Dry Summer Conditions Research Articles

Genetic Differentiation of Abies alba Outside Its Main Range Under Warm Meso- and Sub-Mediterranean Conditions in Italy and Switzerland.

Abies alba is an important European tree species currently mostly found at cool and humid sites in the montane zone. In the past, it grew under markedly warmer and drier climates during the Eemian and mid-Holocene, and cryptic Mediterranean populations confirm the species' capacity to grow under warm, summer-dry conditions. However, it is unknown if warm-loving Mediterranean occurrences are related to specific genetic properties (e.g., subspecies or ecotypes). Investigating the genetics of cryptic warm-loving populations is crucial for a better understanding of past and future population dynamics of A. alba. We genotyped 478 A. alba samples at 174 single-nucleotide polymorphisms (SNP), covering a broad latitudinal range from Southern Italy to Switzerland while accounting for local altitudinal gradients, and combined these newly introduced genotypes with those of other European Abies populations from the literature. Population genetic structure analyses grouped the warm-loving meso- and sub-Mediterranean populations into the same genetic cluster as the mountain populations of each region. The occurrence of three genetic clusters from Northern to Southern Italy is in line with the glacial refugia history. The inferred evolutionary and demographic history suggests a northward expansion of A. alba after glaciation, as well as a trans-Adriatic gene flow between Balkan and Southern Italian populations. Collectively, the combined genotypic data from individuals across the species' range demonstrate that cryptic Mediterranean populations of A. alba align with the local and large-scale genetic structure of populations from its main range, suggesting that the species is able to thrive in a warmer and drier environmental range than hitherto anticipated. This finding implies that it is unneeded to postulate extinct subspecies or ecotypes to explain the occurrence of meso- and sub-Mediterranean Eemian or mid-Holocene silver fir forests, with important implications for future A. alba population dynamics.

Chronic enrichment affects nitrogen removal in tidal freshwater river and estuarine creek sediments.

Population growth in coastal areas increases nitrogen inputs to receiving waterways and degrades water quality. Wetland habitats, including floodplain forests and marshes, can be effective nitrogen sinks; however, little is known about the effects of chronic point source nutrient enrichment on sediment nitrogen removal in tidally influenced coastal systems. This study characterizes enrichment patterns in two tidal systems affected by wastewater treatment facility (WWTF) effluent and assesses the impact on habitat nitrogen removal via denitrification. We collected intact sediment cores from prevalent habitats in a tidal freshwater river (TFZ; swamp forest) and a tidal estuarine creek system (EST; salt marsh) upstream and downstream of a WWTF outfall, and quantified dissolved gas fluxes across the sediment-water interface during wet conditions in early summer and dry conditions in late summer. Data collected during two synoptic water quality monitoring campaigns complimented laboratory experiments to provide environmental context for biogeochemical processing. The two systems exhibited different enrichment patterns such that the river-dominated TFZ system was characterized by consistently elevated nitrate + nitrite concentrations downstream of the WWTF, whereas precipitation and tidal influence affected nutrient distributions in the EST creek. Downstream sediments in TFZ exhibit an apparent saturation response, while upstream rates may be limited by other factors, such as labile organic matter availability. In contrast, downstream sediments in EST denitrify at higher rates than upstream during wet conditions that may enhance transport of effluent. This work provides information on ecosystem functioning in human-influenced environments and can be of use in developing nature-based solutions, such as water treatment wetlands, for nitrogen removal.

Changes in reproduction mediate the effects of climate change and grassland management on plant population dynamics.

Climate change is one of the largest threats to grassland plant species, which can be modified by land management. Although climate change and land management are expected to separately and interactively influence plant demography, this has been rarely considered in climate change experiments. We used a large-scale experiment in central Germany to quantify the effects of grassland management, climate change, and their joint effect on the demography and population growth rate of 11 plant species all native to this temperate grassland ecosystem. We parameterized integral projection models with five years of demographic data to project population growth rate. We hypothesized that plant populations perform better in the ambient than in the future climate treatment that creates hotter and drier summer conditions. Further, we hypothesized that plant performance interactively responds to climate and land management in a species-specific manner based on the drought, mowing, and grazing tolerances as well as the flowering phenology of each species. Due to extreme drought events, over half of our study species went quasi extinct, which highlights how extreme climate events can influence long-term experimental results. We found no consistent support for our expectation that plants perform better in ambient compared with future climate conditions. However, several species showed interactive responses to the treatments, indicating that optimal management strategies for plant performance are expected to shift with climate change. Changes in population growth rates of these species across treatments were mostly due to changes in plant reproduction. Experiments combined with measuring plant demographic responses provide a way to isolate the effects of different drivers on the long-term persistence of species and to identify the demographic vital rates that are critical to manage in the future. Our study suggests that it will become increasingly difficult to maintain species with preferences for moister soil conditions, and that climate and land use can interactively alter demographic responses of the remaining grassland species.

Enhanced Pacific Northwest heat extremes and wildfire risks induced by the boreal summer intraseasonal oscillation

The occurrence of extreme hot and dry summer conditions in the Pacific Northwest region of North America (PNW) has been known to be influenced by climate modes of variability such as the El Niño-Southern Oscillation and other variations in tropospheric circulation such as stationary waves and blocking. However, the extent to which the subseasonal remote tropical driver influences summer heat extremes and fire weather conditions across the PNW remains elusive. Our investigation reveals that the occurrence of heat extremes and associated fire-conducive weather conditions in the PNW is significantly heightened during the boreal summer intraseasonal oscillation (BSISO) phases 6-7, by ~50–120% relative to the seasonal probability. The promotion of these heat extremes is primarily attributed to the enhanced diabatic heating over the tropical central-to-eastern North Pacific, which generates a wave train traveling downstream toward North America, resulting in a prominent high-pressure system over the PNW. The ridge, subsequently, promotes surface warming over the region primarily through increased surface radiative heating and enhanced adiabatic warming. The results suggest a potential pathway to improving subseasonal-to-seasonal predictions of heatwaves and wildfire risks in the PNW by improving the representation of BSISO heating over the tropical-to-eastern North Pacific.

Protected areas, drought, and grazing regimes influence fire occurrence in a fire-prone Mediterranean region

BackgroundExtreme fire seasons in the Mediterranean basin have received international attention due to the damage caused to people, livelihoods, and vulnerable ecosystems. There is a body of literature linking increasingly intense, large fires to a build-up of fuel from rural land abandonment exacerbated by climate change. However, a better understanding of the complex factors driving fires in fire-prone landscapes is needed. We use a global database based on the MODIS Fire CCI51 product, and the Greater Côa Valley, a 340,000-ha area in Portugal, as a case study, to investigate the environmental drivers of fire and potential tools for managing fires in a landscape that has undergone changing agricultural and grazing management.ResultsBetween 2001 and 2020, fires burned 32% (1881.45 km2) of the study area. Scrublands proportionally burnt the most, but agricultural land and forests were also greatly impacted. The risk of large fires (> 1 km2) was highest in these land cover types under dry conditions in late summer. Areas with higher sheep densities were more likely to burn, while cattle density had no apparent relationship with fire occurrence. There was also a 15% lower probability of a fire occurring in protected areas.ConclusionFuture climatic changes that increase drought conditions will likely elevate the risk of large fires in the Mediterranean basin, and abandoned farmland undergoing natural succession towards scrubland will be at particularly high risk. Our results indicate that livestock grazing does not provide a simple solution to reducing fire risk, but that a more holistic management approach addressing social causes and nature-based solutions could be effective in reducing fire occurrence.

Impact of meteorological conditions on the biogenic volatile organic compound (BVOC) emission rate from eastern Mediterranean vegetation under drought

Abstract. A comprehensive characterization of drought's impact on biogenic volatile organic compound (BVOC) emissions is essential for understanding atmospheric chemistry under global climate change, with implications for both air quality and climate model simulation. Currently, the effects of drought on BVOC emissions are not well characterized. Our study aims to test (i) whether instantaneous changes in meteorological conditions can serve as a better proxy for drought-related changes in BVOC emissions compared to the absolute values of the meteorological parameters, as indicated by previous BVOC mixing-ratio measurements and (ii) the impact of a plant under drought stress receiving a small amount of precipitation on BVOC emission rate, and on the manner in which the emission rate is influenced by meteorological parameters. To address these objectives, we conducted our study during the warm and dry summer conditions of the eastern Mediterranean region, focusing on the impact of drought on BVOC emissions from natural vegetation. Specifically, we conducted branch-enclosure sampling measurements in Ramat Hanadiv Nature Park, under natural drought and after irrigation (equivalent to 5.5–7 mm precipitation) for six selected branches of Phillyrea latifolia, the highest BVOC emitter in this park, in September–October 2020. The samplings were followed by gas chromatography–mass spectrometry analysis for BVOC identification and flux quantification. The results corroborate the finding that instantaneous changes in meteorological parameters, particularly relative humidity (RH), offer the most accurate proxy for BVOC emission rates under drought compared to the absolute values of either temperature (T) or RH. However, after irrigation, the correlation of the detected BVOC emission rate with the instantaneous changes in RH became significantly more moderate or even reversed. Our findings highlight that under drought, the instantaneous changes in RH and to a lesser extent in T are the best proxy for the emission rate of monoterpenes (MTs) and sesquiterpenes (SQTs), whereas under moderate drought conditions, T or RH serves as the best proxy for MT and SQT emission rate, respectively. In addition, the detected emission rates of MTs and SQTs increased by 150 % and 545 %, respectively, after a small amount of irrigation.

Lack of management, land-use changes, poor site conditions and drought contribute to the decline of old pollarded oaks

In Europe, people have managed forests and woodlands for centuries. Old pollarded oaks reflect historical legacies, and their conservation is threatened by the abandonment of this traditional forest use. However, site conditions (topography, soil features, land cover, and historical use) and warming-triggered drought stress also contribute to their growth decline, particularly in seasonally dry regions. We investigated two stands of pollarded Mediterranean oaks (Quercus subpyrenaica), where pollarding was abandoned in the 1950s, showing contrasting land cover and tree sizes in north-eastern Spain. Changes in land cover, soil characteristics (texture, pH, and nutrient concentrations), climate conditions, and tree-ring data (basal area increment −BAI−, and ring-width indices) were analysed. The Artosilla site, showing the smallest trees, presented the lowest long-term growth rates (period 1730−2022, mean BAI = 19.7 cm2 yr−1) as compared with the Aineto site with bigger oaks (mean BAI = 32.9 cm2 yr−1). Old trees were found in both sites with ages ranging 293−311 years. The less fertile soils in Artosilla, where pine plantations diminish canopy thermal amplitude, may contribute to the long-term growth decline observed there. Moreover, more major growth suppressions were found in this site, particularly in the 1940s, which suggest a more intensive historical use. Aineto showed a stronger BAI decline since the 1950s, which could be a response to increasingly warmer and drier summer conditions. In contrast, growth in Artosilla is decoupling from soil and atmospheric drought suggesting chronic growth stagnation. Poor site conditions (steeper slope, less fertile soils, intensive historical use) contributed to the decline of pollarded oaks. Active management is required to preserve these unique old, monumental trees.

Climate sensitive tree growth modelling of Myrocarpus frondosus in Southern Brazil using tree-ring time series and distributed generalized additive lag models

Abstract Climate change is expected to strongly affect the functioning of tropical and subtropical forest ecosystems around the globe, and tree-ring analysis is proving increasingly useful for understanding the changing dynamics in these environments. However, traditional dendroecological methods were not originally designed to jointly consider inter-annual and inter-tree variations, often assuming linear growth-climate relationships, and limiting the potential to address in-deep questions regarding the tree growth sensitivity to environmental drivers. In the present study, we applied a flexible generalized additive model to assess the climate-sensitivity of the species Myrocarpus frondosus Allemão growing in a subtropical Atlantic Forest (AF) site in southern Brazil. Tree-ring width time series from 117 stem cores together with monthly climate data of temperature and precipitation covering the period from 1968 to 2021 were used for model construction. The model was designed to simultaneously encompass detrending, to capture nonlinear effects of climate variables and their interactions and to predict mean tree-ring widths for the species. Based on a distributed lag model approach, we also tested the influence of different lengths of lagged climate series over the model accuracy. Both precipitation and temperature proved to be strong drivers of M. frondosus radial growth in the subtropical AF. An interaction effect between these regressor variables revealed a likely water stress scenario arising from warm and dry summer conditions, with strongly negative impacts for the species. Detrimental impacts on tree dormancy period can also be expected due to milder winters, with legacy effects on the radial increments across two subsequent years. In addition to monitoring, the approach applied here meets the needs for more robust predictions of the impacts of future climate conditions on species and communities, contributing to efforts aimed at the management and conservation in tropical and subtropical ecosystems, particularly in the AF.

A review of grass species yields and growth rates in Northland, New Zealand

ABSTRACT Pastoral farming is a major land use in New Zealand's Northland region, with 3,171 farm holdings and a total area of 637,500 hectares in 2022. The region's pasture grasses include temperate (C3) and subtropical and tropical (C4) grasses which support dairy, and sheep and beef production from grazing. In lowland areas, C3 and some annual C4 grasses are prevalent where cultivation occurs, while perennial C4 grasses dominate areas with low soil fertility and summer dry conditions. Grass-based pasture growth rates (kg dry matter/ha/day) from published and unpublished sources were assembled into the AgYields database. Among the resident and sown grasses tested in Kaitaia, Kaikohe, Whangarei and Dargaville, perennial ryegrass represented ∼60% of the total data points. Dominant kikuyu pastures represented 23% and the remaining species represented 17%. Rates of growth ranged from 5 to 120 kg DM/ha/day, being lowest in late autumn-winter and highest in early summer. Data were compared and agronomic traits (i.e. drought tolerance, biomass production and tillering) are discussed to assess species suitability for the Northland environment. The medium-term prospect suggests an urgent need to improve research into management of cocksfoot and tall fescue-based pastures to provide viable alternatives to overcome the decreasing persistence of perennial ryegrass.

Impact of climate change and genetic development on Iowa corn yield

The vulnerability of corn yield to high temperature and insufficient rainfall in the US mid-west is widely acknowledged. The impact of extreme weather and genetic development on corn yield is less well known. One of the main reasons is that the multicollinearity in the variables can lead to confounding results. Here we model the impact of climate and genetic development by employing an elastic net regression model to address the multicollinearity issue. This allows us to develop a more robust multiple regression model with higher predictive accuracy. Using granular data for Iowa from 1981-2018, we find that corn yield is vulnerable to high mean summer temperatures particularly in July, a widening diurnal temperature range in June and dry summer conditions (due to extremely low rainfall) from June-August. We find that overall climate impact reduced average annual yield by 0.7%. We also find that genetic development which led to earlier planting dates, widening duration of the reproductive interval, higher growing degree day accumulation and larger net planted area had a beneficial impact on the Iowa corn yield during 1981-2018 resulting in an average annual yield improvement of 1.8% per annum. This provides a basis for optimism that these genetic developments and management practices will continue to adapt and improve in the future to counter the impact of climate change on corn yield. We have also modelled the impact of future climate change using the latest climate projections from the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC AR6). These climate projections show that the average temperature during the growing season (MayO-October) will increase by 2.4 -2.9 o C by mid-century while the average spring temperature (March and April) will increase by a relatively slower 1.9 -2.3 o C by mid-century. Additionally, climate projections show that both temperature and rainfall will also become more extreme in the future with the changes varying from spring to summer. Our results show that, just due to climate change alone in Iowa corn yield will decline between 1.4-1.7% per annum until mid-century (or 1.2-2.1% per annum until the late twenty first century).

The Physiological Adjustments of Two Xerophytic Shrubs to Long-Term Summer Drought

Adaptive characteristics of plants, such as those associated with photosynthesis and resource use efficiency, are usually affected by synthesis costs and resource availability. The impact of extreme climate events such as long-term drought on plant physiological functions needs to be examined, particularly as it concerns the internal management of water and nitrogen (N) resources. In this study, we evaluated the resource management strategies for water and N by xerophytic shrubs, Artemisia ordosica and Salix psammophila, under extreme summer drought. This was carried out by comparing the plants’ physiological status during periods of wet and dry summer conditions in 2019 and 2021. Compared with the wet period, A. ordosica and S. psammophila both decreased their light-saturated net carbon (C) assimilation rate (Asat), stomatal conductance (gs), transpiration rate (E), leaf N content per leaf area (Narea), and photosynthetic N use efficiency (PNUE) during the summer drought. Whether in wet or dry summers, the gas-exchange parameters and PNUE of A. ordosica were generally greater than those associated with S. psammophila. The instantaneous water use efficiency (IWUE) response to drought varied with species. As a drought-tolerant species, the A. ordosica shrubs increased their IWUE during drought, whereas the S. psammophila shrubs (less drought-tolerant) decreased theirs. The divergent responses to drought by the two species were largely related to differences in the sensitivity of gs, and as a result, E. Compared with A. ordosica, S. psammophila’s inferior plasticity regarding gs response affected its ability to conserve water during drought. Our research illustrates the need for assessing plasticity in gs when addressing plant adaptation to long-term drought. A high dry-season IWUE in xerophytic shrubs can benefit the plants by augmenting their C gain.

Multi-year time series of daily solute and isotope measurements from three Swiss pre-Alpine catchments

Time series analyses of solute concentrations in streamwater and precipitation are powerful tools for unraveling the interplay of hydrological and biogeochemical processes at the catchment scale. While such datasets are available for many sites around the world, they often lack the necessary temporal resolution or are limited in the number of solutes they encompass. Here we present a multi-year dataset encompassing daily records of major ions and a range of trace metals in both streamwater and precipitation in three catchments in the northern Swiss Pre-Alps. These time series capture the temporal variability observed in solute concentrations in response to storm events, snow melt, and dry summer conditions. This dataset additionally includes stable water isotope data as an extension of a publicly available isotope dataset collected concurrently at the same locations, and together these data can provide insights into a range of ecohydrological processes and enable a suite of analyses into hydrologic and biogeochemical catchment functioning.

Increasing radial growth in old-growth high-elevation conifers in Southern California, USA, during the exceptional "hot drought" of 2000-2020.

Hot droughts, droughts attributed to below-average precipitation and exceptional warmth, are increasingly common in the twenty-first century, yet little is known about their effect on coniferous tree growth because of their historical rarity. In much of the American West, including California, radial tree growth is principally driven by precipitation, and narrow ring widths are typically associated with either drier or drought conditions. However, for species growing at high elevations (e.g., Larix lyalli, Pinus albicaulis), growth can be closely aligned with above-average temperatures with maximum growth coinciding with meteorological drought, suggesting that the growth effects of drought span from adverse to beneficial depending on location. Here, we compare radial growth responses of three high-elevation old-growth pines (Pinus jeffreyi, P. lambertiana, and P. contorta) growing in the San Jacinto Mountains, California, during a twenty-first-century hot drought (2000-2020) largely caused by exceptional warmth and a twentieth-century drought (1959-1966) principally driven by precipitation deficits. Mean radial growth during the hot drought was 12% above average while 18% below average during the mid-century drought illustrating that the consequences of environmental stress exhibit spatiotemporal variability. We conclude that the effects of hot droughts on tree growth in high-elevation forests may produce responses different than what is commonly associated with extended dry periods for much of western North America's forested lands at lower elevational ranges and likely applies to other mountainous regions (e.g., Mediterranean Europe) defined by summer-dry conditions. Thus, the climatological/biological interactions discovered in Southern California may offer clues to the unique nature of high-elevation forested ecosystems globally.

Keeping Water in Climate-Changed Headwaters Longer

Climate-change projections for California confidently describe a future with warmer temperatures, more evaporative demand, less snow, more rain, earlier and flashier runoff and streamflow, and drier summer conditions. The future of annual precipitation is much less certain, but a fairly unanimous projection of drier, more drought-prone conditions punctuated by occasional stronger-than-historical storms is almost as common among projections as is the warming itself. Rather than focusing on the less certain annual precipitation changes, we recommend more focus on keeping water in the headwaters longer. Doing so will involve reducing winter flood flows from headwater catchments, reducing the summer aridification (and wildfire risks) there, salvaging some groundwater recharge that would likely otherwise be lost, and overall, perpetuating headwater (and downstream) hydrologies under more historical and natural conditions. Among the available near-term adaptation strategies for keeping water in the headwaters longer, we discuss several examples here: (1) an increased emphasis on soils and percolation management as a priority and co-benefit in forest-health restoration activities; (2) beaver-population restoration or proliferation of beaver-inspired infrastructures; and (3) upstream-focused, forecast-informed reservoir-operation (FIRO) strategies.

Organic layers preserved in ice patches: A new record of Holocene environmental change on the Beartooth Plateau, USA

Growing season temperatures play a crucial role in controlling treeline elevation at regional to global scales. However, understanding of treeline dynamics in response to long-term changes in temperature is limited. In this study, we analyze pollen, plant macrofossils, and charcoal preserved in organic layers within a 10,400-year-old ice patch and in sediment from a 6000-year-old wetland located above present-day treeline in the Beartooth Mountains, Wyoming, to explore the relationship between Holocene climate variability and shifts in treeline elevation. Pollen data indicate a lower-than-present treeline between 9000 and 6200 cal yr BP during the warm, dry summer and cold winter conditions of the early Holocene. Increases in arboreal pollen at 6200 cal yr BP suggest an upslope treeline expansion when summers became cooler and wetter. A possible hiatus in the wetland record at ca. 4200–3000 cal yr BP suggests increased snow and ice cover at high elevations and a lowering of treeline. Treeline position continued to fluctuate with growing season warming and cooling during the late-Holocene. Periods of high fire activity correspond with times of increased woody cover at high elevations. The two records indicate that climate was an important driver of vegetation and treeline change during the Holocene. Early Holocene treeline was governed by moisture limitations, whereas late-Holocene treeline was sensitive to increases in growing season temperatures. Climate projections for the region suggest warmer temperatures could decrease effective growing season moisture at high elevations resulting in a reduction of treeline elevation.

A Large-Diameter Earth–Air Heat Exchanger (EAHX) Built for Standalone Office Room Cooling: Monitoring Results for Hot and Dry Summer Conditions

Earth–air heat exchangers (EAHX) use the soil thermal capacity to dampen the amplitude of outdoor air temperature oscillations. This effect can be used in hot and dry climates for room cooling, and depending on the EAHX design, this cooling can be achieved with very few resources other than those used during EAHX construction. This is an obvious advantage compared to the significant energy consumption and operational costs of refrigeration machines traditionally used in room cooling. Despite the large number of papers on EAHXs available in the scientific literature, very few deal with large-diameter EAHXs (with pipe diameters larger than 0.30 m), and even fewer present monitoring data gathered from a built and functional large-diameter EAHX. The present paper uses monitoring data and provides a detailed quantitative analysis of the performance of a large-diameter EAHX built for standalone cooling of an existing office building. The field monitoring was carried out during a characteristic hot and dry summer period of the south of Portugal. Results show that outdoor air to EAHX exit air temperature gradients reach 9 K and cooling capacities exceed 27 kW. Moreover, the studied EAHX is capable of standalone cooling for outdoor air temperatures up to 33 °C and meets more than 50% of the room design cooling demand for outdoor air temperatures as high as 37 °C. This evidences that large-diameter EAHXs have the potential to achieve significant reductions in CO2 emissions and in energy consumption associated with building cooling in hot and dry climates.

A Spatial Assessment of Current and Future Foliar Hg Uptake Fluxes Across European Forests

AbstractAtmospheric mercury (Hg) is deposited to land surfaces mainly through vegetation uptake. Foliage stomatal gas exchange plays an important role for net vegetation Hg uptake, because foliage assimilates Hg via the stomata. Here, we use empirical relationships of foliar Hg uptake by forest tree species to produce a spatially highly resolved (1 km2) map of foliar Hg fluxes to European forests over one growing season. The modeled forest foliar Hg uptake flux is 23 ± 12 Mg Hg season−1, which agrees with previous estimates from literature. We spatially compared forest Hg fluxes with modeled fluxes of the chemical transport model GEOS‐Chem and find a good overall agreement. For European pine forests, stomatal Hg uptake was shown to be sensitive to prevailing conditions of relatively high ambient water vapor pressure deficit (VPD). We tested a stomatal uptake model for the total pine needle Hg uptake flux during four previous growing seasons (1994, 2003, 2015/2017, 2018) and two climate change scenarios (RCP 4.5 and RCP 8.5). The resulting modeled total European pine needle Hg uptake fluxes are in a range of 8.0–9.3 Mg Hg season−1 (min–max). The lowest pine forest needle Hg uptake flux to Europe (8 Mg Hg season−1) among all investigated growing seasons was associated with unusually hot and dry ambient conditions in the European summer 2018, highlighting the sensitivity of the investigated flux to prolonged high VPD. We conclude, that stomatal modeling is particularly useful to investigate changes in Hg deposition in the context of extreme climate events.

Spatial and temporal analysis of drought-related climate indices for Hungary for 1971–2100

The lack of precipitation may cause severe damage in different sectors, especially in agriculture and forestry, therefore, its analysis is a key element of adaptation strategies in the changing climate. In the present study, we selected different climate indices as important indicators for forests to investigate the current and future wet and dry conditions in summer in Hungary. For the historical period (from 1971), the observation-based HuClim dataset is used, which already shows a slight drying trend in the past 50 years, especially in June. For the future, regional climate model simulations from the EURO-CORDEX program are used, taking into account two different RCP scenarios (a business-as-usual scenario and an intermediate mitigation scenario, i.e., RCP8.5 and RCP4.5, respectively). Since mitigation starts to affect the climate system after about 20 years, results do not differ substantially for the two scenarios until 2060, however, the simulated changes highly depend on the applied RCP scenario in the late 21st century. Based on the De Martonne Index, a large expansion of semi-arid conditions is projected for the future in July and even more in August. The analysis of the Forestry Aridity Index shows that the steppe category will become dominant in 2081–2100, while the category optimal for beech may disappear entirely from Hungary according to the RCP8.5 scenario.

Geomorphic complexity influences coarse particulate organic matter transport and storage in headwater streams

Coarse particulate organic matter (CPOM; organic matter 1–100 mm in diameter, excluding small wood) stored in streams provides an important energy source for aquatic ecosystems, and CPOM transport provides downstream energy subsidies and is a pathway for watershed carbon export. However, we lack understanding of the magnitude of and processes influencing CPOM storage and transport in headwater streams. We assessed how geomorphic complexity and hydrologic regime influence CPOM transport and storage in the Colorado Front Range, USA. We compared CPOM transport during snowmelt in a stream reach with high retentive feature (e.g., wood, cobbles, and other features) frequency to a reach with low retentive feature frequency, assessing how within-a-reach geomorphic context influences CPOM transport. We also compared CPOM transport in reaches with differing valley geometry (two confined reaches versus a wide, multi-thread river bead) to assess the influence of geomorphic variations occurring over larger spatial extents. Additionally, we compared CPOM storage in accumulations in reaches (n = 14) with flowing water or dry conditions in late summer and investigated how small pieces of organic matter [e.g., woody CPOM and small wood (>1 min length and 0.05–1 min diameter or 0.5–1 min length and >0.1 min diameter)] influence CPOM storage. We found that within-a-reach retentive feature frequency did not influence CPOM transport. However, valley geometry influenced CPOM transport, with a higher CPOM transport rate (median: 1.53 g min−1) downstream of a confined stream reach and a lower CPOM transport rate (median: 0.13 g min−1) downstream of a low gradient, multi-thread river bead. Additionally, we found that particulate organic carbon (POC) export (0.063 Mg C) in the form of CPOM was substantially lower than dissolved organic carbon (DOC) export (12.3 Mg C) in one of these headwater streams during the 2022 water year. Dry reaches stored a higher volume of CPOM (mean = 29.18 m3 ha−1) compared to reaches with flowing water (15.75 m3 ha−1), and woody CPOM pieces trapped 37% of CPOM accumulations. Our results demonstrate that the influence of geomorphic context on CPOM transport depends on the scale and type of geomorphic complexity, POC may be lower than DOC export in some headwater streams, and small woody organic material is important for trapping CPOM small streams.

Phenological development of subterranean clover (Trifolium subterraneum L.) in New Zealand in response to different climate change scenarios

Climate predictions for New Zealand for the coming decades suggest rising temperatures (+0.7–3 °C), increased diurnal temperature and variable precipitation patterns that differ around the country and with seasons. The most common pattern of annual precipitation indicates the largest increases in the west of the South Island and the largest decreases in the east of the North Island and coastal Marlborough. The phenophases of subterranean clover were estimated and quantified using a thermal time-based model under different climate scenarios based on greenhouse gases and aerosol pathways over the 21st century, known as the Representative Concentration Pathways (RCPs), at two periods (mid and end of the century). The estimated flowering (R3) and post- flowering (R6-R11) date change showed a consistent trend across all districts. The largest date advances (≥ 5 days) were predicted for the three current latest flowering districts (Mackenzie, Queenstown and Central Otago). A reduction of the plant’s life cycle, for both ‘Early’ and ‘Late’ maturity cultivars may have undesired consequences for forage yield so genetic material with later flowering dates may be useful. Adaptation strategies to mitigate the future warming effects include using ‘Late’ flowering cultivars and greater use of supplementary feed through summer dry conditions.