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Forests around the world are experiencing changes due to climate variability and human land use. How these changes interact and influence the vulnerability of forests are not well understood. In the eastern United States, well‐documented anthropogenic disturbances and land‐use decisions, such as logging and fire suppression, have influenced forest species assemblages, leading to a demographic shift from forests dominated by xeric species to those dominated by mesic species. Contemporarily, the climate has changed and is expected to continue to warm and produce higher evaporative demand, imposing stronger drought stress on forest communities. Here, we use an extensive network of tree‐ring records from common hardwood species across ~100 sites and ~1300 trees in the eastern United States to examine the magnitude of growth response to both wet and dry climate extremes. We find that growth reductions during drought exceed the positive growth response to pluvials. Mesic species such as Liriodendron tulipifera and Acer saccharum, which are becoming more dominant, are more sensitive to drought than more xeric species, such as oaks (Quercus) and hickory (Carya), especially at moderate and extreme drought intensities. Although more extreme droughts produce a larger annual growth reduction, mild droughts resulted in the largest cumulative growth decreases due to their higher frequency. When using global climate model projections, all scenarios show drought frequency increasing substantially (3–9 times more likely) by 2100. Thus, the ongoing demographic shift toward more mesic species in the eastern United States combined with drier conditions results in larger drought‐induced growth declines, suggesting that drought will have an even larger impact on aboveground carbon uptake in the future in the eastern United States. [ABSTRACT FROM AUTHOR]

Since 2013, extreme floods within the Santee River basin (North/South Carolina, USA) caused $1.5B in damage. The instrumental period, however, is too short to determine if recent extreme events are anomalous within a long‐term context. Here, we present reconstructions of storm‐, base‐, and total streamflow for the Santee River using a multi‐species tree‐ring network calibrated to flow data during the period 1923–2018. Tree‐ring data explained higher variance (r = 0.59; p < 0.01; 900–2018) of instrumental baseflow than total streamflow (r = 0.41; p < 0.01; 1500–2018) or stormflow (r = 0.26; p < 0.05; 1690–2018). Our reconstruction reveals a long‐term increase in baseflow over the past millennium. The North Atlantic subtropical high regulates baseflow in the Santee River (r = 0.45; p < 0.01). Recent high levels of baseflow may be connected to the position of the subtropical high, increasing the likelihood of flooding. Plain Language Summary: Tree rings are often used to estimate past levels of streamflow to better place modern extremes into a historical context. Streamflow has two components, baseflow (flow from groundwater) and stormflow (flow contributed from storms). Here, we use tree rings to estimate past streamflow of the Santee River, South Carolina, USA. We find that tree rings are better at representing variations in baseflow rather than stormflow. This connection to baseflow is likely because tree growth is related to long‐term changes in water supply throughout the growing season, and changes in baseflow are more likely to result in changes in annual growth. Additionally, we find that certain species are more sensitive to baseflow than others, with Taxodium distichum (bald cypress) being the most sensitive. We were able to reconstruct baseflow back 1,100 years and found that baseflows increased over this time. Higher levels of baseflow will result in larger flooding events, like the 2013 and 2019 events. The location of the western edge of a large atmospheric high pressure centered off the Atlantic Coast, the North Atlantic subtropical high, has a strong influence on baseflow levels and could explain the increasing trend in reconstructed baseflows. Key Points: Tree rings better represent baseflow compared to stormflow and total streamflowRapid 20th–21st century increases in baseflow escalate flooding susceptibility and are exceptional over the last 1,118 yearsRecent increases in baseflow are related to the position of the western flank of the North Atlantic subtropical high [ABSTRACT FROM AUTHOR]

The impacts of inland flooding caused by tropical cyclones (TCs), including loss of life, infrastructure disruption, and alteration of natural landscapes, have increased over recent decades. While these impacts are well documented, changes in TC precipitation extremes--the proximate cause of such inland flooding--have been more difficult to detect. Here, we present a latewood tree-ring-based record of seasonal (June 1 through October 15) TC precipitation sums (ΣTCP) from the region in North America that receives the most ΣTCP: coastal North and South Carolina. Our 319-y-long ΣTCP reconstruction reveals that ΣTCP extremes (≥0.95 quantile) have increased by 2 to 4 mm/decade since 1700 CE, with most of the increase occurring in the last 60 y. Consistent with the hypothesis that TCs are moving slower under anthropogenic climate change, we show that seasonal ΣTCP along the US East Coast are positively related to seasonal average TC duration and TC translation speed. [ABSTRACT FROM AUTHOR]

Other data on tree growth, stand dynamics or microclimate are necessary to infer the ecological factors that limit photosynthesis and tree growth. This scientific commentary refers to 'Paired analysis of tree ring width and carbon isotopes indicates when controls on tropical tree growth change from light to water limitations' by Brienen et al. (doi: 10.1093/treephys/tpab142). Google Scholar Crossref Search ADS WorldCat 4 Brienen R, Helle G, Pons T, Boom A, Gloor M, Groenendijk P, Clerici S, Leng M, Jones C (2022) Paired analysis of tree ring width and carbon isotopes indicates when controls on tropical tree growth change from light to water limitations. [Extracted from the article]

While forest communities are changing as a result of global environmental change, the impacts of tree species shifts on ecosystem services such as carbon storage are poorly quantified. In many parts of the eastern United States (US), more xeric‐adapted oak‐hickory dominated stands are being replaced with mesic beech‐maple assemblages. To examine the possible impacts of this ongoing change in forest composition, we investigated how two wide‐ranging and co‐occurring eastern US species – Acer saccharum (sugar maple) and Quercus alba (white oak) – respond to interannual climate variability. Using 781 tree cores from 418 individual trees at 18 locations, we found late‐growing season drought reduced A. saccharum growth more than that of Q. alba. A gradient in the growth reduction across latitude was also found in A. saccharum, where southern populations of A. saccharum experienced greater reductions in growth during drought. Drought had a legacy effect on growth for both species, with drought occurring later in the growing season having a larger legacy effect. Consequently, as forests shift from oak to maple dominance, drought in the later part of the growing season is likely to become an increasingly important control on forest productivity. Thus, our findings suggest that co‐occurring species are responding to environmental conditions during different times in the growing season and, therefore, the timing of drought conditions will play an important role in forest productivity and carbon sequestration as forest species composition changes. These findings are particularly important because the projected increases in potential evapotranspiration, combined with possible changes in the seasonality of precipitation could have a substantial impact on how tree growth responds to future climatic change. [ABSTRACT FROM AUTHOR]

Tropical cyclones (TCs) are an important source of precipitation for much of the eastern United States. However, our understanding of the spatiotemporal variability of tropical cyclone precipitation (TCP) and the connections to large-scale atmospheric circulation is limited by irregularly distributed rain gauges and short records of satellite measurements. To address this, we developed a new gridded (0.25° × 0.25°) publicly available dataset of TCP (1948–2015; Tropical Cyclone Precipitation Dataset, or TCPDat) using TC tracks to identify TCP within an existing gridded precipitation dataset. TCPDat was used to characterize total June–November TCP and percentage contribution to total June–November precipitation. TCP totals and contributions had maxima on the Louisiana, North Carolina, and Texas coasts, substantially decreasing farther inland at rates of approximately 6.2–6.7 mm km−1. Few statistically significant trends were discovered in either TCP totals or percentage contribution. TCP is positively related to an index of the position and strength of the western flank of the North Atlantic subtropical high (NASH), with the strongest correlations concentrated in the southeastern United States. Weaker inverse correlations between TCP and El Niño–Southern Oscillation are seen throughout the study site. Ultimately, spatial variations of TCP are more closely linked to variations in the NASH flank position or strength than to the ENSO index. The TCP dataset developed in this study is an important step in understanding hurricane–climate interactions and the impacts of TCs on communities, water resources, and ecosystems in the eastern United States. [ABSTRACT FROM AUTHOR]

Over recent decades, the southeastern United States (Southeast) has become increasingly well represented by the terrestrial climate proxy record. However, while the paleo proxy records capture the region's hydroclimatic history over the last several centuries, the understanding of near surface air temperature variability is confined to the comparatively shorter observational period (1895‐present). Here, we detail the application of blue intensity (BI) methods on a network of tree‐ring collections and examine their utility for producing robust paleotemperature estimates. Results indicate that maximum latewood BI (LWBI) chronologies exhibit positive and temporally stable correlations (r = 0.28–0.54, p < 0.01) with summer maximum temperatures. As such, we use a network of LWBI chronologies to reconstruct August‐September average maximum temperatures for the Southeast spanning the period 1760–2010 CE. Our work demonstrates the utility of applying novel dendrochronological techniques to improve the understanding of the multi‐centennial temperature history of the Southeast. Plain Language Summary: Tree‐ring data are important sources of paleoclimate information, which allow for the longer‐term evaluation of modern climate values and trends. Compared to much of North America, the Southeastern United States (Southeast) contains substantially fewer paleoclimate records from tree rings, and no estimates of past temperature variability which extend before the observational period. Employing a recently developed technique, which uses light reflectance properties of wood to obtain a representative metric of tree‐ring density, we develop a network of temperature‐sensitive tree‐ring records across the Southeast. These records enable us to reconstruct late summer maximum temperatures across the region spanning the period 1760–2023 CE. As few ground‐based, pre‐instrumental temperature records previously existed for this region, our reconstruction allows for an improved understanding of the region's multi‐centennial climatic history. Key Points: Maximum latewood blue intensity from tree rings can effectively be used to develop paleotemperature estimates for the southeastern USThe fidelity of tree‐ring density parameters for paleoclimate reconstruction are influenced by disturbance regimes and microsite conditionsCompared to the last 260 years, regional 20th‐century maximum late summer temperatures are not characterized by unprecedented positive trend [ABSTRACT FROM AUTHOR]

• Methods to extend reconstructions often sacrifice model accuracy in our test basin. • Basin and river size determine which reconstruction method is most appropriate. • Large-scale drought reconstructions may not reflect variability in small basins. Tree-ring reconstructions of streamflow can provide long-term perspectives of flow variability that may be useful in management strategies for water resources. Relative to other portions of the United States, there is a dearth of tree-ring based streamflow reconstructions in the Midwest. The Wabash River is an important water resource in Indiana and Illinois where many sectors rely on it. Here, to better understand the historic hydroclimate within the Wabash River Basin, we reconstructed June–September streamflow for a tributary of the Wabash River using three statistical approaches: the traditional basin approach, and the recently-developed climate-footprint, and drought-reconstruction approaches. Our reconstructions explained 53–71% of the variance for the common period (1941–1984). We find that in our three reconstructions, there are extreme droughts and pluvials that exceed those during the instrumental period, including a sustained five-decade low-flow event in the early 19th century. Overall, we find that the traditional basin approach produced the most robust model but had the shortest reconstruction length of the three approaches, as it requires the predictor chronologies to be derived from within the basin. Our results indicate that there are merits and drawbacks to each approach with the general pattern of sacrificing variance explained for reconstruction length. [ABSTRACT FROM AUTHOR]

Summary: Species‐specific responses of plant intrinsic water‐use efficiency (iWUE) to multiple environmental drivers associated with climate change, including soil moisture (θ), vapor pressure deficit (D), and atmospheric CO2 concentration (ca), are poorly understood.We assessed how the iWUE and growth of several species of deciduous trees that span a gradient of isohydric to anisohydric water‐use strategies respond to key environmental drivers (θ, D and ca). iWUE was calculated for individual tree species using leaf‐level gas exchange and tree‐ring δ13C in wood measurements, and for the whole forest using the eddy covariance method.The iWUE of the isohydric species was generally more sensitive to environmental change than the anisohydric species was, and increased significantly with rising D during the periods of water stress. At longer timescales, the influence of ca was pronounced for isohydric tulip poplar but not for others.Trees' physiological responses to changing environmental drivers can be interpreted differently depending on the observational scale. Care should be also taken in interpreting observed or modeled trends in iWUE that do not explicitly account for the influence of D. [ABSTRACT FROM AUTHOR]

Severe droughts can impart long‐lasting legacies on forest ecosystems through lagged effects that hinder tree recovery and suppress whole‐forest carbon uptake. However, the local climatic and edaphic factors that interact to affect drought legacies in temperate forests remain unknown. Here, we pair a dataset of 143 tree ring chronologies across the mesic forests of the eastern US with historical climate and local soil properties. We found legacy effects to be widespread, the magnitude of which increased markedly in diffuse porous species, sites with deep water tables, and in response to late‐season droughts (August–September). Using an ensemble of downscaled climate projections, we additionally show that our sites are projected to drastically increase in water deficit and drought frequency by the end of the century, potentially increasing the size of legacy effects by up to 65% and acting as a significant process shaping forest composition, carbon uptake and mortality. [ABSTRACT FROM AUTHOR]

The Pecos River provides an important source of water for New Mexico and Texas, US, and Mexico. Severe and prolonged drought combined with increasing temperatures during the early 21st century boosted attention on water resources and allocation management in the American West. We provide a tree-ring-based streamflow reconstruction for the Pecos River for the period 1310-2013 CE for the overarching purpose of placing the current Pecos River streamflow declines in a multi-century context. Over the past ca. 700 years, dry events (n = 93) that lasted at least 2 years were more common than wet events (n = 76), wherein flow was below/above the instrumental mean (61.6 m3 s−1). Although more prolonged droughts occurred during the 15th and 18th centuries, the gage record (1930-2013 CE) captures the full range and variability of flow extremes within the context of the past 700 years. The 11-year drought of 1772-1782 was the highest ranked based on magnitude + intensity below the instrumental mean, slightly edging out the 1415-1425 and 1950-1957 events. The driest events that have occurred from the 14th through the 20th centuries are challenged by flow conditions since the turn of the 21st century. The 2000-2006 and 2011-2013 dry periods ranked 6th and 13th, respectively, though the intensity (-40 m3 s−1 yr−1) of the 2011-2013 event exceeded all higher ranked droughts. The lowest single water-year flow in the reconstruction was shared by years 1904 and 2002, during which the flow of the Pecos River was estimated at 8.1 m3 s−1. Other extreme low-flow years were 1685 (9.5 m3 s−1) and 1579 (9.8 m3 s−1), but are eclipsed by 1904 and 2002 when considering the lower bounds of bootstrapped confidence limits of the reconstruction. Increased flow variability combined with projected increased temperatures and decreased precipitation will likely present new challenges to water resource managers, especially given impending anthropogenic climate change. [ABSTRACT FROM AUTHOR]

• Quercus alba is more sensitive to water availability than Quercus rubra. • Pluvial growth increases do not offset drought growth reductions in either species. • Site-level variation exceeds species-level for drought and pluvial responses. Quercus is one of the most important genera of plants in North America, but is currently undergoing a decrease in abundance and dominance of North American forest ecosystems. Of the two most common North American Quercus species, eastern white oak (Quercus alba) has experienced a slightly greater decline in dominance compared to northern red oak (Quercus rubra). Changes in Quercus demographics are likely due to multiple factors, but also highlight the importance of understanding the growth-climate relationships of these species under shifting climatic regimes. Therefore, we developed a network of tree-ring chronologies and stomatal conductance measurements where Q. alba and Q. rubra co-occur that spans the longitudinal extent of both species' geographic ranges. We compared growth reductions due to drought conditions, and growth increases due to pluvial conditions, of both species. The drought response (by reductions in radial growth and stomatal conductance) of Q. alba was consistently greater than Q. rubra irrespective of temporal or spatial drought dynamics. Similarly, the pluvial response (relative increase in growth) of Q. alba was greater than Q. rubra. We also found that both species exhibit nonlinear relationships to water availability, where increases in growth during pluvial conditions are less than the decreases in growth due to drought conditions. Thus, we concluded that Q. alba is moderately more sensitive to water availability than Q. rubra , which provides new insight for Quercus isohydricity classification, and may indicate different sensitivities to a changing precipitation regime in North America. [ABSTRACT FROM AUTHOR]

Abstract: The synoptic processes that end droughts are poorly understood, yet have significant climatological implications. Here we examined the spatiotemporal patterns of rapid drought cessation (RDC) in the southeastern United States during the1979–2013 warm season (April–November) for three storm types: Frontal, Tropical, and Air mass. We defined RDC as a 1 month shift in soil moisture sufficient to alleviate an existing drought. We found that 73% of all warm‐season droughts were ended by RDC events and the three storm‐type groups ended droughts over similar spatial areas. Frontal storms were the most frequent mechanism for RDC events, yet their occurrences significantly decreased and were negatively related to increases in Northern Hemisphere air temperatures. Projected future warming in the Northern Hemisphere suggests a continued decline in the frequency and relative contribution of Frontal storms as RDC events, potentially influencing the timing and spatial scale of drought cessation in the southeastern U.S. [ABSTRACT FROM AUTHOR]

Understanding the long-term natural flow regime of rivers enables resource managers to more accurately model water level variability. Models for managing water resources are important in Florida where population increase is escalating demand on water resources and infrastructure. The Suwannee River is the second largest river system in Florida and the least impacted by anthropogenic disturbance. We used new and existing tree-ring chronologies from multiple species to reconstruct mean March–October discharge for the Suwannee River during the period 1550–2005 CE and place the short period of instrumental flows (since 1927 CE) into historical context. We used a nested principal components regression method to maximize the use of chronologies with varying time coverage in the network. Modeled streamflow estimates indicated that instrumental period flow conditions do not adequately capture the full range of Suwannee River flow variability beyond the observational period. Although extreme dry and wet events occurred in the gage record, pluvials and droughts that eclipse the intensity and duration of instrumental events occurred during the 16–19th centuries. The most prolonged and severe dry conditions during the past 450 years occurred during the 1560s CE. In this prolonged drought period mean flow was estimated at 17% of the mean instrumental period flow. Significant peaks in spectral density at 2–7, 10, 45, and 85-year periodicities indicated the important influence of coupled oceanic-atmospheric processes on Suwannee River streamflow over the past four centuries, though the strength of these periodicities varied over time. Future water planning based on current flow expectations could prove devastating to natural and human systems if a prolonged and severe drought mirroring the 16th and 18th century events occurred. Future work in the region will focus on updating existing tree-ring chronologies and developing new collections from moisture-sensitive sites to improve understandings of past hydroclimate in the region. [ABSTRACT FROM AUTHOR]

We examined the spatial distribution of monthly, seasonal, and annual changes in comfortable weather hours (CWHs) between 1950 and 2011 and explored the relationship between human wellness and the amount and timing of CWHs. Using a thermohygrometric index based on air temperature and dewpoint temperature recorded every three hours from thirty-five U.S. cities, we determined whether changes in human thermal comfort were coincident with warming and more humid atmospheric conditions. We tested for significant trends in CWHs for every season for each city for nighttime, daytime, and total (i.e., night and day) periods. Although approximately 75 percent of the cities did not experience significant changes in CWHs on an annual basis, total changes in CWHs were marked by increases during spring and decreases in summer conditions, with the largest positive changes in CWHs found during spring nights, spring days, and autumn nights and the largest negative changes during summer nights and days. Spatially, increases in CWHs were principally located west of 117°W and decreases in cities east of 81°W. Significant relationships existed between wellness metrics and seasonal and annual CWHs. Greater CWHs during the summer were positively correlated with happiness and well-being and negatively correlated with obesity. These results suggest that further declines in summer CWHs for cities might affect human wellness, as peak optimal weather conditions shift toward spring and autumn months. [ABSTRACT FROM AUTHOR]

ABSTRACT Tree-ring-based climate reconstructions are typically derived from either (1) a single species from one or multiple locations or (2) multiple species from multiple locations. Here, we investigate the ability of using multiple co-occurring canopy-dominant species from a single location for climate reconstructions based in the eastern United States. Using a variety of techniques, we first compare the climate signals of three canopy-dominant species ( Quercus rubra, Quercus alba, Liriodendron tulipifera) at an old-growth forest in southern Indiana. We then determine if a composite time series of these co-occurring species increases or decreases the reconstruction model skill. Climate-growth correlation analysis of the species reveals strong and consistent relationships with summer [June-August (JJA)] Palmer Drought Severity Index ( PDSI) during the period 1895-2012. We first use a split-sample reconstruction technique to compare the performance of species reconstruction models. We then use a nested technique to build a composite chronology against which to compare the individual species chronologies. The composite chronology of all three species accounts for up to 38% of the mean variation in JJA PDSI, and verification statistics indicate robust statistical skill from 1870 to 2012. The composite chronology reconstruction also outperforms each individual species model, indicating that using multiple co-occurring species increases reconstruction skill, at least from a single study site. Furthermore, model performance is improved by using nested reconstruction techniques, and implicates the potential ability to use multiple co-occurring species across multiple locations in the eastern United States. [ABSTRACT FROM AUTHOR]

Tree-ring-based climate reconstructions are typically derived from either (1) a single species from one or multiple locations or (2) multiple species from multiple locations. Here, we investigate the ability of using multiple co-occurring canopy-dominant species from a single location for climate reconstructions based in the eastern United States. Using a variety of techniques, we first compare the climate signals of three canopy-dominant species (Quercus rubra, Quercus alba, Liriodendron tulipifera) at an old-growth forest in southern Indiana. We then determine if a composite time series of these co-occurring species increases or decreases the reconstruction model skill. Climate-growth correlation analysis of the species reveals strong and consistent relationships with summer [June-August (JJA)] Palmer Drought Severity Index (PDSI) during the period 1895-2012. We first use a split-sample reconstruction technique to compare the performance of species reconstruction models. We then use a nested technique to build a composite chronology against which to compare the individual species chronologies. The composite chronology of all three species accounts for up to 38% of the mean variation in JJA PDSI, and verification statistics indicate robust statistical skill from 1870 to 2012. The composite chronology reconstruction also outperforms each individual species model, indicating that using multiple co-occurring species increases reconstruction skill, at least from a single study site. Furthermore, model performance is improved by using nested reconstruction techniques, and implicates the potential ability to use multiple co-occurring species across multiple locations in the eastern United States. [ABSTRACT FROM AUTHOR]

The longleaf pine (Pinus palustris Mill.) and related ecosystem is an icon of the southeastern United States (US). Once covering an estimated 37 million ha from Texas to Florida to Virginia, the near-extirpation of, and subsequent restoration efforts for, the species has been well-documented over the past ca. 100 years. Although longleaf pine is one of the longest-lived tree species in the southeastern US—with documented ages of over 400 years—its use has not been reviewed in the field of dendrochronology. In this paper, we review the utility of longleaf pine tree-ring data within the applications of four primary, topical research areas: climatology and paleoclimate reconstruction, fire history, ecology, and archeology/cultural studies. Further, we highlight knowledge gaps in these topical areas, for which we introduce the Longleaf Tree-Ring Network (LTRN). The overarching purpose of the LTRN is to coalesce partners and data to expand the scientific use of longleaf pine tree-ring data across the southeastern US. As a first example of LTRN analytics, we show that the development of seasonwood chronologies (earlywood width, latewood width, and total width) enhances the utility of longleaf pine tree-ring data, indicating the value of these seasonwood metrics for future studies. We find that at 21 sites distributed across the species' range, latewood width chronologies outperform both their earlywood and total width counterparts in mean correlation coefficient (RBAR = 0.55, 0.46, 0.52, respectively). Strategic plans for increasing the utility of longleaf pine dendrochronology in the southeastern US include [1] saving remnant material (e.g., stumps, logs, and building construction timbers) from decay, extraction, and fire consumption to help extend tree-ring records, and [2] developing new chronologies in LTRN spatial gaps to facilitate broad-scale analyses of longleaf pine ecosystems within the context of the topical groups presented. [ABSTRACT FROM AUTHOR]

Droughts and landfalling tropical cyclones (TCs; tropical depressions, tropical storms, and hurricanes) are important features of the hydroclimate of the southeastern USA at seasonal, interannual, and interdecadal scales. The societal impacts and climatological aspects of both droughts and Atlantic TCs have been widely addressed in the scientific literature. However, in general, previous research has assessed the two phenomena separately. Recently, the spatiotemporal patterns and hydroclimatic impacts of drought amelioration by landfalling TCs have been analyzed for the southeastern USA, as well as the large-scale dynamic forcing mechanisms that enhance or suppress drought-TC co-occurrence. At multidecadal time scales, both droughts and TCs in this region vary in association with several leading modes of basin-wide and regional climate variability. These climate modes appear to be coherently linked to a background oceanic-atmospheric pattern that either promotes or suppresses the likelihood of both droughts and TC landfalls. The relative frequency of TC landfalls in drought-stricken areas, the importance of these events in the regional moisture budget, and the potential for future changes in the large-scale forcing environment raise fundamental questions about possible changes in the hydroclimate of the southeastern USA, where population growth and rising water demand already place strain on freshwater resources. In this article, we provide a review and synthesis of the recent research on variability in drought, landfalling TCs, the characteristics of the space-time association between these two phenomena in the southeastern USA, and the coherent large-scale oceanic-atmospheric environment that either promotes or suppresses their co-occurrence. Further, we review Global Climate Model projections related to these factors, and we identify avenues for future research on this important topic. [ABSTRACT FROM AUTHOR]

Precipitation from land-falling tropical cyclones (TCs) has a significant hydroclimatic influence in the southeastern United States, particularly during drought years. The frequency with which TCs ended drought conditions was examined for southeastern coastal states from Texas to North Carolina during 1895-2011. The region was divided into the Gulf Coast states (GCS) and the southeastern Atlantic coast states (ACS). The spatiotemporal patterns of tropical cyclone drought busters (TCDBs) were analyzed. Larger-scale ocean-atmosphere influences on TCDBs were examined using chi-squared analysis. The ACS experienced TCDBs more frequently and farther inland compared to the GCS. The number of TCDBs has significantly increased with time in the ACS. TCDBs numbers in the GCS did not exhibit significant increases, but the area alleviated of drought conditions increased significantly in the last 117 years. The dominant larger-scale ocean-atmosphere forcing of TCDBs was a combination of a warm Atlantic Ocean [positive Atlantic multidecadal oscillation index (AMO+)] and weak westerlies [negative North Atlantic Oscillation index (NAO−)]. AMO+ leads to an increase in the number of TCs throughout the North Atlantic basin, and NAO− increases the likelihood of TC landfall by controlling the steering of TCs toward the southeastern United States. [ABSTRACT FROM AUTHOR]

Abstract: We reconstructed tupelo honey yield-per-hive from AD 1800 to 2010 using tree-ring data from the long-lived nectar-source species, Nyssa ogeche. The composite N. ogeche radial growth chronology and honey yield-per-hive were significantly correlated (r =0.556; α =0.009; n =21), suggesting optimal growth conditions are coincident with increased nectar production and that tree-ring data can be used to reconstruct crop history. Tupelo honey yield-per-hive has oscillated between multidecadal-length periods of low and high yields during the past 211 years and is associated with the Atlantic Multidecadal Oscillation (AMO). The expansion of the honey record suggests that the current decline is within the natural range of variability prior to record-keeping. Multidecadal-length variations in tupelo honey yield illustrate how naturally occurring climatic cycles affect crop productivity beyond the length of high-quality agricultural yield records and may offer additional information to better understand interactions between oceanic and atmospheric climate drivers, non-climatic anthropogenic impacts, and yield variability. [Copyright &y& Elsevier]

Abstract: The McDonald Farm (also called the Anderson-Doosing Farm) in Catawba Valley, Virginia dates to 1789 and is registered with the National Register of Historic Places maintained by the National Park Service. According to written accounts, oral histories, and architectural analyses, the construction of four structures (a collapsed cabin, a standing cabin, a barn, and a smokehouse) at the farm likely occurred in the early to mid-19th century. To verify and refine the construction dates of the four structures, we absolutely dated the tree rings in logs used in their construction by comparing their ring patterns with a composite reference tree-ring chronology created from four regional locations. We used established graphical and statistical techniques used in dendrochronology to ensure that all tree rings were dated absolutely with 99.99% certainty. We found cutting dates for the collapsed cabin ranged from 1809 to 1810, making the likely builder Samuel Myers and not Joseph Anderson, who is currently given credit for its construction. The logs in the barn had cutting dates ranging from 1830 to 1831, confirming the 1830 construction date estimated by the historical documents and confirming the builder was Joseph Anderson. The logs from the standing cabin and smokehouse had cutting dates ranging from 1838 to 1840, refining the “mid-19th century construction” listed in the register nomination. Furthermore, the nomination gave credit of the construction of these latter two structures also to Joseph Anderson, but the builder was actually John Gish who owned the farm from 1837 to 1845. Our study demonstrates the benefit and reliability of using dendrochronology to verify and refine construction dates and ownership histories of historic structures in the Southeastern U.S. [Copyright &y& Elsevier]

Abstract: Tupelo honey is derived from the nectar of Ogeechee tupelo (Nyssa ogeche) trees growing in northwest Florida and southern Georgia. Here we use N. ogeche tree rings to reconstruct honey yield to place the current decline since the mid-1980s in a historical context and identify the climatic and hydrologic conditions conducive to optimal honey yields. We sampled two sites on the banks of the Apalachicola River using standard dendrochronological methods and developed a master chronology from 1850 to 2009. A two-staged process was used for the reconstruction of honey yield and we used Monte Carlo analysis to examine the natural range of variability. The reconstruction passed all validation tests and extended the honey record 140 years. We found that the current decline is severe, containing the two lowest-yield years (1997 and 2007) of the extended record. However, a longer duration low-yield period occurred from 1877 to 1898. The relationship between N. ogeche radial growth and July river flow has shifted suggesting that environmental changes may be responsible for the decline in tupelo honey yield. Our results demonstrate the utility of employing tree-rings to extend crop records to allow a broader understanding of yield variations inherent in agriculture. [Copyright &y& Elsevier]

The possible impacts of climatic change on post industrial population patterns in the United States have been largely ignored. In this study, we examined population change in six rural counties of three different regions in the United States. In addition to determining the role of traditional variables known to influence population change, we also examined the potential influence of drought as measured by the Cook et al. (2004) study. We used correlation and regression analysis to determine the driving forces behind population change in each case study county. The traditional variables accounted for the majority of population change. While drought explained a small percentage of the variance in population change, it was significant in three out of the six counties and in each region we examined. Spatially, with the exception of the climatic variables, counties within the same region tended to have similar driving forces for population change. [ABSTRACT FROM AUTHOR]

Vapour pressure deficit (VPD) is a critical measure of the atmospheric demand for water and can be used to assess short‐term and seasonal drought. To provide for probabilistic comparisons of VPD across space and time, we develop a Standardized Vapor Pressure Deficit Index (SVPDI). Similar to the way that other standardised drought indices are used, SVPDI allows for the analysis and comparison of changes in VPD across regions with different base level VPD values. It also should be useful for analysing impacts on vegetation that has varying levels of adaptation to high VPD. We use 1‐, 3‐, 6‐ and 12‐month timescales for the development of SVPDI and show that the gamma distribution is superior to other zero‐limited probability distributions for analysing VPD and, therefore, for calculating SVPDI. Then, focusing on the short‐term variations at the 1‐ and 3‐month timescales, we show how SVPDI has changed globally from 1958 to 2023 and how those changes differ from those of the commonly used Standardized Precipitation Evaporation Index (SPEI). We find that SVPDI shows more widespread drying conditions that also are larger in magnitude compared to those of SPEI. Although the two indices are moderately well correlated across the terrestrial surface, we discover that they are more decoupled in humid and arid regions compared to dry sub‐humid and semi‐arid regions. Using four locations that have recently experienced severe drought, we find that SVPDI generally showed longer drought duration and more severe drought events in the last decade when compared to SPEI. [ABSTRACT FROM AUTHOR]

Bias correction, while widely used with climate‐model output, is not typically applied to paleoclimatic reconstructions. While many reconstruction models have low average error, they still may contain bias, especially in the tails of distributions. Bias correction, used cautiously, can be a valuable procedure that alters interpretations of past events. Analyzing the iconic tree‐ring reconstruction of Upper Colorado River flow, we find that its probability distribution is markedly different from that of observed flow. Using quantile mapping to bias correct the reconstruction, we analyze the full reconstructed record and two events in particular: the 1100s megadrought and the early 1600s pluvial. Overall, bias correction made the 1100s megadrought, the largest in the 1,200+year record, even more extreme. After bias correction, the early 1600s pluvial marginally exceeds the early twentieth century pluvial in magnitude but not in duration. Overall, bias correction should be considered whenever paleoclimatic reconstructions are compared directly to observations. Plain Language Summary: To study past climates, scientists use indicators such as tree‐ring widths that are related to temperature, precipitation, or streamflow. While these indicators usually are very reliable, they sometimes do not perform as well with extreme events such as intense droughts and wet periods. Here, we adopt a method that can correct for these limitations and apply it to a 1,200+year record of streamflow for the Upper Colorado River, a critical source of water for much of the southwestern United States. After using our method, we find that several extreme events from the tree‐ring record of streamflow were even more intense than formerly thought. In particular, the largest drought in the record that occurred during the 1100s was drier and longer lasting after our correction. During the 56‐year duration of the 1100s drought, our correction makes the flow in the river lower by nearly 52 × 109 m3 of water, which is the equivalent of 1.45 times the capacity of Lake Mead (the largest reservoir in the United States). And, while it was known that the early 1900s was among the wettest periods in the last 1,200+ years, we identify a period in the early 1600s that matches it. Key Points: Bias correction makes paleoclimatic models more comparable to observationsAfter bias correction, the 1100s Colorado River megadrought became more extremeThe early 1600s Colorado River pluvial rivals that of the early twentieth century after bias correction [ABSTRACT FROM AUTHOR]

Summer temperatures across eastern North America (hereafter East) will soon reach a level consistently above any observation experienced during the instrumental period. Increasing temperatures will have negative impacts on natural (e.g., water, plant and animal communities) and human (e.g., health, infrastructure, economies) systems upon which the large and growing centres of human population across the region depend. Within the network of Northern Hemisphere tree‐ring temperature proxy records, one of the most obvious geographic holes is the East, where few temperature‐sensitive proxies exist. Here we present the first steps towards building a network of temperature‐sensitive proxy records across the East using blue light intensity (BI) methods applied to the tree rings of multiple temperature sensitive tree species situated from North Carolina to Maine, USA. Our overall objective is to report on the most viable species for BI analysis across different regions of the East (e.g., Southeast US, Midwest US, Northeast US/Canadian Maritimes) by exploring temporal (e.g., since ca. 1900) and spatial relationships between instrumental temperatures and BI metrics. We found BI to be a strong predictor of March–October mean air temperature (R2 = 0.61) across the Northeast US/eastern Canada, and Sep‐Oct maximum air temperature (R2 = 0.42) across the Southeast US. Of all species tested, Tsuga canadensis and Picea rubens contained the strongest BI temperature signal. Adding more BI sites from these and potentially other species, as well as inclusion of other temperature proxies (e.g., ring widths) will allow for the development of a skilful broad‐scale and long‐term temperature field reconstruction across the East. [ABSTRACT FROM AUTHOR]

Latewood ring widths of longleaf pine (Pinus palustris Mill.) are effective recorders of annual variability of tropical cyclone (TC) precipitation (TCP), accounting for approximately half of the explained variance. Based on a regional chronology comprised of data from five sites in coastal North Carolina, we reconstructed TCP during 1750–2015 to examine temporal variability of multidecadal dry and wet TCP regimes, the synoptic controls that contributed to an exceptionally dry phase in 1843–1876, and the effectiveness of using latewood to identify droughts independent of TCP. We found six phases of alternating dry/wet phases occurred during the 250+ years in the reconstruction (duration range = 17–62 years) and the 1843–1876 period of exceptionally narrow latewood widths and low TCP values (i.e., the Great Suppression) was unique during the past quarter millennium. The Great Suppression coincided with a period of anomalously low pressure (relative mean hPa deviation = −60 DAM) over the eastern USA at 500 hPa heights, which strongly affects the steering of TCs. We found that while each dry phase was characterized by a persistence of these steering lows, including the most recent (2006–2016) period absent of major landfalling TCs in the United States, the Great Suppression was unmatched in intensity. Finally, we determined that variability in longleaf pine latewood widths do not reflect overall soil‐moisture conditions, as neither narrow nor wide latewood widths are coincident with variations in non‐TC‐related precipitation. Rather, latewood growth flushes are associated with ephemeral periods of elevated water tables following high‐intensity TC‐related rainfall events. [ABSTRACT FROM AUTHOR]

We provide a 2,508‐year reconstruction (492 BCE–2015 CE) of hydroclimate variability for west‐central New Mexico using the long‐lived conifer Rocky Mountain juniper (Juniperus scopulorum Sarg.). The reconstruction model explains 53% of the instrumental soil moisture variance and all validation statistics indicate a skillful record. More hydroclimate flips (extreme wet‐dry, vice versa) occur during the 20th–21st century than any other century in the past 2,500 years. Yet, drought and pluvial events captured during the instrumental period (since ca. 1900) do not represent the full range and variability of historical conditions. Since ca. 500 BCE, over 50 drought events have surpassed the severity of recent 21st century conditions, including the first documentation of a prolonged and severe drought during the second to third century BCE (Pre‐Ancestral Puebloan). Continued extreme hydroclimate variability (e.g., flips) in the 21st century could create infrastructure challenges for regional water planning authorities in this arid region. Key Points: Over the past 2,500 years, over 50 drought events surpass the severity of the recent 21st century droughts20th to 21st century had more extreme hydroclimate flips than any other periodDocument previously unknown prolonged and severe drought during the second to third century BCE (Pre‐Ancestral Puebloan) [ABSTRACT FROM AUTHOR]

Atmospheric mineral aerosols include multiple, interrelated processes and feedbacks within the context of land-atmosphere interactions and thus are poorly understood. As the largest dust source in the world, North Africa supplies mineral dust aerosols each year to the Caribbean region and southeastern United States that alter cloud processes, ocean productivity, soil development, and the radiation budget. This study uses a suite of Earth Observation and ground-based analyses to reveal a potential novel effect of atmospheric aerosols on Pinus elliottii var. densa cambial growth during the 2010 CE growing season from the Florida Keys. Over the Florida Keys region, the Earth Observation products captured increased aerosol optical thickness with a clear geographical connection to mineral dust aerosols transported from northern Africa. The MODIS Terra and Aqua products corroborated increased Ozone Monitoring Instrument (OMI) aerosol optical thickness values. Anomalously high Aerosol Robotic Network aerosol optical depth data corresponding with low Ångstrom coefficients confirm the presence of transported mineral dust aerosols during the period circa 4-20 July 2010. The fraction of photosynthetically absorbed radiation over the region during July 2010 experienced an anomalous decrease, concurrent with reduced incoming total and direct solar radiation resulting in a reduced growth response in P. elliottii. The authors pose one of the primary mechanisms responsible for triggering growth anomalies in P. elliottii is the reduction of total photosynthetically active radiation due to a dust-derived increase in aerosol optical depth. As a rare long-lived conifer (300+ years) in a subtropical location, P. elliottii could represent a novel proxy with which to reconstruct annual or seasonal mineral dust aerosol fluxes over the Caribbean region. [ABSTRACT FROM AUTHOR]

Uncertainties surrounding tree carbon allocation to growth are a major limitation to projections of forest carbon sequestration and response to climate change. The prevalence and extent to which carbon assimilation (source) or cambial activity (sink) mediate wood production are fundamentally important and remain elusive. We quantified source-sink relations across biomes by combining eddy-covariance gross primary production with extensive on-site and regional tree ring observations. We found widespread temporal decoupling between carbon assimilation and tree growth, underpinned by contrasting climatic sensitivities of these two processes. Substantial differences in assimilation-growth decoupling between angiosperms and gymnosperms were determined, as well as stronger decoupling with canopy closure, aridity, and decreasing temperatures. Our results reveal pervasive sink control over tree growth that is likely to be increasingly prominent under global climate change. [ABSTRACT FROM AUTHOR]

From the 344 state climate divisions in the conterminous United States, nine distinct regions of warm-season drought variability are identified using principal component analysis. The drought metric used is the Palmer hydrological drought index for the period 1895--2008. The focus of this paper is multidecadal drought variability in the Southeast (SEUS) and eastern Gulf South (EGS) regions of the United States, areas in which the low-frequency forcing mechanisms of warm-season drought are still poorly understood. Low-frequency drought variability in the SEUS and EGS is associated with smoothed indexed time series of major ocean--atmosphere circulation features, including two indices of spatiotemporal variability in the North Atlantic subtropical anticyclone (Bermuda high). Long-term warm-season drought conditions are significantly out of phase between the two regions. Multidecadal regimes of above- and below-average moisture in the SEUS and EGS are closely associated with slow variability in sea surface temperatures in the North Atlantic Ocean and with the summer mean position and mean strength of the Bermuda high. Multivariate linear regression indicates that 82%%--92%% of the low-frequency variability in warm-season moisture is explained by two of the three leading principal components of low-frequency variability in the climate indices. The findings are important for water resource managers and water-intensive industries in the SEUS and EGS. The associations identified in the paper are valuable for enhanced drought preparedness and forecasting in the study area and potentially for global models of coupled ocean--atmosphere variability. [ABSTRACT FROM AUTHOR]

Regional reconstructions of air temperature over the past millennium provide critical context for ongoing climate change, but they are temporally limited in the recent period or absent for many parts of the world. We demonstrate the use of latewood blue intensity (LWB) to reconstruct current-year growing (warm) season maximum temperatures (T max) in the low-to-mid latitudes (30°-50°N) of western North America. We present a new tree ring network comprised of 26 LWB chronologies developed from living, high-elevation Engelmann spruce (Picea engelmannii Parry ex Engelm.) sampled across the western United States. The LWB parameter shows strong, positive (r = 0.65–0.73), and temporally-stable correlations with growing season T max. From this network we present 4 regional T max reconstructions, which characterize regional temperature histories across western North America from northern Mexico to southern British Columbia over the past 4 centuries. Our comparison of these 4 temperature reconstructions highlights the spatial patterns of regional temperature trends throughout time. These reconstructions provide important updates and increased data point density to the tree ring temperature proxy network of the Northern Hemisphere. We highlight the use of blue intensity methods at both low- and mid-latitude upper tree line locations to increase the presence of strongly temperature-sensitive records at increasingly lower latitudes of the Northern Hemisphere. • Latewood blue intensity from tree rings is a robust predictor of summer temperatures in the mid-latitudes of North America. • Blue intensity can be used to improve the spatial and temporal coverage of Northern Hemispheric temperature proxy records. • Although sub-regional variability exists over the last few centuries, all records track the recent 20th century warming. • All records indicate that the recent warming trend is highly anomalous in the context of the last several centuries. Increased data point density to the tree ring temperature proxy network of the Northern Hemisphere. We highlight the use of blue intensity methods at both low- and mid-latitude upper tree line locations to increase the presence of strongly temperature-sensitive records at increasingly lower latitudes of the Northern Hemisphere. [ABSTRACT FROM AUTHOR]

Severe drought can cause lagged effects on tree physiology that negatively impact forest functioning for years. These "drought legacy effects" have been widely documented in tree‐ring records and could have important implications for our understanding of broader scale forest carbon cycling. However, legacy effects in tree‐ring increments may be decoupled from ecosystem fluxes due to (a) postdrought alterations in carbon allocation patterns; (b) temporal asynchrony between radial growth and carbon uptake; and (c) dendrochronological sampling biases. In order to link legacy effects from tree rings to whole forests, we leveraged a rich dataset from a Midwestern US forest that was severely impacted by a drought in 2012. At this site, we compiled tree‐ring records, leaf‐level gas exchange, eddy flux measurements, dendrometer band data, and satellite remote sensing estimates of greenness and leaf area before, during, and after the 2012 drought. After accounting for the relative abundance of tree species in the stand, we estimate that legacy effects led to ~10% reductions in tree‐ring width increments in the year following the severe drought. Despite this stand‐scale reduction in radial growth, we found that leaf‐level photosynthesis, gross primary productivity (GPP), and vegetation greenness were not suppressed in the year following the 2012 drought. Neither temporal asynchrony between radial growth and carbon uptake nor sampling biases could explain our observations of legacy effects in tree rings but not in GPP. Instead, elevated leaf‐level photosynthesis co‐occurred with reduced leaf area in early 2013, indicating that resources may have been allocated away from radial growth in conjunction with postdrought upregulation of photosynthesis and repair of canopy damage. Collectively, our results indicate that tree‐ring legacy effects were not observed in other canopy processes, and that postdrought canopy allocation could be an important mechanism that decouples tree‐ring signals from GPP. [ABSTRACT FROM AUTHOR]

Calculating the Palmer Drought Severity Index (PDSI) using the Thornthwaite potential evapotranspiration (PET) method has come under recent scrutiny for overestimating drought conditions when air temperatures exceed the historical baseline. With increasing air temperatures around the world, calculating the PDSI using the Thornthwaite PET method may no longer be the appropriate option. Therefore, various researchers have called for the use of the physically-based Penman–Monteith PET method to estimate PDSI. We present an addition to the PDSI tool developed by Jacobi et al. (2013) that includes an option to use the Penman–Monteith method to calculate PET as an input to the PDSI calculations. Comparisons with a global PDSI dataset also estimated using the Penman–Monteith method indicate good spatial correlation. This addition to the Jacobi et al. (2013) tool allows users to easily calculate a suite of Palmer drought indices using Penman–Monteith potential evapotranspiration for current and future drought projections at any spatial scale. [ABSTRACT FROM AUTHOR]

• Tree growth (via tree-ring widths) is much more sensitive to drought than annual whole-forest carbon uptake. • Likewise, tree growth takes longer to recovery from drought (a 'drought legacy effect'). • This decoupling between growth and carbon uptake may impact the forest carbon cycle through reductions in turnover time. The ability of forests to withstand, and recover from, acute drought stress is a critical uncertainty regarding the impacts of climate change on the terrestrial carbon (C) cycle, but it is unclear how drought responses scale from individual trees to whole forests. Here, we assembled a dataset of tree-ring chronologies co-located within the footprint of eddy covariance towers across North America and Europe, with the aim of quantifying the sensitivity of tree radial growth versus gross primary productivity (GPP) during and following drought. We found that drought induced a large decoupling across C cycle processes, whereby GPP was relatively resistant to water stress despite large reductions in tree-ring widths. This decoupling also occurred in the year following drought (i.e., a 'drought legacy effect'), and was similar in magnitude in response to both summer and winter droughts. By modeling whole-forest C turnover time, we show that a radial growth-GPP decoupling has important ramifications for the forest C cycle, especially if the C not used to support radial growth is instead allocated towards pools with short residence times. Our results demonstrate that quantifications of drought impacts that rely solely on C uptake are missing this fundamental pathway through which drought alters the forest C cycle and the resulting feedbacks to the climate system. [ABSTRACT FROM AUTHOR]