The Southeastern United States (US) has experienced increased population growth and urbanization in recent decades, highlighting the importance of water management and availability. The Black Warrior River basin is in an area with an increasing precipitation trend and no previous streamflow reconstruction. To contextualize current streamflow, we reconstructed over 400 years (1550–2023 CE) of May–July (MJJ) streamflow for the Black Warrior using 10 tree ring chronologies, including a new 36-core bald cypress ( Taxodium distichum ) chronology. Flows >2000 m ^3 s ^−1 occurred in <5% of years, with 90% of years exceeding 200–300 m ^3 s ^−1 . While central flow quantiles showed little long-term trend, upper quantiles (⩾0.90) had strong positive slopes while lower quantiles (⩽0.10) trended slightly downward, demonstrating an increased variance driven by extremes occurring in the last 40 years (beginning in the late 20th century). Our results show that five of the highest MJJ flow years of the reconstruction occurred within the last 40 years, with 1989, 1997, and 2021 all in the 99th percentile of high flow years. These recent extreme flow years reflect the influence of both tropical cyclones (TC) and frontal precipitation, an example of which is 2021 with two intense frontal precipitation events (May 4, ∼108 mm; July 19, ∼55 mm) and a TC (Claudette; ∼110 mm). Correlations show a linkage between increased meridional and zonal wind stress (300 hPa) and decreased geopotential height (500 hPa) with higher flows, consistent with a wavier, southward-displaced North Atlantic Jet (NAJ). Combined with documented increases in TC precipitation in the eastern U.S., our findings emphasize that these widely documented NAJ-driven changes have amplified Black Warrior MJJ streamflow and variability.

Assessing long-term hydroclimatic variability in central Mexico is essential to understand regional water availability and groundwater recharge for urban centers such as Querétaro. This study developed a multi-century winter–spring precipitation reconstruction for the Sierra Gorda Biosphere Reserve (SGBR) using ring width chronologies of Douglas-fir, Pseudotsuga menziesii (Mirb.) Franco. Standard dendrochronological techniques were applied to develop a 284-year master chronology (1731–2015). Following the accepted Subsample Signal Strength criterion (SSS ≥ 0.85) for chronology reliability, the reconstruction was restricted to the 1744–2015 period, yielding a statistically robust 271-year December–April precipitation record. A bootstrapped ordinary least-squares regression model relating tree-ring indices to instrumental December–April precipitation was calibrated and validated using split-sample cross-validation, explaining 46% of the instrumental precipitation variance (R2 = 0.46) and yielding positive verification statistics (RE = 0.38–0.58; CE = 0.37–0.57). Spatial field correlations against gridded climate data (CRU TS4.08) confirmed a broad regional hydroclimatic signal centered over the Sierra Madre Oriental. Continuous wavelet transform (CWT), spectral analysis, superposed epoch analysis (SEA), and wavelet coherence (WTC) revealed significant interannual (2–8 years) and decadal (10–20 years) variability associated with large-scale ocean–atmosphere climate modes, including the El Niño–Southern Oscillation (ENSO), North Atlantic Oscillation (NAO), Atlantic Multidecadal Oscillation (AMO), and Tropical North Atlantic (TNA) index. The pronounced sensitivity of these conifer forests to pre-monsoonal moisture deficits highlights their vulnerability to projected warming and increasing spring evapotranspiration stress. Although the reconstruction is limited to pre-monsoonal (December–April) precipitation, it provides a robust centuries-long baseline for contextualizing regional hydroclimatic variability and supports water-resource management, groundwater conservation, and climate-adaptation strategies in central Mexico.

Bald cypress (Taxodium distichum (L.) Rich.), a foundation species in the bottomland hardwood forests of the southeastern United States, is essential for maintaining ecosystem functions. This study assesses the impacts of environmental changes on bald cypress ring widths and xylogenesis by correlating growth patterns with climatic variables, using ring-width data from 17752022 and cellular development data from the 2023 growing season. We collected biweekly cambium samples from five trees in western Alabama, analyzing the correlation between cell development and environmental factors such as air and water temperatures, precipitation, water levels, solar radiation, and day length. Results indicate that new cell growth is significantly influenced by day length (r 2 = 0.84, p 0.01) and maximum water temperature (r 2 = 0.59, p 0.01), with water temperature potentially playing a role in initiating the growing season, which typically starts in late May and ends by early September. Notably, an intense precipitation event in early July, delivering 7.34 cm of rain, coincided with a mid-season increase in cell production after trees started to decrease production following the summer solstice, underscoring the sensitivity of bald cypress to acute hydro-meteorological events. The cessation of growth corresponded with the drying of the site, indicating water availability as a possible factor for ending the growth phase. These findings underscore the complex interaction between bald cypress and its changing environment, providing insights into its adaptive strategies to climatic variability and highlighting the ecological importance of this species in forecasting and managing wetland resilience.

Streamflow variability is a critical component of water availability across the South Atlantic-Gulf (SAG) water resource region of the United States, yet long-term coherence among basins remains poorly understood. We developed independent May-July streamflow reconstructions for the Roanoke River (South Atlantic), Pascagoula River (southern Mississippi Basin), and St. Johns River (northern and central Florida) spanning 1100-2015 CE. Each reconstruction is highly skillful (RE = 0.39-0.62; CE = 0.39-0.62) and explains 51-63% of observed variance. Across the 916-year record, only five droughts affected all three basins simultaneously, yet three occurred since 2000 (2006, 2007, 2011). These 21st-century droughts were broader and more spatially coherent than comparable events in 1491 and 1587. Basin-to-basin comparisons reveal shared low-flow years were most frequent between the Pascagoula and St. Johns Rivers (15 events), followed by Roanoke-Pascagoula (12) and Roanoke-St. Johns (9). When the St. Johns River experienced low [high] flows, the Pascagoula River had a 40% [48%] likelihood of concurrent extremes-the highest regional coherence observed. Low-flow events for individual basins lasted 2-3 years on average, with the longest drought persisting 26 years on the St. Johns (1459 CE). For both the Pascagoula and St. Johns River, return intervals based on observational streamflow records underestimated the recurrence frequency of extreme events like the early-2000s low flow event by 100-500 years. In contrast, observationally based return intervals on the Roanoke overestimate the length of time between the driest events, indicating severe droughts are more likely to occur than previously thought. These findings illustrate the risk of multi-basin droughts in the SAG region, particularly for the closely linked Pascagoula and St. Johns basins. Future drought planning and water-resource management must account not only for drought in individual basins, but the complex effects of synchronous hydrologic drought across the region.

Forest carbon and water budgets, and their coupling through water-use efficiency (WUE; the ratio of carbon uptake to water loss), are influenced by multiple factors, including forest structure, climate, topography, soil, and management strategies. Drivers of forest productivity and water use are generally well understood at scales of individual trees to stands. However, as that scale extends to landscapes and biomes, the relative importance of these drivers may change, challenging our ability to predict changes in regional forest health. Here, we applied multiscale geographically weighted regression to quantify the influence of environmental factors and forest management types on net primary production (NPP), evapotranspiration (ET), and WUE across two ecologically contrasting U.S. forest regions: the Southeast (SEUS) and the Pacific Northwest (PNW). Results revealed that the relationships between NPP, ET, and WUE and predictors were relatively uniform across the SEUS, likely due to the region's relatively homogeneous humid climate and management approaches. In contrast, the effects of predictors in the PNW were less uniform due to its complex topography, climatic gradients, and diverse management types. Results also indicated clear regional contrasts in the effects of forest management on carbon-water dynamics. In the SEUS, ecological management maximized WUE in most locations, whereas in the PNW, shifting to preservation management produced the greatest increase in WUE. This study presents a spatially explicit framework for enhancing regional carbon and water budget predictions and informing forest management under changing environmental conditions.

Cahokia was the first and largest precolonial city outside of Mesoamerica in what is now the United States. Monuments and exotic goods were central to public life at Cahokia, but no high-resolution timeline of monumental construction or long-distance material import exists for the site. Wooden marker posts, serving as both public monuments and exotic artifacts, offer ideal sources of evidence for documenting the chronology and spatial scale of Cahokian material networks and community histories. In this paper, we employ 14C dating of a cosmic event archived in tree-rings to determine that the largest known marker post in the Cahokia area, the Mitchell Log, was felled around 1124 CE. Sr isotope ratios of the wood rule out a local source, and suggest the tree was transported at least 180 kilometers. Together, the date, provenance, and context of the Mitchell Log (1) establish a historical datum for the peak influence of the Cahokia polity, (2) prompt new questions about the long-distance transport of thousands of other such marker posts, and (3) identify a significant event in the history of this precolonial phenomenon.

Increasing drought pressure under anthropogenic climate change may jeopardize the potential of tropical forests to capture carbon in woody biomass and act as a long-term carbon dioxide sink. To evaluate this risk, we assessed drought impacts in 483 tree-ring chronologies from across the tropics and found an overall modest stem growth decline (2.5% with a 95% confidence interval of 2.2 to 2.7%) during the 10% driest years since 1930. Stem growth declines exceeded 10% in 25% of cases and were larger at hotter and drier sites and for gymnosperms compared with angiosperms. Growth declines generally did not outlast drought years and were partially mitigated by growth stimulation in wet years. Thus, pantropical forest carbon sequestration through stem growth has hitherto shown drought resilience that may, however, diminish under future climate change.

Instrumental records of hydroclimatic extremes (e.g., drought, pluvial flooding, tropical cyclones) are temporally and spatially limited, making long-term assessments of the drivers of these events difficult. Paleo-reconstructions of these extreme events are therefore essential in understanding and evaluating future risk, especially within vulnerable coastal communities. In dendrochronology, δ18O (18O/16O) is a known proxy for reconstructing various hydroclimatic parameters (i.e., temperature, atmospheric humidity, streamflow). The tree takes up δ18O in source water for the development of woody tissue, with the isotopic ratio stored within the α-cellulose of annual tree rings. However, cellulose-derived δ18O from baldcypress (Taxodium distichum), the longest-lived species in the region, has never been investigated in studies of hydroclimate. In this exploratory study, we evaluate the use of δ18O-depletion in baldcypress latewood as a proxy for various southeastern hydroclimatic extremes to the comparable instrumental period. Results of baldcypress latewood δ18O over the Choctawhatchee River Basin were then compared to various climate indices and the instrumental tropical cyclone record, with correlations of varying strength expressed between the produced δ18O time series and precipitation, streamflow, self-calibrated Palmer Drought Severity Index, and maximum summer temperature. Large decreases in baldcypress δ18O latewood are determined to be reflective of regional TC precipitation. In direct interspecies comparisons, baldcypress δ18O is shown to be more sensitive to drought conditions than nearby longleaf pine (Pinus palustris) δ18O. Results of these comparisons reveal the future potential of the proxy in multivariate climate reconstructions.

Platanus orientalis is a key riparian species in central Iran with the potential to serve as a climate and streamflow proxy within this region. However, there are limited studies concerning its dendrochronological potential and climate-growth relationships. Therefore, this study investigates the dendroclimatic potential of P. orientalis along the riparian ecosystem of the Zayandeh-Rud River in central Iran. A total of 50 trees were sampled and analyzed at two distinct basin sites, representing varying elevations, climate characteristics, and water availability. Our findings reveal that the tree-ring width index (TRWI) at the lower basin site, which is characterized by higher temperatures, and lower precipitation, is positively affected by streamflow in May and July. This relationship is highly dependent on the amount of precipitation in the upper and lower basin sites. Moreover, analyses reveal a significant negative relationship between TRWI and temperature during the growing season at the lower basin site. In contrast, trees at the upper basin site, characterized by higher precipitation, show weaker climate-growth relationships. These findings imply that P. orientalis tree-rings could provide insight into long-term climatic patterns within riparian ecosystems in central Iran.

Abstract 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.

Heavy precipitation events increased over the last century in response to higher atmospheric temperature and associated increases in water vapor content, but little evidence shows that increased heavy precipitation changed flood trends. Short records, containing few extreme flood observations, limit statistical examination of relationships between global temperature, heavy precipitation, and extreme floods. We synthesized European and North American sediment-based paleoflood records extending through at least 900 CE. These records captured flood variability during the warmer Medieval Climate Anomaly (MCA) and cooler Little Ice Age (LIA). Twelve paleoflood chronologies chosen for the analysis suggest an increase in flood frequency since 1000 CE. The largest magnitude floods mostly occurred between 1000 and 1300 CE after peak MCA temperature during a relatively drier overall climate regime. The association found between large magnitude floods during a drier climate may be explained by increased atmospheric water vapor capacity from warmer temperatures that intensified precipitation events. Despite limitations in the number of studies available, extreme flood observations reveal a pattern of large magnitude floods in the late MCA and frequent floods in the LIA. Therefore, temperature-precipitation relationships may influence flood variability, and flood magnitude will likely become more extreme as global temperatures rise.

We describe the utility of false rings in Taxodium distichum (i.e. baldcypress) as a proxy for hydroclimatic extreme events in three different river basins (Pascagoula, Mobile, and Choctawhatchee) that discharge into the northern Gulf of Mexico. False rings occur as a result of a change in the environmental limiting resource for tree stem growth, and in T. distichum , false ring production is usually a result of increases in mid-growing season water availability. Our results show that false ring occurrence (from 1931 to 2018) is similar across sites but occur in different years, suggesting that false ring production is indicative of tree response to its local environment. False ring production in T. distichum has previously been correlated with summer streamflow, the season when tropical cyclone precipitation (TCP) is highest. To assess a stand-wide response, we define high false ring (HFR) years as all years when ⩾ 20% of trees produced a false ring. We show total TCP in July is the best predictor for HFR years in T. distichum , and false ring production in smaller river basins captures local TCP better than larger river basins. Additionally, HFR years coincide with summers of anomalously high precipitation, anomalously low temperatures, and a positive phase of the North Atlantic Oscillation. 77% of HFR years occur in seasons when there is heavy tropical cyclone activity near sample sites, building a foundation to use false ring records as robust TCP proxies with hydroclimate reconstruction potential.

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.

The Po River Basin (PRB) is Italy’s largest river system and provides a vital water supply source for varying demands, including agriculture, energy (hydropower), and water supply. The current (2022) drought has been associated with low winter–early spring (2021–2022) snow accumulation in higher elevations (European Alps) and a lack of late spring–early summer (2022) precipitation, resulting in deficit PRB streamflow. Many local scientists are now estimating a 50- to 100-year (return period) drought for 2022. Given the importance of this river system, information about past (paleo) drought and pluvial periods would provide important information to water managers and planners. Annual streamflow data were obtained for thirteen gauges that were spatially located across the PRB. The Old World Drought Atlas (OWDA) provides annual June–July–August (JJA) self-calibrating Palmer Drought Severity Index (scPDSI) data for 5414 grid points across Europe from 0 to 2012 AD. In lieu of tree-ring chronologies, this dataset was used as a proxy to reconstruct PRB regional streamflow. Singular value decomposition (SVD) was applied to PRB streamflow gauges and gridded scPDSI data for two periods of record, referred to as the short period of record (SPOR), 1980 to 2012 (33 years), and the long period of record (LPOR), 1967 to 2012 (46 years). SVD serves as both a data reduction technique, identifying significant scPDSI grid points within the selected 450 km search radius, and develops a single vector that represents the regional PRB streamflow variability. Due to the high intercorrelations of PRB streamflow gauges, the SVD-generated PRB regional streamflow vector was used as the dependent variable in regression models for both the SPOR and LPOR, while the significant scPDSI grid points (cells) identified by SVD were used as the independent variables. This resulted in two highly skillful regional reconstructions of PRB streamflow from 0 to 2012. Multiple drought and pluvial periods were identified in the paleo record that exceed those observed in the recent historical record, and several of these droughts aligned with paleo streamflow reconstructions of neighboring European watersheds. Future research will utilize the PRB reconstructions to quantify the current (2022) drought, providing a first-time paleo-perspective of drought frequency in the watershed.

Interannual variability in the global land carbon sink is strongly related to variations in tropical temperature and rainfall. This association suggests an important role for moisture-driven fluctuations in tropical vegetation productivity, but empirical evidence to quantify the responsible ecological processes is missing. Such evidence can be obtained from tree-ring data that quantify variability in a major vegetation productivity component: woody biomass growth. Here we compile a pantropical tree-ring network to show that annual woody biomass growth increases primarily with dry-season precipitation and decreases with dry-season maximum temperature. The strength of these dry-season climate responses varies among sites, as reflected in four robust and distinct climate response groups of tropical tree growth derived from clustering. Using cluster and regression analyses, we find that dry-season climate responses are amplified in regions that are drier, hotter and more climatically variable. These amplification patterns suggest that projected global warming will probably aggravate drought-induced declines in annual tropical vegetation productivity. Our study reveals a previously underappreciated role of dry-season climate variability in driving the dynamics of tropical vegetation productivity and consequently in influencing the land carbon sink. Dry-season climate variability is a primary driver of tropical tree growth, according to observations from a pantropical tree-ring network.

The Apalachicola–Chattahoochee–Flint (ACF) basin is arguably the most litigated interstate river system in the eastern United States. Given the complicated demands for water use within this basin, it has been difficult to ascertain if the recent multi-decadal decline in streamflow is a product of human disturbance, changing climate, natural variability, or some combination of the above factors. To overcome these challenges, we examined unimpaired streamflow and precipitation within and adjacent to the ACF basin, upstream of the Apalachicola River at Chattahoochee, and the Florida streamflow station (ARCF), which has historically been identified to be representative of hydrologic variability in the ACF basin. Several of the upstream, unimpaired, streamflow stations selected were identified in rural watersheds where land-cover changes and human disturbance were minimal during the study period. When applying a series of statistical evaluations, ARCF streamflow variability generally reflects the natural variability of the ACF basin. Additionally, unimpaired streamflow variability from the neighboring Choctawhatchee River compared favorably with ARCF variability. The recent multi-decadal decline was consistent in all records, with the 2000s being the most severe in the historic record.

The forests of northern Mexico and the southwestern United States have been subjected to warmer temperatures, persistent drought, and more intense and widespread wildfire. Tree-ring data from four conifer species native to these borderlands forests are compared with regional and large-scale precipitation and temperature data. These species include Abies durangensis, Pinus arizonica, Pinus cembroides, and Pseudotsuga menziesii. Twelve detrended and standardized ring-width chronologies are derived for these four species, all are cross-correlated during their common interval of 1903–2000 (r = 0.567 to 0.738, p < 0.01), and all load positively on the first principal component of radial growth, which alone represents 56% of the variance in the correlation matrix. Correlation with monthly precipitation and temperature data for the study area indicates that all four species respond primarily to precipitation during the cool season of autumn and winter, October–May (r = 0.71, p < 0.01, 1931–2000), and to temperature primarily during the late spring and early summer, January–July (r 0 −0.67, p < 0.01, 1931–2000), in spite of differences in phylogeny and microsite conditions. The instrumental climate data for the region indicate that warmer conditions during the January–July season most relevant to radial growth are beginning to exceed the warmest episode of the 20th century in both intensity and duration. The strong negative correlation between temperature and tree growth indicates that these four conifer species may be challenged by the warmer temperatures forecast in the coming decades for the borderlands region due to anthropogenic forcing. This information could constitute a baseline to analyze the impact of climate change in other regions of Mexico and the USA, where conifer species are of great ecological and socioeconomical importance.