Shoulder Seasons Research Articles

Living mulch cover crops for weed control in small-scale applications

AbstractA primary challenge of managing vegetable production on a small land base is the maintenance and building of soil quality. Previous studies have demonstrated the benefits of cover crops for improved soil quality; however, small growers struggle to fit cover crops into rotations. Small-scale growers with limited available land are under significant pressure to maximize their saleable yield and often work to maximize output by using intensive cropping practices that may include both early and late season crops, thus limiting the typical shoulder season windows in which cover crops can be grown. In-season living mulches may be an effective strategy to provide small-scale growers the benefits of cover crops with less land commitment than cover crops used in typical rotations. However, research on living mulches is generally not suited to small-scale organic production systems due to the typical reliance on chemical herbicide to suppress mulches. An experiment was designed with the goal of evaluating living mulch systems for space-limited organic vegetable production. In a 2-year study, four living mulch crops (buckwheat (Fagopyrum esculentum), field pea (Pisum sativum), crimson clover (Trifolium incarnatum) and medium red clover (Trifolium pratense)) and a cultivated control with no mulch cover were planted in early spring each year. Snap beans (Phaseolus vulgarisvar. Tavera), transplanted bell peppers (Capsicum annuumvar. Revolution), and transplanted fall broccoli (Brassica oleraceavar. Imperial) were then planted directly into living mulches. During each summer growing season, living mulches and weeds were mown between-rows and hand-weeded in-row approximately every 10–14 days as needed for management. Labor times for mowing and cultivation were found to be higher in all treatments relative to the cultivated control. An inverse relationship between living mulch biomass and weed biomass was observed, demonstrating that living mulches may contribute to weed suppression. However, lower vegetable yields were seen in the living mulch treatments, most likely due to resource competition among vegetables, living mulches and weeds. High pre-existing weed seedbank and drought conditions likely increased competition and contributed to reduced vegetable yield.

Simulation and experimental demonstration of model predictive control in a building HVAC system

This article presents the framework and results of implementing optimization-based control algorithm for building HVAC systems and demonstrates its benefits through reduced building energy consumption as well as improved thermal comfort along with lessons learned. In particular, a practically effective and computationally efficient model predictive control algorithm is proposed to optimize building energy usage while maintaining thermal comfort in a multi-zone medium-sized commercial building. This article has two themes. Driven by the challenge of fully evaluating the benefit of the proposed model predictive controller against baseline control, a model predictive control design framework is first presented with its performance benchmarked based on a high-fidelity building HVAC simulation environment to verify its effectiveness and feasibility. Following the same model predictive control design framework, the experimental results from the same building located at the Philadelphia Navy Yard are then presented. For the simulation study, the performance of the model predictive control algorithm was estimated relative to baseline days with exactly the same internal loads and outdoor conditions, and it was estimated that model predictive control reduced the total electrical energy consumption by around 17.5%. For the subsequent experimental demonstration, the performance of the model predictive control algorithm was estimated relative to baseline days with similar outdoor air temperature patterns during the cooling and shoulder seasons, and it was concluded that model predictive control reduced the total electrical energy consumption by more than 20% on average while improving thermal comfort in terms of zone air temperature.

Discharge, legacy effects and nutrient availability as determinants of temporal patterns in biofilm metabolism and accrual in an arctic river

Summary Significant changes in the timing of thawing and freezing, annual discharge and nutrient supply are anticipated for arctic river ecosystems due to climate warming. Our understanding of the effects of such changes, however, is poor. Since biofilms are both critical to ecosystem processes and subject to control by combinations of freezing dynamics, discharge and nutrient supply, the effects of climate warming on arctic river ecosystems may be substantial. We studied biofilm accrual and metabolism in the Kuparuk River of Alaska with three objectives. First, we assessed biofilm activity during the open‐water season, including the poorly known ‘shoulder seasons’ (periods shortly after the spring thaw and then before autumn freezing). Second, we assessed how discharge and freezing dynamics may affect temporal patterns in biofilm activity. Third, we assessed biofilm response to increases in concentrations predicted as the climate warms. Our study consisted of an upstream reference reach and a downstream treatment reach where H3PO4 was experimentally added for two years (2011–2012; ˜0.3 μm increase). We used archived reference‐reach data from 1983 to 2014 to assess discharge–chlorophyll relationships. Mean biofilm gross primary production (GPP) in the reference reach during 2011 and 2012 was 15.4 ± 2.2 (mean ± S.E.) and 13.4 ± 2.5 mg C m−2 h−1, respectively, with spring shoulder season values being significantly higher than the summer values that are more routinely measured. An analysis of a 31‐year record from the reference reach revealed that biofilm chlorophyll biomass was significantly (R2 = 0.39, P < 0.001) related to the discharge regime of the previous summer. This ‘legacy effect’ is attributable to bedfast ice within the river channel during winter that protects biofilms from scour during the spring thaw. Before–after‐control–impact (BACI) analysis showed significant and positive effects on mean biofilm chl‐a biomass in the treatment reach. This treatment effect was associated with a parallel increase in GPP. High biofilm activity in the Kuparuk River during the shoulder seasons indicates its potential significance to the energetics of arctic river ecosystems, particularly in the context of climate change. The related ‘legacy effect’ probably underlies the scope for rapid recovery of biofilm activity during the spring. Finally, increases in at concentrations predicted as the climate warms are likely to result in increases in summer biofilm biomass and metabolism. Further studies of biofilm processes during the shoulder seasons, and how these are affected by shifts in discharge, freezing dynamics and nutrient supply, are required for a comprehensive understanding of the effects of climate warming on arctic river ecosystems.

Modelling climate change impacts on tourism demand: A comparative study from Sardinia (Italy) and Cap Bon (Tunisia)

Tourism represents an important source of income and employment in many Mediterranean regions, including the island of Sardinia (Italy) and the Cap Bon peninsula (Tunisia). Climate change may however impact tourism in both regions, for example, by altering the regions' climatic suitability for common tourism types or affecting water availability. This paper assesses the potential impacts of climate change on tourism in the case study regions of Sardinia and Cap Bon. Direct impacts are studied in a quantitative way by applying a range of climate scenario data on the empirically estimated relationship between climatic conditions and tourism demand, using two different approaches. Results indicate a potential for climate-induced tourism revenue gains especially in the shoulder seasons during spring and autumn, but also a threat of climate-induced revenue losses in the summer months due to increased heat stress. Annual direct net impacts are nevertheless suggested to be (slightly) positive in both case study regions. Significant climate-induced reductions in total available water may however somewhat counteract the positive direct impacts of climate change by putting additional water costs on the tourism industry.

Full scale experimentation on a new translucent passive solar wall combining silica aerogels and phase change materials

This paper presents the first passive solar wall providing simultaneously super insulation, heat storage and daylighting to the inner space. The wall’s external layer is composed of a silica aerogels bed for high insulation and solar radiation transmission. The second layer, internal, is composed of glass bricks filled with a eutectic phase change material (PCM) for heat storage and restitution. The whole wall is translucent. The experimentations carried out to characterize thermal and optical properties of the materials used are described. Then results are given for a full scale comparative experimentation on a twin zones building located in the south of France for the solar wall and a standard opaque high thermal capacity wall. Results show the heat losses through the wall are very low while the heat and light gains are high: The U value of the solar wall is 0.59Wm−1K−1 and 0.72Wm−1K−1 respectively when the PCM is in liquid and solid state. With the test building in free floating condition, the temperature difference between the outdoor and indoor air provided by the wall is about 9°C in winter. The wall can provide up to 500lux to the inner environment, which is sufficient for conference rooms. The tested wall has proven more effective in winter and shoulder season, particularly for cold sunny climates, but may cause overheating in summer.

Climate warming causes intensification of the hydrological cycle, resulting in changes to the vernal and autumnal windows in a northern temperate forest

AbstractClimate warming is likely to lead to complex effects on northern forests of the temperate forest biome. We investigated whether rising temperatures altered the timing of snowmelt and snowpack accumulation or extended the forest growing season length in the Turkey Lakes Watershed in central Ontario. Archived satellite imagery was used to track changes in timing of snowpack loss/gain and canopy leaf on/off; the periods between these events were defined as the vernal (spring) and autumnal (fall) windows. We found only a slight extension of the growing season into the autumn period and no increase in the width of the vernal or autumnal windows, indicating that forest growth is not responding significantly to temperature increases during these windows. Archived time series of temperature, precipitation and discharge data for a nested set of catchments ranging in size from headwater (<10 ha) to regional (103 ha) catchments were used to track changes in the magnitude, timing and partitioning of precipitation into evapotranspiration and discharge. We found an intensification of hydrological cycling, with (1) a higher dryness index (PET/P) during the summer growing season and (2) earlier spring snowmelt discharges, and later more concentrated autumn storm discharges during the shoulder seasons. This intensification of the hydrological cycle during the summer growth season and the vernal and autumnal windows may not only limit opportunities for enhanced forest growth, but may be contributing to the recent observations of forest decline within this biome. Copyright © 2015 John Wiley & Sons, Ltd.

Evaluating the distribution of water resources in western Canada using synoptic climatology and selected teleconnections. Part 2: summer season

AbstractMinor changes to seasonal air temperature and precipitation can have a substantial impact on the availability of water resources within large watersheds. Two such watersheds, the north‐flowing Mackenzie and east‐flowing Saskatchewan Basins, have been identified as highly vulnerable to such changes and, therefore, selected for study as part of the Climatic Redistribution of western Canadian Water Resources project. This project aims to evaluate spatial and temporal changes to water resource distribution through the analysis of a suite of hydroclimatic and streamflow variables. As part of this analysis, dominant summer (May–October) circulation patterns at 500 hPa for 1950–2011 are identified using the method of self‐organizing maps. Surface climate variables associated with these patterns are then identified, including both daily air temperature and precipitation and seasonal Standardized Precipitation Evapotranspiration Index values. Statistical methods are applied to assess the relationships between dominant circulation patterns and the Southern Oscillation Index (SOI) and Pacific Decadal Oscillation (PDO). Results indicate that mid‐summer (July–August) is dominated by a split‐flow blocking pattern, resulting in cool (warm), wet (dry) conditions in the southern (northern) portion of the study area. By contrast, the shoulder season (May and October) is dominated by a trough of low pressure over the North Pacific Ocean. The frequency of weak split‐flow blocking is higher during positive SOI and negative PDO, whereas ridging over the western continent is more frequent during negative SOI and positive PDO. Results from this analysis increase our knowledge of processes, controlling the distribution of summer water resources in western Canada. Copyright © 2014 John Wiley & Sons, Ltd.

Assessing the forecast skill of Arctic sea ice extent in the GloSea4 seasonal prediction system

An assessment of the ability of the Met Office seasonal prediction system, GloSea4, to accurately forecast Arctic sea ice concentration and extent over seasonal time scales is presented. GloSea4 was upgraded in November 2010 to include the initialization of the observed sea ice concentration from satellite measurements. GloSea4 is one of only a few operational seasonal prediction systems to include both the initialization of observed sea ice followed by its prognostic determination in a coupled dynamical model of sea ice. For the forecast of the September monthly mean ice extent the best skill in GloSea4, as judged from the historical forecast period of 1996–2009, is when the system is initialized in late March and early April near to the sea ice maxima with correlation skills in the range of 0.6. In contrast, correlation skills using May initialization dates are much lower due to thinning of the sea ice at the start of the melt season which allows ice to melt too rapidly. This is likely to be due both to a systematic bias in the ice-ocean forced model as well as biases in the ice analysis system. Detailing the forecast correlation skill throughout the whole year shows that for our system, the correlation skill for ice extent at five to six months lead time is highest leading up to the September minimum (from March/April start dates) and leading up to the March maximum (from October/November start dates). Conversely, little skill is found for the shoulder seasons of November and May at any lead time.

Predicted responses of arctic and alpine ecosystems to altered seasonality under climate change

Global climate change is already having significant impacts on arctic and alpine ecosystems, and ongoing increases in temperature and altered precipitation patterns will affect the strong seasonal patterns that characterize these temperature-limited systems. The length of the potential growing season in these tundra environments is increasing due to warmer temperatures and earlier spring snow melt. Here, we compare current and projected climate and ecological data from 20 Northern Hemisphere sites to identify how seasonal changes in the physical environment due to climate change will alter the seasonality of arctic and alpine ecosystems. We find that although arctic and alpine ecosystems appear similar under historical climate conditions, climate change will lead to divergent responses, particularly in the spring and fall shoulder seasons. As seasonality changes in the Arctic, plants will advance the timing of spring phenological events, which could increase plant nutrient uptake, production, and ecosystem carbon (C) gain. In alpine regions, photoperiod will constrain spring plant phenology, limiting the extent to which the growing season can lengthen, especially if decreased water availability from earlier snow melt and warmer summer temperatures lead to earlier senescence. The result could be a shorter growing season with decreased production and increased nutrient loss. These contrasting alpine and arctic ecosystem responses will have cascading effects on ecosystems, affecting community structure, biotic interactions, and biogeochemistry.

Climate change impacts on mass movements — Case studies from the European Alps

This paper addresses the current knowledge on climate change impacts on mass movement activity in mountain environments by illustrating characteristic cases of debris flows, rock slope failures and landslides from the French, Italian, and Swiss Alps. It is expected that events are likely to occur less frequently during summer, whereas the anticipated increase of rainfall in spring and fall could likely alter debris-flow activity during the shoulder seasons (March, April, November, and December). The magnitude of debris flows could become larger due to larger amounts of sediment delivered to the channels and as a result of the predicted increase in heavy precipitation events. At the same time, however, debris-flow volumes in high-mountain areas will depend chiefly on the stability and/or movement rates of permafrost bodies, and destabilized rock glaciers could lead to debris flows without historic precedents in the future. The frequency of rock slope failures is likely to increase, as excessively warm air temperatures, glacier shrinkage, as well as permafrost warming and thawing will affect and reduce rock slope stability in the direction that adversely affects rock slope stability. Changes in landslide activity in the French and Western Italian Alps will likely depend on differences in elevation. Above 1500m asl, the projected decrease in snow season duration in future winters and springs will likely affect the frequency, number and seasonality of landslide reactivations. In Piemonte, for instance, 21st century landslides have been demonstrated to occur more frequently in early spring and to be triggered by moderate rainfalls, but also to occur in smaller numbers. On the contrary, and in line with recent observations, events in autumn, characterized by a large spatial density of landslide occurrences might become more scarce in the Piemonte region.

Experimental investigation of multifunctional VRF system in heating and shoulder seasons

The top three end uses which are space heating, space cooling, and water heating accounted for close to 41 percent of site energy consumption in U.S. building primary energy consumption. A multifunctional variable refrigerant flow (MFVRF) system is finding its way into buildings since it can simultaneously provide space cooling, space heating and hot water. The MFVRF system was installed in an office building and fully instrumented to measure the performance of the system under a wide range of outdoor weather conditions. The effects of a part-load ratio (PLR), a hot water demand and a heat recovery operation mode on the performance of the MFVRF system were investigated in a field test for the heating and shoulder seasons. As the hot water demand for the MFVRF system increased, the PLR was improved, which resulted in an increase in system heating performance. In the heat recovery operation mode, the heat absorbed from the indoor units operating in the cooling mode was transferred to other indoor units operating in the heating mode. The daily performance factor was 2.14 and 3.54 when the ratio of daily total cooling energy to daily total energy was 13.0% and 28.4%, respectively, at the similar outdoor weather conditions. This enhancement was attributed to the waste heat recovered during the heat recovery operation mode and the decrease in pressure ratio, which is a result of the improvement of the compressor efficiency. The performance of the MFVRF system for the heating and shoulder seasons was improved by transferring the recovered energy to the indoor space and supplying the hot water.

Changing sea ice conditions and marine transportation activity in Canadian Arctic waters between 1990 and 2012

Declining sea ice area in the Canadian Arctic has gained significant attention with respect to the prospect of increased shipping activities. To investigate relationships between recent declines in sea ice area with Arctic maritime activity, trend and correlation analysis was performed on sea ice area data for total, first-year ice (FYI), and multi-year ice (MYI), and on a comprehensive shipping dataset of observed vessel transits through the Vessel Traffic Reporting Arctic Canada Traffic Zone (NORDREG zone) from 1990 to 2012. Links to surface air temperature (SAT) and the satellite derived melt season length were also investigated. Between 1990 and 2012, statistically significant increases in vessel traffic were observed within the NORDREG zone on monthly and annual time-scales coincident with declines in sea ice area (FYI, MYI, and total ice) during the shipping season and on a monthly basis. Similarly, the NORDREG zone is experiencing increased shoulder season shipping activity, alongside an increasing melt season length and warming surface air temperatures (SAT). Despite these trends, only weak correlations between the variables were identified, although a step increase in shipping activity is apparent following the former summer sea ice extent minimum in 2007. Other non-environmental factors have also likely contributed to the observed increase in Arctic shipping activity within the Canadian Arctic, such as tourism demand, community re-supply needs, and resource exploration trends.

Projections for the 21st century of the climate potential for beach‐based tourism in the Mediterranean

ABSTRACTClimate is a primary resource for beach‐based tourism. It defines the length and quality of the tourist season and plays a major role in destination choices and revenues. The Mediterranean is coincidentally one of the most visited tourist destinations and sensitive areas to climate change worldwide. Social, economic and environmental adaptation to climate change in this region should necessarily evaluate the Mediterranean and European climate resource for beach‐based tourism as well as its projected changes. To this end, the second‐generation climate index for tourism (CIT) has been adopted. ERA‐Interim reanalysis have been used as the regional observed baseline, thus providing daily atmospheric data to derive CIT. For projections, meteorological variables have been obtained from a set of regional climate models (RCMs) within the ENSEMBLES European project. A quantile–quantile adjustment has been applied to the CIT cumulative distribution functions based on each individual RCM output to properly correct biases at regional and local scales. Furthermore, an ensemble strategy is adopted to further cope with uncertainties arising from RCM errors and boundary conditions. The spatial distribution of present climate potential confirms the Mediterranean coast as the most suitable region in Europe for carrying out beach leisure activities. Excellent climatic conditions prevail in most of this coastal region during summer. However, the optimal climate asset is projected to noticeably deteriorate in summer across the Mediterranean, whereas only slightly improving in northwestern Europe by 2075–2094. On the other hand, a general enhancement of ideal climate potential is expected for the shoulder seasons in the former region. That is, optimal climatic conditions may shift from the present peak demand season to spring and autumn. These potential impacts might lead to important drawbacks for the current strongly seasonal‐adjusted beach‐based tourism industry in the Mediterranean. Therefore, main tourism stakeholders will likely need to face these challenges through adaptation and mitigation strategies.

Possible impacts of climate change on debris-flow activity in the Swiss Alps

This study uses a long dataset of past debris flows from eight high-elevation catchments in the Swiss Alps for which triggering conditions since AD 1864 have been reconstructed. The torrents under investigation have unlimited sediment supply and the triggering of debris flows is thus mainly controlled by climatic factors. Based on point-based downscaled climate scenarios for meteorological stations located next to the catchments and for the periods 2001–2050 and 2051–2100, we study the evolution of temperature and rainfall above specific thresholds (10, 20, 30, 40 and 50 mm) and durations (1, 2 or 3 days). We conclude that the drier conditions in future summers and the wetting of springs, falls and early winters are likely to have significant impacts on the behavior of debris flows. Based on the current understanding of debris-flow systems and their reaction to rainfall inputs, one might expect only slight changes in the overall frequency of events by the mid-21st century, but possibly an increase in the overall magnitude of debris flows due to larger volumes of sediment delivered to the channels and an increase in extreme precipitation events. In the second half of the 21st century, the number of days with conditions favorable for the release of debris flows will likely decrease, especially in summer. The anticipated increase of rainfall during the shoulder seasons (March, April, November, December) is not expected to compensate for the decrease in future heavy summer rainfall over 2 or 3 days.

The Importance of Spring and Autumn Atmospheric Conditions for the Evaporation Regime of Lake Superior

AbstractFeedbacks between ice extent and evaporation have long been suspected to be important for Lake Superior evaporation because it is during autumn and winter when latent heat fluxes are highest. Recent direct measurements of evaporation made at the Stannard Rock Lighthouse have provided new information on the physical controls on Lake Superior evaporation, in particular that evaporation can react within hours to days to a change in synoptic conditions. However, the large heat capacity of the lake creates a strong seasonal cycle of energy storage and release. There is a complex interaction among heat storage, evaporation, and ice cover that is highly dependent on atmospheric conditions in the spring and autumn “shoulder seasons.” Small changes in conditions in November and March caused by synoptic-scale events can have profound impacts on annual evaporation, the extent of ice cover, and the length of the ice-covered period. Early winter air temperatures in November and December dictate the nature of ice formation and much of the winter evaporative flux. Decreased ice cover, by itself, does not necessarily lead to enhanced annual evaporation losses. Rather, a combination of low ice cover and warm spring air temperatures, leading to an early breakup, can significantly lengthen the next evaporation season and cause greater cumulative water loss the subsequent year. The influence of individual synoptic events on annual evaporation is notable enough that the research community should ensure that their role is properly captured in numerical models to provide sound predictions of future Laurentian Great Lakes evaporation regimes.

Revisiting factors controlling methane emissions from high-Arctic tundra

Abstract. The northern latitudes are experiencing disproportionate warming relative to the mid-latitudes, and there is growing concern about feedbacks between this warming and methane production and release from high-latitude soils. Studies of methane emissions carried out in the Arctic, particularly those with measurements made outside the growing season, are underrepresented in the literature. Here we present results of 5 yr (2006–2010) of automatic chamber measurements at a high-Arctic location in Zackenberg, NE Greenland, covering both the growing seasons and two months of the following freeze-in periods. The measurements show clear seasonal dynamics in methane emission. The start of the growing season and the increase in CH4 fluxes were strongly related to the date of snowmelt. Within each particular growing season, CH4 fluxes were highly correlated with the soil temperature (R2 > 0.75), which is probably explained by high seasonality of both variables, and weakly correlated with the water table. The greatest variability in fluxes between the study years was observed during the first part of the growing season. Somewhat surprisingly, this variability could not be explained by commonly known factors controlling methane emission, i.e. temperature and water table position. Late in the growing season CH4 emissions were found to be very similar between the study years (except the extremely dry 2010) despite large differences in climatic factors (temperature and water table). Late-season bursts of CH4 coinciding with soil freezing in the autumn were observed during at least three years. The cumulative emission during the freeze-in CH4 bursts was comparable in size with the growing season emission for the year 2007, and about one third of the growing season emissions for the years 2009 and 2010. In all three cases the CH4 burst was accompanied by a corresponding episodic increase in CO2 emission, which can compose a significant contribution to the annual CO2 flux budget. The most probable mechanism of the late-season CH4 and CO2 bursts is physical release of gases accumulated in the soil during the growing season. In this study we discuss possible links between growing season and autumn fluxes. Multiannual dynamics of the subsurface CH4 storage pool are hypothesized to be such a link and an important driver of intearannual variations in the fluxes, capable of overruling the conventionally known short-term control factors (temperature and water table). Our findings suggest the importance of multiyear studies with a continued focus on shoulder seasons in Arctic ecosystems.

Seasonal dynamics of methane emissions from a subarctic fen in the Hudson Bay Lowlands

Abstract. Ecosystem-scale methane (CH4) flux (FCH4) over a subarctic fen at Churchill, Manitoba, Canada was measured to understand the magnitude of emissions during spring and fall shoulder seasons, and the growing season in relation to physical and biological conditions. FCH4 was measured using eddy covariance with a closed-path analyser in four years (2008–2011). Cumulative measured annual FCH4 (shoulder plus growing seasons) ranged from 3.0 to 9.6 g CH4 m−2 yr−1 among the four study years, with a mean of 6.5 to 7.1 g CH4 m−2 yr−1 depending upon gap-filling method. Soil temperatures to depths of 50 cm and air temperature were highly correlated with FCH4, with near-surface soil temperature at 5 cm most correlated across spring, fall, and the shoulder and growing seasons. The response of FCH4 to soil temperature at the 5 cm depth and air temperature was more than double in spring to that of fall. Emission episodes were generally not observed during spring thaw. Growing season emissions also depended upon soil and air temperatures but the water table also exerted influence, with FCH4 highest when water was 2–13 cm below and lowest when it was at or above the mean peat surface.

Synoptic climatology and recent climate trends at Lake El'gygytgyn

Abstract. We developed a synoptic climatology for Lake El'gygytgyn, Chukotka Russia, and explored modern climate trends affecting air temperatures there to aid in paleoclimate reconstructions of a 3.6 million-year-old sediment core taken from the lake. Our self-organized mapping (SOM) approach identified 35 synoptic weather patterns, based on sea level pressure, that span the range of synoptic patterns influencing the study domain over the 1961–2009 NCEP/NCAR analysis period. We found strong seasonality in modern weather patterns, with summer weather primarily characterized by weak low pressure systems over the Arctic Ocean or Siberia and winter weather primarily characterized by strong high pressure over the Arctic Ocean and strong low pressure in the Pacific Ocean. In general, the primary source of variation in air temperatures came from the dominant patterns in each season, which we identify in the text, and nearly all of the dominant weather patterns here have shown increasing temperatures. We found that nearly all of the warming in mean annual temperature over the past 50 yr (about 3 °C) occurred during sub-freezing conditions on either side of summer (that is, spring and fall). Here we found that the most summer-like weather patterns (low pressures to the north) in the shoulder seasons were responsible for much of the change. Finally, we compared the warmest 15 yr of the record (1995–2009) to the coolest (1961–1975) and found that changes in thermodynamics of weather were about 3 to 300 times more important than changes in frequency of weather patterns in controlling temperature variations during spring and fall, respectively. That is, in the modern record, general warming (local or advected) is more important by orders of magnitude than changes in storm tracks in controlling air temperature at Lake El'gygytgyn. We conclude with a discussion of how these results may be relevant to the paleoclimate reconstruction efforts and how this relevancy could be tested further.

Development and application of a building energy performance metric for green roof systems

This study develops a thermal performance metric for vegetated roof systems. The Dynamic Benefit of Green Roofs (DBGR) is the ratio of Heating, Ventilation and Air-Conditioning (HVAC) energy use for a building with a conventional roof to that of a building with a green roof. If the green roof results in lower energy use than a conventional roof with the same level of thermal resistance the value of DBGR is greater than unity.Data from a field study in Portland Oregon were used to validate the green roof model incorporated within a whole-building energy simulation program. This model was then used to estimate the DBGR for a new construction office building in four climates: Portland, Oregon; Chicago, Illinois; Atlanta, Georgia; and Houston, Texas. Results suggest that a green roof in Atlanta and Houston would provide net annual HVAC energy savings compared with a traditional roof. The Chicago case, with severe winter and mild spring/summer/fall, resulted in a smaller energy savings. The DBGR for Portland was less than unity, suggesting a net energy consumption penalty associated with the green roof. This was due, in part, to the undesirable evaporative cooling in the shoulder seasons which led to increased building heating loads.

Premium or Discount in Hotel Room Rates? The Dual Effects of a Central Downtown Location

The hotel industry generally recognizes the advantages of a central business district location, resulting in higher demand, pricing ability, and profitability. What research has not done is to consider the negative effects of agglomeration and competition among centrally located hotels. Reasoning that hotels engage in price competition through revenue management, the authors developed a theoretical framework of bounded price competition. The authors theorize that rate-based competition would intensify among contiguous hotels, but they also propose that such rate-based competition is contingent on demand levels. When demand is strong, one would not expect rate-based competition. A test of this hypothesis using data from the downtown Chicago hotel market supported that a central location has a dual effect on hotel room rates. Hotels see higher premiums in the peak season, due to strong demand, and steeper discounts in shoulder seasons, as a result of competition with nearby hotels. The findings also suggest that existing models, which do not consider hotel spacing, may have overestimated the central location premium.