12 Months Ending 4/19 Wettest For Contiguous US In Meteorological Records Going Back To 1895

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Above: Vehicles wade through flooded Kingwood Drive as thunderstorms hit the Kingwood, Texas, area north of Houston on Tuesday, May 7, 2019. Periods of flash flooding are expected to continue into the weekend in southeast Texas, where more than 10" of rain fell on Tuesday. Image credit: Jason Fochtman/Houston Chronicle via AP.

The 12 months ending in April 2019 were the wettest year-long period in U.S. records going back to 1895, according to the monthly U.S. climate summary issued Wednesday by the NOAA National Centers for Environmental Information. Averaged across the contiguous U.S., the total of 36.20” made the period from May 2018 to April 2019 the first year-long span ever to top 36”. The old record for any 12-month period was 35.78”, from April 2015 to March 2016.

Given the fierce drought-related impacts of the 2010s—including multiple deadly wildfire disasters from Tennessee to California—it may seem a bit counterintuitive that the nation has actually been getting wetter overall. Across the contiguous U.S., average yearly precipitation has risen by about 2” over the past century, from around 29” to just over 31” (see Figure 1). For the entire nation, including Alaska and Hawaii, precipitation increased by about 4% in the period from 1901 to 2015, according to the U.S. National Assessment.


Figure 1. Annual precipitation across the contiguous U.S. has increased by about 7% over the past century. Blue bar shows the linear increase since 1895, while the red curve is a smoothed version of the year-to-year numbers in green. When averaged over running four-year periods (not shown), the past four years are the wettest on record for the contiguous U.S. Image credit: NOAA/NCEI.

Of course, the averages above obscure a lot of regional and temporal variability, and the devil of drought impact lies in those details. U.S. climate is famously variable from year to year, decade to decade, and region to region (see Figure 2). As human-produced greenhouse gases boost temperatures over the long haul, both globally and nationally, the most intense precipitation episodes are getting even heavier, while the intense droughts that do occur in places like California are increasingly “hot” droughts, where the heat pulls moisture from vegetation and the landscape more effectively. We may see similar tendencies toward hot droughts in other parts of the U.S. as the climate continues to warm. The upshot is that drought impacts can intensify in a warming world even in places where the long-term precipitation average, across both wet and dry periods, is unchanged or even rising slightly.

A 2018 study found that California’s wet season is likely to get compressed into a shorter window, likely leading to precipitation “whiplash” between wet winters and hot, dry summers.


Figure 2. Seasonal changes in precipitation over the United States. Changes are the average for present-day (1986–2015) minus the average for the first half of the last century (1901–1960 for the contiguous United States, 1925–1960 for Alaska and Hawai‘i) divided by the average for the first half of the century. Image credit: Fig. 7.1, Chapter 7, Climate Science Special Report, U.S. National Climate Assessment.

EDIT

http://www.canadianinquirer.net/2019/05/09/greenhouse-gases-causing-canadian-arctic-seas-to-acidify-quicker-report/

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1. K&R for visibility. nt