The frequency, intensity, and duration of extreme droughts, with devastating impacts on tree growth and survival, have increased with climate change over the past decades. Assessing growth resistance ...and resilience to drought is a crucial prerequisite for understanding the responses of forest functioning to drought events. However, the responses of growth resistance and resilience to extreme droughts with different durations across different climatic zones remain unclear. Here, we investigated the spatiotemporal patterns in growth resistance and resilience in response to extreme droughts with different durations during 1901–2015, relying on tree‐ring chronologies from 2389 forest stands over the mid‐ and high‐latitudinal Northern Hemisphere, species‐specific plant functional traits, and diverse climatic factors. The findings revealed that growth resistance and resilience under 1‐year droughts were higher in humid regions than in arid regions. Significant higher growth resistance was observed under 2‐year droughts than under 1‐year droughts in both arid and humid regions, while growth resilience did not show a significant difference. Temporally, tree growth became less resistant and resilient to 1‐year droughts in 1980–2015 than in 1901–1979 in both arid and humid regions. As drought duration lengthened, the predominant impacts of climatic factors on growth resistance and resilience weakened and instead foliar economic traits, plant hydraulic traits, and soil properties became much more important in both climatic regions; in addition, such trends were also observed temporally. Finally, we found that most of the Earth system models (ESMs) used in this study overestimated growth resistance and underestimated growth resilience under both 1‐year and 2‐year droughts. A comprehensive ecophysiological understanding of tree growth responses to longer and intensified drought events is urgently needed, and a specific emphasis should be placed on improving the performance of ESMs.
Assessing tree growth resistance and resilience to drought is crucial for understanding the forest functioning facing to the intensified drought. Relying on pancontinental tree‐ring observations, we revealed that tree growth resistance and resilience under 1‐year droughts were higher in humid regions than in arid regions. Higher growth resistance was observed under 2‐year droughts than 1‐year droughts, but the growth resilience did not differ significantly. Under longer drought, the effects of plant functional traits and soil properties became much more important. These findings provide crucial insights into the ecophysiological improvements of Earth system models.
Extreme precipitation and consequent floods are some of California's most damaging natural disasters, but they are also critical to the state's water supply. This motivates the need to better ...understand the long‐term variability of these events across the region. This study examines the possibility of reconstructing extreme precipitation occurrences in the Sacramento River Watershed (SRW) of Northern California using a network of tree‐ring based moisture proxies across the Western US. We first develop a gridded reconstruction of the cold‐season standardized precipitation index (SPI) west of 100°W. We then develop an annual index of regional extreme precipitation occurrences in the SRW and use elastic net regression to relate that index to the gridded, tree‐ring based SPI. These regressions, built using SPI data across the SRW only and again across a broader region of the Western US, are used to develop reconstructions of interannual variability in extreme precipitation frequency back to 1400 CE. The SPI reconstruction is skillful across much of the West, including the Sacramento Valley and Central Oregon. The reconstructed SPI also captures historical interannual variations in extreme SRW precipitation, although individual events may be under‐ or over‐estimated. The reconstructions show more SRW extremes from 1580 to 1700 and 1850 to 1915, a dearth of extremes prior to 1550, and a 2–8 year oscillation after 1550. Using tree‐ring proxies beyond the SRW often dampens the reconstructed extremes, but these data occasionally help to identify known extreme events. Overall, reconstructions of SRW extreme precipitation can help to understand better the historic variability of these events.
Key Points
Tree‐ring based moisture proxies were used to reconstruct extreme precipitation in the Sacramento River Watershed back to 1400 CE
Tree‐ring based proxies in the Intermountain West can improve reconstructions in some years, but can also dampen the magnitude of extremes
Extreme precipitation was prevalent from 1580 to 1700 and 1850 to 1915, very rare from 1400 to 1550, and exhibited a 2–8 year oscillation after 1550
Mexico has suffered a long history and prehistory of severe sustained drought. Drought over Mexico is modulated by ocean-atmospheric variability in the Atlantic and Pacific, raising the possibility ...for long-range seasonal climate forecasting, which could help mediate the economic and social impacts of future dry spells. The instrumental record of Mexican climate is very limited before 1920, but tree-ring chronologies developed from old-growth forests in Mexico can provide an excellent proxy representation of the spatial pattern and intensity of past moisture regimes useful for the analysis of climate dynamics and climate impacts. The Mexican Drought Atlas (MXDA) has been developed from an extensive network of 252 climate sensitive tree-ring chronologies in and near Mexico. The MXDA reconstructions extend from 1400 CE–2012 and were calibrated with the instrumental summer (JJA) self-calibrating Palmer Drought Severity Index (scPDSI) on a 0.5° latitude/longitude grid extending over land areas from 14 to 34°N and 75–120°W using Ensemble Point-by-Point Regression (EPPR) for the 1944–1984 period. The grid point reconstructions were validated for the period 1920–1943 against instrumental gridded scPDSI values based on the fewer weather station observations available during that interval. The MXDA provides a new spatial perspective on the historical impacts of moisture extremes over Mexico during the past 600-years, including the Aztec Drought of One Rabbit in 1454, the drought of El Año de Hambre in 1785–1786, and the drought that preceded the Mexican Revolution of 1909–1910.
The El Niño/Southern Oscillation (ENSO) is the most important ocean-atmospheric forcing of moisture variability detected with the MXDA. In fact, the reconstructions suggest that the strongest central equatorial Pacific sea surface temperature (SST) teleconnection to the soil moisture balance over North America may reside in northern Mexico. This ENSO signal has stronger and more time-stable correlations than computed for either the Atlantic Multidecadal Oscillation or Pacific Decadal Oscillation. The extended Multivariate ENSO Index is most highly correlated with reconstructed scPDSI over northern Mexico, where warm events favor moist conditions during the winter, spring, and early summer. This ENSO teleconnection to northern Mexico has been strong over the past 150 years, but it has been comparatively weak and non-stationary in the MXDA over central and southern Mexico where eastern tropical Pacific and Caribbean/tropical Atlantic SSTs seem to be more important. The ENSO teleconnection to northern Mexico is weaker in the available instrumental PDSI, but analyses based on the millennium climate simulations with the Community Earth System Model suggest that the moisture balance during the winter, spring, and early summer over northern Mexico may indeed be particularly sensitive to ENSO forcing. Nationwide drought is predicted to become more common with anthropogenic climate change, but the MXDA reconstructions indicate that intense “All Mexico” droughts have been rare over the past 600 years and their frequency does not appear to have increased substantially in recent decades.
The Mexican Drought Atlas uses 252 climate sensitive tree-ring chronologies to reconstruct the summer Palmer Drought Severity Index at 1501 0.5° latitude/longitude grid points over Mexico and adjacent land areas. Four severe droughts are depicted here, including three previously documented events (a,c,d) and the reconstructed drought that afflicted much of Mexico soon after Conquest (b). Display omitted
•The Mexican Drought Atlas (MXDA) provides reconstructed PDSI maps from 1400 to 2012.•MXDA provides a detailed spatial perspective on severe droughts in Mexican history.•ENSO is the strongest ocean-atmospheric forcing detected with the MXDA.
Latewood width tree‐ring chronologies from arid‐site conifers in the southwestern United States are correlated with precipitation during portions of the summer monsoon season. The onset date and ...length of the monsoon season varies across the region, and these regional differences in summer rainfall climatology may impact the strength and timing of the warm season precipitation response of latewood chronologies. The optimal latewood response to summer precipitation is computed on a daily basis using 67 adjusted latewood chronologies (LWa) from the southwestern United States, adjusted to remove correlation with preceding earlywood growth. Most LWa chronologies are significantly correlated with precipitation summed over a period of approximately 4 weeks (29 days) in early summer. This early summer precipitation signal is present in most ponderosa pine chronologies across the study area. It is also evident in Douglas‐fir chronologies, but only from southern Arizona and New Mexico. The Julian date of summer precipitation onset increases from south to north in the instrumental precipitation data for the southwestern United States. The timing of the early summer season precipitation response in most LWa chronologies also tends to occur later in the summer from southeastern Arizona into northern New Mexico and eastern Colorado. Principal components analysis of the LWa chronologies reproduces two of the three most important spatial modes of early summer precipitation covariability seen in the instrumental data. The first PC of LWa is related to the same atmospheric circulation features associated with PC1 of instrumental early summer precipitation, including cyclonic circulation over the southwestern United States and moisture advection from the eastern Pacific. Correlation analyses between antecedent cool season precipitation and early summer rainfall using instrumental and tree‐ring reconstructed precipitation indicates that the tree‐ring data reproduce the multi‐decadal variability in correlation between seasons seen in the instrumental data.
Latewood width tree‐ring chronologies from the southwestern United States have been a useful proxy for reconstructing summer precipitation. However, the onset and importance of summer rains varies across the region, and this appears to affect the optimal latewood growth response to moisture. Using daily precipitation data, this study demonstrates that latewood width tree‐ring chronologies from the southwestern United States are correlated with early summer precipitation, and the optimal growth response appears to track the northward migration of the monsoon season.
ABSTRACT
Recent studies have pointed out the statistical occurrence of dual‐season droughts detected in tree‐ring chronologies over the southwestern US region that is not well described by ...instrumental observed records of the 20th century. In this study, a multi‐statistical approach that evaluates persistent dual‐season drought using a mode‐of‐variability oriented approach is proposed, considering a new network of tree‐ring earlywood (EW)‐ and latewood‐adjusted (LWadj) chronologies from throughout southwestern North America. To determine dominant patterns of spatiotemporal variability, empirical, orthogonal functions, canonical correlation analysis, and multi‐taper‐method singular value decomposition analyses were applied, with focus on variability from inter‐annual to centennial periods and highlighting the multi‐decadal signals inherent to proxy record network. During the instrumental period, we demonstrate that EW and LWadj networks of tree‐ring chronologies are able to capture the associated precipitation responses of cool and warm season atmospheric teleconnections. Considering the four‐century period of the complete tree‐ring network, we explore the possibility of a dual summer–winter variability signal in the low‐frequency climate regime. EW and LWadj seem to be coherent in‐phase at the very low‐frequency scale (50–100 years spectral band). This provocative result is supported by major historic documented multi‐year droughts of the region since 1650. Thus, the temporal variation of these chronologies time series and its associated spatial pattern strongly suggest that this low‐frequency mode might represents an important spatiotemporal variation of droughts in the Southwest; however, the source of this signal is still an open question and of great interest for drought planning and resource management in the region.
The Samalá River in western Guatemala is critical for sustaining diverse agricultural production systems, from staple crop production in the upper basin to sugar cane in the lowlands. The streamflow ...from the Samalá River also supports hydroelectric power generation within the basin. The watershed is home to more than a hundred settlements including cities, towns, and villages, some of which have experienced extreme hydrological events, including destructive flooding from the river. However, the Samalá River streamflow record, only 38 years in length (1979–2016), is too short to assess the full range of hydrological variability for this economically important region, including Guatemala’s second largest city –Quetzaltenango. This paper presents a tree-ring based reconstruction of mean August streamflow for 125 years (1889–2013). Our results suggest that annual tree-ring width measurements from Abies guatemalensis are correlated with monthly mean streamflow records in the upper Samalá River basin. This association seems to be modulated in part by variability in the ENSO 3.4 region in the Pacific Ocean, suggesting decreased streamflow during the warm events of the sea surface temperature in the Pacific Ocean. The record indicates that single year events of low streamflow dominate the record. Nevertheless, a period of up to 8 consecutive years below-average streamflow is shown in the record between 1905 and 1912. Overall, this extended record of streamflow suggests that tree-ring studies in the area have the potential to provide useful inputs in the future that can be utilized by stakeholders and decision-makers within the Samalá watershed involving the management of discharge for crop irrigation, hydropower production, and disaster mitigation.
The Sun's role in climate variability is now a subject of debates, especially in the context of understanding contribution of solar forcing to modern global warming. Besides, there are some evidences ...of the approaching new Grand Solar Minimum with Little Ice Age climatic conditions. This expectation is based on the occurrence of the extended solar minimum of 2006–2009. To investigate the possible Sun-climate connection the regional tree-ring chronology covering the period from 1445 to 2005 was analyzed. A total of 36 timber cores of pine Pinus sylvestris L. were sampled near the northern tree-line at Loparskaya station (68.6 N, 33.3 E), including the oldest living pine with more than 560 years of age. The data were processed using modern methods adopted in dendrochronology (cross-dating and standardization) with the help of COFECHA and ARSTAN programs. The analysis revealed significant cooling events, coinciding with the Spoerer (1400–1540), Maunder (1645–1715), Dalton (1790–1830), and Gleissberg (1880–1910) Grand Solar Minima. The application of MTM-spectrum and wavelet decomposition analysis identified the existence of the main cycles of solar activity (5.4, 11.7 and 22 years) in tree-ring width variations. As possible extraterrestrial forcings of climate change we consider here variations in solar irradiance and cosmic ray intensity modulated by the interplanetary magnetic field. As solar and cosmic ray activity indicators we used the annual sunspot number, geomagnetic aa index and Be^10 cosmogenic isotope records. To examine the relationship in time-frequency scale between tree-ring growth and solar activity, the cross wavelet transform and wavelet coherence analysis were applied to the time series. The wavelet coherence analysis identified that the 11 yr and 22 yr periodicities were clearly manifested in the all solar-tree rings connections during and around the Grand Minima of solar activity including the Maunder minimum, when, as is known, sunspots were practically absent. These results confirm the existence of solar activity effect on climate and tree growth above the Arctic Circle and are important for understanding the modern climatic processes.
•We analyzed tree-ring chronology (1445–2005) from Peninsula, Northwestern Russia.•In polar tree-ring data, significant periodicities associated with solar cycles (5.4, 11.7 and 22 years) were found.•Polar tree growth response on solar impact is more pronounced during and around the Grand Minima of solar activity.•Cycles of 11- and 22 yr were persisted in tree ring-cosmic rayconnections even during the Maunder minimum when sunspots were practically absent.•Connection between tree rings and sunspots was higher during other Grand Minima (the Dalton and Gleissberg) and just after the Maunder minimum.
Given the challenge to estimate representative long-term natural variability of streamflow from limited observed data, a hierarchical, multilevel Bayesian regression (HBR) was developed to ...reconstruct the 1489–2006 annual streamflow data at six Athabasca River Basin (ARB) gauging stations based on 14 tree ring chronologies. Seven nested models were developed to maximize the applications of available tree ring predictors. Based on results of goodness-of-fit tests, the HBR developed was skillful and reliable in reconstructing the streamflow of ARB. From five centuries of reconstructed streamflow for ARB, five or six abrupt change points are detected. The streamflow time series obtained from a backward moving, 46-year window for six gauging sites in ARB vary significantly over five centuries (1489–2006) and at times could exceed the 90% and/or 95% confidence intervals, denoting significant non-stationarities. Apparently changes in the mean state and the lag-1 autocorrelation of reconstructed streamflow across the gauging sites can be similar or radically different from each other. These nonstationary features imply that the default stationary assumption is not applicable in ARB. Further, the reconstructed streamflow shows statistically significant oscillations at interannual, interdecadal and multidecadal time scales and are teleconnected to climate patterns such as El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO) and Atlantic Multi-decadal Oscillation (AMO). A composite analysis shows that La Niña (El Niño), cold (warm) PDO, and cold (warm) AMO events are typically associated with increased (decreased) streamflow anomalies of ARB. The reconstructed streamflow data provides us the full range of streamflow variability and recurrence characteristics of extremes spanned over five centuries from which it is useful for us to evaluate and manage the current water systems of ARB more effectively and a better risk analysis of future droughts of ARB.
Display omitted
•Hierarchical Bayesian regression model (HBR) was built for streamflow reconstruction.•Representative results are obtained for six gauges in the Athabasca River Basin (ARB).•Five centuries of reconstructed streamflow for ARB show significant nonstationarities.•The traditional stationary assumption of streamflow is not valid in ARB.•Reconstructed streamflow for ARB is teleconnected to large scale climate patterns.
Prof. Dr. Dieter Eckstein (1939-2021) was a leading scientist, teacher, mentor, leader, promoter and motivator in the field of dendrochronology and wood biology. After graduating in wood science and ...receiving a PhD in dendrochronology, he was professor of wood biology at the University of Hamburg. From 1995-2004, he was Director of the Department of Wood Biology, University of Hamburg, and of the Institute of Wood Biology and Wood Protection at the Federal Research Centre for Forestry and Forest Products in Hamburg, Germany. His work had a decisive influence on the development of wood anatomy, wood biology and dendrochronology and his laboratory was a reference point for dendrochronology worldwide. He supported dendrochronologists throughout Europe and around the world in their pioneering work to establish dendrochronology laboratories and develop dendrochronology in numerous countries, including Slovenia.
Prof. Dr. Dieter Eckstein (1939 - 2021) significantly influenced the global development of dendrochronology and the underlying science of wood biology. Eckstein’s research areas included ...dendroclimatology, xylogenesis, ecophysiology, and quantitative wood anatomy. His personal and collaborative work continues to improve our understanding of both the natural environment and human cultural development. The techniques he developed and championed resolved long-standing difficulties in the application of tree-ring science to understand both natural processes and human effects on tree and forest development. As importantly, he nurtured and promoted both the careers and the lives of many fellow scholars and students around the world. Here we present a systematic bibliography of more than 280 publications that illustrates the development of tree-ring research in Europe and elsewhere throughout the almost 50 years of Eckstein’s career. Throughout his scientific career, Eckstein pioneered, developed, and promoted research opportunities with his students and co-workers at the University of Hamburg and beyond. His greatest legacy for his students and colleagues, and which we are challenged to continue, is to continue to build the international spirit of a "dendrofamily".
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