May 2015 Wettest Month For Lower 48 States On Record - NOAA

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This May was the United States’ wettest month in all 121 years of record-keeping, according to the National Oceanic and Atmospheric Administration (NOAA). A total of 4.36 inches fell across the lower 48 states last month — 1.45 inches more than average, NOAA said Monday. Fifteen states saw precipitation that was “much above average” in May, and Oklahoma and Texas experienced their wettest month on record, with precipitation levels “more than twice the long-term average,” according to NOAA.

These records aren’t surprising for Oklahoma and Texas, which have been battling severe storms and major flooding over the last several weeks. These floods have swept away homes and have killed at least 28 people in the states. Scientists don’t yet know how much climate change played into these floods, but they noted to ThinkProgress last month that climate change is expected to make severe flooding like this more common.

“There are several factors that have created conditions that made it more likely to have this disastrous situation, and I would say the majority of them are natural factors,” Brenda Ekwurzel, a senior climate scientist with the Union of Concerned Scientists, told ThinkProgress. “However, there’s a definite climate assist that creates the likelihoods of the odds of it being a more severe event.”

Along with this increased chance of heavy rainfall, scientists also say that some regions will see longer, more intense periods of drought — periods that then could be followed by heavy, intense rainfall. Warmer air can hold more moisture, which means that moisture can collect in the atmosphere for longer than usual and then fall all at once on a region. This “weather whiplash” exacerbates the risk of flooding, as the heavy rain can simply run off the surface of the dry, hard earth, rather than being absorbed by it.

EDIT

http://thinkprogress.org/climate/2015/06/08/3667277/may-wettest-month-on-record/