This problem applies specifically to deforestation. Since forests have a climate of their own, cutting vast areas of trees will have an impact on water patterns. How can it have such an impact? Forests acts as an enormous reservoir of water, which attracts humidity and creates rain clouds.
Rain clouds are formed when the water evaporates from the surface and when plants experience transpiration. Transpiration in plants is similar to sweating in humans. The forest follows a hydraulic cycle by absorbing the water when it rains and releasing it by evapotranspiration, which is the phenomenon of evaporation and transpiration explained earlier.
With deforestation, this hydraulic regulation is destroyed and reduces the absorption capacity. Therefore, rain continues to fall just as much after the trees are cut, but it floods the ground and streams down to a nearby river. While streaming down, it brings an important amount of mud, which can be extremely destructive, and fills up the river with it. The river loses his depth and expands in width when ground elements are deposited in the bottom, which floods part of the surrounding.
Also, the water becomes unsafe for drinking because of the accumulation of mud which reduces the amount of drinkable water available for humans and animals. Deforestation leads later on to desertification, which is the case for some parts of Africa. Rain and drinkable water are becoming more and more scarce.