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1. Sixfold Increase in Historical Northern Hemisphere Concurrent Large Heatwaves Driven by Warming and Changing Atmospheric Circulations

   https://doi.org/10.1175/JCLI-D-21-0200.1  

   ( February 2022 , Journal of Climate)

   Simultaneous heatwaves affecting multiple regions (referred to as concurrent heatwaves) pose compounding threats to various natural and societal systems, including global food chains, emergency response systems, and reinsurance industries. While anthropogenic climate change is increasing heatwave risks across most regions, the interactions between warming and circulation changes that yield concurrent heatwaves remain understudied. Here, we quantify historical (1979–2019) trends in concurrent heatwaves during the warm season [May–September (MJJAS)] across the Northern Hemisphere mid- to high latitudes. We find a significant increase of ∼46% in the mean spatial extent of concurrent heatwaves and ∼17% increase in their maximum intensity, and an approximately sixfold increase in their frequency. Using self-organizing maps, we identify large-scale circulation patterns (300 hPa) associated with specific concurrent heatwave configurations across Northern Hemisphere regions. We show that observed changes in the frequency of specific circulation patterns preferentially increase the risk of concurrent heatwaves across particular regions. Patterns linking concurrent heatwaves across eastern North America, eastern and northern Europe, parts of Asia, and the Barents and Kara Seas show the largest increases in frequency (∼5.9 additional days per decade). We also quantify the relative contributions of circulation pattern changes and warming to overall observed concurrent heatwave day frequency trends. While warming has a predominant and positive influence on increasing concurrent heatwave frequency, circulation pattern changes have a varying influence and account for up to 0.8 additional concurrent heatwave days per decade. Identifying regions with an elevated risk of concurrent heatwaves and understanding their drivers is indispensable for evaluating projected climate risks on interconnected societal systems and fostering regional preparedness in a changing climate.

   Heatwaves pose a major threat to human health, ecosystems, and human systems. Simultaneous heatwaves affecting multiple regions can exacerbate such threats. For example, multiple food-producing regions simultaneously undergoing heat-related crop damage could drive global food shortages. We assess recent changes in the occurrence of simultaneous large heatwaves. Such simultaneous heatwaves are 7 times more likely now than 40 years ago. They are also hotter and affect a larger area. Their increasing occurrence is mainly driven by warming baseline temperatures due to global heating, but changes in weather patterns contribute to disproportionate increases over parts of Europe, the eastern United States, and Asia. Better understanding the drivers of weather pattern changes is therefore important for understanding future concurrent heatwave characteristics and their impacts.

    

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2. The climate‐driven distribution and response to global change of soil‐borne pathogens in agroecosystems

   https://doi.org/10.1111/geb.13662  

   Peng, Ziheng ; Liu, Yu ; Qi, Jiejun ; Gao, Hang ; Li, Xiaomeng ; Tian, Qi ; Qian, Xun ; Wei, Gehong ; Jiao, Shuo ( March 2023 , Global Ecology and Biogeography)

   Soil‐borne pathogens severely affect crop production, but the present distribution of agricultural soil‐borne pathogens and their response to global changes are unexplored at large spatial scales. Here, we examine the nationwide‐scale distribution patterns, dominant taxa and environmental drivers of fungal soil‐borne pathogens, and their response to warming, nutrient enrichment and their interaction.

   China.

   July and August 2019.

   Fungal plant pathogens.

   Through nationwide field surveys of 711 top‐ and subsoil samples in 51 cropland locations, we investigated the distribution patterns, environmental drivers and dominant taxa of fungal plant pathogens. We then conducted a mesocosm experiment with soils collected at 40 survey locations to evaluate the response patterns of fungal pathogens to global changes, including warming, nutrient enrichment and their interaction.

   We observed that the abundance and richness of potential soil‐borne pathogens were higher in the topsoil than in the subsoil. Mean annual temperature and mean annual precipitation as the main drivers had a stronger effect on the abundance, richness and community of pathogens in the topsoil than subsoil. Two phylotypes, belonging to genusFusarium, were the dominant soil‐borne pathogens accounting for approximately one third of total abundance, and their abundances (e.g. relative and absolute abundance via quantitative polymerase chain reaction) were negatively correlated with precipitation and temperature. The mesocosm experiment simulating global changes further revealed that the abundance and richness distributions of soil pathogens predicted the direction of their response to global changes, with a positive response in pathogen‐poor soil and negative in pathogen‐rich soil. We further constructed spatial atlases of the dominant soil‐borne pathogens and their responses to global changes in agricultural fields.

   Our findings suggest that the current distribution of potential soil‐borne pathogens is regulated by climate, which could affect their future dynamics and is vital to agricultural practices for pathogen control and crop production.

    

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3. Projected Changes to Hydroclimate Seasonality in the Continental United States

   https://doi.org/10.1029/2021EF002019  

   Marvel, Kate ; Cook, Benjamin I. ; Bonfils, Céline ; Smerdon, Jason E. ; Williams, A. Park ; Liu, Haibo ( August 2021 , Earth's Future)

   Future changes to the hydrological cycle are projected in a warming world, and any shifts in drought risk may prove extremely consequential for natural and human systems. In addition to long‐term moistening, drying, or warming trends, perturbations to the annual cycle of regional hydroclimate variables may also have substantial impacts. We analyze projected changes in several hydroclimate variables across the continental United States, along with shifts in the amplitude and phase of their annual cycles. We find that even in regions where no robust change in the annual mean is expected, coherent changes to the annual cycle are projected. In particular, we identify robust regional phase shifts toward earlier arrival of peak evaporation in the northern regions, and peak runoff and total soil moisture in the western regions. Changes in the amplitude of the annual cycle of total and surface soil moisture are also projected, and reflect changes to the annual cycle in surface water supply and demand. Whether changes become detectable above the background noise of internal variability depends strongly on the future scenario considered, and significant changes to the annual cycle are largely avoided in the lowest‐forcing scenario.

    

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4. A global perspective on the climate‐driven growth synchrony of neighbouring trees

   https://doi.org/10.1111/geb.13090  

   Tejedor, Ernesto ; Serrano‐Notivoli, Roberto ; de Luis, Martin ; Saz, Miguel Angel ; Hartl, Claudia ; St. George, Scott ; Büntgen, Ulf ; Liebhold, Andrew M. ; Vuille, Mathias ; Esper, Jan ; et al ( March 2020 , Global Ecology and Biogeography)

   Previous work demonstrated the global variability of synchrony in tree growth within populations, that is, the covariance of the year‐to‐year variability in growth of individual neighbouring trees. However, there is a lack of knowledge about the causes of this variability and its trajectories through time. Here, we examine whether climate can explain variation in within‐population synchrony (WPS) across space but also through time and we develop models capable of explaining this variation. These models can be applied to the global tree cover under current and future climate change scenarios.

   Global.

   1901–2012.

   Trees.

   We estimated WPS values from a global tree‐ring width database consisting of annual growth increment measurements from multiple trees at 3,579 sites. We used generalized linear mixed effects models to infer the drivers of WPS variability and temporal trends of global WPS. We then predicted WPS values across the global extent of tree cover. Finally, we applied our model to predict future WPS based on the RCP 8.5 (2045–2065 period) emission scenario.

   Areas with the highest WPS are characterized by a combination of environments with both high mean annual temperature (>10°C) and low precipitation (<300 mm). Average WPS across all temperate forests has decreased historically and will continue to decrease. Potential implications of these patterns include changes in forest dynamics, such as higher tree growth and productivity and an increase in carbon sequestration. In contrast, the WPS of tropical forests of Central and South America will increase in the near future owing to reduced annual precipitation.

   Climate explains WPS variability in space and time. We suggest that WPS might have value as an integrative ecological measure of the level of environmental stress to which forests are subjected and therefore holds potential for diagnosing effects of global climate change on tree growth.

    

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5. Pervasive alterations to snow-dominated ecosystem functions under climate change

   https://doi.org/10.1073/pnas.2202393119  

   Wieder, William R. ; Kennedy, Daniel ; Lehner, Flavio ; Musselman, Keith N. ; Rodgers, Keith B. ; Rosenbloom, Nan ; Simpson, Isla R. ; Yamaguchi, Ryohei ( July 2022 , Proceedings of the National Academy of Sciences)

   Climate change projections consistently demonstrate that warming temperatures and dwindling seasonal snowpack will elicit cascading effects on ecosystem function and water resource availability. Despite this consensus, little is known about potential changes in the variability of ecohydrological conditions, which is also required to inform climate change adaptation and mitigation strategies. Considering potential changes in ecohydrological variability is critical to evaluating the emergence of trends, assessing the likelihood of extreme events such as floods and droughts, and identifying when tipping points may be reached that fundamentally alter ecohydrological function. Using a single-model Large Ensemble with sophisticated terrestrial ecosystem representation, we characterize projected changes in the mean state and variability of ecohydrological processes in historically snow-dominated regions of the Northern Hemisphere. Widespread snowpack reductions, earlier snowmelt timing, longer growing seasons, drier soils, and increased fire risk are projected for this century under a high-emissions scenario. In addition to these changes in the mean state, increased variability in winter snowmelt will increase growing-season water deficits and increase the stochasticity of runoff. Thus, with warming, declining snowpack loses its dependable buffering capacity so that runoff quantity and timing more closely reflect the episodic characteristics of precipitation. This results in a declining predictability of annual runoff from maximum snow water equivalent, which has critical implications for ecosystem stress and water resource management. Our results suggest that there is a strong likelihood of pervasive alterations to ecohydrological function that may be expected with climate change. 

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