Future forecast: More extreme precipitation ahead

A recent study examining the upcoming National Climate Assessment has revealed alarming conclusions about the future of heavy precipitation days in the United States. Researchers from the Scripps Institution of Oceanography at UC San Diego and the DOE Lawrence Berkeley National Laboratory (Berkeley Lab) predict that the extreme rain or snow days that once occurred only once in a century could become multiple occurrences in an individual’s lifetime.

By analyzing a comprehensive 30-terabyte data set, called Localized Constructed Analogs Version 2 (LOCA2), researchers were able to examine temperature and precipitation patterns on a scale of approximately six kilometers (3.9 miles). In contrast, most advanced climate models have a much broader focus, looking at regions ranging from 50 to 250 kilometers (30 to 400 miles). This new data set offers a far more granular view of weather patterns in the United States, providing valuable insights for local planners.

Dan Feldman, staff scientist at the Berkeley Lab and the project’s principal investigator, explains the significance of this new approach: 

“With this data set, we’re able to look at the impacts of actual weather pattern changes across the United States at an extremely granular level. We see that there is a lot more extreme weather that is likely to happen in the future – and by looking at actual weather patterns, we show that changes in extreme precipitation will actually be more extreme than previously estimated. Land use managers and planners should expect more extremes, but location matters.”

The LOCA2 data set is an update to a similar analysis conducted in 2016, which informed the Fourth National Climate Assessment (NCA) in 2018. The NCA serves as a guide for the U.S. government to plan for, mitigate, and adapt to climate changes impacting the country. The Fifth NCA is anticipated to be released later this year.

Covering the lower 48 states of the United States, southern Canada, and northern Mexico, LOCA2 incorporates 27 updated climate models from the Coupled Model Intercomparison Project (CMIP6) and more than 70 years of weather data. 

David Pierce, a scientist at Scripps Oceanography and the developer of LOCA and LOCA2, emphasizes the importance of these improvements: “We’ve spent a lot of effort improving the representation of extreme wet days, which is important for understanding both the likelihood of flooding and the availability of water for agricultural, commercial, and residential use.”

LOCA2 climate projections offer daily information through the end of the century for three different greenhouse gas emissions scenarios, known as Shared Socioeconomic Pathways (SSPs). The data set is freely available for planners and decision-makers to utilize.

The study supports what climate scientists have long predicted: as the world continues to warm, weather events will become increasingly extreme. LOCA2 findings suggest that the heaviest days of rain and snowfall across much of North America will release 20 to 30 percent more moisture than they currently do. This increased precipitation will likely occur in winter, potentially exacerbating flooding in areas such as the upper Midwest and the west coast.

Feldman emphasizes the practical applications of the research: “The big picture is clear: it’s getting warmer and wetter. This research translates that bigger picture into more practical data for infrastructure and operations planning. With this more detailed look at local impacts, we can help local officials make better-informed decisions, such as how long to make an airport runway, how much resilience to include for constructing buildings or bridges, or where to put crops or culverts.”

The improved LOCA2 data set was generated by better identifying and preserving extreme weather events in the past, allowing models to more accurately reflect extremes in future simulations.

“We undertook a Herculean effort of personnel and computer time not just to produce a bunch of numbers, but to produce local projections that are relevant and useful,” Feldman said. “We do so by recognizing how heat waves and storms have occurred and will occur at the local level, and projecting those forward.”

Seasonal and regional weather predictions

The researchers participating in this study have discovered significant trends in precipitation patterns across North America, according to a new study utilizing the Localized Constructed Analogs Version 2 (LOCA2) data set. While the data varies at the local level, substantial trends were identified across the region by the end of the century.

Most notably, a significant portion of North America will experience roughly the same or fewer number of days with precipitation, the same or fewer number of days with light and medium amounts of precipitation, and a large increase in the number of days with the most extreme precipitation (the top 1 percent and 0.1 percent of storms). 

David Pierce, the lead author of the paper on extreme precipitation published in the Journal of Hydrometeorology, explains the implications: “People will be more affected by the really rare and most extreme events, because those are showing the biggest increase. The wettest day you would expect to see in five years, or 50 years, or 500 years – those extreme events are going to be substantially wetter, and that’s a really big issue, because it has implications for flooding and run-off.”

The research findings reveal that southern Canada and most of the United States will see increases in extreme precipitation days that occur primarily in winter. The wettest days of precipitation will increase by 20-30 percent, depending on the emissions scenario and the severity of the storm.

Meanwhile, Arizona, New Mexico, and northern Mexico can expect increases in extreme precipitation days that occur primarily in autumn. The wettest days of precipitation will increase by 10-30 percent, depending on the emissions scenario and storm intensity. 

Although the region becomes drier overall, the number of days with extreme precipitation events still goes up, indicating that the precipitation will often occur in larger storms.

Pierce finds the consistency of the pattern intriguing: “It’s quite interesting that you see the same kind of pattern of fewer low- and medium- precipitation days and more extreme precipitation days across pretty much the entire country.” 

He points out that understanding the changing nature of precipitation and the frequency of extreme events is valuable in two ways: “One is for building new infrastructure in the future, and one is for understanding impacts upon existing facilities already there.”

How climate change impacts global weather patterns

Climate change has far-reaching impacts on global weather patterns, both now and in the future. As greenhouse gas concentrations in the atmosphere increase, the planet’s average temperature rises, leading to significant alterations in weather patterns worldwide. Some of the most notable impacts include:

1. Temperature changes: As global temperatures rise, heatwaves and extremely hot days become more frequent and intense. These events can lead to heat stress, droughts, and an increased risk of wildfires. Moreover, warmer temperatures also contribute to more intense cold spells in some regions due to disruptions in atmospheric circulation patterns.
2. Precipitation patterns: Climate change affects precipitation patterns, causing some regions to experience more intense and frequent rainfall, while others face extended periods of drought. Heavy precipitation events are expected to increase, leading to a higher risk of flash floods, landslides, and soil erosion. Meanwhile, drought-prone areas may see more prolonged and severe dry spells, with negative consequences for agriculture, water supplies, and ecosystems.
3. Storm intensity: Warmer ocean temperatures contribute to the increased intensity of tropical storms and hurricanes. As sea surface temperatures rise, more energy is available to fuel these storms, resulting in stronger winds, heavier rainfall, and more devastating storm surges.
4. Polar amplification: Climate change has a greater impact on the polar regions, where temperatures are rising faster than the global average. This phenomenon, known as polar amplification, leads to the accelerated melting of ice sheets and glaciers, contributing to sea-level rise and potentially disrupting ocean and atmospheric circulation patterns.
5. Changes in jet streams: Jet streams are fast-moving air currents that significantly influence weather patterns. Climate change is believed to be affecting the behavior of jet streams, making them more wavy and sluggish, which can lead to more persistent and extreme weather events, such as heatwaves, cold spells, and flooding.
6. El Niño and La Niña events: Climate change may influence the frequency and intensity of El Niño and La Niña events, which are naturally occurring climate phenomena that significantly impact global weather patterns. These events can lead to severe droughts, floods, and other extreme weather conditions in various parts of the world.

In the future, if greenhouse gas emissions continue to rise unabated, these climate change-induced shifts in global weather patterns are expected to become more pronounced, posing significant challenges to ecosystems, human societies, and economies. However, by taking action to mitigate climate change and adapting to its consequences, we can reduce the severity of these impacts and build a more resilient world.

This research was funded by the Department of Defense and Department of Energy through the Strategic Environmental Research and Development Program (SERDP). The NASA High-End Computing Capability (HECC) Program provided resources supporting this work through the NASA Earth Exchange (NEX), Earth Science Division, and the NASA Advanced Supercomputing (NAS) Division at Ames Research Center.

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