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Yeah, climate change is real. A new study of precipitation trends in the US shows that extreme rain and snow events have become significantly more common and larger since 1948. The trend is most dramatic in the northeastern part of the country. This means more flash floods, casualties, damage, etc. And more expense for governments tasked with rebuilding. Yes, this is really happening - it's not just our imagination. Keep the sandbags ready.

Regional Trends Toward Increased Extreme Rainstorm
and Snowstorm Frequency 1948-2011

The map above shows percent increase in frequency of extreme events by region. An increase of 50 percent means that extreme events that happened once a year around 1950 now happen once every eight months. (This doesn't necessarily mean total annual precipitation has risen at every site - the study only addresses extreme events.) At the same time, the magnitude of the most extreme storms has increased.

Follow me over the squiggle for more.

The study, conducted by Environment America, is based on daily precipitation records at 3748 weather stations across the 48 contiguous states over the period 1948-2011. Results are presented for both collectively and state by state, which is cool, because you can see what's happening where you live.

The reason, of course, is global warming. Warmer water evaporates faster, and warmer air holds more water vapor, providing more fuel for storms:

The water-holding capacity of the air increases roughly exponentially with temperature. Using satellites and ground-based measurements, scientists have found that the water content of the atmosphere is now increasing at a rate of about 1.3 percent per decade, consistent with expected changes given the temperature increases that have occurred.
Extreme precipitation events, defined as the 64 largest one-day events at each station (one for each year), have increased 30 percent nationwide. This means an event that happened once a year in the mid-20th century now happens every 9.3 months. But this increase is not homogeneous. The largest increase has been in New England. In New Hampshire the increase is 115% - the mid-20th century annual event now happens more than twice a year. By contrast, the increase along the West Coast is the most modest. Altogether, frequency of extreme events has risen signifcantly in 45 states and fallen in one (Oregon).

In addition to becoming more common, extreme events are becoming larger. This means the biggest storms are getting bigger. Averaged over all 48 states, the largest events are now 10 percent larger than mid-20th century. Again, the trend is more pronounced in the Northeast.

At the state level, Vermont and New Hampshire experienced the largest growth in total precipitation from the biggest annual rainstorms or snowstorms, increasing 35 and 33 percent, respectively, from 1948 to 2011. Among states along the Eastern Seaboard, Massachusetts, New York, Maine, Pennsylvania, New Jersey, Connecticut and Delaware all experienced increases of 20 percent or more.

In total, 43 states experienced a significant increase in total precipitation produced by the largest annual storm at each weather station. Four states—Rhode Island, Arizona, Florida and California— either did not experience a trend, or did not have enough data to draw a valid conclusion. Only one state, Oregon, showed a significant decrease.

Fascinatingly, the increase in precipitation per event becomes more pronounced at the very extreme. In other words, the the top 0.1 percent of the largest events are increasing in size faster than the top 1 percent, and so on. (It's a lot like what's been happening with individual income.)

The More Extreme the Storm, the Greater the Change

This figure shows that the very largest storms are getting bigger, faster, than other storms. All storm categories are defined relative to the local climate at each weather station used in this analysis. For example, the far right column represents the change over time in the amount of total precipitation produced by the largest 0.1 percent of storm events at each weather station we used across the contiguous United States.
Global temperatures have increased about 1°F since 1948. And with this we have gotten a dramatic change for the worse in our weather. One can only imagine what will happen if temperature continues to rise unchecked, as will happen if the current business-as-usual approach continues.

h/t to Climate Progress for highlighting this study.

And PS - this issue is of personal interest. In my little town, we've noticed that flash flooding has gotten to the point we need permanent sandbagging to keep water out of the basement:

Originally posted to Climate Hawks on Fri Aug 03, 2012 at 05:48 PM PDT.

Also republished by Community Spotlight.


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