| 1. |
- Lundmark, Linda, 1975-, et al.
(författare)
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Effects of climate change and extreme events on forest communities in the European North
- 2008
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Ingår i: Climatic Change. - : SpringerLink. - 0165-0009 .- 1573-1480. ; 87:1-2, s. 235-249
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Tidskriftsartikel (refereegranskat)abstract
- The European north is increasingly affected by changes in climate and climate variability. These changes and their causes are global in scope but specific impacts vary considerably between different regions. Recent incidents and events show that forest-resource based regions have difficulties in alleviating adverse effects of these changes. Also, the future socio-economic impact is to date unexplored. Norrbotten in Sweden, Lappi in Finland and Arkhangelsk oblast in Russia are regions that differ significantly in terms of their socio-economic characteristics and capacities. A modified employment multiplier model is used to predict future changes. Scenarios of changing forest resources provide quantitative estimations of the sensitivity of regional employment. These estimates are used to assess and discuss the adaptive capacities of the regions. Results show that Arkhangelsk oblast is more vulnerable to climate variability than Norrbotten and Lappi. This is due to the continued dependency on natural resources in combination with different capacities to counteract negative effects or to take advantage of the opportunities offered by climate change in this region
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| 2. |
- Skarin, Anna, et al.
(författare)
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Reindeer use of low Arctic tundra correlates with landscape structure
- 2020
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Ingår i: Environmental Research Letters. - : Institute of Physics (IOP). - 1748-9326. ; 15
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Tidskriftsartikel (refereegranskat)abstract
- Rapid climate change in Arctic regions is linked to the expansion of woody taxa (shrubification), and an increase in biomass as tundra becomes greener. Reindeer and caribou (Rangifer tarandus) are considered able to suppress vegetative greening through grazing and trampling. Quantifying reindeer use of different land cover types can help us understand their impact on the growth and recruitment of deciduous shrubs, many of which serve as fodder (e.g. Salix spp.), in favourable habitats, such as naturally denuded landslides in permafrost areas. Understanding the spatial distribution of reindeer pressure on vegetation is important to project future patterns of greening, albedo, snow capture, active layer development, and the overall resilience of tundra rangelands under ongoing climate change. Here we quantify reindeer habitat use within the low Arctic tundra zone of Yamal, West Siberia estimated from pellet-group counts, and also how active layer thickness (ALT) relates to reindeer use. Our results confirm intensive use by reindeer of terrain with high June-July time integrated normalised difference vegetation index, steeper slopes, ridges, upper slopes and valleys, and a preference for low erect shrub tundra. These sites also seem to have a shallower ALT compared to sites less used by reindeer, although we did not find any direct relationship between ALT and reindeer use. Low use of tall Salix habitats indicated that reindeer are unlikely to suppress the growth of already tall-erect woody taxa, while they exert maximum pressure in areas where shrubs are already low in stature, e.g. ridgetops. Reindeer ability to suppress the regrowth and expansion of woody taxa in landslide areas (i.e. concavities) seems limited, as these types were less used. Our results suggest that reindeer use of the landscape and hence their effects on the landscape correlates with the landscape structure. Future research is needed to evaluate the role and efficiency of reindeer as ecosystem engineers capable of mediating the effects of climate change.
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| 3. |
- Berndtsson, Ronny, et al.
(författare)
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Drivers of changing urban flood risk : A framework for action
- 2019
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Ingår i: Journal of Environmental Management. - : Elsevier. - 0301-4797 .- 1095-8630. ; 240, s. 47-56
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on drivers for changing urban flood risk. We suggest a framework for guiding climate change adaptation action concerning flood risk and manageability in cities. The identified key drivers of changing flood hazard and vulnerability are used to provide an overview of each driver's impact on flood risk and manageability at the city level. We find that identified drivers for urban flood risk can be grouped in three different priority areas with different time horizon. The first group has high impact but is manageable at city level. Typical drivers in this group are related to the physical environment such as decreasing permeability and unresponsive engineering. The second group of drivers is represented by public awareness and individual willingness to participate and urbanization and urban sprawl. These drivers may be important and are manageable for the cities and they involve both short-term and long-term measures. The third group of drivers is related to policy and long-term changes. This group is represented by economic growth and increasing values at risk, climate change, and increasing complexity of society. They have all high impact but low manageability. Managing these drivers needs to be done in a longer time perspective, e.g., by developing long-term policies and exchange of ideas.
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| 4. |
- Gál, Csilla V
(författare)
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A városi tér szerkezete és hatása a mikroklímára [Urban space and structure and its effect on the urban microclimate]
- 2017
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Ingår i: 43. Meteorológiai Tudományos Napok. 2017. November 23-24. Mikro- és mezoskálájú légköri folyamatok modellezése. Az előadások összefoglalói.. - Budapest, Hungary. - 9789639931145
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Konferensbidrag (refereegranskat)abstract
- A városok sajátos éghajlata, a városklíma, a természetes környezethez képest módosult éghajlattal jellemezhető. A klímaparaméterek városi módosulásának hátterében a beépített felszínek megváltozott energiaháztartása áll. Míg a városok éghajlata markánsan elkülönül a környező természetes területek éghajlatától, a városokon belül is jelentős klimatikus különbségek alakulnak ki. Ezen különbségek kialakulására alapvető hatással van a beépítettség foka, valamint a zöld területek részaránya. A városokon belüli éghajlati különbségek tanulmányozása mérések és numerikus szimulációk révén lehetséges. Utóbbiak segítségével széleskörűen tanulmányozható a beépítettség, a városokra jellemző mesterséges anyagok, valamint a városon belül alkalmazott zöld- és kék infrastruktúra elemeinek hatása a kialakuló mikro- és lokális éghajlatra, illetve mindezek hatása a lakosok komfortérzetére. Eme ismeretanyagra alapozva megfogalmazhatók olyan várostervezési irányelvek, melyekkel az éghajlatváltozással kombinálódó városklíma negatív hatásai mérsékelhetőek, s a városlakók számára klimatikus szempontból élhetőbb környezet teremthető.Tanulmányomban Budapest jellemző városi beépítési formáit, s a köztük lévő mikroklimatikus különbségeket vizsgálom numerikus szimulációk útján, különös tekintettel a nyári hőterhelés mérséklésére irányuló várostervezési beavatkozások eredményességére az egyes beépítési formák esetén. Az egyik ilyen beavatkozás az épülethomlokzatok albedójának növelése nagyobb sugárzás-visszaverő képességű anyagok, illetve festékek alkalmazása révén. Egy másik jellemző beavatkozás a zöldterületek részarányának növelése, melyet tanulmányomban a lombkorona borítás értékének változtatásával vizsgálok. A különféle beépítési formák, homlokzat albedók és korona borítottság értékek komplex hatásának feltárására az ENVI-met szimulációs software-t alkalmaztam. Az eredmények alapján elmondható, hogy a megnövekedett albedó következtében a napsugárzásnak kitett homlokzatok hőmérséklete – s ez által az épületek hőterhelése is – csökken. A visszavert sugárzási hányad megnövekedése azonban az épületek között sugárzás többletként jelenik meg, mely többlet a nem módosított albedójú felületek (utak, terek) nagyobb sugárzási terheléséhez és ezáltal a városi határréteg felmelegedéséhez vezet. Ezzel ellentétben, a korona borítottság növelése a városi határrétegben a rövidhullámú sugárzás és a léghőmérséklet csökkenését eredményezi. Mivel ezen tényezők hatása a lakosok komfortérzetét és az épületeket érő hőterhelést is előnyösen befolyásolja, a közterületek fásítása a nyári hőterhelés mérséklésére irányuló várostervezési beavatkozás egyik hatásos eszköze lehet.
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| 5. |
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| 6. |
- Gál, Csilla V, et al.
(författare)
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Heat mitigation with shade trees : the role of landscape design and tree parameters in ameliorating summertime heat stress in a Central-European square
- 2017
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Konferensbidrag (refereegranskat)abstract
- Climate change projections for Central Europe indicate a significant rise in summertime temperatures and an increase in the frequency and severity of extreme heat events. Combined with the peculiar climate of cities—characterized by the Urban Heat Island effect and reduced ventilation due to high building density—climate change is expected to have more pronounced effects in urban environments. Shade trees are demonstrated to be one of the most effective means to mitigate heat stress in cities. However, very few studies have evaluated systematically the impact of different landscape design and tree parameters (e.g. the species selection or the spatial distribution) on the heat mitigation effectiveness of shade trees. This study aims to assess the role of vegetation transmissivity, canopy size and tree distribution in a medium-sized Central-European square. The rectangular Bartók Square, located in the inner city of Szeged (Hungary), was selected as a study area. The numerical simulations were carried out with the radiation model SOLWEIG (v.2015a). The necessary meteorological data, collected on clear and warm summer day, was obtained from a nearby weather station run by the Hungarian Weather Service. The default model was built on the basis of available GIS data and utilized tree related parameters from detailed field measurements (tree location, canopy size and shape, etc.). Crown transmissivity data originated from a preliminary, long-term radiation measurement survey covering the vegetation period. Alternative scenarios were constructed with the following characteristics:1) keeping the original tree layout of the square, the initial tree crown transmissivity of 0.0678 was changed to small (0.0243) and high (0.1328) values;2) keeping the original canopy volume, two additional scenarios were introduced with evenly distributed trees of different crown sizes: that of several small trees and of fewer large ones;3) keeping the original canopy volume and using the same number and size of trees, we assessed the role of tree distribution by introducing a scenario were the trees were arranged along the bounding facades of the square—this scenario was compared to the evenly distributed configuration. In order to evaluate the impact of vegetation, all scenarios are reported in reference to a theoretical, nonvegetated square. Since several studies revealed that mean radiant temperature (Tmrt) plays a key role in summertime heat stress in the European context, this parameter was selected as performance indicator. Tmrt combines the heat effect of all short-and long-wave radiation fluxes reaching the human body. Our results indicate that when shade is provided for the facades only, the nighttime Tmrt surplus nearly disappears. However, while horizontal long-wave radiation fluxes have a greater impact on human thermal comfort due to the different absorption coefficients of the human body (0.7 vs. 0.95 for short and long-wave radiation, respectively), providing shade for the facades only is not a successful daytime heat mitigation strategy in open urban places. Comparing the influence of vegetation transmissivity revealed that low transmissivity species were able to reduce Tmrt by only 2C on average during the day. According to our case study, when transmissivity and canopy volume is kept constant, considerable mean radiant temperature reduction can be achieved by evenly distributed mature trees.
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| 7. |
- Gál, Csilla V
(författare)
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Mean radiant temperature modeling, A comparative model evaluation
- 2018
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Konferensbidrag (refereegranskat)abstract
- As a result of the changing climate with trends of rising temperatures and increasing extreme heat events, urban planners and city officials have recently taken a great interest in improving the climate of cities and maintaining comfortable outdoor conditions in spite of these trends.In order to meet the demand for this special knowledge and to deliver scientific assistance, several numerical models have emerged with an aim to assess the microclimate of cities and their influence on human thermal comfort over the course of the past decade. While these tools differ both in the human thermal comfort indices they deliver and in their numerical modeling approach, they all rely on the calculation of mean radiant temperature—the driving parameter of outdoor human thermal comfort. While the assessment of models lags behind the perpetual software updates and releases, the documentation of many such models is also lacking or insufficient. In addition, a great deal of existing validation studies assess clear cut situations where the site is either sunlit or in shade, whereas conditions in the urban environment are generally more complex. Given both the growing importance the outdoor thermal environment of cities and the role played by these tools, reporting on their performance is of high importance.The aim of this study is to assess the ability of several recently emerged or updated microclimate models to reproduce mean radiant temperature (Tmrt) in a complex urban setting. The evaluation is made against field data obtained by integral radiation measurements. Results indicate that most microclimate models underestimate Tmrt both at sunlit locations and at night, whereas in shade Tmrt is generally overestimated. These errors are related to the surface temperature parametrization, the isotropic sky assumption, simplifications in the reflected shortwave radiation calculation and the incorrect representation of a standing person.
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| 8. |
- Gál, Csilla V, et al.
(författare)
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Mean radiant temperature modeling outdoors : A comparison of three approaches
- 2020
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Konferensbidrag (refereegranskat)abstract
- As a result of both urbanization and climate change, the thermal environment of cities is deteriorating steadily. Thus, urban planner and city officials are increasingly under the pressure maintain livable environments in cities. The quickest and most economic means to assessing the performance of various urban heat mitigation strategies is via numerical modeling. Owing to these advantages, the approach gained popularity over the past decade, as well as resulted in the proliferation of microclimate models. The driving parameter of outdoor human thermal comfort is radiation, which is accounted for via mean radiant temperature (Tmrt). While this parameter is at the center of most outdoor thermal comfort indices, it is also rather challenging to measure and calculate. Along with the recent emergence of microclimate models, the ways of calculating outdoor Tmrt also multiplied. However, beyond individual model validations, very few studies have attempted to compare the performance of different models. Thus, the aim of this paper is to assess the performance of three microclimate models in estimating Tmrt in the urban environment. The reviewed models are VTUF-3D, the Grasshopper add-ons of Rhinoceros 3D and the latest ENVI-met version utilizing the Indexed View Sphere (IVS) algorithm. The adopted spatial resolution in each model were not identical. In the case of ENVI-met and VTUF-3D, 3 and 5 meter resolutions were used, respectively. The Grasshopper add-on was set to calculate surface temperatures at 6 m resolution and view factors (along with Tmrt) for a denser, 3-meter spatial grid. The model assessment utilized data from a 26-hours-long integral radiation measurement, conducted in Szeged (Hungary). The observations were undertaken along the four bounding facades of Bartók Square during a clear summer day in 2016. According to the preliminary results, ENVI-met performs the best when the observation sites are exposed to direct solar radiation. However, it underestimates Tmrt values by up to 10 ºC when the sites are in shade and during night. In general, both VTUF-3D and the Grasshopper add-on underestimate Tmrt values considerably during sunlit conditions (exceeding 20 ºC at times), but reproduce radiative conditions well at night (with errors remaining below 4 ºC). One reason for the above errors is the way Tmrt is calculate by these models. While Tmrt calculations differ in each model, at the core of their adopted approaches is a Tmrt estimation developed for indoor environments---which was later adopted to outdoors. One of the lingering simplification is the assumption of a seated posture and/or the conceptualization of the human body as a sphere. The other transferred simplification is the assumption of small temperature differences between the surrounding surfaces. These assumptions not only diminish the impact of horizontal fluxes, but also depict a less diverse radiative environment.
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| 9. |
- Gál, Csilla V
(författare)
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Microclimate assessment of urban block typologies, a simulation approach
- 2012
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Urban environments are characterized by a diversity of microclimates. To manage this complexity, assessments generally involve a certain kind of simplification: either an areal constriction (e.g. the analysis of distinct urban squares), or a spatial reduction (e.g. the reliance on the urban canyon model). This paper approaches the task at the scale of the urban block. In the analysis of metropolitan urban block typologies, the study adopts Probáld's concept of microclimate assemblages. With the presented approach, the research aims to compliment existing urban microclimate assessments. Utilizing the numerical modelENVI‐met, this paper focuses on the effect of building configurations.
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| 10. |
- Gál, Csilla V
(författare)
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Modeling mean radiant temperature in outdoor spaces : A comparative numerical simulation and validation study
- 2018
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Konferensbidrag (refereegranskat)abstract
- Cities are increasingly under pressure to address the challenges of climate change. One of the most pressing and unifying issue in this respect is the maintenance of comfortable outdoor conditions despite rising air temperatures and increasing extreme heat events. As a means to inform urban planner and city officials, the assessment of outdoor thermal comfort conditions—either via numerical modeling or field measurements—have gained popularity over the past decade. While measurements can deliver highly accurate data, they are expensive and time-consuming endeavors that can only inform us about the conditions in an existing environment on a specific day and time of the year. In contrast, numerical modeling allows us to evaluate alternative urban design scenarios as well as to grasp the spatial and temporal variability of outdoor human thermal comfort conditions.Given the advantages of numerical modeling and the increasing computational power of personal computers, several tools have emerged with an aim to assess the microclimate and human thermal comfort impacts of urban planning and design decisions. While these tools differ both in the human thermal comfort indices they deliver and in their numerical modeling approach, they all rely on the calculation of mean radiant temperature, in one way or another. Mean radiant temperature (Tmrt), the driving parameter of human thermal comfort in outdoor spaces, requires the modeling of both short- and long waver radiation fluxes. While different calculation methods exist to deriving this parameter, most models also introduce some kind of numerical simplification to increase computational speed. The multitude of numerical approaches in deriving Tmrt, coupled with the high spatial and temporal variability of this parameter, can result in a range of values delivered by these tools. Given both the growing importance of improving the outdoor thermal environment of cities and the role these tools play in it, reporting on their performance is of high importance.The aim of this study is to assess popular microclimate models in their ability to reproduce the complex radiative environment of cities, as indicated by Tmrt, and to inform to the research and design community about their performance, compared to integral radiation measurement derived filed data. While the documentation of some numerical simulation tools is lacking or incomplete, this paper will nevertheless attempt to shed lights on the reasons behind the disparities in the derived Tmrt values. Initial results indicate that most microclimate models have a tendency to underestimate nighttime Tmrt together with daytime values when the location is exposed to the sun. In contrast, when the locations become shaded, Tmrt values are generally overestimated. In general, these errors indicate issues with surface temperature parametrization and point to the greatest challenge of the numerical simulation community.
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