Unrelenting rains catapulted May to the second-wettest month on record in the U.S., leaving vast tracts of farmlands flooded across the nation's midsection, and jeopardizing this year's corn crop.

The big picture: The May precipitation total for the Lower 48 states was 4.41 inches, which was 1.5 inches above average, according to the National Oceanic and Atmospheric Administration (NOAA). The past 12 months have been the wettest such period on record for the Lower 48 since such records began in 1895, with rains especially concentrated in the Midwest, Plains and Northeast.

Rainfall during this period was 37.68 inches, which was 7.73 inches above average for the period, the previous all-time 12-month record was 36.2 inches, set this April.

Context: A combination of heavy rainfall and spring snowmelt has led to record flooding along numerous rivers in the Midwest and Plains, rivaling or exceeding the great floods of the past century, including 1927 and 1993.

Hydroclimate extremes, including droughts and heavy precipitation events, as well as sharp whiplash-like swings between the two, are expected to become more common and severe as the climate continues to warm due to human activities.

Kansas, Nebraska and Missouri ranked the wettest May on record, NOAA found, while 7 other states ranked in their top 5 wettest for the month.

Already, a statistically robust uptick in heavy precipitation events has been observed in many of the Lower 48 states.

This is related to the fact that a warmer atmosphere with warmer oceans can carry more water vapor, which gets wrung out as heavy precipitation during storm events.

However, no climate attribution study has been conducted on the heavy rains in May or the past year, limiting how far scientists can go in tying these events to climate change.

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