The relationship between deforestation and floods have been studied and well documented in academic circles of hydrologist and environmental scientists .
Below is just a portion of one article in plain language that suggests some of the contributing
Forests 'n flooding
At its root, the flood equation is pretty simple: If a river cannot handle the load of water it's required to carry, it must rise. With enough water, it must rise above its banks and flood.
The faster water runs from the watershed into the river, the higher a flood will be. Thus anything that increases runoff speed -- like excessive pavement or ditching of farmland -- will contribute to floods.
Deforestation plays several roles in the flooding equation because trees prevent sediment runoff and forests hold and use more water than farms or grasslands.
Some rainwater stays on the leaves, and it may evaporate directly to the air (the more water used in the watershed, the less remains to run off).
Leaves reduce raindrop impact, and gentler rain causes less erosion.
Tree roots absorb water from the soil, making the soil drier and able to store more rainwater.
Tree roots hold the soil in place, reducing the movement of sediment that can shrink river channels downstream.
The loss of trees played a major role in the huge Yangtze flood of 1998, says Janet Abramovitz of Worldwatch, who observes that the Yangtze watershed had lost 85 percent of its forest cover in the past few decades. Although two other causes of trouble that we'll examine shortly were also at play -- loss of wetlands and river engineering -- Abramovitz says the Chinese government "was trying to blame it all on heavy rains, maybe El Nino or global warming." She says a new, $2 billion plan to reforest the Yangtze basin is "Certainly ... a very clear sign from the government that deforestation was a problem