Question

In which way deforestation affects rainfall.
a) It increases rainfall
b) It decreases rainfall

Answer 1

Hint: Forests cover more than $30\%$ of the Earth's surface. Through their role in water evaporation,which creates clouds that reflect back sunlight and keeps the temperature on earth down. Forests also create fresh water runoff for the streams and rivers through rainfall.

Complete answer:
Deforestation is the permanent removal of trees to make room for something besides forest cover. This may include clearing the land for agriculture, grazing, or using the timber for fuel, construction or manufacturing.
Deforestation has led to significant reduction in tropical rainfall far from the area where trees have been cut down. This is generally because air passing over the forests picks up moisture given by trees and plants that fuels rain all over the world. When the trees disappear from a forest area, so does some of that rain.
This would primarily result in disrupting the forest’s water cycle. Trees that absorb water from rain also release moisture back into the air via the process of evapotranspiration and this moisture in turn fuels further rainfall. When forests patches are cleared, evapotranspiration and more water runs off into rivers leaving less moisture for the formation of rain.

Additional information:
The effects of deforestation on rainfall are:
a) A big part of the rainfall over tropical forests comes from water vapour that is carried by the atmosphere from elsewhere. But ‘recycled’ rain, the water that is pumped by trees from soil into the atmosphere through a process
called evapotranspiration also forms a major part. Water mainly exits from forests either as run-off into streams and rivers, or as evapotranspiration that is carried away by the atmosphere. Therefore the atmospheric transport of water vapor into the forest is basically balanced by the exit of water in the form of vapor and run-off.
b) Deforestation considerably reduces evapotranspiration and so inhibits water
recycling. Additionally this decreases the amount of moisture carried away by the atmosphere, reducing rainfall in
regions to which the moisture is transported. Decreasing evapotranspiration may result in increased localized run-off and raise river levels.

So, the correct answer is option b) It decreases rainfall.

Notes:
Multiple factors including human and natural origin, cause deforestation. Natural factors such as natural forest fires or parasite-caused diseases result in deforestation. Nevertheless, human activities are among the top main causes of global deforestation. The expansion of agriculture has caused nearly $80\%$ of global deforestation, with the construction of infrastructures such as roads or dams, together with mining activities and urbanization, making up the remaining causes of deforestation.