| 1. |
- Aminipouri, M., et al.
(author)
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Urban tree planting to maintain outdoor thermal comfort under climate change: The case of Vancouver's local climate zones
- 2019
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In: Building and Environment. - : Elsevier BV. - 0360-1323. ; 158, s. 226-236
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Journal article (peer-reviewed)abstract
- Spatiotemporal variation of mean radiant temperature (Tmrt), a major driver of outdoor human thermal comfort, is driven by exposure to solar and longwave radiation, which in turn respond to local patterns of shading, wind speed, air humidity and air temperature. In this study, the SOlar and LongWave Environmental Irradiance Geometry (SOLWEIG) model was used to simulate how changes in minimum and maximum air temperature and solar radiation under Representative Concentration Pathways (RCP) 4.5 and 8.5 climate projections would change Tmrt in Vancouver over the 2070-2100 period. With micrometeorological variables representative of a changed climate, days with Tmrt above 65 degrees C were predicted to increase three-to five-fold under RCP 4.5 and 8.5, respectively. SOLWEIG was also used to quantify the potential of maximum feasible street tree cover to reduce Tmrt for the hottest day on record for Vancouver (July 29, 2009), and an end-of-century hot day under the two future climate scenarios. SOLWEIG simulations with maximum feasible street tree cover under RCP 4.5 demonstrated an average reduction of 1.3 degrees C in Tmrt, compared to the contemporary extreme heat day with current street trees. However, average Tmrt increased by 1.9 degrees C under the RCP 8.5 scenario even with maximum feasible street tree cover, relative to the contemporary extreme heat day. We conclude that adding street trees has the potential to offset Tmrt increases under the RCP 4.5 scenario, however this measure is insufficient to maintain contemporary Tmrt under the RCP 8.5 scenario.
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| 2. |
- Andersson-Sköld, Yvonne, et al.
(author)
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An integrated method for assessing climate-related risks and adaptation alternatives in urban areas
- 2015
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In: Climate Risk Management. - : Elsevier BV. - 2212-0963. ; 7, s. 31-50
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Journal article (peer-reviewed)abstract
- © 2015 The Authors. The urban environment is a complex structure with interlinked social, ecological and technical structures. Global warming is expected to have a broad variety of impacts, which will add to the complexity. Climate changes will force adaptation, to reduce climate-related risks. Adaptation measures can address one aspect at the time, or aim for a holistic approach to avoid maladaptation. This paper presents a systematic, integrated approach for assessing alternatives for reducing the risks of heat waves, flooding and air pollution in urban settings, with the aim of reducing the risk of maladaptation. The study includes strategies covering different spatial scales, and both the current climate situation and the climate predicted under climate change scenarios. The adaptation strategies investigated included increasing vegetation; selecting density, height and colour of buildings; and retreat or resist (defend) against sea-level rise. Their effectiveness was assessed with regard to not only flooding, heat stress and air quality but also with regard to resource use, emissions to air (incl. GHG), soil and water, and people's perceptions and vulnerability. The effectiveness of the strategies were ranked on a common scale (from -3 to 3) in an integrated assessment. Integrated assessments are recommended, as they help identify the most sustainable solutions, but to reduce the risk of maladaptation they require experts from a variety of disciplines. The most generally applicable recommendation, derived from the integrated assessment here, taking into account both expertise from different municipal departments, literature surveys, life cycle assessments and publics perceptions, is to increase the urban greenery, as it contributes to several positive aspects such as heat stress mitigation, air quality improvement, effective storm-water and flood-risk management, and it has several positive social impacts. The most favourable alternative was compact, mid-rise, light coloured building design with large parks/green areas and trees near buildings.
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| 3. |
- Gebregiorgis, Daniel, et al.
(author)
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Does the IOD independently influence seasonal monsoon patterns in Northern Ethiopia?
- 2019
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In: Atmosphere. - : MDPI AG. - 2073-4433. ; 10:8
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Journal article (peer-reviewed)abstract
- The dominant large-scale interannual modes in the tropical Pacific and Indian Oceans-El Niño southern oscillation (ENSO) and the Indian Ocean Dipole (IOD)-dominate seasonal rainfall patterns in Ethiopia. However, there is a clear interaction between ENSO and the IOD, and it is unclear whether the IOD has an independent influence on seasonal monsoon patterns in Northern Ethiopia. We use monthly rainfall records from 15 stations from two drought-prone regions in Northern Ethiopia (Afar and Amhara) for the period 1966-2006 to explore relationships between rainfall and circulation patterns and sea surface temperature (SST) anomalies over the tropical Indo-Pacific region. Our analysis confirms that regional summer monsoon (Kiremt) rainfalls in these regions are predominantly modulated by ENSO.Warm and cold ENSO episodes (El Niño/La Nina) are associated with below and above average summer monsoon rainfall, respectively. Lagged relationship between the IOD and Kiremt rainfall shows that positive/negative phases of the IOD are generally conducive to Kiremt rainfall increases/decreases over large parts of Ethiopia. Regression models based on the large-scale circulation indices NINO3.4 and a Dipole Mode Index (DMI)NO-ENSO representing the "ENSO-free IOD" also highlight the role of ENSO. However, the relative-weights for the models with DMINO-ENSO, calculated using Akaike Information Criteria (AIC), were 1.5 and 1.1 times the weights for the ENSO only models for the Afar and Amhara regions, respectively. This suggests that the IOD has an independent regional influence. This is in line with the conception of the IOD as a unique coupled-mode in the tropics, and may have important implications in boosting seasonal forecasting skills in the regions. No statistically significant trends were found in the regional and modeled rainfall time-series.
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| 4. |
- Holmer, Björn, 1943, et al.
(author)
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How to transform the standing man from a box to a cylinder – a modified methodology to calculate mean radiant temperature in field studies and models
- 2015
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In: ICUC9 – 9 th International Conference on Urban Climate jointly with 12th Symposium on the Urban Environment. 20-24 July, Toulouse, France.
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Conference paper (other academic/artistic)abstract
- Mean radiant temperature (Tmrt) has shown to be an important meteorological variable in studies of human comfort and health. The Tmrt is calculated as the surface temperature of a standing man approximated as a cylinder emitting the same amount of longwave radiation as all short- and longwave radiation fluxes received from the surrounding four cardinal points and down- and upwards. The calculation was introduced by Höppe in 1992 and has then been used both in models (e.g. SOLWEIG) and field studies. However, the formula by Höppe describes in fact a man shaped like a box and not a cylinder, which has resulted in some peculiar features noticed in studies of Tmrt such as a secondary daytime minimum and an influence of the orientation of the field equipment. A methodology to change the box man to a cylindrical man is proposed. It will remove the peculiarities that have been observed in earlier studies. The methodology is based on the partition of the observed shortwave fluxes in direct and diffuse radiation. The minimum shortwave radiation of the four cardinal points is used as diffuse radiation since it is monitored by a sensor that is not sunlit. By subtraction of this quantity the horizontal direct fluxes are obtained. Calculation of the resultant flux of the sunlit sensors and adjustment for solar angle gives the direct shortwave radiation. The surface of the standing man (as a cylinder) perpendicular to the direct radiation must be determined and the direct shortwave radiation received by the standing man can be calculated. Then the sum of the shortwave fluxes can be calculated. The diffuse and longwave fluxes can be calculated according to the Höppe formula since they differ little with direction. In the SOLWEIG model the direct shortwave radiation is used as an input. Thus the calculation according to the new methodology is easy to apply, only the solar position needs to be added. The new methodology is tested by model calculations with SOLWEIG and field studies in both high-latitude Gothenburg, Sweden and low-latitude Ouagadougou, Burkina Faso. The secondary minimum disappears. In Gothenburg at a site with SVF=0.95 the noon depression of Tmrt by the Höppe formula was about 2 °C and there was an overestimation of 1.5-1.7 °C two-three hours before and after noon.differences in summer. In Ouagadougou data from an open site (SVF=0.83) in the dry season the differences were slightly smaller. Sites with lower SVF and much reflected direct shortwave radiation differed less from the Tmrt obtained with the Höppe formula.
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| 5. |
- Lau, Kevin Ka-Lun, 1983, et al.
(author)
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The effect of urban geometry on mean radiant temperature under future climate change: a study of three European cities
- 2015
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In: International journal of biometeorology. - : Springer Science and Business Media LLC. - 0020-7128 .- 1432-1254. ; 59:7, s. 799-814
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Journal article (peer-reviewed)abstract
- Future anthropogenic climate change is likely to increase the air temperature (T a ) across Europe and increase the frequency, duration and magnitude of severe heat stress events. Heat stress events are generally associated with clear-sky conditions and high T a , which give rise to high radiant heat load, i.e. mean radiant temperature (T mrt ). In urban environments, T mrt is strongly influenced by urban geometry. The present study examines the effect of urban geometry on daytime heat stress in three European cities (Gothenburg in Sweden, Frankfurt in Germany and Porto in Portugal) under present and future climates, using T mrt as an indicator of heat stress. It is found that severe heat stress occurs in all three cities. Similar maximum daytime T mrt is found in open areas in all three cities despite of the latitudinal differences in average daytime T mrt . In contrast, dense urban structures like narrow street canyons are able to mitigate heat stress in the summer, without causing substantial changes in T mrt in the winter. Although the T mrt averages are similar for the north–south and east–west street canyons in each city, the number of hours when T mrt exceeds the threshold values of 55.5 and 59.4 °C—used as indicators of moderate and severe heat stress—in the north–south canyons is much higher than that in the east–west canyons. Using statistically downscaled data from a regional climate model, it is found that the study sites were generally warmer in the future scenario, especially Porto, which would further exacerbate heat stress in urban areas. However, a decrease in solar radiation in Gothenburg and Frankfurt reduces T mrt in the spring, while the reduction in T mrt is somewhat offset by increasing T a in other seasons. It suggests that changes in the T mrt under the future scenario are dominated by variations in T a . Nonetheless, the intra-urban differences remain relatively stable in the future. These findings suggest that dense urban structure can reduce daytime heat stress since it reduces the number of hours of high T mrt in the summer and does not cause substantial changes in average and minimum T mrt in the winter. In dense urban settings, a more diverse urban thermal environment is also preferred to compensate for reduced solar access in the winter. The extent to which the urban geometry can be optimized for the future climate is also influenced by local urban characteristics.
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| 6. |
- Lindberg, Fredrik, 1974, et al.
(author)
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The impact of urban planning strategies on heat stress in a climate-change perspective
- 2016
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In: Sustainable Cities and Society. - : Elsevier BV. - 2210-6707. ; 25, s. 1-12
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Journal article (peer-reviewed)abstract
- Spatial and temporal characteristics of outdoor heat stress for a redevelopment area in Gothenburg, Sweden, in a climate change perspective, using mean radiant temperature (Tmrt) as a proxy for heat stress are presented. The impact of climate change on Tmrt was evaluated using statistically downscaled data from a regional climate model. The simulated average Tmrt for the future scenarios was not higher than for today’s climate, because the increased longwave radiation fluxes caused by higher temperatures were offset by reduced shortwave radiation fluxes caused by increased cloudiness. The spatial pattern of Tmrt in the study area during warm and clear weather is primarily governed by the shadow patterns of buildings and vegetation. The highest average-daytime Tmrt was found at open locations, but because open areas also have the highest frequency of sunlit occasions, this does not necessarily imply that open areas are most prone to heat-stress. When considering only occasions during clear and warm weather situations, the highest Tmrt were usually found close to sun-exposed, south-facing walls. Under these criteria, denser urban environments have lower heat stress than more open urban environments. The warmest areas were also found to be the warmest areas in the future as well. Tree-shadows are an effective measure to reduce daytime Tmrt. Trees was found to have the largest impact on Tmrt in open areas where vegetation is sparse, especially when the distance to the nearest “cool” place is used as a measure of heat-stress.
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| 7. |
- persson, gunn, et al.
(author)
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Från utsläppsscenarier till lokal nederbörd och översvämningsrisker
- 2015
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Reports (other academic/artistic)abstract
- Inom det av MSB finansierade projektet ”Nederbörd och översvämningar i framtidens Sverige − ett system till stöd för klimatanpassning” har SMHI ansvarat för hydrologisk och hydraulisk modellering samt framtagande av tidsserier med lokalt klimat för framtida förhållanden. Två metoder att bearbeta klimatdata har använts; SMHI:s Distributionsbaserad skalering (DBS) och en statistisk metod utarbetad vid Göteborgs universitet. Hydrologiska modeller har satts upp för Ätran och Torneälven och har sedan använts för beräkningar med de framtagna tidsserierna, som omfattar både SRES- och RCP-scenarier. Flöden med 100 års och 200 års återkomsttid har därefter beräknats liksom Beräknat högsta flöde (Bhf). Hydrauliska modeller för Falkenberg vid Ätran och Haparanda vid Torneälven har satts upp och beräkningar av vattennivåer har gjorts utifrån flödesberäkningarna och antaganden om havsnivåer. Därefter har översvämningsskikt applicerats på kartor. Samtliga beräkningar pekar mot ökande årsmedeltemperatur och årsmedelnederbörd i framtiden. För Ätrans avrinningsområde beräknas att antalet dygnstemperaturer kring noll grader och kring 15°C minskar till förmån för fler dagar med 5-10°C och från 15°C uppemot 25°C. Dagar med mindre än 10 mm nederbörd blir färre och dagar med 10-40 mm ökar. För Torneälvens avrinningsområde ser de riktigt låga dygnstemperaturerna ut att minska och istället blir det fler dagar med temperaturer strax under noll grader. En ökning av antalet dagar med medeltemperaturer kring 15°C ökar. Dagar med några mm nederbörd minskar och dagar med 5-25 mm ökar. Samtliga beräkningar pekar på ökad intensiv nederbörd och antalet torra dagar minskar enligt nästan alla beräkningar. Generellt sett ökar samtliga beräknade flöden för Ätran och för Torneälven ser de ut att minska mot slutet av seklet. Det dimensionerande snötäcket minskar för Ätran med 30-80%. Även för Torneälven ses minskande snötäcke i de flesta scenarier på ca 10-60%. Medeltillrinningen ser ut att öka både för Torneälven och för Ätran. Den maximala tillrinningen minskar troligen för Torneälven, vilket till stor del kan kopplas till mindre snömängder, och ökar för Ätran, vilket beror på ökad nederbörd. För Torneälven ses en förskjutning mot tidigare flödestoppar på våren, kopplat till en tidigare snösmältning. Havsvattenståndet har stor betydelse för vattennivåerna i Ätran ända upp till Tullbron. Uppströms Tullbron är det storleksordningen på flödet som styr hur hög vattennivån blir i Ätran. Havet påverkar vattennivåerna i mynningen vid Torneälven och längs kusten. Uppströms i Torneälven är det storleksordningen på flödet som styr vattennivåerna, och därmed risken för översvämning. Summary
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| 8. |
- Rayner, D.P. 1973, et al.
(author)
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A multi-state weather generator for daily precipitation for the Torne River basin, northern Sweden/western Finland
- 2016
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In: Advances in Climate Change Research. - : Elsevier BV. - 1674-9278. ; 7:1-2, s. 70-81
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Journal article (peer-reviewed)abstract
- This paper describes a new weather generator e the 10-state empirical model e that combines a 10-state, first-order Markov chain with a non-parametric precipitation amounts model. Using a doubly-stochastic transition-matrix results in a weather generator for which the overall precipitation distribution (including both wet and dry days) and the temporal-correlation can be modified independently for climate change studies. This paper assesses the ability of the 10-state empirical model to simulate daily area-average precipitation in the Torne River catchment in northern Sweden/western Finland in the context of 3 other models: a 10-state model with a parametric (Gamma) amounts model; a wet/dry chain with the empirical amounts model; and a wet/dry chain with the parametric amounts model. The ability to accurately simulate the dis- tribution of multi-day precipitation in the catchment is the primary consideration. Results showed that the 10-state empirical model represented accumulated 2- to 14-day precipitation most realistically. Further, the dis- tribution of precipitation on wet days in the catchment is related to the placement of a wet day within a wet-spell, and the 10-state models represented this realistically, while the wet/dry models did not. Although all four models accurately reproduced the annual and monthly averages in the training data, all models underestimated inter-annual and inter-seasonal variance. Even so, the 10-state empirical model performed best. We conclude that the multi-state model is a promising candidate for hydrological applications, as it simulates multi-day precipitation well, but that further development is required to improve the simulation of interannual variation.
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| 9. |
- Rayner, D.P. 1973, et al.
(author)
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A statistical downscaling algorithm for thermal comfort applications
- 2015
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In: Journal of Theoretical and Applied Climatology. - : Springer Science and Business Media LLC. - 0177-798X .- 1434-4483. ; 122:3-4, s. 729-742
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Journal article (peer-reviewed)abstract
- We describe a new two-step modeling framework for investigating the impact of climate change on human comfort in outdoor urban environments. In the first step, climate change scenarios for air temperature and solar radiation (global, diffuse, direct components) are created using a change-factor algorithm. The change factors are calculated by comparing ranked daily regional climate model outputs for a future-period and a present-day period, and then changes consistent with these daily change factors are applied to historical hourly climate observations. In the second step, the mean-radiant-temperature (Tmrt) is calculated using the SOLWEIG (SOlar and LongWave Environmental Irradiance Geometry) model. Tmrt, which describes the radiant heat exchange between a person and their surroundings, is one of the most important meteorologically derived parameters governing human energy balance and outdoor thermal comfort, especially during warm and sunny days.We demonstrate that change factors can be applied independently to maximum air temperature and daily global solar radiation, and show that the outputs from the algorithm, when aggregated to daily values, are consistent with the driving regional climate model. Finally, we demonstrate how to obtain quantitative information from the scenarios regarding the potential impact of climate change on outdoor thermal comfort, by calculating changes in the distribution of hourly summer day-time Tmrt and changes in the number of hours with Tmrt >55 °C.
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| 10. |
- Thorsson, Sofia, 1972, et al.
(author)
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Present and projected future mean radiant temperature for three European cities
- 2017
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In: International Journal of Biometeorology. - : Springer Science and Business Media LLC. - 0020-7128 .- 1432-1254. ; 61:9, s. 1531-1543
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Journal article (peer-reviewed)abstract
- © 2017 The Author(s)Present-day and projected future changes in mean radiant temperature, Tmrt in one northern, one mid-, and one southern European city (represented by Gothenburg, Frankfurt, and Porto), are presented, and the concept of hot spots is adopted. Air temperature, Ta, increased in all cities by 2100, but changes in solar radiation due to changes in cloudiness counterbalanced or exacerbated the effects on Tmrt. The number of days with high Tmrt in Gothenburg was relatively unchanged at the end of the century (+1 day), whereas it more than doubled in Frankfurt and tripled in Porto. The use of street trees to reduce daytime radiant heat load was analyzed using hot spots to identify where trees could be most beneficial. Hot spots, although varying in intensity and frequency, were generally confined to near sunlit southeast-southwest facing walls, in northeast corner of courtyards, and in open spaces in all three cities. By adding trees in these spaces, the radiant heat load can be reduced, especially in spaces with no or few trees. A set of design principles for reducing the radiant heat load is outlined based on these findings and existing literature.
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