). This vapor rises, cools, and forms clouds that rain downwind. When large areas are deforested, this moisture supply is cut off. Additionally, cleared land is often darker and less reflective, absorbing more sunlight and heating up, which can change local wind patterns and push rain clouds away. The result: less rainfall over the cleared area and sometimes even in neighboring regions that depended on that moisture.
A deeper explanation
The mechanism hinges on the 'biotic pump' theory: forests not only release moisture but also create low-pressure zones that pull in moist air from oceans. This maintains a continuous cycle of rainfall. Deforestation breaks this cycle—less transpiration reduces atmospheric moisture, the surface warms, and the pressure gradient weakens. This can trigger a feedback loop: less rain dries the soil, making fires more likely, which clears more forest and further reduces rainfall. Beyond the local scale, large deforestation (e.g., in the Amazon) can reduce rainfall hundreds of kilometers away, jeopardizing agriculture and water supplies across entire continents. This concept is vital for understanding why protecting forests is not just about carbon storage but also about sustaining the rainfall that billions of people depend on.