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The vapor pressure deficit reflects the difference between how much moisture the atmosphere could and actually does hold, a factor that fundamentally affects evapotranspiration, ecosystem functioning, and vegetation carbon uptake. Its spatial variability and long-term trends under natural versushuman-influenced climate are poorly known despite being essential for predicting future effects on natural ecosystems and human societies such as crop yield, wildfires, and health. Here we combine regionally distinct reconstructions of pre-industrial summer vapor pressure deficit variability from Europe’s largest oxygen-isotope network of tree-ring cellulose with observational records and Earth system model simulations with and without human forcing included. We demonstrate that an intensification of atmospheric drying during the recent decades across different European target regions is unprecedented in a pre-industrial context and that it is attributed to human influence with more than 98% probability. The magnitude of this trend is largest in Western and Central Europe, the Alps and Pyrenees region, and the smallest in southern Fennoscandia. In view of the extreme drought and compound events of the recent years, further atmospheric drying poses an enhanced risk to vegetation, specifically in the densely populated areas of the European temperate lowlands.

ABSTRACTAdvances in accelerator mass spectrometry have resulted in an unprecedented amount of new high-precision radiocarbon (14C) -dates, some of which will redefine the international 14C calibration curves (IntCal and SHCal). Often these datasets are unaccompanied by detailed quality insurances in place at the laboratory, questioning whether the 14C structure is real, a result of a laboratory variation or measurement-scatter. A handful of intercomparison studies attempt to elucidate laboratory offsets but may fail to identify measurement-scatter and are often financially constrained. Here we introduce a protocol, called Quality Dating, implemented at ETH-Zürich to ensure reproducible and accurate high-precision 14C-dates. The protocol highlights the importance of the continuous measurements and evaluation of blanks, standards, references and replicates. This protocol is tested on an absolutely dated German Late Glacial tree-ring chronology, part of which is intercompared with the Curt Engelhorn-Center for Archaeometry, Mannheim, Germany (CEZA). The combined dataset contains 170 highly resolved, highly precise 14C-dates that supplement three decadal dates spanning 280 cal. years in IntCal, and provides detailed 14C structure for this interval.

ABSTRACTAs the worldwide standard for radiocarbon (14C) dating over the past ca. 50,000 years, the International Calibration Curve (IntCal) is continuously improving towards higher resolution and replication. Tree-ring-based 14C measurements provide absolute dating throughout most of the Holocene, although high-precision data are limited for the Younger Dryas interval and farther back in time. Here, we describe the dendrochronological characteristics of 1448 new 14C dates, between ~11,950 and 13,160 cal BP, from 13 pines that were growing in Switzerland. Significantly enhancing the ongoing IntCal update (IntCal20), this Late Glacial (LG) compilation contains more annually precise 14C dates than any other contribution during any other period of time. Thus, our results now provide unique geochronological dating into the Younger Dryas, a pivotal period of climate and environmental change at the transition from LG into Early Holocene conditions.

Changes to the Amazon hydrological cycle have important consequences for world's largest tropical forest, and the biodiversity it contains. However, a scarcity of long‐term climate data in the region makes it hard to contextualize recent observed changes in Amazon hydrology. Here, we explore to what extent tree‐ring oxygen isotope (δ18OTR) chronologies can inform us about hydrological changes in the Amazon over the past two centuries. Two δ18OTRrecords from northern Bolivia and the Ecuadorian Andes are presented. The Ecuador record spans 1799–2012 (n= 16 trees) and the Bolivia record spans 1860–2014 (n= 32 trees), making them the longest δ18OTRrecords from the Amazon, and among the most highly‐replicated δ18OTRrecords from the tropics to date. The two chronologies correlate well at interannual and decadal timescales, despite coming from sites more than 1,500 km apart. Both δ18OTRrecords are strongly related to interannual variation in Amazon River discharge measured at Óbidos, and accumulated upwind precipitation, suggesting a common climatic driver. In both records a strong increase in δ18OTRwas observed up until approximately 1950, consistent with positive trends in the few other existing δ18O proxy records from across the Amazon. Considering all possible drivers of this long‐term increase, a reduction in rainout fraction over the basin driven by rising sea surface temperatures in the North Atlantic is suggested as the most likely cause. The upward trend in δ18OTRreverses over the past 1–2 decades, consistent with the observed strengthening of the Amazon hydrological cycle since approximately 1990. Long‐term climate measurements from the Amazon are few and far between, so information about the climate in the past needs to come from alternative sources. This is essential to provide context for current climate variability such as the strengthening of the Amazon water cycle since the 1990s. One way we can reconstruct historical climate is using stable oxygen isotopes recorded in tree rings. Previous work has shown that tree‐ring oxygen isotopes from the western Amazon can tell you about the amount of rainfall over the entire basin. Here, we present tree‐ring isotope records from Ecuador and Bolivia that span the past two centuries, making them the longest tree‐ring oxygen isotope records from the region to date. We find that the two records are very similar to one another, despite coming from sites that are more than 1,500 km apart, suggesting they are both influenced by the same climatic factors. We explore the climate signals that these records contain, including interpreting a long‐term positive trend in the isotope record until around 1950. We conclude that the most likely cause of this trend is a long‐term reduction in the fraction of incoming water vapor that falls as rainfall over the Amazon. We present two well‐replicated tree‐ring oxygen isotope (δ18OTR) records from tropical South America spanning the past two centuriesThese records capture important large‐scale climate signals, including interannual variation in Amazon basin‐wide precipitationA multi‐decadal long‐term increase in δ18OTRis interpreted as being primarily driven by a long‐term reduction in rainout fraction We present two well‐replicated tree‐ring oxygen isotope (δ18OTR) records from tropical South America spanning the past two centuries These records capture important large‐scale climate signals, including interannual variation in Amazon basin‐wide precipitation A multi‐decadal long‐term increase in δ18OTRis interpreted as being primarily driven by a long‐term reduction in rainout fraction

Large earthquakes can increase the amount of water feeding stream flows, raise groundwater levels, and thus grant plant roots more access to water in water‐limited environments. We examine growth and photosynthetic responses of Pine plantations to the Maule Mw8.8 earthquake in headwater catchments of Chile's Coastal Range. We combine high‐resolution wood anatomic (lumen area) and biogeochemical (δ13Cof wood cellulose) proxies of daily to weekly tree growth sampled from trees on floodplains and close to ridge lines. We find that, immediately after the earthquake, at least two out of six tree trees on valley floors had increased lumen area and decreased δ13C, while trees on hillslopes had a reverse trend. Our results indicate a control of soil water on this response, largely consistent with models that predict how enhanced postseismic vertical soil permeability causes groundwater levels to rise on valley floors, but fall along the ridges. Statistical analysis with boosted regression trees indicates that streamflow discharge gained predictive importance for photosynthetic activity on the ridges, but lost importance on the valley floor after the earthquake. We infer that earthquakes may stimulate ecohydrological conditions favoring tree growth over days to weeks by triggering stomatal opening. The weak and short‐lived signals that we identified, however, show that such responses are only valid under water‐limited, rather than energy‐limited tree, growth. Hence, dendrochronological studies targeted at annual resolution may overlook some earthquake effects on tree vitality. Earthquakes deform and shake Earth's surface and the ground below. These changes may affect groundwater flow. Groundwater level may rise in the valley bottom and drop along higher elevated ridges. Trees depend on such groundwater resources, particularly in dry climates. Hence, we expect contrasting responses of trees after earthquakes: at higher elevations, access to groundwater may be impeded, but enabled in the valley bottoms. Thus, earthquake‐enhanced tree growth should be pronounced only on valley floors, with opposite responses happening along ridges. We test this hypothesis in pine forest plantations that were affected by the 2010 Maule earthquake, Chile. We find that tree growth increased following the earthquake because of enhanced photosynthesis on valley floors, but decreased on upper hillslopes due to increased water stress. Overall, these responses are small but measurable. Our study is the first to combine state‐of‐the‐art isotopic and wood anatomic proxies that we quantified at the cellular scale. Our results provide novel insights into the impacts of earthquakes on soil water and tree growth at an unprecedented daily to weekly resolution. Earthquakes may stimulate tree growth by promoting photosynthesisDirection of tree growth change depends on local topographic positionFirst dendroecohydrological study to explore earthquake‐water‐vegetation interactions at scale of cells Earthquakes may stimulate tree growth by promoting photosynthesis Direction of tree growth change depends on local topographic position First dendroecohydrological study to explore earthquake‐water‐vegetation interactions at scale of cells