Deforestation means cutting down of trees or forests.
Trees give out a huge amount of water in the form of water vapour during transpiration. Trees transpire and play an important role in the water cycle as it adds moisture to the air which brings rainfall.
Deforestation will lead to the reduction of water vapour and this affects cloud formation and thus it results in less rainfall. As a result of less rainfall, soil will be dry and this leads to lower water intake in the trees thus interrupting the water cycle process and reducing rainfall.