Maps show extreme rains and dangerous droughts this summer

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Despite record rainfall this summer, the country risks falling behind on its average annual rainfall


Large areas of drought have been

interspersed with rare deluges

Percentage of Normal Precipitation

in the last 90 days

Five places has seen extremely rare 1,000-year floods, often the equivalent of a rainy season in a single day.

Note: Data for Alaska and

Hawaii is not available

Large areas of drought have been

interspersed with rare deluges

Percentage of Normal Precipitation

in the last 90 days

Five places has seen extremely rare 1,000-year floods, often the equivalent of a rainy season in a single day.

Note: Data for Alaska and

Hawaii is not available

Large areas of drought have been

interspersed with rare deluges

Percentage of normal precipitation in the last 90 days

Five places has seen extremely rare 1,000-year floods, often the equivalent of a rainy season in a single day.

Note: Data for Alaska and

Hawaii is not available

Large areas of drought were interspersed with rare deluges

Percentage of normal precipitation in the last 90 days

Five places has seen extremely rare 1,000-year floods, often the equivalent of a rainy season in a single day.

Note: Data for Alaska and Hawaii not available

Comment

Like an unbalanced seesaw, precipitation this summer has oscillated between too much and too little across the United States. Record rainfall in pockets of the country has caused unprecedented flooding; meanwhile, other communities aspired to a few drops as droughts worsened.

Weather conditions have always brought variable rainfall across the country, but this summer has seen a new era of extreme rainfall events brought on by a global warming: Wet events get wetter and dry events get drier.

“[A] a striking feature on weather maps this summer has been the relatively close proximity of extreme heat events to extreme precipitation events, as well as the number of such events,” said Greg Carbin, head of the forecast operations branch at the center. weather forecast from NOAA, in an email. “You might expect one or the other, but this summer we saw both.”

Much of the United States experienced significantly below average or above average precipitation; very few places are on par with long-term average precipitation amounts, as shown in the precipitation departures from normal map above.

The map below shows the total amount of precipitation over the summer, highlighting how precipitation varies by geography. It also shows how small amounts of rain can have a big effect in places that don’t typically get much rain in the summer, such as the western United States, sometimes resulting in unusual flooding in those places.


Desiccated in the west,

soggy in the southeast

Precipitation observed in the last 90 days

Note: Data for Alaska and

Hawaii is not available

Desiccated in the west,

soggy in the southeast

Precipitation observed in the last 90 days

Note: Data for Alaska and

Hawaii is not available

Parched in the west, soggy in the southeast

Precipitation observed in the last 90 days

Note: Data for Alaska and

Hawaii is not available

Parched in the west, soggy in the southeast

Precipitation observed in the last 90 days

Note: Data for Alaska and Hawaii not available

This summer, the most notable precipitation departures from normal occurred in the southwestern United States, which received about 100 to 150 percent more rain than its long-term average due to an active monsoon season.

The southwest monsoon is a seasonal wind shift that brings moisture from the Gulf of Mexico and the Pacific Ocean to the southwest and parts of southern California. Thunderstorms during the monsoon season can provide up to 50-70% of the region’s total rainfall. This year, the monsoon started in mid-June, about two weeks earlier than normal, and has continued.

“Probably the most interesting feature for me was the reincarnation of the [S]the southwest monsoon this year, which brought many flood risks to the arid southwest of the United States,” John Abatzoglou, a climatologist at the University of California, Merced, wrote in an email. .

For example, heavy rains in Carlsbad Caverns National Park in southern New Mexico trapped 200 people for several hours until authorities rescued them. Twice in about two weeks, in late July and early August, floodwaters poured into Las Vegas casinos as the city received its greatest amount of monsoon rain in a decade.

Carbin added that the monsoon pattern helped break monthly precipitation records near the Arizona-New Mexico border. “In fact, there are places in this region that have experienced monthly precipitation amounts in July and August that have not been seen before at least in the last 50 years.”

Death Valley sizzles weeks after record wettest day

The summer’s most devastating rains spread through the southwest and central states, where record downpours produced a season’s worth of rain in a single day. The most notable single-day rainfall occurred in St. Louis, western Kentucky, eastern Illinois, Death Valley, California and Dallas. All five rainfall events were exceptionally rare, estimated at just 0.1 percent chance of occurring in any given year.

The torrents of rain caused severe flooding that engulfed communities, damaged infrastructure and prompted emergency relief. Thirty-eight people died during rain in western Kentucky and at least one person died during flooding in Dallas.

Several other regions also experienced unusual and severe rain events. In June, 2 to 3 inches of rain fell in Yellowstone National Park and melted the snow, causing historic flooding and landslides and washing away roads and homes. Near-record rainfall in Jackson, Mississippi on August 24 destroyed the city’s main water treatment plant, leaving some neighborhoods without running water.

“Summer thunderstorms have been particularly intense this year,” said Daniel Swain, a climatologist at the University of California, Los Angeles. “It is precisely the type of extreme precipitation that we expect to increase the most in a warming climate.”

Record rains hit drought-stricken areas. It is not good news.

In recent years, a greater amount of rain in the United States has occurred in the form of intense one-day events. The data show that nine of the first 10 years of extreme one-day precipitation events have occurred in the past three decades.

Swain said the gradual warming of the atmosphere has increased the frequency of these extreme one-day events. A warmer atmosphere can “hold” more water; the atmosphere can hold about 4% more water for each additional degree Fahrenheit of warming. Since 1979, average temperatures in the United States have increased between 0.32 and 0.55 degrees Fahrenheit per decade.

But while extreme precipitation events have recorded impressive rainfall rates, they are not large enough to compensate for the vast stretches of drought. Swain said that in addition to low rainfall, a warmer atmosphere causes more soil evaporation, worsening drought conditions.

The western United States, particularly California, is the most drought-affected region in the country. The drought is mainly due to the recent lack of rain and snowfall in winter as well as rising temperatures, which accelerate evaporation.

By itself, Abatzoglou said, California’s paltry summer rainfall isn’t too alarming, as typical summer rainfall “is almost zero.” A good streak of storms and snowfall in fall and winter could put a damper on the drought, although full recovery is likely to take several years.

Southwest drought most extreme in 1,200 years

Yet the lack of summer rainfall has severely affected the northeast. Boston had its fourth driest July on record. Only about a half inch of rain fell in Providence, RI in July, about 2.5 inches below average. Drought conditions extended between New Jersey and coastal Maine.

Much of the central and southern plains also experienced limited rainfall and well above normal temperatures, during which the drought spread and intensified.

As of August 30, about 65% of the country was experiencing abnormally dry to exceptional drought conditions.

“The generally smaller footprint of these extreme precipitation events was offset by widespread drought,” NOAA’s Carbin wrote in his email. “…My own year-to-date precipitation analysis puts 2022 slightly below normal when looking at high-end monthly precipitation coverage (10 inches or more).”

But Carbin said rainfall totals could increase quickly, even catastrophically, if the Atlantic hurricane season resumes. In recent years, many places have experienced tropical rainfall that has dropped large amounts of water.

An excessively wet year 2021 in the eastern United States shows the fingerprints of climate change

Last year, the remnants of Hurricane Ida unloaded a historic deluge in the northeast around September 1. Newark received over eight inches of rain and had its wettest day on record. Although Ida was an exception, most extreme tropical cyclone rainfall tends to occur later in September and sometimes in October, Carbin said.

“So it is not yet time to rule out a threat of heavy tropical cyclone rains,” he said.

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