Extreme Precipitation in the United States of America

Precipitation changes from year to year and across decades, with variations in its amount, intensity, frequency, and form (e.g., snow or rain) influencing both the environment and society.

Precipitation, encompassing both its amount and timing, is crucial for maintaining soil moisture and stream flow. As a fundamental part of the water cycle, it delivers water from the atmosphere to the Earth's surface. The patterns of precipitation are primarily determined by the climate system, influenced by atmospheric and oceanic circulation, as well as the amount of water returning to the atmosphere. Hydrological extreme events, such as floods and droughts, are closely tied to these precipitation patterns.

The Intensification of Extreme Precipitation

With global warming, extreme precipitation events are expected to intensify across much of the world. As temperatures rise, the concentration of atmospheric water vapor increases, following the thermodynamic principle that saturation concentration grows by about 6–7% per degree of warming. This increase supplies additional moisture for precipitation, thereby amplifying the intensity of extreme hydrological events.

Changing Precipitation Trends

Global warming directly influences precipitation trends by intensifying evaporation rates and leading to surface drying, which in turn increases the frequency and severity of droughts. The air's water-holding capacity rises by approximately 7% per 1°C of warming, allowing storms of all types—thunderstorms, extra-tropical rain or snowstorms, and tropical cyclones—to produce more intense precipitation due to the additional atmospheric moisture.

Ecosystems and communities are already feeling the effects of these changes. Observations by NOAA show that global temperatures have risen about 1.1°C from 1901 to 2020, with sea level rise accelerating significantly since 1993. Glaciers are shrinking rapidly, atmospheric CO₂ levels have increased by 40% since the Industrial Revolution, and snow is melting earlier compared to long-term averages.

The 2014 National Climate Assessment explains that wet regions are becoming wetter, while dry areas are getting drier, consistent with the intensification of the global hydrological cycle. These changes vary by region and season, significantly impacting water resources dependent on snowpack and the timing of its melt.

Regional Variations in Precipitation in the United States

Precipitation trends in the United States differ widely by region. Southern states are experiencing reduced precipitation during winter and spring, while northern regions are becoming wetter overall. The Pacific Northwest sees wetter winters but drier summers, and nearly all parts of the country are observing reduced rainfall during summer.

Heavy precipitation events are becoming stronger and more frequent, while droughts are increasingly common, particularly in the western United States. Snowpack, an essential source of freshwater, is diminishing due to higher temperatures, causing it to melt earlier in the year. This shift reduces its reliability as a water source during warm and dry seasons.

The Effects of Climate Change on Precipitation

Climate change accelerates the Earth's water cycle, resulting in more frequent and intense storms, while contributing to drying in some areas. Storm-affected regions face increased precipitation and heightened flooding risks, whereas areas distant from storm tracks experience reduced rainfall and a greater likelihood of drought.

These changes disrupt natural processes and have wide-ranging effects on human well-being and ecosystems. Rainfall, snowfall, and snowmelt timing affect the availability of surface and groundwater for drinking, irrigation, and industry. Sudden changes in precipitation patterns can strain ecosystems, as plant and animal species may not adapt quickly enough.

Adapting to Changing Precipitation Patterns

Adapting to changing precipitation patterns involves a variety of strategies. Municipalities can improve infrastructure to withstand extreme rain events, while governments can restrict construction in floodplains. Communities can prepare for droughts by adopting advanced water management techniques, such as conserving natural drainage systems like wetlands.

Although the projections of a climate change-impacted future may seem daunting, they are not inevitable. Many of the challenges are already known, and ongoing research continues to reveal new solutions. Experts believe there is still time to avoid the worst outcomes by limiting global warming and rapidly reducing emissions. Investments in new technologies and infrastructure to curb greenhouse gas emissions can mitigate these risks and spur economic growth through job creation.