Six hundred years of South American tree rings reveal an increase in severe hydroclimatic events since mid-20th century

South American (SA) societies are highly vulnerable to droughts and pluvials, but lack of long-term climate observations severely limits our understanding of the global processes driving climatic variability in the region. The number and quality of SA climate-sensitive tree ring chronologies have significantly increased in recent decades, now providing a robust network of 286 records for characterizing hydroclimate variability since 1400 CE. We combine this network with a self-calibrated Palmer Drought Severity Index (scPDSI) dataset to derive the South American Drought Atlas (SADA) over the continent south of 12°S. The gridded annual reconstruction of austral summer scPDSI is the most spatially complete estimate of SA hydroclimate to date, and well matches past historical dry/wet events. Relating the SADA to the Australia–New Zealand Drought Atlas, sea surface temperatures and atmospheric pressure fields, we determine that the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) are strongly associated with spatially extended droughts and pluvials over the SADA domain during the past several centuries. SADA also exhibits more extended severe droughts and extreme pluvials since the mid-20th century. Extensive droughts are consistent with the observed 20th-century trend toward positive SAM anomalies concomitant with the weakening of midlatitude Westerlies, while low-level moisture transport intensified by global warming has favored extreme rainfall across the subtropics. The SADA thus provides a long-term context for observed hydroclimatic changes and for 21st-century Intergovernmental Panel on Climate Change (IPCC) projections that suggest SA will experience more frequent/severe droughts and rainfall events as a consequence of increasing greenhouse gas emissions

Tree rings reveal globally coherent signature of cosmogenic radiocarbon events in 774 and 993 CE

This study was funded by the WSL-internal COSMIC project (5233.00148.001.01), the ETHZ (Laboratory of Ion Beam Physics), the Swiss National Science Foundation (SNF Grant 200021L_157187/1), and as the Czech Republic Grant Agency project no. 17-22102s.Though tree-ring chronologies are annually resolved, their dating has never been independently validated at the global scale. Moreover, it is unknown if atmospheric radiocarbon enrichment events of cosmogenic origin leave spatiotemporally consistent fingerprints. Here we measure the 14C content in 484 individual tree rings formed in the periods 770–780 and 990–1000 CE. Distinct 14C excursions starting in the boreal summer of 774 and the boreal spring of 993 ensure the precise dating of 44 tree-ring records from five continents. We also identify a meridional decline of 11-year mean atmospheric radiocarbon concentrations across both hemispheres. Corroborated by historical eye-witness accounts of red auroras, our results suggest a global exposure to strong solar proton radiation. To improve understanding of the return frequency and intensity of past cosmic events, which is particularly important for assessing the potential threat of space weather on our society, further annually resolved 14C measurements are needed.Publisher PDFPeer reviewe

Crecimiento radial de Abies pinsapo en el sur de Chile: relaciones con el clima local y su comparación con poblaciones naturales en España

Se estudió la relación entre el crecimiento de un rodal de Abies pinsapo de 43 años de edad cercano a la ciudad de Valdivia, Chile, y la variabilidad del clima local. Los objetivos fueron identificar los factores y periodos climáticos que regulan su crecimiento radial, comparando paralelamente sus tasas de crecimiento con dos rodales naturales de la especie en España, país que junto a Marruecos alberga sus últimas poblaciones. Las tasas de crecimiento en Valdivia fueron similares o superiores a los sitios de su hábitat natural, favorecidas en Chile por veranos cálidos y poco lluviosos, así como por abundantes precipitaciones invernales. A nivel de madera temprana y tardía, la primera se relacionó con las condiciones de los veranos previos, demostrando su relación con sustancias de reserva, mientras que la madera tardía, presentó una señal climática dominada por características de la estación de crecimiento corriente. Estos resultados indican que el clima templado-lluvioso de la región de Los Ríos, menos extremo que el clima de montaña de su hábitat natural, favorece el crecimiento de la especie constituyendo un hábitat alternativo para su conservación. Aquí la temperatura de verano favorece su crecimiento, a diferencia de su hábitat natural, donde el déficit hídrico es el factor que controla su crecimiento. Esta información puede ser relevante para la conservación ex-situ de una de las coníferas más amenazadas por el cambio climático y la presión humana en el sur de la península ibérica. ----------ABSTRACT---------- The relationship between the growth of 43-year old specimens of an Abies pinsapo Boiss stand located in the city of Valdivia (Chile) and the climatic variability of this site was studied. The objectives were to define the climatic response function and identify the climatic variables and periods that regulate radial growth rates and to compare the annual radial growth with those characterizing two natural stands of the same species growing in Spain provinces, which, together with Morocco, shelters its last populations. Growth rates in Valdivia, Chile, were similar to or even higher than those in their natural habitat, showing a predilection for warm summers with little rain, as well as for abundant winter precipitation. In relation to the early wood (EW) and late wood (LW) series, the first one was related with prevalent dominant climatic conditions of the previous summer. This may be related to stored food. Late wood showed a climatic signal controlled by dominant conditions of the current growing season. These results indicate that the temperate-rainy climate in Los Ríos Region (Chile), milder than the mountain climate in its original habitat, favors the growth of this species and therefore constitutes an alternative habitat for its conservation. Here, summer temperatures favor its growth, differing from its natural habitat, where soil-water availability is the major factor controlling its growth. This information can be relevant for ex-situ conservation of one of the most severely threatened conifers by climate change and human pressure in the south of the Iberian Peninsula

The 2010-2015 megadrought in central Chile: Impacts on regional hydroclimate and vegetation

Since 2010 an uninterrupted sequence of dry years, with annual rainfall deficits ranging from 25 to 45 %, has prevailed in central Chile (western South America, 30-38 degrees S). Although intense 1-or 2-year droughts are recurrent in this Mediterranean-like region, the ongoing event stands out because of its longevity and large extent. The extraordinary character of the so-called central Chile megadrought (MD) was established against century long historical records and a millennial tree-ring reconstruction of regional precipitation. The largest MD-averaged rainfall relative anomalies occurred in the northern, semi-arid sector of central Chile, but the event was unprecedented to the south of 35 degrees S. ENSO-neutral conditions have prevailed since 2011 (except for the strong El Nino in 2015), contrasting with La Nina conditions that often accompanied past droughts. The precipitation deficit diminished the Andean snowpack and resulted in amplified declines (up to 90 %) of river flow, reservoir volumes and groundwater levels along central Chile and westernmost Argentina. In some semi-arid basins we found a decrease in the runoff-to-rainfall coefficient. A substantial decrease in vegetation productivity occurred in the shrubland-dominated, northern sector, but a mix of greening and browning patches occurred farther south, where irrigated croplands and exotic forest plantations dominate. The ongoing warming in central Chile, making the MD one of the warmest 6-year periods on record, may have also contributed to such complex vegetation changes by increasing potential evapotranspiration. We also report some of the measures taken by the central government to relieve the MD effects and the public perception of this event. The understanding of the nature and biophysical impacts of the MD helps as a foundation for preparedness efforts to confront a dry, warm future regional climate scenario

Streamflow variability in the Chilean Temperate-Mediterranean climate transition (35\ub0S\u201342\ub0S) during the last 400\ua0years inferred from tree-ring records

As rainfall in South-Central Chile has decreased in recent decades, local communities and industries have developed an understandable concern about their threatened water supply. Reconstructing streamflows from tree-ring data has been recognized as a useful paleoclimatic tool in providing long-term perspectives on the temporal characteristics of hydroclimate systems. Multi-century long streamflow reconstructions can be compared to relatively short instrumental observations in order to analyze the frequency of low and high water availability through time. In this work, we have developed a Biobío River streamflow reconstruction to explore the long-term hydroclimate variability at the confluence of the Mediterranean-subtropical and the Temperate-humid climate zones, two regions represented by previous reconstructions of the Maule and Puelo Rivers, respectively. In a suite of analyses, the Biobío River reconstruction proves to be more similar to the Puelo River than the Maule River, despite its closer geographic proximity to the latter. This finding corroborates other studies with instrumental data that identify 37.5°S as a latitudinal confluence of two climate zones. The analyzed rivers are affected by climate forcings on interannual and interdecadal time-scales, Tropical (El Niño Southern Oscillation) and Antarctic (Southern Annular Mode; SAM). Longer cycles found, around 80-years, are well correlated only with SAM variation, which explains most of the variance in the Biobío and Puelo rivers. This cycle also has been attributed to orbital forcing by other authors. All three rivers showed an increase in the frequency of extreme high and low flow events in the twentieth century. The most extreme dry and wet years in the instrumental record (1943–2000) were not the most extreme of the past 400-years reconstructed for the three rivers (1600–2000), yet both instrumental record years did rank in the five most extreme of the streamflow reconstructions as a whole. These findings suggest a high level of natural variability in the hydro-climatic conditions of the region, where extremes characterized the twentieth century. This information is particularly useful when evaluating and improving a wide variety of water management models that apply to water resources that are sensitive to agricultural and hydropower industries.Fil: Muñoz, Ariel A.. Pontificia Universidad Católica de Valparaíso; ChileFil: González Reyes, Alvaro. Universidad de Chile; ChileFil: Lara, Antonio. Universidad Austral de Chile; ChileFil: Sauchyn, David. University of Regina; CanadáFil: Christie, Duncan. Universidad Austral de Chile; ChileFil: Puchi, Paulina. Pontificia Universidad Católica de Valparaíso; ChileFil: Urrutia Jalabert, Rocío. Universidad Austral de Chile; ChileFil: Toledo Guerrero, Isadora. Pontificia Universidad Católica de Valparaíso; ChileFil: Aguilera Betti, Isabella. Pontificia Universidad Católica de Valparaíso; ChileFil: Mundo, Ignacio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Sheppard, Paul R.. University of Arizona; Estados UnidosFil: Stahle, Daniel. University of Arkansas for Medical Sciences; Estados UnidosFil: Villalba, Ricardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Provincia de Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales. Universidad Nacional de Cuyo. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; ArgentinaFil: Szejner, P.. University of Arizona; Estados UnidosFil: LeQuesne, Carlos. Universidad Austral de Chile; ChileFil: Vanstone, Jessica. University of Regina; Canad

Dental caries, gingival health, and oral hygiene of long term survivors of paediatric malignant diseases.

Fifty two children who had had cancer and been treated with chemotherapy, and who were long term event free, were examined for caries prevalence, gingival health, and oral hygiene and compared with a control group. A higher dental caries prevalence for the 14-17 year age group was noted. The restorative index was significantly lower in the age group 10-13. There were no significant differences in gingival index, plaque index, or toothbrushing frequency. It is concluded that these patients should be considered as at high risk for caries after cancer treatment. Professional dental follow up should be integrated in the medical follow up

Unusual Southern Hemisphere tree growth patterns induced by changes in the Southern Annular Mode

Recent changes in the summer climate of the Southern Hemisphere extra-tropics are primarily related to the dominance of the positive phase of the Southern Annular Mode. This shift in the behaviour of the Southern Annular Mode—essentially a measure of the pressure gradient between Southern Hemisphere mid and high latitudes—has been predominantly induced by polar stratospheric ozone depletion. The concomitant southward expansion of the dry subtropical belts could have consequences for forest growth. Here, we use tree-ring records from over 3,000 trees in South America, Tasmania and New Zealand to identify dominant patterns of tree growth in recent centuries. We show that the foremost patterns of growth between 1950 and 2000 differed significantly from those in the previous 250 years. Specifically, growth was higher than the long-term average in the subalpine forests of Tasmania and New Zealand, but lower in the dry-mesic forests of Patagonia. We further demonstrate that variations in the Southern Annular Mode can explain 12–48% of the tree growth anomalies in the latter half of the twentieth century. Tree-ring-based reconstructions of summer Southern Annular Mode indices suggest that the high frequency of the positive phase since the 1950s is unprecedented in the past 600 years. We propose that changes in the Southern Annular Mode have significantly altered tree growth patterns in the Southern Hemisphere