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Colorado’s devastating fires have ended a year worth of climate disasters. In 2021, one side of the country was too wet while the other was dangerously dry.

Colorado’s devastating fires have ended a year worth of climate disasters. In 2021, one side of the country was too wet while the other was dangerously dry.

Several cars and a large pickup truck are piled up against a bridge after being swept downstream by a flood.

Along with a lingering global pandemic and climate disasters, 2021 was filled to the brim with them, some so intense that even scientists who study them were shocked.

Extreme rainstorms have turned into raging flash floods It swept through mountain towns across EuropeKilling More than 200 people. All over Asia Extreme rainfall inundated large areasFlooded China subway stations. Record breaking heat waves in The Pacific Northwest, Europe and the Arctic. Wildfires Californian communities were swept away by the storm, Canada, Greece Australia.

Boulder, Colorado, is a region that was so Extremely dryOn December 30, 2021, the following will be a Strong wind stormsent grass fires racing though neighborhoods in Superior, Louisville, burning There are hundreds of homesWithin hours. Officials claimed that the winds were so strong that there was no stopping them. Little firefighters could do this! but evacuate homes and businesses in the fires’ paths.

In the U.S., the damage from the most severe weather and climate catastrophes is expected to be substantial In 2021, it will be more than US$100 billion. Many of these extreme weather phenomena have been Climate change caused by humansThese are a glimpse into what to expect in an ever-warming world.

The United States has a distinctive feature: there was a sharp national precipitation split, with one end of the country being too wet while the other was too dry.

As a climate scientistI study the effect of global warming upon precipitation and the water cycles. Here’s what happened with precipitation in the U.S. in 2021 and why we’re likely to see similar scenarios in the future.

The east-west climate divide

In 2021, the eastern United States weathered storm after hurricane. Tennessee records for rainfallThe August flash floods were deadly The Hurricane Ida remnantsAfter Hurricane Katrina, the front merged with another one and became so powerful that they set records for rainfall and flooded basement apartments in New York and Pennsylvania. Severe storms Many states were hit by deadly tornadoesDecember

Nearly the entire West was also in some state of emergency. Stage of droughtFuelling the economy Wildfires that sweptThrough forests Towns and cities.

This type of east-west weather divide can also be augmented La NiñaPeriodical phenomenon caused by Pacific Ocean temperatures. It tends to make the Southwest dryter than normal, while the North and most of the eastern half are wetter.

Another thing is happening: Global warming fuels extreme rainfall and dryness.

Several cars and a large pickup truck are piled up against a bridge after being swept downstream by a flood.
In August 2021, flash flooding in Tennessee caused damage to homes and vehicles.
AP Photo/John Amis

Three impacts of global climate change on rainfall

Three things are especially important when the planet heats up and precipitation occurs.

1) Global warming causes more evaporation, which leads to more drying of land/plants and more overall precipitation.

Higher temperature increases evaporation from Earth’s surface, drying out vegetation and soils, which can fuel wildfires. It also increases the atmosphere’s capacity to hold moisture at a rate of about 7% per degree Celsius that the planet warms. Global precipitation will increase as more moisture evaporates. Expected to increaseNevertheless, this increase is not uniform.

2) Global warming causes more intense precipitation.

Higher temperatures will require more moisture to reach the level of condensation necessary to precipitation. Therefore, light precipitation will become less common. However, heavier rainfall events are more likely when there is more moisture in the atmosphere.

In addition, storm systems are fueled by latent heat – the energy released into the atmosphere when water vapor condenses to liquid water. Latent heat in storms is also increased by the presence of moisture in the air, which can increase their intensity.

Research has shown that both are the The frequency and intensity of heavy precipitation has increased.Since the 1950s, most land areas have been covered.

People walk down stairs into a flooded subway station.
In September 2021, the remnants of Hurricane Ida submerged subway stations in New York City.
David Dee Delgado/Getty Images

3) Global warming tends make wet areas wetter and dry areas drier.

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Because of the uneven distribution of precipitation, it is not evenly distributed across the globe. Global atmosphere circulation pattern. This global circulation brings moisture to places where winds come together, such as the tropical regions where we find most of the world’s rainforests, and away from places where winds diverge, such as the midlatitudes where most world’s deserts are located.

Assuming there are no significant changes to global wind patterns, increased evaporation will mean that more moisture is transported from dry regions to wet areas into the storm tracks at higher latitudes. Global circulation patterns may also be affected by global warming. Shifting in the world’s wet and dry regions.

Rows of dead trees lie on their sides in a flat field.
Due to lack of water, a California farmer had to remove almond groves from his property in June 2021.
Robyn Beck/AFP via Getty Images

Mountains, moisture and the east/west divide

These dynamics are also affected locally by factors such as the land’s shape, the type of plants and the presence or absence of major water bodies.

The rain shadow of mountains means that the western U.S. is mostly dry, with the exception the West Coast. The West mountain ranges force the west’s westerly winds upward from the Pacific Ocean. The wind moves up and the air cools, forming precipitation on the mountain’s windward side. The moisture has already evaporated by the time that the wind reaches to the leeward end of the mountains. The relative humidity drops further as the wind descends the mountains.

In areas with low moisture supply, higher temperatures mean less humidity and more rain. Snowpacks in the mountains would be reduced if there was more precipitation and higher temperatures. Spring melts earlier. All of these changes are likely increase the West’s aridity.

People looking from a viewing platform at Lake Mead, where a white ring on the stone walls shows how far water has dropped below normal.
The ‘bathtub ring’ around Lake Mead in July 2021 reflected record low water levels in the Colorado River reservoir, which fell below 35% capacity and triggered water use restrictions.
Photo by David McNew/Getty Images

The east coast of the United States receives a lot of moisture from the Gulf of Mexico and the North Atlantic, which is carried by the easterly trading wind. An abundance of moisture means more rain and stronger storms due to an increase in temperature.

This is What years do precipitation records show?What is it? Projections for future precipitationBased on climate models. Both show a decrease for annual precipitation in West which is likely to mean more droughts and an increase for East due to global warming.

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This article was last updated Dec. 30, 2021 with the fires that erupted in Boulder County, Colorado.

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