Abstract
Changing characteristics of precipitation extremes have been reported
mainly using parameters like the frequency of occurrence and the
magnitude. As climate changes, the spatio-temporal characteristics of
rainfall extremes are also likely to get modified. Though there exist
studies noting the changing the temporal distribution, the spatial
extent of extreme rainfall events has received less attention. We show
that 31% of the fractional increase in the number of rainfall extremes
of the Indian summer monsoon from 1951 to 2015 is size-change related.
We find that the average size of rainfall extreme is significantly
increasing after 1980. Depending on the number of connected grids
experiencing simultaneous extreme rainfall, we classify them as small,
medium and large events. 90 % of large events have occurred after 1980
and these have the strongest rainfall intensity among all types. They
are more likely to cause floods, hence important. These events are
invariably associated with a monsoon low-pressure system (LPS) and occur
in the southwest sector of an LPS within 400 km from its centre. Strong
surface pressure anomalies that persist for more than a week are present
in different parts of the globe when these events occur, suggesting
preferred planetary-scale conditions that favour their formation. Thus
giving hopes of their advanced prediction and facilitating flood hazard
mitigation.