Hans Hooyberghs

Assessing Seasonality in the Surface Urban Heat Island of London

AbstractThis paper assesses the seasonality of the urban heat island (UHI) effect in the Greater London area (United Kingdom). Combining satellite-based observations and urban boundary layer climate modeling with the UrbClim model, the authors are able to address the seasonality of UHI intensity, on the basis of both land surface temperature (LST) and 2-m air temperature, for four individual times of the day (0130, 1030, 1330, and 2230 local time) and the daily means derived from them. An objective of this paper is to investigate whether the UHI intensities that are based on both quantities exhibit a similar hysteresis-like trajectory that is observed for LST when plotting the UHI intensity against the background temperature. The results show that the UrbClim model can satisfactorily reproduce both the observed urban–rural LSTs and 2-m air temperatures as well as their differences and the hysteresis in the surface UHI. The hysteresis-like seasonality is largely absent in both the observed and modeled 2-m ...

Heat and health in Antwerp under climate change: Projected impacts and implications for prevention

Background Excessive summer heat is a serious environmental health problem in several European cities. Heat-related mortality and morbidity is likely to increase under climate change scenarios without adequate prevention based on locally relevant evidence. Methods We modelled the urban climate of Antwerp for the summer season during the period 1986–2015, and projected summer daily temperatures for two periods, one in the near (2026–2045) and one in the far future (2081–2100), under the Representative Concentration Pathway (RCP) 8.5. We then analysed the relationship between temperature and mortality, as well as with hospital admissions for the period 2009–2013, and estimated the projected mortality in the near future and far future periods under changing climate and population, assuming alternatively no acclimatization and acclimatization based on a constant threshold percentile temperature. Results During the sample period 2009–2013 we observed an increase in daily mortality from a maximum daily temperature of 26 °C, or the 89th percentile of the maximum daily temperature series. The annual average heat-related mortality in this period was 13.4 persons (95% CI: 3.8–23.4). No effect of heat was observed in the case of hospital admissions due to cardiorespiratory causes. Under a no acclimatization scenario, annual average heat-related mortality is multiplied by a factor of 1.7 in the near future (24.1 deaths/year CI 95%: 6.78–41.94) and by a factor of 4.5 in the far future (60.38 deaths/year CI 95%: 17.00–105.11). Under a heat acclimatization scenario, mortality does not increase significantly in the near or in the far future. Conclusion These results highlight the importance of a long-term perspective in the public health prevention of heat exposure, particularly in the context of a changing climate, and the calibration of existing prevention activities in light of locally relevant evidence.

Cold-related mortality vs heat-related mortality in a changing climate: A case study in Vilnius (Lithuania)

Introduction: Direct health effects of extreme temperatures are a significant environmental health problem in Lithuania, and could worsen further under climate change. This paper attempts to describe the change in environmental temperature conditions that the urban population of Vilnius could experience under climate change, and the effects such change could have on excess heat‐related and cold‐related mortality in two future periods within the 21st century. Methods: We modelled the urban climate of Vilnius for the summer and winter seasons during a sample period (2009–2015) and projected summertime and wintertime daily temperatures for two prospective periods, one in the near (2030–2045) and one in the far future (2085–2100), under the Representative Concentration Pathway (RCP) 8.5. We then analysed the historical relationship between temperature and mortality for the period 2009–2015, and estimated the projected mortality in the near future and far future periods under a changing climate and population, assuming alternatively no acclimatisation and acclimatisation to heat and cold based on a constant‐percentile threshold temperature. Results: During the sample period 2009–2015 in summertime we observed an increase in daily mortality from a maximum daily temperature of 30 °C (the 96th percentile of the series), with an average of around 7 deaths per year. Under a no acclimatisation scenario, annual average heat‐related mortality would rise to 24 deaths/year (95% CI: 8.4–38.4) in the near future and to 46 deaths/year (95% CI: 16.4–74.4) in the far future. Under a heat acclimatisation scenario, mortality would not increase significantly in the near or in the far future. Regarding wintertime cold‐related mortality in the sample period 2009–2015, we observed increased mortality on days on which the minimum daily temperature fell below − 12 °C (the 7th percentile of the series), with an average of around 10 deaths a year. Keeping the threshold temperature constant, annual average cold‐related mortality would decrease markedly in the near future, to 5 deaths/year (95% CI: 0.8–7.9) and even more in the far future, down to 0.44 deaths/year (95% C: 0.1–0.8). Assuming a “middle ground” between the acclimatisation and non‐acclimatisation scenarios, the decrease in cold‐related mortality will not compensate the increase in heat‐related mortality. Conclusion: Thermal extremes, both heat and cold, constitute a serious public health threat in Vilnius, and in a changing climate the decrease in mortality attributable to cold will not compensate for the increase in mortality attributable to heat. Study results reinforce the notion that public health prevention against thermal extremes should be designed as a dynamic, adaptive process from the inception. HighlightsThe relationship between temperature and health is studied for Vilnius, Lithuania.Mortality attributable to heat and cold is assessed historically and under RCP8.5.Projected population transitions and acclimatisation or its absence are modelled.The decreases in cold‐related mortality do not compensate for the additional heat‐related deaths.Both heat‐health prevention and enhanced cold‐health prevention are urgently needed.

Influence of climate change on summer cooling costs and heat stress in urban office buildings

Indoor climatic conditions are strongly influenced by outdoor meteorological conditions. It is thus expected that the combined effect of climate change and the urban heat island effect negatively influences working conditions in urban office buildings. Since office buildings are particularly vulnerable to overheating because of the profound internal heat gains, this is all the more relevant. The overheating in office buildings leads to elevated cooling costs or, because additional work breaks are required by legislation in some countries, productivity losses. We have developed a methodology incorporating urban climate modelling and building energy simulations to assess cooling costs and lost working hours in office buildings, both for current-day and future climate, extending towards the end of the twenty-first century. The methodology is tailored to additionally assess the impact and benefits of adaptation measures, and it is designed to be transferable from one city to another. Results for a prototype building located in three different European cities (Antwerp, Bilbao and London) illustrate the challenge in keeping Western-European office buildings comfortable until the end of the twenty-first century without adaptation measures, and the beneficial effect of adequate adjustments. The results further illustrate the large decreases in cooling costs (up to 30%) caused by the introduction of (external) shading and increased night-time ventilation in actively cooled buildings, and the improvements in working conditions in free-running buildings caused by moving workers to cooler locations and splitting workdays in morning and evening shifts.

Assessing Climate Change in Cities Using UrbClim

The urban heat island effect, in which air temperatures tend to be higher in urban environments than in rural areas, is known to exacerbate the heat impact on population health. We introduce a new urban climate model, further referred to as UrbClim, designed to study the urban heat island effect at a spatial resolution of a few hundred metres. Despite its simplicity, UrbClim is found to be of the same level of accuracy as more sophisticated models, while also being much faster than high-resolution mesoscale climate models. Because of that, the model is well suited for long time integrations, in particular for applications in urban climate projections. In this contribution, we present temperature maps for London, including an assessment of the present-day climate, and projections for the future (2081–2100).

Evaluation of Regional Measures in order to Improve the Air Quality in the North-West European Hot Spot Region

The effects of four regional emission scenarios on the concentrations of PM10, PM2.5, NO2 and EC (elementary carbon) in the North-West European (NWE) Hot Spot region have been studied. The emission estimates were provided by TNO, regional calculations were carried out for the years 2009 and 2020 using the BelEUROS model (Deutsch et al. 2009) on a 15 × 15 km2 grid. The effect of a highway speed limit reduction to 90 km/h on all highways in the NWE region (Belgium, France, Germany, Luxemburg, the Netherlands and the UK) showed up to 4.4% lower concentrations of EC and up to 3.5% reduction of NO2 concentrations (mean over Belgium). The introduction of low emission zones (LEZ) in all cities in the NWE region with more than 50.000 inhabitants and more than 700 inhabitants/km2 resulted in a reduction of 1.8% of the EC-concentrations (mean over Belgium). However, in the areas that actually make part of a LEZ the EC concentration is reduced by 19% and hence this scenario could be more effective in terms of population exposure. In the healthy diet scenario, 75% less meat production in Europe was assumed, leading basically to lower ammonia emissions (reduction of approximately 30%). This scenario results in significant reductions (4.2% as a mean over Belgium) in particulate matter (PM2.5) concentrations due to a reduction of secondary aerosol formation. EC-concentrations are not affected by this scenario. Finally, a pellet stoves scenario was calculated in which 20% of the non-wood energy consumption (gas, oil) in the residential combustion sector had been converted to pellet stoves. This scenario resulted in considerable increases in emissions and in an increase of EC-concentrations by up to 21% as a mean value over Belgium. PM2.5-concentrations increase by up to 4%. Results for all scenarios are available for the whole NWE region.

Is the Recent Decrease in Belgian Air Pollution Concentration Levels Due to Meteorology or to Emission Reductions

Recent years have shown significant decrease in concentrations levels of particulate matter (PM10) and nitrogen dioxide (NO2) in Belgium. For ozone (O3), no such trend is found. Recent years, however, did not feature many periods with unfavourable meteorological dispersion conditions, casting some ambiguity on the underlying reasons for the decrease. This study tries to separate the impact of weather effects from emission reductions in the long-term trend. We build a statistical model explaining the daily averaged concentrations based on 32 meteorological parameters, the day of the week, the month of the year and the year itself, for the period 2004–2014. The 32 meteorological parameters are those considered to train the neural network prediction model OVL. Many of these meteo variables have only a small predictability and are intercorrelated with each other. Therefore, only those meteo parameters are used that have a significant impact on concentration levels. This procedure is applied for the complete time series and for each air quality monitoring location separately. In order to avoid overfitting, the same analysis is done, restricted to the data of even-numbered years, and the regression is then applied to the odd-numbered years. It is shown that the statistical parameters remain reasonably constant, which proves that the amount of overfitting is not significant. The results show, on average over all measurement locations, a range of yearly meteorological effects of 1.9 µg/m3 for NO2, 3.1 µg/m3 for PM10 and 2.7 µg/m3 for O3. Meteorology combined with the residuals of the statistical fit show a range of 1.2 µg/m3 for NO2, 2.9 µg/m3 for PM10 and 4.4 µg/m3 for O3. Finally, the long-term trend shows a range of 5.3 µg/m3 for NO2, 11.1 µg/m3 for PM10 and 2.3 µg/m3 for O3, with clearly decreasing trends for NO2 and PM10, and an oscillating trend for O3. Differences between rural, urban background, urban and industrial stations exist but are rather small. We can conclude that the major trend in air pollution (Belgium) is a long-term trend, linked to emission changes, and it can be expected that the concentration decreases of the last years will not suddenly disappear in the near future given unchanged policy. Furthermore, it can be concluded that emission reductions at the local, regional, European and worldwide scale are the dominant factors explaining the improvement of air quality.

Can Aircraft-Based Remote-Sensing NO 2 Measurements Combined with High Resolution Model Data Improve NO 2 Exposure Estimates over Urban Areas?

As part of the STEREO-III BUMBA (Belgian Urban NO2 Monitoring Based on APEX hyperspectral data) project, we try to exploit the synergy between NO2 column measurements derived from the aircraft-based APEX hyperspectral imaging system and high-resolution model data from a combined land use regression-Gaussian plume model system for the complex city-port region of Antwerp (Belgium). The resulting model maps are then used to determine the NO2-exposure of the population of the region.