Wet Winter Research Articles

Early Holocene permafrost retreat in West Siberia amplified by reorganization of westerly wind systems

Rapid permafrost degradation and peatland expansion occurred in Eurasia during the Early Holocene and may be analogous to the region’s response to anthropogenic warming. Here we present a 230Th-dated, multiproxy speleothem record with subdecadal sampling resolution from Kyok-Tash Cave, at the modern permafrost margin in the northern Altai Mountains, southwestern Siberia. Stalagmite K4, covering the period 11,400 to 8,900 years before present, indicates an absence of stable permafrost within three centuries of the Younger Dryas termination. Between 11,400 and 10,400 years ago, speleothem δ18O is antiphased between the Altai and Ural ranges, suggesting a reorganization of the westerly wind systems that led to warmer and wetter winters over West Siberia and Altai, relative to the zonally adjacent regions of Northern Eurasia. At the same time, there is evidence of peak permafrost degradation and peatland expansion in West Siberia, consistent with the interpreted climate anomaly. Based on these findings, we suggest that modern permafrost in Eurasia is sensitive to feedbacks in the ocean-cryosphere system, which are projected to alter circulation regimes over the continent.

Changing hydroclimate dynamics and the 19th to 20th century wetting trend in the English Channel region of northwest Europe

Northwestern Europe has experienced a trend of increasingly wet winters over the past 150 years, with few explanations for what may have driven this hydroclimatic change. Here we use the Old World Drought Atlas (OWDA), a tree-ring based reconstruction of the self-calibrating Palmer Drought Severity Index (scPDSI), to examine this wetting trend and place it in a longer hydroclimatic context. We find that scPDSI variability in northwestern Europe is strongly correlated with the leading mode of the OWDA during the last millennium (1000–2012). This leading mode, here named the ‘English Channel’ (EC) mode, has pronounced variability on interannual to centennial timescales and has an expression in scPDSI similar to that of the East Atlantic teleconnection pattern. A shift in the EC mode from a prolonged negative phase to more neutral conditions during the 19th and 20th centuries is associated with the wetting trend over its area of influence in England, Wales, and much of northern continental Europe. The EC mode is the dominant scPDSI mode from approximately 1000–1850, after which its dominance waned in favor of the secondary ‘North–South’ (NS) mode, which has an expression in scPDSI similar to that of the winter North Atlantic Oscillation (NAO). We examine the dynamical nature of both of these modes and how they vary on interannual to centennial timescales. Our results provide insight into the nature of hydroclimate variability in Europe before the widespread availability of instrumental observations.

The geochemistry of Irish rivers

Study regionIreland Study focusMultiple studies have established that catchment geology and weathering regime strongly influence surface water chemistry, and that geochemical cycling can vary due to seasonal climatic conditions. However, fewer studies have focused on the influence these controls in a holistic manner. We relate the water chemistry of a country-wide Irish river survey to atmospheric input, underlying geology, and the influence of bogs. Climatic conditions were defined by an atypically wet winter and an unusually dry summer, providing the opportunity to investigate river chemistry variation across hydrologic conditions. Sampling included 21 of Ireland’s 22 largest rivers ranked by discharge, first-order and second-order streams draining bog lands, a second-order stream draining a limestone catchment, and downstream transects along the River Shannon. All samples were analyzed for major elements, selected trace elements, and nutrients, and a subset was analyzed for δ34SSO4. New hydrological insightsMost catchments were dominated by carbonate weathering with little contribution from the weathering of aluminosilicates. River water composition also varied geographically along the prevailing wind direction due to inputs from marine aerosols, with additional weathering components important in some systems. Seasonal influences could be seen in the chemistry of the headwaters of the River Shannon, while the lower reaches of the river exhibited less variable behavior throughout seasonal changes, likely due to the influence of lakes in the River Shannon system.

Hot Spots and Climate Trends of Meteorological Droughts in Europe–Assessing the Percent of Normal Index in a Single-Model Initial-Condition Large Ensemble

Drought, caused by a prolonged deficit of precipitation, bears the risk of severe economic and ecological consequences for affected societies. The occurrence of this significant hydro-meteorological hazard is expected to strongly increase in many regions due to climate change, however, it is also subject to high internal climate variability. This calls for an assessment of climate trends and hot spots that considers the variations due to internal variability. In this study, the percent of normal index (PNI), an index that describes meteorological droughts by the deviation of a long-term reference mean, is analyzed in a single-model initial-condition large ensemble (SMILE) of the Canadian regional climate model version 5 (CRCM5) over Europe. A far future horizon under the Representative Concentration Pathway 8.5 is compared to the present-day climate and a pre-industrial reference, which is derived from pi-control runs of the CRCM5 representing a counterfactual world without anthropogenic climate change. Our analysis of the SMILE reveals a high internal variability of drought occurrence over Europe. Considering the high internal variability, our results show a clear overall increase in the duration, number and intensity of droughts toward the far future horizon. We furthermore find a strong seasonal divergence with a distinct increase in summer droughts and a decrease in winter droughts in most regions. Additionally, the percentage of summer droughts followed by wet winters is increasing in all regions except for the Iberian Peninsula. Because of particularly severe drying trends, the Alps, the Mediterranean, France and the Iberian Peninsula are suggested to be considered as drought hot spots. Due to the simplicity and intuitivity of the PNI, our results derived from this index are particularly appropriate for region-specific communication purposes and outreach.

Regional Rodent-Borne Infectious Diseases in North America: What Wilderness Medicine Providers Need to Know.

Rodents can transmit infectious diseases directly to humans and other animals via bites and exposure to infectious salivary aerosols and excreta. Arthropods infected while blood-feeding on rodents can also transmit rodent-borne pathogens indirectly to humans and animals. Environmental events, such as wet winters, cooler summers, heavy rains, and flooding, have precipitated regional rodent-borne infectious disease outbreaks; these outbreaks are now increasing with climate change. The objectives of this review are to inform wilderness medicine providers about the environmental conditions that can precipitate rodent-borne infectious disease outbreaks; to describe the regional geographic distributions of rodent-borne infectious diseases in North America; and to recommend prophylactic treatments and effective prevention and control strategies for rodent-borne infectious diseases. To meet these objectives, Internet search engines were queried with keywords to identify scientific articles on outbreaks of the most common regional rodent-borne infectious diseases in North America. Wilderness medicine providers should maintain high levels of suspicion for regional rodent-borne diseases in patients who develop febrile illnesses after exposure to contaminated freshwater after heavy rains or floods and after swimming, rafting, or paddling in endemic areas. Public health education strategies should encourage limiting human contact with rodents; avoiding contact with or safely disposing of rodent excreta; avoiding contact with contaminated floodwaters, especially contact with open wounds; securely containing outdoor food stores; and modifying wilderness cabins and campsites to deter rodent colonization.

Archaeological prospection north of Schinias rowing centre in Marathon at the site of ancient Trikorynthos

AbstractA large‐scale geophysical survey was carried out at the foothills of a topographic table hosting the ruins of the ancient city ‘Trikorynthos’, in the area of Marathon, north of Athens. The explored site assumed to host remnants of ancient constructions belonging to the ancient city. Although the explored site is associated with the final phase of the famous Marathon battle, it was not expected to bear any signs of that event. Because the bulk of the survey had to be during the dry period, resistivity mapping could not be carried out. Further, tests of magnetic prospecting proved unsuccessful, leaving the electrical resistivity tomography (ERT) survey as the only alternative. Therefore, a total area of about 10 000 m2 was covered by ERTs during the dry months of 2001. A few months later, during the wet winter period, about 5500 m2 were explored by resistivity mapping. The electrical tomographic imaging was extensive, leading to the collection of a large volume of tomographic data. The distance between the measured electrical sections was ranging from 0.6 to 2.4 m at places, depending on the nature of the expected targets. The large number of ERTs carried out renders the survey as one of the largest worldwide of this kind. Processing and interpretation of the tomographic data was carried out in three‐dimensional (3D) using custom‐built algorithms. The inverted data were combined to produce depth slices and 3D images. A few months after the ERT survey, the wet winter conditions allowed the conduct of resistance mapping. Thus, spatially limited resistivity mapping was carried out to complement the ERT survey. The whole operation resulted in detecting and mapping various concealed structures, some of which were verified by the subsequent excavation. Therefore, the ancient use of the area is revealed by the combined result of the geophysical investigation and excavation. In fact, the area should had comprised a road network with extended cemetery westwards and rural premises at the TEST side.

Observed and estimated consequences of climate change for the fire weather regime in the moist-temperate climate of the Czech Republic

The occurrence of major wildfires in countries such as Portugal, Italy and Spain (2017) and Sweden (2018) indicated that wildfires pose a risk across Europe. While Central Europe has not been at the center of such events, observed climate data and climate projections suggest a tendency toward more years with wet and warm winters and dry and hot summers as well as fuel accumulation, leading to more hazardous conditions. Although some existing studies analyzed the differences in wildfire occurrence in this territory based on terrain, soil or vegetation characteristics, the effects of climate change have not been properly appraised. To fill this knowledge gap, we used and tested an ensemble of nine fuel aridity metrics, including three dedicated fire danger rating indices, and evaluated their level of agreement with actual fire occurrence, their ability to explain the interannual variability in wildfire frequency, and their temporal trends. The analysis covered the entire territory of the Czech Republic at 500 m spatial resolution. Two periods were included based on observed (1956–2015) and projected (2020–2100) meteorological data using ensembles of five regional climate models (RCMs) and five global circulation models (GCMs) based on Euro-CORDEX and CMIP5 datasets. For the future, we considered Representative Concentration Pathway (RCP) 4.5. Our results showed that since 1956, most of the Czech territory has exhibited an increasing frequency of fire weather days (i.e., days with highly conducive wildfire conditions) and an increasing area affected by weather conducive to wildfire occurrence, with the trends accelerating after 2000. The annual variation in the fuel aridity levels (derived solely from meteorological data) explained more than 2/3 of the reported wildfire variability during 1991–2015 over the Czech Republic. The future projections based on the RCM or GCM ensembles indicated a significant increase in fuel aridity and an increase in the area under fire-conducive conditions. Recommendations derived from such robust results are provided for stakeholders seeking to implement adaptation measures.

Mitigation of Suspendable Road Dust in a Subpolar, Oceanic Climate

Tire and road wear particles (TRWP) are a significant source of atmospheric particulate matter and microplastic loading to waterways. Road wear is exacerbated in cold climate by the widespread use of studded tires. The goal of this research was to assess the anthropogenic levers for suspendable road dust generation and climatic conditions governing the environmental fate of non-exhaust particles in a wet maritime winter climate. Sensitivity analyses were performed using the NORTRIP model for the Capital region of Reykjavík, Iceland (64.1° N). Precipitation frequency (secondarily atmospheric relative humidity) governed the partitioning between atmospheric and waterborne PM10 particles (55% and 45%, respectively). Precipitation intensity, however, increased proportionally most the drainage to waterways via stormwater collection systems, albeit it only represented 5% of the total mass of dust generated in winter. A drastic reduction in the use of studded tires, from 46% to 15% during peak season, would be required to alleviate the number of ambient air quality exceedances. In order to achieve multifaceted goals of a climate resilient, resource efficient city, the most important mitigation action is to reduce overall traffic volume. Reducing traffic speed may help speed environmental outcomes.

Grazing in California's Mediterranean Multi-Firescapes

The California landscape is layered and multifunctional, both historically and spatially. Currently, wildfire size, frequency, and intensity are without precedent, at great cost to human health, property, and lives. We review the contemporary firescape, the indigenous landscape that shaped pre-contact California's vegetation, the post-contact landscape that led us to our current situation, and the re-imagined grazing-scape that offers potential relief. Vegetation has been profoundly altered by the loss of Indigenous management, introduction of non-native species, implantation of inappropriate, militarized, forest management from western Europe, and climate change, creating novel ecosystems almost always more susceptible to wildfire than before. Vegetation flourishes during the mild wet winters of a Mediterranean climate and dries to a crisp in hot, completely dry, summers. Livestock grazing can break up continuous fuels, reduce rangeland fuels annually, and suppress brush encroachment, yet it is not promoted by federal or state forestry and fire-fighting agencies. Agencies, especially when it comes to fire, operate largely under a command and control model, while ranchers are a diverse group not generally subject to agency regulations, with a culture of autonomy in decision-making and a unit of production that is mobile. Concerns about potential loss of control have limited prescribed burning despite landowner and manager enthusiasm. Agriculture and active management in general are much neglected as an approach to developing fire-resistant landscape configurations, yet such interventions are essential. Prescribed burning facilitates grazing; grazing facilitates prescribed burning; both can reduce fuels. Leaving nature “to itself” absent recognizing that California's ecosystems have been irrecoverably altered has become a disaster of enormous proportions. We recommend the development of a database of the effects and uses of prescribed fire and grazing in different vegetation types and regions throughout the state, and suggest linking to existing databases when possible. At present, livestock grazing is California's most widespread vegetation management activity, and if purposefully applied to fuel management has great potential to do more.

Investigating the controls on greenhouse gas emission in the riparian zone of a small headwater catchment using an automated monitoring system

AbstractRiparian zones as the transition zone between terrestrial and aquatic ecosystems play an important role in C and N cycling and greenhouse gas (GHG) emissions. As such, they may help to mitigate climate change but could also accelerate it, depending on the particular processes affected by changes in the hydrologic regime. Hydrological observations indicated frequent shallow groundwater in the riparian zone, especially near the stream and during the wet winter and spring seasons with consequently frequent occurrence of soil water saturation. The redox potential was mainly governed by the soil water regime: under water saturation conditions, the redox potential of the soil decreased and returned to the oxic state after soil drainage. We found that soil temperature and soil water content were the main drivers of the variations in CO2 fluxes, with highest CO2 emission during summer and the lowest emissions in the winter period (162.2–5.4 mg CO2–C m−2 h−1). The annual average daily N2O emission rate was low (2.3 μg N2O‐N m−2 h−1), with the highest average daily N2O emission in March as a result of low temperature and partial soil saturation after heavy precipitation events (37.5 μg N2O‐N m−2 h−1). Our study showed that continuous measurement of redox potential, soil temperature, and soil water content can improve the understanding of GHG emissions in riparian zones.

Climate windows of intra-annual growth and post-drought recovery in Mediterranean trees

Forests store large amounts of carbon as wood, but this storage potential depends on seasonal radial growth and how it is driven by climate. Therefore, we need a better understanding on how intra-annual radial increment rates determine growth responses to climate variability. There is a large gap of knowledge on the climate windows, i.e. the effective climatic time-window for tree growth, and predictors of intra-annual growth, particularly in seasonally dry biomes such as Mediterranean forests where growth may show several seasonal peaks. We described the radial increment rates of five tree species inhabiting mesic (Quercus ilex, Quercus faginea, Arbutus unedo) and xeric (Pinus halepensis, Juniperus thurifera) sites using dendrometers. Then, we related those rates and tree-ring width to climate data using correlations and model selection. All species presented bimodal patterns of radial increment rates with a major peak in spring and a minor peak in autumn, being this pattern most marked in Q. ilex, A. unedo and J. thurifera. Differences in climate-rates relationships were greater between species than between sites. Wet and cool conditions in winter and spring increased spring rates, but the climatic time-windows were longer in some species (Q. ilex, J. thurifera) and shorter in others (Q. faginea, P. halepensis). Similarly, wet and cool conditions also enhanced autumn rates in the xeric site, but warm conditions did it in the mesic site. Rainy autumn conditions reduced A. unedo rates. Climate-growth associations at intra- and inter-annual scales were consistent in species showing long intra-annual climatic time-windows such as Q. ilex. Our findings confirm the importance of wet winters and cool springs for radial growth in some species, and the relevance of autumn growth in A. unedo. Similar studies on intra-annual radial increment rates and climatic time-windows of forest growth and productivity can reveal which will be the species most impacted by drought.

Experimental seed sowing reveals seedling recruitment vulnerability to unseasonal fire.

Unseasonal fire occurrence is increasing globally, driven by climate change and other human activity. Changed timing of fire can inhibit postfire seedling recruitment through interactions with plant phenology (the timing of key processes, e.g., flower initiation, seed production, dispersal, germination), and therefore threaten the persistence of many plant species. Although empirical evidence from winter-rainfall ecosystems shows that optimal seedling recruitment is expected following summer and autumn (dry season) fires, we sought experimental evidence isolating the mechanisms of poor recruitment following unseasonal (wet season) fire. We implemented a seed-sowing experiment using nine species native to fire-prone, Mediterranean-climate woodlands in southwestern Australia to emulate the timing of postfire recruitment and test key mechanisms of fire seasonality effects. For seeds sown during months when fire is unseasonal (i.e., August-September: end of the wet winter season), seedling recruitment was reduced by up to 99% relative to seeds sown during seasonal fire months (i.e., May-June: end of the dry summer season) because of varying seed persistence, seedling emergence, and seedling survival. We found that up to 70 times more seedlings emerged when seeds were sown during seasonal fire months compared to when seeds were sown during unseasonal fire months. The few seedlings that emerged from unseasonal sowings all died with the onset of the dry season. Of the seeds that failed to germinate from unseasonal sowings, only 2% survived exposure on the soil surface over the ensuing hot and dry summer. Our experimental results demonstrate the potential for unseasonal fire to inhibit seedling recruitment via impacts on pregermination seed persistence and seedling establishment. As ongoing climate change lengthens fire seasons (i.e., unseasonal wildfires become more common) and managed fires are implemented further outside historically typical fire seasons, postfire seedling recruitment may become more vulnerable to failure, causing shifts in plant community composition towards those with fewer species solely dependent on seeds for regeneration.

Importance of resilient pastures for New Zealand’s agricultural soil carbon stocks

New Zealand’s agricultural pastures contain significant soil carbon (C) stocks that are susceptible to change when impacted by management and natural processes (e.g., climate). Inputs of C to these pastoral soils is through photosynthetic uptake of atmospheric CO2 either on-site or elsewhere. Changes in soil C stocks are in response to the management of the system that alters the input-output balance. Increasing the resilience of pastures to climatic events such as hot and dry summers or cool and wet winters can increase inputs of C to the soil while sustaining above-ground production and so provide an opportunity for C sequestration. Furthermore, increased pasture for grazing can reduce the need for management practices identified as detrimental for soil C stocks such as irrigation or the production of cropped supplemental feed. A reduction in the need for renewal and its associated soil C losses, and the establishment of a more diverse sward, especially if deeper-rooting species are included, has the potential for increasing soil C stocks provided the diversity can be maintained. From a soil C perspective, a resilient pasture maximises CO2 uptake to ensure adequate above- and below-ground inputs to maintain or increase soil C stocks and minimise the need for management activities detrimental to soil C.

Paleoproductivity Modes in Central Mediterranean During MIS 20—MIS 18: Calcareous Plankton and Alkenone Variability

AbstractPaleoproductivity is reconstructed across a Mediterranean benchmark record, the Early/Middle Pleistocene Montalbano Jonico section, cropping out in southern Italy. High‐resolution coccolithophore and alkenone data (C37 and C37:2/C38:2 ratio) were collected in order to extend the data set on Mediterranean paleoproductivity pattern and forcing mechanisms. The multi‐proxy record indicates low productivity during glacial and stadial phases and enhanced productivity during interglacial and interstadials. Increased surface water turbidity, cold‐water temperature and polar‐subpolar low salinity water incursion appear as the dominant controls for low productivity during Marine Isotope Stage (MIS) 20. Enhanced productivity during MIS 19c was sustained by warmer surface waters, coupled with a seasonal precipitation regime, providing higher nutrient availability. Productivity increases during interstadials with respect to stadials, in relation with enhanced land‐derived nutrient input through river discharge during wetter winters. The productivity scenario we propose is similar to those reconstructed from deep‐sea records in the central and western Mediterranean during Dansgaard‐Oeschger oscillations over the last 70 ka. This indicates that similar forcing mechanisms acted on productivity dynamics on a regional scale over different times. We suggest that migration of the westerly wind system over the Mediterranean and the polar water inflow influenced productivity on a regional scale. The acquired data set provides new evidences on the environmental significance of the C37:2/C38:2 ratio and on its relation with surface water productivity.

Microbial diversity alteration reveals biomarkers of contamination in soil-river-lake continuum

Microbial communities inhabiting soil-water-sediment continuum in coastal areas provide important ecosystem services. Their adaptation in response to environmental stressors, particularly mitigating the impact of pollutants discharged from human activities, has been considered for the development of microbial biomonitoring tools, but their use is still in the infancy. Here, chemical and molecular (16S rRNA gene metabarcoding) approaches were combined in order to determine the impact of pollutants on microbial assemblages inhabiting the aquatic network of a soil-water-sediment continuum around the Ichkeul Lake (Tunisia), an area highly impacted by human activities. Samples were collected within the soil-river-lake continuum at three stations in dry (summer) and wet (winter) seasons. The contaminant pressure index (PI), which integrates Polycyclic aromatic hydrocarbons (PAHs), alkanes, Organochlorine pesticides (OCPs) and metal contents, and the microbial pressure index microgAMBI, based on bacterial community structure, showed significant correlation with contamination level and differences between seasons. The comparison of prokaryotic communities further revealed specific assemblages for soil, river and lake sediments. Correlation analyses identified potential "specialist" genera for the different compartments, whose abundances were correlated with the pollutant type found. Additionally, PICRUSt analysis revealed the metabolic potential for pollutant transformation or degradation of the identified "specialist" species, providing information to estimate the recovery capacity of the ecosystem. Such findings offer the possibility to define a relevant set of microbial indicators for assessing the effects of human activities on aquatic ecosystems. Microbial indicators, including the detection of “specialist” and sensitive taxa, and their functional capacity, might be useful, in combination with integrative microbial indices, to constitute accurate biomonitoring tools for the management and restoration of complex coastal aquatic systems.

Density and Subsurface Burrowing of a Desert-Dwelling Land Snail, Helminthoglypta greggi, in the Western Mohave Desert

This paper reports on the subsurface burrowing of the desert-dwelling land snail Helminthoglypta greggi in the western Mohave Desert. By excavating into the soil layer, we found that the majority of live snails were burrowed into the soil beneath rocks as well as shrubs, and in both disturbed and undisturbed areas. Live snails were found as deep as 50 cm in the soil layer, and shells as deep as 55 cm. Densities averaged 4.3 live snails per square meter of surface area and 10.1 snails per cubic meter of excavated soil. When these densities are multiplied by a conservative habitat estimate, these snails may number in the millions. Burrowing into the soil layer during wet winter periods allows these snails to escape lethally high temperatures in summer, lethally low temperatures in winter, and desiccation in all seasons. The significance of these findings is twofold. First, it is essential that soil sampling be included in surveys for other Helminthoglypta, as well as for other land snails inhabiting arid environments, or their population number, occupancy, and habitat breadth may be underestimated. Second, like H. greggi, it may be that other species of land snails have been considered rare simply because of inadequate sampling and incomplete understanding of the nature and extent of their habitat use.

Projected changes of regional lake hydrologic characteristics in response to 21st century climate change

ABSTRACT Inland lakes are socially and ecologically important components of many regional landscapes. Exploring lake responses to plausible future climate scenarios can provide important information needed to inform stakeholders of likely effects of hydrologic changes on these waterbodies in coming decades. To assess potential climate effects on lake hydrology, we combined a previously published spatially explicit, processed-based hydrologic modeling framework implemented over the lake-rich landscape of the Northern Highlands Lake District within the United States with an ensemble of climate change scenarios for the 2050s (2041–2070) and 2080s (2071–2100). Model results quantify the effects of climate change on water budgets and lake stage elevations for 3692 lakes and highlight the importance of landscape and hydrologic setting for the response of specific lake types to climate change. All future climate projections resulted in loss of ice cover and snowpack as well as increased evaporation, but variability in climate projections (warmer conditions, wet winters combined with wet or dry summers) interacted with lake characteristics and landscape position to produce variable lake hydrologic changes. Water levels for drainage lakes (lakes with substantial surface water inflows and outflows) showed nearly no change, whereas minimum water levels for seepage lakes (minimal surface water fluxes) decreased by an average of up to 2.64 m by the end of the 21st century. Our physically based modeling approach is parsimonious and computationally efficient and can be applied to other lake-rich regions to investigate interregional variability in lake hydrologic response to future climate scenarios.

Different response of earlywood vessel features of Fraxinus mandshurica to rapid warming in warm-dry and cold-wet areas

Xylem anatomical features are constantly adapting to changing environmental conditions, and are directly related to the key functions and physiological processes of trees. However, little is known about the responses of xylem to recent rapid warming in many areas. Based on the anatomical features of the xylem of Fraxinus mandshurica Rupr. from 14 sites in two contrasting areas (warm-dry and cold-wet) of northeast China, the plasticity response and adaptation strategies of radial growth, earlywood vessels (EWV), and hydraulic features of F. mandshurica to climate change were studied. Results showed that, compared with the cold-wet area, F. mandshurica in warm-dry area had wider rings, larger vessel area, higher number of vessels (VN), larger hydraulic diameters (Dh) and higher theoretical tree-ring hydraulic conductivity (Kh). On the contrary, the vessel density (VD), percentage of EWV (PC) and xylem-specific theoretical hydraulic conductivity (Ks) in warm-dry area was lower than those in cold-wet area. In these two areas, the RW, mean vessel area (MVA), total vessel area (TVA), VN, Dh, and Kh were significantly positively correlated with temperature, and negatively correlated with winter moisture. However, the PC, VD, and Ks were inversely related to climate factors in the two areas. F. mandshurica can adjust the density and proportion of EWV by changing the configuration of earlywood and latewood to cope with the interannual climate change and balance the hydraulic efficiency and safety. Rapid warming significantly increased the growing season length and hydraulic efficiency of F. mandshurica in warm-dry and cold-wet areas, thus maximizing carbon fixation. This provides a potential physiological explanation for the growth increase and range expansion of the main broadleaf tree species in temperate zone of northeast China in recent years. F. mandshurica in warm-dry areas benefits greatly from continuous climate warming, but the risk of hydraulic failure may increase.

Climate Shapes the Geographic Distribution and Introgressive Spread of Color Ornamentation in Common Wall Lizards.

AbstractClimate can exert an effect on the strength of sexual selection, but empirical evidence is limited. Here, we tested whether climate predicts the geographic distribution and introgressive spread of sexually selected male color ornamentation across 114 populations of the common wall lizard, Podarcis muralis. Coloration was highly structured across the landscape and did not reflect genetic differentiation. Instead, color ornamentation was consistently exaggerated in hot and dry environments, suggesting that climate-driven selection maintains geographic variation in spite of gene flow. Introgression of color ornamentation into a distantly related lineage appears to be ongoing and was particularly pronounced in warm climates with wet winters and dry summers. Combined, these results suggest that sexual ornamentation is consistently favored in climates that allow a prolonged reproductive season and high and reliable opportunities for lizard activity. This pattern corroborates theoretical predictions that such climatic conditions reduce the temporal clustering of receptive females and increase male-male competition, resulting in strong sexual selection. In summary, we provide compelling evidence for the importance of climate for the evolution of color ornamentation, and we demonstrate that geographic variation in the strength of sexual selection influences introgression of this phenotype.

Preconditions for extreme wet winters over the contiguous United States

We identify physical factors leading to extreme wet winters over the contiguous U.S. and examine whether preconditions operated during winter 2019 (December 2018 to February 2019) when record precipitation occurred that led to billion-dollar flood disasters along the Missouri and Mississippi Rivers. Models and observations are used to determine the effect of slow-varying forcing that may lead to practical forecast skill for extreme wet winters. Atmospheric models indicate that sea surface temperatures during strong eastern Pacific El Niño events like 1983 and 1998 can drive extreme wet winters over the contiguous U.S. These strong El Niños shift the distribution of contiguous U.S. precipitation to wetter conditions with a mean wetting of 1.5–2.0 standard deviations of the interannual variability. The shift to wetter conditions leads to a fivefold increase in the probability of wet winters of the magnitude observed in 2019. On longer timescales, observations indicate contiguous U.S. winter precipitation has increased over the last century. Analysis of historical coupled model simulations indicate anthropogenically-forced shifts to wetter conditions over the last century of 0.2–0.4 standard deviations of the interannual variability. While increasing the risk of extreme wet winters like 2019, this effect is a limited source of predictability during any particular winter. Concerning 2019 specifically, preconditioning factors of the risk for extreme contiguous U.S. winter wetness were weak or absent and offered little practical early warning. The ongoing central Pacific El Niño that winter did not significantly alter the risk of the wetness, and thus the extreme 2019 conditions are judged not to have been a seasonal forecast of opportunity.