Persistent Snow Cover Research Articles

Deriving Snow Cover Metrics for Alaska from MODIS

Moderate Resolution Imaging Spectroradiometer (MODIS) daily snow cover products provide an opportunity for determining snow onset and melt dates across broad geographic regions; however, cloud cover and polar darkness are limiting factors at higher latitudes. This study presents snow onset and melt dates for Alaska, portions of western Canada and the Russian Far East derived from Terra MODIS snow cover daily 500 m grid data (MOD10A1) and evaluates our method for filling data gaps caused by clouds or polar darkness. Pixels classified as cloud or no data were reclassified by: spatial filtering using neighboring pixel values; temporal filtering using pixel values for days before/after cloud cover; and snow-cycle filtering based on a time series assessment of a pixel’s position within snow accumulation, cover or melt periods. During the 2012 snow year, these gap-filling methods reduced cloud pixels from 27.7% to 3.1%. A total of 12 metrics (e.g., date of first and last snow, date of persistent snow cover and periods of intermittence) for each pixel were calculated by snow year. A comparison of MODIS-derived snow onset and melt dates with in situ observations from 244 weather stations generally showed an early bias in MODIS-derived dates and an effect of increasing cloudiness exacerbating bias. Our results show that mean regional duration of seasonal snow cover is 179–311 days/year and that snow cover is often intermittent, with 41% of the area experiencing ≥2 snow-covered periods during a snow season. Other regional-scale patterns in the timing of snow onset and melt are evident in the yearly 500 m gridded products publically available at http://static.gina.alaska.edu/NPS_products/MODIS_snow/.

Individual Variations of Winter Surface Air Temperature over Northwest and Northeast China and Their Respective Preceding Factors

AbstractBased on monthly mean surface air temperature (SAT) from 71 stations in northern China and NCEP/NCAR and NOAA-CIRES (Cooperative Institute for Research in Environmental Sciences) twentieth century reanalysis data, the dominant modes of winter SAT over northern China were explored. The results showed that there are two modes that account for a majority of the total variance over northern China. The first mode is unanimously colder (warmer) over the whole of northern China. The second mode is characterized by a dipole structure that is colder (warmer) over Northwest China (NWC) and warmer (colder) over Northeast China (NEC), accounting for a fairly large proportion of the total variance. The two components constituting the second mode, the individual variations of winter SAT over NWC and NEC and their respective preceding factors, were further investigated. It was found that the autumn SAT anomalies are closely linked to persistent snow cover anomalies over Eurasia, showing the delayed effects on wi...

Winter Management of Yearling Steers in a Grass‐Fed Beef Production System

The role of winter pasture management for beef production systems requires clarification. We designed four pasture management systems to sustain a 0.5 kg average daily gain (ADG) of spring‐born steers during fall and winter. The experiment was conducted at West Virginia University, Reedsville Experimental Farm. Treatments replicated three times on 0.81 ha grazing units included: (i) naturalized grazingland with haylage (NGH), (ii) orchardgrass (Dactylis glomerata L.) cultivated pastureland, animals moved to drylot with hay (OCD), (iii) orchardgrass cultivated pastureland with haylage (OCH), and (iv) tall fescue (Lolium arundinaceum, Schreb., Darbysh.) cultivated pastureland with haylage (TCH). Grasslands were stockpiled from August and N (84 kg ha−1) was applied to all except NGH. Grazing began in November and ended in January with a stocking density of 4.9 steers ha−1hay or haylage were fed until April. Pelleted soybean (Glycine max L.) hulls (PSH) were fed when ADG fell below 0.5 kg. Herbage disappearance was highest in TCH (1521 kg ha−1). Herbage accumulation of TCH was reduced more by dry weather during stockpiling. Differences in nutritive value between grasslands were small, as OCH and OCD had greater crude protein (CP) whereas NGH had lower CP. No differences in ADG were found between treatments; however, in 2006–2007 and 2008–2009 with early and persistent snow cover, supplementation was required, being significant in 2006–2007. Yearling steers can be maintained during winter with a combination of stockpiled and conserved forages fed to achieve gains of 0.5 kg ha−1d−1.

Tillage Management and Seasonal Effects on Denitrifier Community Abundance, Gene Expression and Structure over Winter.

Tillage effects on denitrifier communities and nitrous oxide (N2O) emissions were mainly studied during the growing season. There is limited information for the non-growing season, especially in northern countries where winter has prolonged periods with sub-zero temperatures. The abundance and structure of the denitrifier community, denitrification gene expression and N2O emissions in fields under long-term tillage regimes [no-tillage (NT) vs conventional tillage (CT)] were assessed during two consecutive winters. NT exerted a positive effect on nirK and nosZ denitrifier abundance in both winters compared to CT. Moreover, the two contrasting managements had an opposite influence on nirK and nirS RNA/DNA ratios. Tillage management resulted in different denitrifier community structures during both winters. Seasonal changes were observed in the abundance and the structure of denitrifiers. Interestingly, the RNA/DNA ratios were greater in the coldest months for nirK, nirS and nosZ. N2O emissions were not influenced by management but changed over time with two orders of magnitude increase in the coldest month of both winters. In winter of 2009-2010, emissions were mainly as N2O, whereas in 2010-2011, when soil temperatures were milder due to persistent snow cover, most emissions were as dinitrogen. Results indicated that tillage management during the growing season induced differences in denitrifier community structure that persisted during winter. However, management did not affect the active cold-adapted community structure.

Microhabitat use by mountain pygmy‐possum (Burramys parvus): Implications for the conservation of small mammals in alpine environments

AbstractThe Australian alpine region harbours a wide range of species, many of which are endemic and of high conservation value. Among these species, the endangered mountain pygmy‐possum, Burramys parvus, is of particular interest because this specialized marsupial is highly sensitive to extreme temperatures. The selection of microhabitats by B. parvus is a critical but poorly understood element of its biological characteristics. To understand the microhabitat preferences of B. parvus, we performed detailed investigations of the thermal properties of alpine boulder fields. The selection of a preferred microclimate was demonstrated by comparing temperatures and environmental conditions in preferred and non‐preferred boulder fields. The variability of the daily temperature depended on the depth at which measurements were made within the boulder fields. Temperatures were more stable as depth increased. The results suggest that B. parvus prefers to occupy deep boulder fields at high elevations with good rock structure (small rock and cavity size with multiple layers) and long snow duration because these boulder fields can provide a favourable microclimate. At 1 m depth, the maximum temperatures in the hottest part of the year were 1.27°C cooler in preferred compared to non‐preferred boulder fields. In the coldest part of the year, immediately following the melting of persistent snow cover, the minimum temperatures at a depth of 1 m were 1.67°C warmer in preferred compared to non‐preferred boulder fields. On average, the snow duration was 27 days greater in the boulder fields preferred by B. parvus than in non‐preferred boulder fields. Our results emphasize the value of boulder field microhabitats as thermal refuges for small mammals in rocky habitats within alpine environments in the light of continuing habitat loss and climate change.

Spatio-Temporal Change of Snow Cover and Its Response to Climate over the Tibetan Plateau Based on an Improved Daily Cloud-Free Snow Cover Product

Using new, daily cloud-free snow-cover products, this study examines snow cover dynamics and their response to climate change. The results demonstrate that the daily cloud-free snow-cover products not only posses the advantages of the AMSR-E (unaffected by weather conditions) and MODIS (relatively higher resolution) products, but are also characterized by high snow and overall classification accuracies (~85% and ~98%, respectively), substantially greater than those of the existing daily snow-cover products for all sky conditions and very similar to, or even slightly greater than, those of the daily MODIS products for clear-sky conditions. Using the snow-cover products, we analyzed the snow cover dynamics over the Tibetan Plateau and determined that the maximum number of snow-covered days (SCD) in a year followed a decreasing tendency from 2003 to 2010, with a decrease in snow-covered area (SCA) equivalent to 55.3% of the total Tibetan Plateau area. There is also a slightly increasing tendency in the maximum snow cover area (SCA), and a slightly decreasing tendency in the persistent snow cover area (i.e., pixels of SCD > 350 days) was observed for the 8-year period, which was characterized by increases in temperature (0.09 °C/year) and in precipitation (0.26 mm/year). This suggests that, on the Tibetan Plateau, changes in temperature and precipitation exert a considerable influence on the regional SCD and SCA, as well as the distribution of persistent snow cover.

Spatio-Temporal Change of Snow Cover and Its Response to Climate over the Tibetan Plateau Based on an Improved Daily Cloud-Free Snow Cover Product

Using new, daily cloud-free snow-cover products, this study examines snow cover dynamics and their response to climate change. The results demonstrate that the daily cloud-free snow-cover products not only posses the advantages of the AMSR-E (unaffected by weather conditions) and MODIS (relatively higher resolution) products, but are also characterized by high snow and overall classification accuracies (~85% and ~98%, respectively), substantially greater than those of the existing daily snow-cover products for all sky conditions and very similar to, or even slightly greater than, those of the daily MODIS products for clear-sky conditions. Using the snow-cover products, we analyzed the snow cover dynamics over the Tibetan Plateau and determined that the maximum number of snow-covered days (SCD) in a year followed a decreasing tendency from 2003 to 2010, with a decrease in snow-covered area (SCA) equivalent to 55.3% of the total Tibetan Plateau area. There is also a slightly increasing tendency in the maximum snow cover area (SCA), and a slightly decreasing tendency in the persistent snow cover area (i.e., pixels of SCD > 350 days) was observed for the 8-year period, which was characterized by increases in temperature (0.09 °C/year) and in precipitation (0.26 mm/year). This suggests that, on the Tibetan Plateau, changes in temperature and precipitation exert a considerable influence on the regional SCD and SCA, as well as the distribution of persistent snow cover.

Non‐growing‐season soil respiration is controlled by freezing and thawing processes in the summer monsoon‐dominated Tibetan alpine grassland

AbstractThe Tibetan alpine grasslands, sharing many features with arctic tundra ecosystems, have a unique non‐growing‐season climate that is usually dry and without persistent snow cover. Pronounced winter warming recently observed in this ecosystem may significantly alter the non‐growing‐season carbon cycle processes such as soil respiration (Rs), but detailed measurements to assess the patterns, drivers of, and potential feedbacks on Rs have not been made yet. We conducted a 4 year study on Rs using a unique Rs measuring system, composed of an automated soil CO2 flux sampling system and a custom‐made container, to facilitate measurements in this extreme environment. We found that in the nongrowing season, (1) cumulative Rs was 82–89 g C m−2, accounting for 11.8–13.2% of the annual total Rs; (2) surface soil freezing controlled the diurnal pattern of Rs and bulk soil freezing induced lower reference respiration rate (R0) and temperature sensitivity (Q10) than those in the growing season (0.40–0.53 versus 0.84–1.32 µmol CO2 m−2 s−1 for R0 and 2.5–2.9 versus 2.9–5.6 for Q10); and (3) the intraannual variation in cumulative Rs was controlled by accumulated surface soil temperature. We found that in the summer monsoon‐dominated Tibetan alpine grassland, surface soil freezing, bulk soil freezing, and accumulated surface soil temperature are the day‐, season‐, and year‐scale drivers of the non‐growing‐season Rs, respectively. Our results suggest that warmer winters can trigger carbon loss from this ecosystem because of higher Q10 of thawed than frozen soils.

Physiographic and climatic controls on snow cover persistence in the Sierra Nevada Mountains

AbstractThe persistence of snow cover across mountainous landscapes influences land‐atmosphere energy exchange, water availability, the partitioning of snowmelt into various hydrologic pathways, vegetation productivity, and fluxes of nutrients. Understanding the processes controlling snow cover persistence has been limited as relationships between physiography, climate, and snow persistence are nonlinear and difficult to characterize empirically. The work detailed herein uses 7 years of remotely sensed snow cover persistence observed from the Moderate Resolution Imaging Spectroradiometer over the Sierra Nevada Mountains as a dependent variable in binary regression tree models with a suite of independent variables comprised of both physiographic and climatic metrics. Annual snow cover persistence over 2001–2007 revealed significant inter‐annual variability, with domain‐average snow persistence values exceeding 4.01 (i.e. early April) in the wettest year of 2005 and reaching as low as 2.90 (i.e. late February) in the driest year of 2007. Regression tree models revealed that elevation was the most important explanatory variable regarding snow cover persistence, ranking first in the hierarchical models in 10 out of 13 watersheds. Precipitation (Feather and Owens River basins) and temperature (Kern River basin) were the first‐ranking variables in the remaining three watersheds. Second, the order variables of importance included vegetation, which ranked between 2nd and 5th in 10 of 13 watersheds, and slope, which ranked 4th and 5th in 12 of the 13 watersheds. Interestingly, solar radiation and aspect were of tertiary importance but were more influential in watersheds with north–south orientation (e.g. in the Feather, Mokelumne and Stanislaus watersheds). These results have implications for understanding the sensitivity of snow cover persistence to changes in climate as watersheds where elevation and/or temperature strongly influence snow cover persistence may be more sensitive to future warming. Further work is needed to identify associated ecosystem sensitivities to future changes in snow cover persistence. Copyright © 2014 John Wiley & Sons, Ltd.

Anatomy of wintertime ozone associated with oil and natural gas extraction activity in Wyoming and Utah

Abstract Winter maximum daily 8-hour average (MDA8) ozone concentrations in the Upper Green River Basin, Wyoming (UGRBWY) and the Uintah Basin, Utah (UBUT) have frequently exceeded 100 ppb in January, February and March, in the past few years. Such levels are well above the U.S. air quality standard of 75 ppb. In these two remote basins in the Rockies, local ozone precursor emissions result from intense oil and gas extraction activities that release methane, volatile organic compounds (VOCs), and nitrogen oxides (NOx) to the atmosphere. These emissions become trapped beneath a stable and shallow (∼50–200 m) boundary layer maintained in low wind conditions. Wintertime surface ozone formation conditions are more likely in the UBUT than in the UGRBWY as the topography of the UBUT is an enclosed basin whereas the UGRBWY is open on its southern perimeter thus allowing for more air turnover. With snow-covered ground, high ozone events regularly begin in mid-December and last into early March in the UBUT whereas they usually do not begin in earnest until about a month later in the UGRBWY and may persist until mid-March. Winters without snow cover and the accompanying cold pool meteorological conditions do not experience high ozone events in either basin. For nine years with ozone observations in the UGRBWY (2005–2013) and four in the UBUT (2010–2013), all years with adequate (≥6 inches) and persistent snow cover, experienced days with ozone values ≥75 ppb except in 2012 in the UGRBWY when persistent high wind (>5 m/s) conditions were prevalent. Year to year differences in the occurrences of high ozone episodes appear to be driven primarily by differing meteorological conditions rather than by variations in ozone precursor levels.

Estimating winter trends in climatic variables in the Chic-Chocs Mountains, Canada (1970-2009)

This paper presents an analysis of winter climate variability based on daily mean temperature and precipitation data since 1970 in the Chic-Chocs Mountain range (located in the Gaspe Peninsula, Eastern Quebec, Canada). Mountain environments are particularly sensitive to rapid climate change and are therefore good indicators of recent global warming. The main goal of this study is to demonstrate how joint probability temperature/precipitation distributions can be used to estimate winter condition changes (trends) for six meteorological stations in the study area (the altitudinal range for the stations is from 5 to 574 m). The presence and persistence of snow cover was also estimated. Previous studies have shown a lack of evidence of significant trends in snow-cover characteristics (density, depth and snow water equivalent (SWE)) from the early 1980s to the present, despite an increase in temperature over the same period. A reanalysis of these data sets in addition to the use of a combination of temperature and precipitation data categorized into four modes (warm/wet, warm/dry, cold/wet and cold/dry) was also performed. Despite this new analysis, no clear evidence of climate change could be found in the study area over the last four decades. The results revealed that patterns and trends are quite different from one station to another, but when the environment is taken into account (valley or plateau, coastal versus inland) some apparent patterns emerge.

Heavy snow in Polish–German lowlands – Large-scale synoptic reasons and economic impacts

Large-scale synoptic conditions and economic impact of heavy snow in Polish–German lowlands were analysed. During intense snowfalls, negative anomalies of sea level pressure (SLP) and 500hPa level appear over central Europe, resulting in a low pressure system. Snow cover persistence is possible under positive anomalies of SLP over the majority of the continent, except for its south western part where weak negative anomalies are observed.

Long-term vegetation dynamic in the Northwestern Caucasus: which communities are more affected by upward shifts of plant species?

We studied long-term (25–31 years) dynamics of alpine communities at the Teberda Reserve, NW Caucasus, Russia, to test the following hypotheses: (1) lower altitude species increase and high altitude species decrease their abundance as a consequence of climate warming; (2) such changes in abundance are more significant in communities with short growth season (due to persistent snow cover) compared to exposed communities; (3) species with similar changes in abundance have similar functional traits. Four alpine communities with different positions in relief were considered in order of winter snow cover: alpine lichen heaths (ALH), Festuca varia grasslands (FVG), Geranium-Hedysarum meadows (GHM), and snowbed communities (SBC).

Overwintering potential of the stripe rust pathogen (Puccinia striiformis) in central Alberta

In central Alberta, stripe rust (Puccinia striiformis) of wheat and barley has become more prevalent and this disease is generally more severe on winter wheat than spring wheat. This study was carried out to determine the potential role of winter wheat in overwintering and transmission of inoculum to subsequent spring crops. Field plants of winter wheat, infected in the autumn, were sampled during January to May from 2008 to 2011 in central Alberta. The pathogen's viability was established using in vivo growth parameters and pathogen detection was determined using PCR. Approximately 4–20% of urediniospores sampled from pustules on winter wheat during January to March–April of each year were viable. Latent mycelia were intermittently observed on winter wheat sampled from January to May in each of 2008 and 2010. The fungus was detected using PCR intermittently from winter to early spring. Persistent snow cover was found to be critical for the survival of overwintering inoculum, as viable pustules and urediniospores rarely survived after snow melt. There was higher stripe rust severity in spring wheat or barley seeded near winter wheat compared with the same crops seeded near spring wheat, for all years of field testing. The epidemiological significance of overwintering inoculum is discussed in relation to stripe rust management in central Alberta.

Monitoring changes of snow cover, lake and vegetation phenology in Nam Co Lake Basin (Tibetan Plateau) using remote SENSING (2000–2009)

The changes of environmental factors such as snow cover, vegetation and hydrologic regime of lakes can reflect ecosystem responses to changing climate. A series of satellite imagery-based environmental data archives including variations in snow cover, vegetation phenology and lake level were mapped in the Nam Co Lake Basin for the period 2000–2009. Results of the synthesis indicate that throughout this period, the average annual snow cover was 19.87% of the total basin, and there is an obvious relation between the elevation and a clear decreasing southeast–northwest trend in snow-cover persistence. Snow mainly happens from October to May. The multi-year mean water storage of Nam Co Lake is 86.40×109m3, with a lake level increase of approximately 2.06m during the study period. Vegetation phenology showed obvious variation with advanced start of season (SOS) and slightly extended duration of season (DOS). The mean DOS for the Nam Co Lake Basin was 154days from 2000 to 2009. Affected by air temperature, the SOS dates coincided with snowmelt. The seasonal-variability of climate factors was also studied. The satellite-derived continuous and multiple datasets offer the advantage of monitoring the temporal and spatial trends of each of these metrics and mapping extensive, remote in mountainous areas with no in-situ data such as represented by the Tibetan Plateau.

Response of alpine plant flower production to temperature and snow cover fluctuation at the species range boundary

Surface temperatures have risen globally during the last 30 years, especially in alpine areas. It is recognized that these increases are influencing phenology, physiology and distribution of plants. However, few studies have addressed the effects of climate warming at the species range boundary, where plants are expected to be more stressed. We analysed 11-year data sets of inflorescence production of four alpine plants (Carex foetida, Leucanthemopsis alpina, Senecio incanus, Silene suecica) at the southern boundary of their distribution range in the N-Apennines (N-Italy), in relation to air temperature and snow cover persistence. Inflorescence production of all species fluctuated greatly and was significantly affected by the variation of the mean temperature of June/July. We found significant relationships also between species data series and the snow cover persistence. Moreover, species responded differently to such parameters. One species showed a significant decrease of the reproductive effort, whereas the other three showed a stable trend of inflorescence production. We have shown that some alpine species are favoured by increased temperature and reduced snow cover even at the boundary of their range, where they are thought to be particularly sensitive to warming. However, the aptitude to cope with climate change might be limited by competition against thermophilous species migrating from lower altitude and in some cases by the low altitude of mountain peaks that prevent species upward migration. The individualistic response of species to climate change found here, support the statement that the composition of plant communities might rapidly change in the future.

Graminan breakdown by fructan exohydrolase induced in winter wheat inoculated with snow mold

Fructan structures vary widely among plant species. Graminan-type fructans, extensions of sucrose through β-(2,6)-linked fructosyl units with branches of β-(2,1)-linked fructosyl units, accumulate in tissues of winter wheat ( Triticum aestivum) during cold hardening and are metabolized under persistent snow cover. Snow molds such as Typhula ishikariensis and Microdochium nivale opportunistically infect wheat under snow cover. Snow mold-resistant wheat cultivars tend to heavily accumulate and slowly metabolize water-soluble carbohydrates including graminans in comparison with snow mold-susceptible cultivars. We observed time-dependent changes in the amounts of water-soluble carbohydrates in snow mold-inoculated wheat tissues, and accumulated fructan levels significantly decreased as a result of snow mold inoculation and incubation under snow cover, especially in a snow mold-susceptible wheat cultivar. Three candidates for fructan exohydrolase (FEH) cDNAs with high homology to cell wall invertases were isolated from wheat leaf tissues inoculated with snow mold and incubated under snow cover. The substrate specificity of enzymes encoded by the isolated clones was analyzed by recombinant proteins expressed in Pichia pastoris. The recombinant protein (Wfh-sm3m) encoded by one ( Wfh-sm3) of the isolated clones preferentially degraded 6-kestotriose and possessed minor hydrolase activity to 1-kestotriose and 1,1-kestotetraose. Moreover, Wfh-sm3m hydrolyzed almost all graminans that accumulated in hardened wheat tissues. Wfh-sm3 transcripts increased in wheat leaf tissues inoculated with snow mold and incubated under snow cover. These results suggest that Wfh-sm3 encodes a 6-FEH with minor 1-FEH activity and is associated with degradation of fructans in wheat leaf tissues during inoculation and incubation under snow cover.

Synoptic conditions of the occurrence of snow cover in central European lowlands

AbstractIn the central European lowlands, snowiness increases meridionally from the south to the north and latitudinally from the west to the east. Taking into account the spatial variability in the occurrence of snow cover, four regions of snow cover were distinguished using the principal component analysis (PCA). Furthermore, circulation patterns responsible for intense snowfalls and persistence of snow in each region were analysed. Composite maps of the sea level pressure (SLP) and 500‐hPa geopotential height means and anomalies were constructed for the days on which snow depth increased by ≥ 5 cm and for days on which the snow cover lasted for at least 3 days. Contour maps show negative anomalies of SLP and 500‐hPa heights over central Europe, associated with organized low‐pressure systems. The lows may differ in the intensity and localization, depending on the region. In the south‐western part of central Europe, heavy snowfalls usually appear as a result of cold‐air fronts in the colder parts of Mediterranean cyclones, the centres of which are often situated over the Italian Peninsula. Another typical location of cyclones or troughs of low pressure causing heavy snowfalls is the Baltic Sea region, where meteorological fronts appear quite frequently. Such a location of cyclonic systems causes snowfalls particularly frequently in the most snowy north‐western part of central Europe. The cyclonic activity over the continent that brings snowfalls is simultaneous to the weakening of Icelandic Low and significant positive SLP anomalies over the north Atlantic. The persistence of snow cover in the central European lowlands is possible under the positive anomalies of SLP over most of the continent, except for its south‐western part where weak negative anomalies are observed. At the same time, positive anomalies of 500‐hPa geopotential heights appear over the northern Atlantic and Scandinavia. Copyright © 2010 Royal Meteorological Society

Ecosystem Feedbacks to Climate Change in California: Development, Testing, and Analysis Using a Coupled Regional Atmosphere and Land Surface Model (WRF3–CLM3.5)

Abstract A regional atmosphere model [Weather Research and Forecasting model version 3 (WRF3)] and a land surface model [Community Land Model, version 3.5 (CLM3.5)] were coupled to study the interactions between the atmosphere and possible future California land-cover changes. The impact was evaluated on California’s climate of changes in natural vegetation under climate change and of intentional afforestation. The ability of WRF3 to simulate California’s climate was assessed by comparing simulations by WRF3–CLM3.5 and WRF3–Noah to observations from 1982 to 1991. Using WRF3–CLM3.5, the authors performed six 13-yr experiments using historical and future large-scale climate boundary conditions from the Geophysical Fluid Dynamics Laboratory Climate Model version 2.1 (GFDL CM2.1). The land-cover scenarios included historical and future natural vegetation from the Mapped Atmosphere-Plant-Soil System-Century 1 (MC1) dynamic vegetation model, in addition to a future 8-million-ha California afforestation scenario. Natural vegetation changes alone caused summer daily-mean 2-m air temperature changes of −0.7° to +1°C in regions without persistent snow cover, depending on the location and the type of vegetation change. Vegetation temperature changes were much larger than the 2-m air temperature changes because of the finescale spatial heterogeneity of the imposed vegetation change. Up to 30% of the magnitude of the summer daily-mean 2-m air temperature increase and 70% of the magnitude of the 1600 local time (LT) vegetation temperature increase projected under future climate change were attributable to the climate-driven shift in land cover. The authors projected that afforestation could cause local 0.2°–1.2°C reductions in summer daily-mean 2-m air temperature and 2.0°–3.7°C reductions in 1600 LT vegetation temperature for snow-free regions, primarily because of increased evapotranspiration. Because some of these temperature changes are of comparable magnitude to those projected under climate change this century, projections of climate and vegetation change in this region need to consider these climate–vegetation interactions.

Influence of snow cover distribution on soil temperature and nutrient dynamics in alpine pedoenvironments

In Alpine sites snow is present on the ground from six to eight months per year in relation to elevation and exposure. Water is therefore immobilized into the solid state for the greater part of the winter season and released to the ground in a short period during spring snowmelt. In these areas, snow distribution exercises a fundamental role in influencing soil temperature and nutrient dynamics, in particular of nitrogen, with great consequences on plant nutrition. The dormant vegetation period, the low temperatures and the persistent snow cover suggest that soil biological activity is only concentrated during summer. As a matter of fact, soils covered with a consistent snow cover are isolated from the air temperature and can not freeze during winter. A snowpack of sufficient thickness, accumulated early in winter, insulates the ground from the surrounding atmosphere maintaining soil temperature closed to 0 °C during the whole winter season. The elevation of the snow line and the shorter permanence of snow on the ground, as a result of global warming (IPCC, 1996, 2001), might reduce the insulation effect of the snowpack, exposing soils of the mountain belt to lower temperatures and to a greater frequency of freeze/thaw cycles, which might alter organic matter dynamics and soil nutrient availability. Such thermal stresses may determine the lysis of microbial cells and the consequent increase of nitrogen and carbon mineralization by the survived microorganisms. Moreover, the freeze/thaw cycles can determine the exposure of exchange surfaces not available before, with release of organic matter of non-microbial origin, which may become available to surviving microorganisms for respiration. The reduced or absent microbial immobilization may cause the accumulation of remarkable amounts of inorganic nitrogen in soil, potentially leachable during spring snowmelt, when plants have not still started the growing season. Changes of snow distribution in alpine sites can consequently have a great impact on the thermal regime and nutrient cycle of soils. The environmental implications have to be estimated for a long time, through specific studies that aim to evidence the indirect effects of climatic change on characteristics of alpine pedoenvironments.