Interview Madhavan Nair Rajeevan,

Extreme event prediction, a priority research

By: Staff Reporter

G’nY. Are the number and intensity of extreme rainfall events rising in India?

Mr Madhavan Nair Rajeevan : Yes, the number and intensity of extreme rainfall events are rising in India. Heavy rainfall events generally occur over central India, northeast India and along the west coast. For example, frequency of heavy rainfall events (with 15 cm or more in 24 hours) over central India is about ten events in the monsoon season. However, frequency of heavy rainfall events (exceeding 15 cm in 24 hours) has increased from about 7 to 15 during the last 50 years (that is about 80 per cent and an appreciable change).

Rainstorms are large scale heavy rainfall events (with area more than 50,000 sq km) and persisting for more than two days. These events are primarily responsible for large-scale floods in India. An analysis of rainstorms over India suggests that there is an increase of 100 per cent in rainstorm days over India during the last 50 years (increase from about five days to ten days now).

G’nY. If indeed there are changes in the number of extreme events, can it be ascribed to climate change?

Mr Madhavan Nair Rajeevan : In general, the changes in extreme rainfall events can be attributed to global warming. With global temperatures rising, increase in frequency of heavy rainfall events is possible, due to increase in moisture content in the atmosphere and more instability of the atmosphere. However, one individual event cannot be attributed to global warming. An analysis of 100 years of data suggests that there is an epochal variation which is attributed to natural variability. However, there is an appreciable effect of global warming overriding the natural variability.

G’nY. Has Indian science garnered adequate strength to predict such events on different time scales?

Mr Madhavan Nair Rajeevan : Yes, to some extent. These heavy rainfall events are predictable at least 2-3 days in advance. High resolution numerical models are capable of predicting these events. There is a problem in exact location of heavy rainfall event.  However, magnitude and structure is well predicted 2-3 days in advance. There is a hope that the lead time of accurate prediction can be increased to 4-5 days.

G’nY. What is the likely impact of global warming in general and of Bay of Bengal warming in particular and its effect on monsoons?

Mr Madhavan Nair Rajeevan : Global warming in general and the Indian Ocean warming in particular can have an impact on monsoon. Even though there are many ambiguities in establishing a clear relationship between the global warming and the Indian monsoon, increase in heavy rainfall events and rainstorms is likely to be influenced by the global warming.

G’nY. What are the prospects of climate projections at regional/local levels and for planning mitigation and adaptation methods?

Mr Madhavan Nair Rajeevan : The IPCC climate models suggest that with the global warming, the mean monsoon rainfall is likely to increase. However, rainy days (days with 2.5 mm of rainfall) are likely to decrease. This clearly suggests that whenever it rains, it will be heavy, a clear indication that heavy rainfall events are likely to increase in future.

G’nY. What has been envisaged to enhance the Ministry’s extreme event prediction capability?

Mr Madhavan Nair Rajeevan : It is the priority of the Ministry of Earth Sciences to not only predict mean monsoon rainfall, but to predict extremes events too. This is a challenging task. However, we hope to achieve the improvement of prediction skill of these events. We are planning to have the second phase of the monsoon mission, in which the focus will be on extremes

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