Quarterly Journal of the Royal Meteorological Society
Ongoing urbanization highlights the need for a better understanding and high resolution modelling... more Ongoing urbanization highlights the need for a better understanding and high resolution modelling of the urban climate. In this study, we combine rural observations by WMO surface stations, weather radar data and urban crowd‐sourced observations with very fine‐scale modelling efforts for Amsterdam, The Netherlands. As a model, we use the Weather Research and Forecasting (WRF) mesoscale model with 3D variational data assimilation at a 100‐m resolution in the innermost model domain. In order to enable the assimilation of observations within the urban canopy, we develop a scheme to reduce urban temperature biases by adjusting urban fabric temperatures. The scheme is tested against independent urban observations for the summer month of July 2014 and specifically for a hot period and an extreme precipitation event. We find data assimilation reduces biases in temperature and wind speed. Within the city, the most significant improvement is the reduction of negative temperature biases durin...
PET (Physical Equivalent Temperature) heat map valid for 1 July 2015 on 1 meter resolution. This ... more PET (Physical Equivalent Temperature) heat map valid for 1 July 2015 on 1 meter resolution. This is a hot summer day with a PET exceedance probability of ~1: 5.5 years
In the Netherlands, municipalities and other sub-national governments have to conduct climate str... more In the Netherlands, municipalities and other sub-national governments have to conduct climate stress tests to examine the societal impact of heat load by citizens. So far, these parties have been hindered by the abundance of contrasting urban heat maps produced with different metrics and methods by different agencies. To unify the stress tests, we present a methodology for a standardized urban heat map at 1-m spatial resolution by selecting the Physical Equivalent Temperature (PET) as metric for heat stress. First we present an empirical regression model for PET, based on a variety of weather data and street configurations in the human thermal energy balance model Rayman. Thereafter, this empirical PET-model is evaluated for the midsized town Wageningen (the Netherlands). Meteorological observations taken at a nearby reference site and straightforward geographical data have been used as model input. Also, established methods were applied and elaborated to account for the urban heat island effect and wind speed reduction in the city. The presented method is validated against bike traverse observations of PET. Wind speed is the most challenging feature to map, due to its unsteady and local behaviour in cities. As a result, an afternoon averaged PET heat map is demonstrated as standard for an extreme heat day (1:1000 summer half year days), and a cumulative exceedance PET heat map for a representative year. Furthermore, a heat map is projected for 2050 according a warm climate change scenario.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
In the Netherlands, there will be an urgent need for additional housing by the year 2040, which m... more In the Netherlands, there will be an urgent need for additional housing by the year 2040, which mainly has to be realized within the existing built environment rather than in the spatial extension of cities. In this data-driven study, we investigated the effects of different urban planning strategies on heat stress for the current climate and future climate scenarios (year 2050) for the urban agglomeration of The Hague. Heat stress is here expressed as the number of days exceeding minimum temperatures of 20 °C in a year. Thereto, we applied a diagnostic equation to determine the daily maximum urban heat island based on routine meteorological observations and straightforward urban morphological properties including the sky-view factor and the vegetation fraction. Moreover, we utilized the Royal Netherlands Meteorological Institute’s (KNMI) climate scenarios to transform present-day meteorological hourly time series into the future time series. The urban planning strategies differ in ...
Many cities have expanded during the 20th century, and consequently some weather stations are cur... more Many cities have expanded during the 20th century, and consequently some weather stations are currently located closer to cities than before. Due to the urban heat island (UHI) effect, those weather stations may show a positive bias in their 2-m temperature record. In this study, we estimate the impact of urbanization on the temperature record of WMO station De Bilt (The Netherlands). This station has a long historical record, but the nearby city of Utrecht and its suburbs expanded during the 20th century. The temperature rise due to urbanization is estimated by conducting representative mesoscale model simulations for the land-use situation for the years 1900 and 2000. This is performed for 14 different episodes of a week, each representing a typical large-scale flow regime (Grosswettertypes) in both the winter and the summer season. Frequency distributions of these flow regimes are used to estimate an average temperature rise. We find that the model results with two rather different atmospheric boundary-layer schemes, robustly indicate that the urbanization during the 20th century has resulted in a temperature rise of 0.22 ± 0.06 K. This is more than a factor of 2 higher than a previously estimated temperature trend by using observed temperature records of stations close to De Bilt.
This paper reports on the canopy layer urban heat island (UHI) and human comfort in a range of sm... more This paper reports on the canopy layer urban heat island (UHI) and human comfort in a range of small to large cities and villages in the Netherlands. To date, this subject has not been substantially studied in the Netherlands, since it has a relatively mild oceanic (Cfb) climate and impact was assumed to be minor. To fill this knowledge gap, this paper reports on observations of a selected network of reliable hobby meteorologists, including several in The Hague and Rotterdam. A number of alternative measures were also used to quantify UHI, i.e., the generalized extreme value distribution and return periods of UHI and adverse human comfort; its uncertainties were estimated by the statistical method of bootstrapping. It appeared essential to distinguish observations made at roof level from those made within the urban canyon, since the latter related more closely to exposure at pedestrian level and to urban canyon properties in their close neighborhood. The results show that most Dutch cities experience a substantial UHI, i.e., a mean daily maximum UHI of 2.3 K and a 95 percentile of 5.3 K, and that all cities experience a shadow effect in the morning when cities remain cooler than the rural surroundings. Also, an evident relation between the median of the daily maximum UHI and its 95 percentile was discovered. Furthermore, the 95 percentile of the UHI appears well correlated with population density. In addition, we find a significant decrease of UHI and the percentage of surface area covered by green vegetation, but the relation with open water remains unclear.
2018 IEEE 14th International Conference on e-Science (e-Science), 2018
In this study, we improve the Weather Research and Forecasting mesoscale model (WRF) performance ... more In this study, we improve the Weather Research and Forecasting mesoscale model (WRF) performance by incorporating observations of a variety of sources using data assimilation and nudging techniques on a resolution up to 100 meter for urban areas. Our final goal is to create a 15 year climatological urban re-analysis data archive of (hydro)meteorological variables for Amsterdam which is named ERA-urban. This will enable us to trace trends in thermal comfort and extreme precipitation.
Quarterly Journal of the Royal Meteorological Society
Ongoing urbanization highlights the need for a better understanding and high resolution modelling... more Ongoing urbanization highlights the need for a better understanding and high resolution modelling of the urban climate. In this study, we combine rural observations by WMO surface stations, weather radar data and urban crowd‐sourced observations with very fine‐scale modelling efforts for Amsterdam, The Netherlands. As a model, we use the Weather Research and Forecasting (WRF) mesoscale model with 3D variational data assimilation at a 100‐m resolution in the innermost model domain. In order to enable the assimilation of observations within the urban canopy, we develop a scheme to reduce urban temperature biases by adjusting urban fabric temperatures. The scheme is tested against independent urban observations for the summer month of July 2014 and specifically for a hot period and an extreme precipitation event. We find data assimilation reduces biases in temperature and wind speed. Within the city, the most significant improvement is the reduction of negative temperature biases durin...
PET (Physical Equivalent Temperature) heat map valid for 1 July 2015 on 1 meter resolution. This ... more PET (Physical Equivalent Temperature) heat map valid for 1 July 2015 on 1 meter resolution. This is a hot summer day with a PET exceedance probability of ~1: 5.5 years
In the Netherlands, municipalities and other sub-national governments have to conduct climate str... more In the Netherlands, municipalities and other sub-national governments have to conduct climate stress tests to examine the societal impact of heat load by citizens. So far, these parties have been hindered by the abundance of contrasting urban heat maps produced with different metrics and methods by different agencies. To unify the stress tests, we present a methodology for a standardized urban heat map at 1-m spatial resolution by selecting the Physical Equivalent Temperature (PET) as metric for heat stress. First we present an empirical regression model for PET, based on a variety of weather data and street configurations in the human thermal energy balance model Rayman. Thereafter, this empirical PET-model is evaluated for the midsized town Wageningen (the Netherlands). Meteorological observations taken at a nearby reference site and straightforward geographical data have been used as model input. Also, established methods were applied and elaborated to account for the urban heat island effect and wind speed reduction in the city. The presented method is validated against bike traverse observations of PET. Wind speed is the most challenging feature to map, due to its unsteady and local behaviour in cities. As a result, an afternoon averaged PET heat map is demonstrated as standard for an extreme heat day (1:1000 summer half year days), and a cumulative exceedance PET heat map for a representative year. Furthermore, a heat map is projected for 2050 according a warm climate change scenario.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
In the Netherlands, there will be an urgent need for additional housing by the year 2040, which m... more In the Netherlands, there will be an urgent need for additional housing by the year 2040, which mainly has to be realized within the existing built environment rather than in the spatial extension of cities. In this data-driven study, we investigated the effects of different urban planning strategies on heat stress for the current climate and future climate scenarios (year 2050) for the urban agglomeration of The Hague. Heat stress is here expressed as the number of days exceeding minimum temperatures of 20 °C in a year. Thereto, we applied a diagnostic equation to determine the daily maximum urban heat island based on routine meteorological observations and straightforward urban morphological properties including the sky-view factor and the vegetation fraction. Moreover, we utilized the Royal Netherlands Meteorological Institute’s (KNMI) climate scenarios to transform present-day meteorological hourly time series into the future time series. The urban planning strategies differ in ...
Many cities have expanded during the 20th century, and consequently some weather stations are cur... more Many cities have expanded during the 20th century, and consequently some weather stations are currently located closer to cities than before. Due to the urban heat island (UHI) effect, those weather stations may show a positive bias in their 2-m temperature record. In this study, we estimate the impact of urbanization on the temperature record of WMO station De Bilt (The Netherlands). This station has a long historical record, but the nearby city of Utrecht and its suburbs expanded during the 20th century. The temperature rise due to urbanization is estimated by conducting representative mesoscale model simulations for the land-use situation for the years 1900 and 2000. This is performed for 14 different episodes of a week, each representing a typical large-scale flow regime (Grosswettertypes) in both the winter and the summer season. Frequency distributions of these flow regimes are used to estimate an average temperature rise. We find that the model results with two rather different atmospheric boundary-layer schemes, robustly indicate that the urbanization during the 20th century has resulted in a temperature rise of 0.22 ± 0.06 K. This is more than a factor of 2 higher than a previously estimated temperature trend by using observed temperature records of stations close to De Bilt.
This paper reports on the canopy layer urban heat island (UHI) and human comfort in a range of sm... more This paper reports on the canopy layer urban heat island (UHI) and human comfort in a range of small to large cities and villages in the Netherlands. To date, this subject has not been substantially studied in the Netherlands, since it has a relatively mild oceanic (Cfb) climate and impact was assumed to be minor. To fill this knowledge gap, this paper reports on observations of a selected network of reliable hobby meteorologists, including several in The Hague and Rotterdam. A number of alternative measures were also used to quantify UHI, i.e., the generalized extreme value distribution and return periods of UHI and adverse human comfort; its uncertainties were estimated by the statistical method of bootstrapping. It appeared essential to distinguish observations made at roof level from those made within the urban canyon, since the latter related more closely to exposure at pedestrian level and to urban canyon properties in their close neighborhood. The results show that most Dutch cities experience a substantial UHI, i.e., a mean daily maximum UHI of 2.3 K and a 95 percentile of 5.3 K, and that all cities experience a shadow effect in the morning when cities remain cooler than the rural surroundings. Also, an evident relation between the median of the daily maximum UHI and its 95 percentile was discovered. Furthermore, the 95 percentile of the UHI appears well correlated with population density. In addition, we find a significant decrease of UHI and the percentage of surface area covered by green vegetation, but the relation with open water remains unclear.
2018 IEEE 14th International Conference on e-Science (e-Science), 2018
In this study, we improve the Weather Research and Forecasting mesoscale model (WRF) performance ... more In this study, we improve the Weather Research and Forecasting mesoscale model (WRF) performance by incorporating observations of a variety of sources using data assimilation and nudging techniques on a resolution up to 100 meter for urban areas. Our final goal is to create a 15 year climatological urban re-analysis data archive of (hydro)meteorological variables for Amsterdam which is named ERA-urban. This will enable us to trace trends in thermal comfort and extreme precipitation.
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Papers by Sytse Koopmans