The United States is no stranger to bone-chilling winter cold, despite a warming climate. A recent study has shed light on why this phenomenon persists, pointing to two specific patterns in the polar vortex – a swirling mass of cold air high in the stratosphere. These variations can steer extreme cold to different regions of the country, often contradicting broader warming trends.

Researchers from an international team, including Prof. Chaim Garfinkel (Hebrew University), Dr. Laurie Agel and Prof. Mathew Barlow (University of Massachusetts), Prof. Judah Cohen (MIT and Atmospheric and Environmental Research AER), Karl Pfeiffer (Atmospheric and Environmental Research Hampton), and Prof. Jennifer Francis (Woodwell Climate Research Center), have published their findings in Science Advances.

The study reveals that since 2015, the Northwest US has experienced more of these cold outbreaks due to a shift in stratospheric behavior tied to broader climate cycles. In contrast, other regions may experience milder winters. Understanding this relationship can improve long-range forecasting, allowing cities, power grids, and agriculture to better prepare for winter extremes – even as the climate warms overall.

“It’s not just about warming everywhere all the time,” explained the researchers. “Climate change also means more complex and sometimes counterintuitive shifts in where extreme weather shows up.”

The work was funded by a US NSF-BSF grant by Chaim Garfinkel of HUJI and Judah Cohen of AER&MIT, highlighting the importance of international collaboration in addressing global climate challenges.

The West Coast of the United States is no stranger to massive floods caused by atmospheric rivers. These powerful storms bring much-needed moisture to the region, but also pose a significant threat to communities and ecosystems. A new study has shed light on the hidden trigger behind these devastating events: wet soils that cannot absorb more water when a storm hits.

The research, published in the Journal of Hydrometeorology, analyzed over 43,000 atmospheric river storms across 122 watersheds on the West Coast between 1980 and 2023. The findings reveal that flood peaks were 2-4.5 times higher on average when soils were already wet. This means that even weaker storms can generate major floods if their precipitation meets a saturated Earth.

Lead author Mariana Webb, completing her Ph.D. at DRI and the University of Nevada, Reno, explained that flooding from any event is not just a function of storm size and magnitude but also depends on what’s happening on the land surface. The study demonstrates the key role that pre-event soil moisture can have in moderating flood events.

Interestingly, flood magnitudes do not increase linearly as soil moisture increases. There’s a critical threshold of soil moisture wetness above which you start to see much larger flows. This research also untangled the environmental conditions of regions where soil moisture has the largest influence on flooding.

In arid places like California and southwestern Oregon, storms that hit when soils are already saturated are more likely to cause floods. In contrast, in lush Washington and the interior Cascades and Sierra Nevada regions, watersheds tend to have deeper soils and snowpack, leading to a higher water storage capacity. Although soil saturation can still play a role in driving flooding in these areas, accounting for soil moisture is less valuable for flood management because soils are consistently wet or insulated by snow.

The study highlights the importance of integrating land surface conditions into impact assessments for atmospheric rivers. Webb worked with DRI ecohydrologist Christine Albano to produce the research, building on Albano’s extensive expertise studying atmospheric rivers, their risks, and their impacts on the landscape.

While soil saturation is widely recognized as a key factor in determining flood risk, Mari’s work helps to quantify the point at which this level of saturation leads to large increases in flood risk across different areas along the West Coast. Advances in weather forecasting allow us to see atmospheric rivers coming toward the coast several days before they arrive. By combining atmospheric river forecast information with knowledge of how close the soil moisture is to critical saturation levels for a given watershed, we can further improve flood early warning systems.

Increased monitoring in watersheds identified as high-risk, including real-time soil moisture observations, could significantly enhance early warning systems and flood management as atmospheric rivers become more frequent and intense. By tailoring flood risk evaluations to a specific watershed’s physical characteristics and climate, the study could improve flood-risk predictions.

The accumulation of microplastics in our environment is a growing concern. These tiny particles have been found to harm marine life, contaminate food chains, and even enter our own bodies through various pathways. However, predicting where these particles will accumulate and therefore where remediation efforts should focus has been difficult due to the many factors contributing to their dispersal and deposition.

New research from MIT shows that one key factor in determining where microparticles are likely to build up is related to the presence of biofilms. These thin, sticky biopolymer layers are shed by microorganisms and can accumulate on surfaces, including riverbeds or seashores. The study found that when these particles land on sediment infused with biofilms, they are more likely to be resuspended by flowing water and carried away.

The research involved a flow tank with a bottom lined with fine sand, sometimes mixed with biological material simulating natural biofilms. Water mixed with tiny plastic particles was pumped through the tank for three hours, and then the bed surface was photographed under ultraviolet light that caused the plastic particles to fluoresce, allowing a quantitative measurement of their concentration.

The results revealed two different phenomena affecting how much plastic accumulated on the different surfaces. Immediately around the rods simulating above-ground roots, turbulence prevented particle deposition. Additionally, as the amount of simulated biofilms in the sediment bed increased, the accumulation of particles also decreased.

The researchers concluded that the biofilms filled up the spaces between the sand grains, leaving less room for the microparticles to fit in. The particles were more exposed because they penetrated less deeply into the sand grains, making them easier to resuspend and carry away by the flowing water.

This research provides a “nice lens” to offer guidance on where to find microplastic hotspots versus not-so-hot areas. For example, in mangrove ecosystems, microplastics may accumulate preferentially in the outer edges, which tend to be sandy, while the interior zones have sediment with more biofilm. This suggests that the sandy outer regions may be potential hotspots for microplastic accumulation.

The work was supported by Shell International Exploration and Production through the MIT Energy Initiative. While other factors like turbulence or roughness of the bottom surface complicate this, it provides a framework to categorize habitats and prioritize monitoring and protection efforts.