Because human deforest cause forest decreased have impact many such as the problem of flood because don't have grass absorbs water when it rains.Problem of global warming because the forest is a source of the turnover of oxygen, carbon, water and other substances, deforestation causes the accumulation of carbon, plants and wildlife were less because no housing,No source of food, etc.,and improper land use because have buildings stand in the way of filling soil adjust water or bog. These can cause the destruction of water and natural drainage when heavy rains caused flooding น้ำล้น the easy.hese create the destruction of natural drainage system and water retention system when heavy rain condition arises.