How to predict for floods and Droughts ?

It is useful to consider these disaster phenomena together in the context of predictability because both floods and droughts are manifestations of the same weather element, viz., water. Floods occur due to excess of water whereas lack of water results in droughts. Therefore, the predictability of floods and droughts in fact means the predictability of water, i.e., rain and run off. Further, as about 80% of the annual rainfall occurs in the summer monsoon season of June to September, the predictability of floods and droughts depends heavily on the predictability of the monsoon rains in the particular area.

There are additional aspects, which determine whether a particularly heavy rainfall will result in floods or scarcity of rain will create drought. For example, repeated occurrences of heavy rainfall over an area already soaked with rain will certainly give floods. Excess water in a river, due to heavy rains in the upper regions of the river, will create flood downstream. Absence (or lack) of drainage in any area will aggravate flooding there. Similarly, repeated seasons of scanty rainfall will lead to drought conditions.

Therefore, predictability of floods and droughts hinges on (i) the predictability of rainfall (predictability of the monsoon); (ii) whether the earlier rainfall in the area has been frequent or infrequent; (Hi) whether any river flowing through the area is bringing excess water from upstream regions; and (iv) whether there is a drainage problem resulting in accumulation of water in the area. As these aspects are either predictable or monitorable, it is reasonable to conclude that floods and droughts have a reasonably good predictability.