How extreme rainfall days within India change with the El Nino-La Nina cycle. Blue shades mean extreme rain is more likely, and brown shades mean less likely, during El Nino summers compared to La Nina summers.
New research led by City College of New York scientist Spencer A. Hill challenges generations-old beliefs about how El Ni帽o events influence rainfall during the Indian summer monsoon. Entitled 鈥淢ore extreme Indian monsoon rainfall in El Ni帽o summers,鈥 the study appears in the journal .
鈥淥ur key finding is that you tend to get more days with extreme amounts of rainfall within India, not less, in El Ni帽o summers. An El Ni帽o event means that ocean surface temperatures in the eastern equatorial Pacific Ocean are warmer than usual,鈥 said Hill, assistant professor, in CCNY鈥檚 Department of Earth and Atmospheric Sciences. 鈥淭his finding was unexpected, because it has been known for over a century that El Ni帽os do precisely the opposite, meaning they promote drought, for total rainfall summed over the rainy season, June through September.鈥
Hill, whose affiliations include the CUNY Graduate Center Departments of Earth and Environmental Sciences and of Physics, as well as Columbia University鈥檚 Lamont-Doherty Earth Observatory, however pointed out that these changes are not distributed uniformly within India. 鈥淭he increases in extreme daily rainfall under El Ni帽o compared to La Ni帽a are concentrated in central India and in the southwestern coastal band, whereas in the southeast and northwest the signal is opposite, meaning daily extreme rainfall is less likely in El Ni帽o summers,鈥 he noted.
Highlighting the importance of the study, Hill said that extreme rain events come every summer, destroying infrastructure and killing people through flooding and landslides. The World Bank estimates that some 80 million people live in extreme poverty in the world鈥檚 most populous country of more than 1.45 billion. 鈥淏etter predictions of when and where extreme rainfall events are likely to occur give society better chances to prepare, such as perhaps by earlier and better warnings or pre-mobilizing aid.鈥
And this novel work will continue beyond this study thanks to a new three-year $408,862 grant awarded to Hill this fall by the National Science Foundation [NSF]. 鈥淚n this new NSF grant we will investigate how and why the type of storms responsible for much of this extreme rainfall, called monsoon low-pressure systems, change depending on whether there are El Ni帽o or La Ni帽a conditions,鈥 said Hill.
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