Los Angeles is burning, and the fires’ most important connection to climate is accelerating hydroclimate pulses.
After years of severe droughts, numerous atmospheric rivers* flooded the US state of California with record levels of rain in the 2022-23 winter, leaving settlements in the mountains under snow, valleys being flooded due to rain and melting snow, triggering hundreds of landslides. . (*Water vapor currents that occur as a result of the transport of high levels of water vapor in the troposphere layer of the atmosphere.)
As reported by Popular Science Turkish, after a second extremely wet winter in the northern parts of the state, resulting in abundant grass and shrubs, 2024 brought a second record-hot summer and now a record-dry start to 2025’s rainy season. In addition, very dry vegetation was burned by a series of forest fires that caused damage over time.
These events are the latest examples of “hydroclimate pulses” — rapid transitions between heavy rain and dangerously dry weather — that are on the rise around the world, according to a paper published two days ago in Nature Reviews.
“The findings show that hydroclimate impacts are already increasing due to global warming, and further warming will bring even larger increases,” says Daniel Swain, a climate scientist in the Department of Agriculture and Natural Resources at the University of California, Los Angeles, and lead author of the paper:
“This cascade of impacts in California doubled the fire danger: first by causing much greater growth of flammable grasses and brush in the months leading up to fire season, and then by drying out that vegetation to extraordinary levels with extreme drought and heat.”
According to an international research team of climate researchers, global weather records have found that hydroclimate pulses have increased from 31 percent to 66 percent worldwide since the mid-20th century; That is, even more than the amount that climate models say should happen. Climate change means that this rate of increase is increasing. The same potentially mild climate models show that pulses would more than double if global temperatures rose 3 degrees Celsius above pre-industrial levels.
The world is currently on track to go beyond the 1.5 C limit targeted in the Paris Agreement. For the review, the researchers synthesized hundreds of previously published scientific articles and added their own analysis.
The main culprit behind these accelerating impacts and the main factor driving the “expanding atmospheric sponge” is human-induced climate change. The atmospheric sponge, the atmosphere’s ability to evaporate, absorb and release water, expands by 7 percent for every 1 degree Celsius the planet warms, researchers say.
“The problem here is that the sponge grows exponentially, like compound interest in the bank,” Swain says. “This rate of expansion increases with rising temperature.
The global consequences of hydroclimate pulses include not only floods and droughts, but also the increased danger of rapid transition between these two states; these include the growth and burning cycle of overwet, then overdrying shrubs, and landslides on oversaturated hillsides where recent fires have eliminated plants with roots that bind the soil and absorb rain. Swain says that the destructive power of these transitions accelerates when there is even a fraction of a degree of warming.
In many previous studies on climate impacts, only the precipitation part of the equation was taken into account and the increased evaporation demand was not taken into account. A thirstier atmosphere draws more water from plants and soil, worsening drought conditions beyond just missing rain.
“The expansion of the atmospheric sponge effect may offer a unifying explanation for some of the most visible, crucial, and recently accelerated effects of climate change,” says Swain. “The planet is actually warming at a linear rate, but there has been a lot of discussion about the accelerating effects of climate over the last 5 to 10 years. “This increase in hydroclimate pulses through an exponentially growing atmospheric sponge offers a potentially convincing explanation.”
This acceleration and the expected increase in rapid water cycles will have important consequences for water management.
“We can’t just look at extreme rains or extreme droughts because we need to safely manage these increasing water flows while preparing for increasingly dry interludes,” Swain says. “That’s why ‘co-management’ is an important paradigm. “It leads us to more holistic evidence about which interventions and solutions are most appropriate, rather than assessing drought and flood threats in isolation.”
In many regions, traditional management designs include slower solutions, such as diverting floodwaters so they quickly flow to the sea, or allowing rain to percolate into a groundwater table. But researchers say that taken alone, each of these options leaves cities vulnerable to the other side of climate blows.
“The hydroclimate in California is unstable,” says paper co-author John Abatzoglou, a climate scientist at the University of California – Merced. “But as we saw a few years ago, one of the driest three-year periods of the century had transitioned to once-in-a-lifetime snow cover in the spring of 2023. “Such transitions have both tested our water infrastructure systems and advanced discussions about future-proofing water security around stormwater management in an increasingly volatile hydroclimate.”
Hydroclimate pulses are expected to increase in northern Africa, the Middle East, South Asia, northern Eurasia, and tropical regions of the Pacific and Atlantic, but these transitions will also be felt in most other regions.
“Pulses of increased hydroclimate could translate into one of the more universal types of global changes on a warming Earth,” Swain says.
Although winds fueled spectacular wildfires in California this week, it was the lack of rain driven by those blows that kept Southern California through fire season.
“There is little evidence that climate change increases or decreases the scale or likelihood of wind events in Southern California,” Swain says. “However, climate change is increasing the overlap between the extremely dry vegetation conditions seen during the season and the occurrence of these wind events. “This is ultimately the underlying case connecting climate change to the wildfires in Southern California.”
In a high warming scenario, the state of California would face an increase in both the wettest and driest years and seasons by the end of the century.
“The less warming there is, the less increase we will see in hydroclimate pulses,” Swain says. “So anything that reduces the amount of warming from climate change will directly slow or reduce the increase in pulse. But we are still on track to see global warming of 2 to 3 degrees Celsius this century; Therefore, we may see a further increase in coups in the future. “This needs to be seriously taken into account in risk assessments and adaptation activities.”
The research was supported by the California Nature Conservancy and the Swedish National Science Foundation.
Source: www.cumhuriyet.com.tr
