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1. Vulnerability to Water Shortage Under Current and Future Water Supply‐Demand Conditions Across U.S. River Basins

   https://doi.org/10.1029/2021EF002278  

   Heidari, Hadi ; Arabi, Mazdak ; Warziniack, Travis ( October 2021 , Earth's Future)

   Climate change, population growth, urbanization, and interactions thereof may alter the water supply‐demand balance and lead to shifts in water shortage characteristics at different timescales. This study proposes an approach to improve the vulnerability assessments of U.S. river basins to the shortage at the interannual to decadal timescales by characterizing shifts in intensity, duration, and frequency (IDF) of water shortage events from current (1986–2015) to future (2070–2099) periods. The results indicate that under the driest future climate projection, the frequency and intensity of over‐year (D > 12 months) events at the monthly scale and decadal (D > 10 years) events at the annual scale tend to increase in the Southwest, Southern, middle Great Plain, and Great Lakes regions. Conversely, the frequency of interannual (D < 12 months) events at the monthly scale and annual (D > 1 year) and multi‐year (D > 3 years) events at the annual scale is likely to increase in the West Coast regions. Besides, river basins with a higher rate of aridification are likely to experience more frequent over‐year (D > 12 months) events, while river basins with a decrease in aridification were projected to undergo more frequent interannual (D < 12 months) events due to an increase in the variability of extreme weather anomalies within a year. The findings of this study provide new insights to understand and characterize vulnerability to water shortage under current and future water supply‐demand conditions and can inform the development of effective mitigation and/or adaptation strategies.

    

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2. The role of blocking circulation and emerging open water feedbacks on Greenland cold‐season air temperature variability over the last century

   https://doi.org/10.1002/joc.6879  

   Ballinger, Thomas J. ; Hanna, Edward ; Hall, Richard J. ; Carr, J. Rachel ; Brasher, Saber ; Osterberg, Erich C. ; Cappelen, John ; Tedesco, Marco ; Ding, Qinghua ; Mernild, Sebastian H. ( November 2020 , International Journal of Climatology)

   Substantial marine, terrestrial, and atmospheric changes have occurred over the Greenland region during the last century. Several studies have documented record‐levels of Greenland Ice Sheet (GrIS) summer melt extent during the 2000s and 2010s, but relatively little work has been carried out to assess regional climatic changes in other seasons. Here, we focus on the less studied cold‐season (i.e., autumn and winter) climate, tracing the long‐term (1873–2013) variability of Greenland's air temperatures through analyses of coastal observations and model‐derived outlet glacier series and their linkages with North Atlantic sea ice, sea surface temperature (SST), and atmospheric circulation indices. Through a statistical framework, large amounts of west and south Greenland temperature variance (up tor² ~ 50%) can be explained by the seasonally‐contemporaneous combination of the Greenland Blocking Index (GBI) and the North Atlantic Oscillation (NAO; hereafter the combination of GBI and NAO is termed GBI). Lagged and concomitant regional sea‐ice concentration (SIC) and the Atlantic Multidecadal Oscillation (AMO) seasonal indices account for small amounts of residual air temperature variance (r² < ~10%) relative to the GBI. The correlations between GBI and cold‐season temperatures are predominantly positive and statistically‐significant through time, while regional SIC conditions emerge as a significant covariate from the mid‐20th century through the conclusion of the study period. The inclusion of the cold‐season Pacific Decadal Oscillation (PDO) in multivariate analyses bolsters the air temperature variance explained by the North Atlantic regional predictors, suggesting the remote, background climate state is important to long‐term Greenland temperature variability. These findings imply that large‐scale tropospheric circulation has a strong control on surface temperature over Greenland through dynamic and thermodynamic impacts and stress the importance of understanding the evolving two‐way linkages between the North Atlantic marine and atmospheric environment in order to more accurately predict Greenland seasonal climate variability and change through the 21st century.

    

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3. Soil organic carbon stability in forests: Distinct effects of tree species identity and traits

   https://doi.org/10.1111/gcb.14548  

   Angst, Gerrit ; Mueller, Kevin E. ; Eissenstat, David M. ; Trumbore, Susan ; Freeman, Katherine H. ; Hobbie, Sarah E. ; Chorover, Jon ; Oleksyn, Jacek ; Reich, Peter B. ; Mueller, Carsten W. ( January 2019 , Global Change Biology)

   Rising atmospheric CO₂concentrations have increased interest in the potential for forest ecosystems and soils to act as carbon (C) sinks. While soil organic C contents often vary with tree species identity, little is known about if, and how, tree species influence thestabilityof C in soil. Using a 40 year old common garden experiment with replicated plots of eleven temperate tree species, we investigated relationships between soil organic matter (SOM) stability in mineral soils and 17 ecological factors (including tree tissue chemistry, magnitude of organic matter inputs to the soil and their turnover, microbial community descriptors, and soil physicochemical properties). We measured five SOM stability indices, including heterotrophic respiration, C in aggregate occluded particulate organic matter (POM) and mineral associated SOM, and bulk SOM δ¹⁵N and ∆¹⁴C. The stability of SOM varied substantially among tree species, and this variability was independent of the amount of organic C in soils. Thus, when considering forest soils as C sinks, the stability of C stocks must be considered in addition to their size. Further, our results suggest tree species regulate soil C stability via the composition of their tissues, especially roots. Stability of SOM appeared to be greater (as indicated by higher δ¹⁵N and reduced respiration) beneath species with higher concentrations of nitrogen and lower amounts of acid insoluble compounds in their roots, while SOM stability appeared to be lower (as indicated by higher respiration and lower proportions of C in aggregate occluded POM) beneath species with higher tissue calcium contents. The proportion of C in mineral associated SOM and bulk soil ∆¹⁴C, though, were negligibly dependent on tree species traits, likely reflecting an insensitivity of some SOM pools to decadal scale shifts in ecological factors. Strategies aiming to increase soil C stocks may thus focus on particulate C pools, which can more easily be manipulated and are most sensitive to climate change.

    

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4. Progress and opportunities in advancing near‐term forecasting of freshwater quality

   https://doi.org/10.1111/gcb.16590  

   Lofton, Mary E. ; Howard, Dexter W. ; Thomas, R. Quinn ; Carey, Cayelan C. ( April 2023 , Global Change Biology)

   Near‐term freshwater forecasts, defined as sub‐daily to decadal future predictions of a freshwater variable with quantified uncertainty, are urgently needed to improve water quality management as freshwater ecosystems exhibit greater variability due to global change. Shifting baselines in freshwater ecosystems due to land use and climate change prevent managers from relying on historical averages for predicting future conditions, necessitating near‐term forecasts to mitigate freshwater risks to human health and safety (e.g., flash floods, harmful algal blooms) and ecosystem services (e.g., water‐related recreation and tourism). To assess the current state of freshwater forecasting and identify opportunities for future progress, we synthesized freshwater forecasting papers published in the past 5 years. We found that freshwater forecasting is currently dominated by near‐term forecasts of waterquantityand that near‐term waterqualityforecasts are fewer in number and in the early stages of development (i.e., non‐operational) despite their potential as important preemptive decision support tools. We contend that more freshwater quality forecasts are critically needed and that near‐term water quality forecasting is poised to make substantial advances based on examples of recent progress in forecasting methodology, workflows, and end‐user engagement. For example, current water quality forecasting systems can predict water temperature, dissolved oxygen, and algal bloom/toxin events 5 days ahead with reasonable accuracy. Continued progress in freshwater quality forecasting will be greatly accelerated by adapting tools and approaches from freshwater quantity forecasting (e.g., machine learning modeling methods). In addition, future development of effective operational freshwater quality forecasts will require substantive engagement of end users throughout the forecast process, funding, and training opportunities. Looking ahead, near‐term forecasting provides a hopeful future for freshwater management in the face of increased variability and risk due to global change, and we encourage the freshwater scientific community to incorporate forecasting approaches in water quality research and management.

    

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5. Large‐scale disturbance legacies and the climate sensitivity of primary Picea abies forests

   https://doi.org/10.1111/gcb.14041  

   Schurman, Jonathan S. ; Trotsiuk, Volodymyr ; Bače, Radek ; Čada, Vojtěch ; Fraver, Shawn ; Janda, Pavel ; Kulakowski, Dominik ; Labusova, Jana ; Mikoláš, Martin ; Nagel, Thomas A. ; et al ( February 2018 , Global Change Biology)

   Determining the drivers of shifting forest disturbance rates remains a pressing global change issue. Large‐scale forest dynamics are commonly assumed to be climate driven, but appropriately scaled disturbance histories are rarely available to assess how disturbance legacies alter subsequent disturbance rates and the climate sensitivity of disturbance. We compiled multiple tree ring‐based disturbance histories from primaryPicea abiesforest fragments distributed throughout five European landscapes spanning the Bohemian Forest and the Carpathian Mountains. The regional chronology includes 11,595 tree cores, with ring dates spanning the years 1750–2000, collected from 560 inventory plots in 37 stands distributed across a 1,000 km geographic gradient, amounting to the largest disturbance chronology yet constructed in Europe. Decadal disturbance rates varied significantly through time and declined after 1920, resulting in widespread increases in canopy tree age. Approximately 75% of current canopy area recruited prior to 1900. Long‐term disturbance patterns were compared to an historical drought reconstruction, and further linked to spatial variation in stand structure and contemporary disturbance patterns derived from LANDSAT imagery. Historically, decadal Palmer drought severity index minima corresponded to higher rates of canopy removal. The severity of contemporary disturbances increased with each stand's estimated time since last major disturbance, increased with mean diameter, and declined with increasing within‐stand structural variability. Reconstructed spatial patterns suggest that high small‐scale structural variability has historically acted to reduce large‐scale susceptibility and climate sensitivity of disturbance. Reduced disturbance rates since 1920, a potential legacy of high 19th century disturbance rates, have contributed to a recent region‐wide increase in disturbance susceptibility. Increasingly common high‐severity disturbances throughout primaryPiceaforests of Central Europe should be reinterpreted in light of both legacy effects (resulting in increased susceptibility) and climate change (resulting in increased exposure to extreme events).

    

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