It has been reported that extreme rainfall events are increasing over India and widespread floods have increased threefold over the last several decades from an average of two events per year to six events per year. But the link between extreme rainfall events and rising incidence of floods remains tenuous.
A new study by Australian and American researchers reported in journal Water Resources Research has confirmed that increased extreme rainfall events do not necessarily lead to increased floods. Many hydraulic factors such as physiography, drainage, catchment size and vegetation cover are critical for peak flood conditions.
One of the most important factors for extreme rainfall is the rate at which atmospheric moisture is increasing with global warming. As per Clausius-Clapeyron equation, the capacity of air to hold moisture increases by seven per cent for each degree of warming.
The increase in extreme rainfall is due to a combination of this increase in moisture as well as changes in atmospheric circulation.
Specifically for India, the impact of extreme rain on rivers and streamflow is complicated by dams, reservoirs, urbanization and other land use changes as well as increased evaporative losses due to global warming. Seven rivers that serve hydropower production are reported to have experienced a decrease in rainfall and streamflow, while climate projections indicate a wetter monsoon in a warmer world and a potential increase in hydropower production.
The caveat is that climate models may not fully capture past monsoon trends and may be unreliable for future projections.
This is a ‘India Science Wire’ story, edited by Clean-Future Team