Drought and floods are a part of natural hydrologic cycle. There will be some years when the rainfall is less than normal leading to a drought; and some other years there will be spells of very intense rainfall, causing floods. In a large country like India, it often happens that in the same year there is drought at some places and floods at other places.
Droughts. There was a time when drought meant famine and widespread deaths. (see answer to Q13). Now that it is possible to bring in food from distances over thousands of kilometres, drought does not mean famine. Now the main problem with drought is loss of livelihoods, increased poverty, migration in search of work, and related distress; and death of cattle heads.
Ground water is the best protection against drought. Because the ground water level does not fluctuate from year to year depending on rainfall and if the ground water is used in a sustainable manner, there will be sufficient ground water available for domestic use and for cattle even during a drought year. However, in recent years there has been over exploitation of ground water in many areas and this has lead to increased distress during droughts.
There is no doubt that the ground water, for that matter any resource, must be used in a sustainable manner. The main problem with our ground water is not less of recharge, but too much of extraction.
Floods. Flood is a situation when the river flow enters the area where there is human activity going on. When there is a spell of intense rainfall, i.e. a lot of rain occurring in a short period of time, the sudden increase in river flow needs more width and temporarily spreads on a wider area. The areas thus claimed by the river are called flood plains of the river. Population and economic pressures have driven the mankind to create habitations and take up other human activity in the flood plains. In this area, occasional floods are inevitable.
Floods can not be prevented. They can only be managed. The common flood management practices are:
Flood embankments: These are useful in providing quick protection to vital areas like major cities and installations.
Reservoirs. Flood control reservoirs store the flood waters and release them slowly after the flood is over. Construction of a reservoir takes time but is the most reliable method of flood protection.
Forests: Forests intercept some rain, increase the percolation, slow down the overland flow of water and thus reduce the intensity of floods. However it must be understood that the effects of a forest are significant only for small to medium floods. For large devastating floods, the effects of a forest are not so significant.
To understand this further, consider following analogy. Suppose some water is poured over a person's head and it is intended to observe how much of it will flow down to his shoulders. Does it matter whether the man is bald (no forest) or has a good growth of hair ?
That depends on how much water is poured. If a teaspoonful is poured, it certainly makes a difference. If the man is bald then all the water will quickly flow down to his shoulders while if the man has a good hair, then none will. But this difference will be less significant if a cupful of water is poured. And if a bucketful of water is poured on his head, then it makes no real difference whether the man is bald or hairy.
Likewise, forests will protect from small floods, will reduce the intensity of medium floods and will have only an insignificant effect on large floods.