Y. Gao, J.S. Fu

Climate change-related heat waves and intense storms are projected to hit Eastern U.S. cities especially hard.

We know by now that climate change is capable of making bad weather events worse. Heat waves will become longer, hotter, more frequent. Droughts will get drier, flood levels higher, freakish storms less freakish in their regularity. But nothing makes this prospect sound quite so scary as some very specific numbers.

So here are some new ones to ponder. This latest data comes from a recent study, published in the journal Environmental Research Letters, which used a high-resolution climate modeling system to project bad news down to an impressively local level, examining what we might see in the 20 largest cities east of the Mississippi come the late 2050s.

By then, researchers from the University of Tennessee at Knoxville have calculated, heat waves in New York City could be 3.58 degrees Celsius hotter in intensity than they are now, with the average one lasting nearly two days longer (these projections are compared to a baseline of climate data between 2001 and 2004). Cleveland has it the worst, with a heat wave temperature increase of 3.71 degrees Celsius, followed by Philadelphia (3.69). The researchers project that heat waves will grow worse particularly across the Northeast and Midwest, bringing the North and South to roughly equal hot-weather fates.

This set of maps from the study shows, on the left, the four-year average of heat wave intensity calculated from 2001-2004 ("intensity" is defined as the average minimum temperature over three consecutive sweltering nights). The middle map shows a three-year average from our projected future climate, in 2057-2059. And the map on the right illustrates the difference between the two (those numbers are degrees Celsius).

This second series shows how the duration of heat waves will get worse (in number of days per heat wave):

And this series shows the worsening frequency of heat waves in events per year. Miami is projected to have the hardest time among the 20 largest Eastern metros, with as many as 7.55 more heat waves per year two generations from now.

All maps from "Projected changes of extreme weather events in the eastern United States based on a high resolution climate modeling system" in Environmental Research Letters (Y. Gao, J.S. Fu, J.B. Drake, Y. Liu, J-F Lamarque) 

Most climate projections are done at the regional or national level, but in this case the researchers combined high-resolution topography, land use information and climate modeling to create projections on a scale as small as a few kilometers wide. Using the technique (there were supercomputers involved), they were able to pinpoint projected effects on cities, and not just states.

They also looked at extreme precipitation, which is projected to increase pretty much everywhere, by about 35 percent or more. "Extreme precipitation” in this case refers to those days with ridiculously heavy rainfall (in the 95th percentile of all rainy days in a given year for a particular location). Philadelphia could get hit the hardest on the precipitation front (with an increase of 315 millimeters per year), followed by Baltimore (227), Virginia Beach (210), and Boston (207).

Those locations, you may have noticed, are on hook for the worst changes in heat waves as well. As the researchers conclude:

Considering both heat waves and extreme precipitation, the northeast region shows the largest increases. Thus, it is important that the northeast take actions to mitigate the impact from climate change in the next several decades.

Where have we heard that before?

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