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2021’s climate disasters revealed an east-west weather divide, with one side of the country too wet, the other dangerously dry
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2021’s climate disasters revealed an east-west weather divide, with one side of the country too wet, the other 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 pandemic global, 2021 was also filled with climate disasters. Some were so severe that they shocked even scientists who study them.

Extreme rainstorms have turned into raging flash floods The wind blew through mountain towns in EuropeThe act of killing Over 200 people. Asia. Extreme rainfall has overflowed large areasFlooded China’s subway stations. Record breaking heat waves in The Pacific Northwest, Europe and the Arctic. Wildfires California was swept by the winds, Canada, GreeceAnd Australia. These were only a few extremes.

The damage caused by the worst weather and climate disasters is expected in the United States alone. In 2021, it will be more than US$100 billion.

Many of these extreme weather conditions have been Climate change is human-causedThey give a glimpse at what to expect in a rapidly changing 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 am a researcher who studies the effects of global warming on precipitation, and the water cycle. 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 divide in weather

The east coast of the United States has weathered many storms in 2021. Tennessee records for rainfallFlash flooding caused by the storms in August led to deadly flash flooding. The Hurricane Ida remnantsThe storm surged into a new front just days after Hurricane Katrina hit Louisiana. It became so intense that it set rainfall records, flooded subway stations and basement apartments in New York City and Pennsylvania, with devastating results.

In the meantime, almost all of West was in some 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.

However, there is another factor: Global warming causes extreme dryness and precipitation.

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 destroyed homes and cars in Tennessee.
AP Photo/John Amis

3 effects of global warming on rainfall

When the planet warms, precipitation is responsible for three things.

1) Global warming causes more precipitation.

Higher temperature increases evaporation from Earth’s surface. 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 becomes more severe as more moisture evaporates. Expected to riseNevertheless, 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. Light precipitation will therefore be less frequent. 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. Storm systems are also more intense when there is more moisture in the atmosphere.

Research has shown that both the Heavy precipitation events have become more frequent and intense.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 to make dry places wetter, and wet places dryer.

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 that there are no significant changes in the global wind patterns and evaporation, an increase in moisture and evaporation will result in more moisture being transported from dry areas to moist areas and into storm tracks at higher altitudes. Global circulation patterns could 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.
A California farmer pulled out his almond groves due to lack of water in June 2021.
Robyn Beck/AFP via Getty Images

Mountains, moisture, and the east-west division

These dynamics are also affected locally by factors such as the shape and type of land, the plants that live there, and the presence of major water sources.

The rain shadow of mountains means that the western U.S. is mostly dry, with the exception the West Coast. The mountain ranges of the West force the westerly wind, which comes from the Pacific Ocean, upwards. The wind moves up and the air cools, forming precipitation on the mountain’s windward side. The moisture is already gone by the time the wind reaches leeward side. 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. A higher temperature and less precipitation would reduce the snowpack in the mountains. Premature melting in spring. 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 this important Colorado River reservoir. The reservoir was reduced to 35% capacity, which prompted water restrictions.
Photo by David McNew/Getty Images

The easterly trade winds carry plenty of moisture to the Gulf of Mexico and North Atlantic, which in turn provides ample moisture for the eastern U.S. An abundance of moisture means more rain and stronger storms due to an increase in temperature.

This is What years have precipitation records shown?What is it? Projections for future precipitationThese are based on climate models. Both models show a decrease of annual precipitation in West, which could indicate longer periods of drought and an increase in East with global warming.

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