Urban Heat Island Effects and Human Comfort in a Mild Cfb Climate Exploring Long Term Observations by Hobby Meteorologists in The Netherlands

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1 Urban Heat Island Effects and Human Comfort in a Mild Cfb Climate Exploring Long Term Observations by Hobby Meteorologists in The Netherlands Gert-Jan Steeneveld, Sytse Koopmans, Bert Heusinkveld, Bert van Hove, Bert Holtslag

2 Context: The Netherlands in a mild Cfb climate? Some last month new items National heat plan activated Warnings for the elderly Road works limited due to heat Climatology July T max 22.1 ºC T min 12.5 ºC T mean 17.4 ºC Heat makes fish die due to low O 2

Research Aim & Motivation Objectives: Quantify UHI intensity and heat stress in the Netherlands Relationship with city characteristics Statistical modelling Benchmark database

3 Research Aim & Motivation Objectives: Quantify UHI intensity and heat stress in the Netherlands Relationship with city characteristics Statistical modelling Benchmark database Observations by hobby meteorologists: Delft Many Dutch cities have large areas of surface water Many hobby meteorologists live in urban areas Historical data files National coverage

4 Method Link each hobby station to rural weather station Correction for UHI during neutral (windy) conditions Selection based on metadata and instrumental set-up Typically years of data Classification based on site description 24 cities Inhabitants:

5 Results: Typical Diurnal Cycle ( T u-r ) (max) UHI (K) Voorburg (Den Haag) Time(h)

6 Results: Frequency Distributions Rotterdam UHI max = maximum value during a 24 hour period

7 First assessment UHI max effect Netherlands City* Time period Median 95 Percentile Rotterdam 12/ / The Hague 12/ / Voorburg 01/ / Delft 01/ / Leiden 03/ / Haarlem 12/ / Purmerend 01/ / Heerhugowaard 01/ / Houten 07/ / Apeldoorn 01/ / Leeuwarden 01/ / Assen 01/ / Groningen 01/ / Steeneveld et al., JGR, 2011

8 First assessment UHI max effect Netherlands 8 Roof stations 7 Median UHI 95Perc UHI Rdam C-Hobby Rdam C-WUR Rdam-S-WUR Rdam-E-WUR Ijsselmonde The Hague Delft Haarlem Purmerend Leeuwarden Apeldoorn Wageningen Heemskerk Heerhugowaard Leiden Doornenburg Losser Damwoude IJsselmuiden Groningen Tilburg Assen Cap. ad Ijssel Gouda Houten Rdam-R UHI (K) Voorburg City

9 Netherlands compared with Europe 14 NL Current 95 perc max UHI 12 Oke 1973 Memon et al UHI (K) E E E E E E E+08 Population

10 UHI vs Greenness and Population density Greenness estimated based on Googlemaps TM and idealised absorption spectrum of green vegetation

11 Leiden Rotterdam-Rijnmond Rotterdam Wageningen

12 Validation detection green & water cover fraction Estimated fraction (-) Green cover fraction Water cover fraction y = x R 2 = y = 0.918x R 2 = Observed Fraction (-)

13 Test GEV distribution Extreme meteo data often follow General Extreme Value distribution F ( x) = exp 1 κ α ( x µ ) 1 κ µ: middle value measure κ: shape parameter α: the scale parameter UHI max also follows GEV distribution Reduced variable = -log(-log(n/(n tot +1))) o = obs UHI max ; GEV fit Calculation return period: T = 1/(1 - F) Overeem et al. (2008)

WBGT = 0.7 x T nwb + 0.2 x T g + 0.1 x T a Approximation*: AWBGT 0.567 x T a + 0.

14 How serious? Indicator Thermal Comfort/Heat Stress: Wet Bulb Globe Temperature (WBGT) T nwb T a T g WBGT = 0.7 x T nwb x T g x T a Approximation*: AWBGT x T a x e a AWBGT >27.7 Severe heat stress >32 Cancellation sport events Bi-modal distribution (dominance by either T a or e a ) *

15 Heat stress: WBGT (threshold 27.7 o C) City* Median 95 Percentile 98 Percentile Rotterdam The Hague Voorburg Delft Leiden Purmerend Heerhugowaard Houten Apeldoorn Leeuwarden Assen Wageningen Groningen Steeneveld et al., JGR, (2011)

16 Heat stress: WBGT 35 Median AWBGT 95Perc AWBGT 98Perc AWBGT 30 Roof stations Rdam C-Hobby Rdam C-WUR Rdam-S-WUR Rdam-E-WUR Ijsselmonde The Hague Delft Haarlem Purmerend Leeuwarden Apeldoorn Wageningen Heemskerk Heerhugowaard Leiden Doornenburg Losser Damwoude IJsselmuiden Groningen Tilburg Assen Cap. ad Ijssel Gouda Houten Rdam-R Voorburg AWBGT (ºC) City

17 Conclusions Observations hobby meteorologists useful Representative observations (?) (heterogeneity, limited time series) UHI intensity substantial in NL No clear/easy link between UHI and number of inhabitants, but closer > relation with population density Green vegetation cover prevents UHI. No clear link between open water fraction Several cities experience severe heat stress for some days per year

Acknowledgements The hobby meteorologists: K. Piening, H. Beek, S. Rosdorff, M. van der Hoeven, M. van der Molen, M. de Kleer, M. Borgardijn, S. Roelvink, W. ter Haar, F. Bijlsma, R. Zwolsman, R.

18 Acknowledgements The hobby meteorologists: K. Piening, H. Beek, S. Rosdorff, M. van der Hoeven, M. van der Molen, M. de Kleer, M. Borgardijn, S. Roelvink, W. ter Haar, F. Bijlsma, R. Zwolsman, R. Khoe, J. Kruijsen, O. de Zwart, J. Effing, W. van Dijk, M. Peters, M. van Maanen, W. van der Velde, J. Spruijt, H. Lankamp, H. van der Heide, G. van t Klooster, C. Pel, M. Gosselink, F. Brouwer, W. van Duijn. The Royal Netherlands Meteorological Institute for providing the observations for rural areas Jan Elbers (Alterra) for providing parts of the Rotterdam observations Steeneveld, G.J., S. Koopmans, B. G. Heusinkveld, L.W.A. van Hove, and A. A.M. Holtslag (2011), Quantifying Urban Heat Island Effects And Human Comfort For Cities Of Variable Size And Urban Morphology In The Netherlands., J. Geophys. Res., doi: /2011jd Gert-Jan.Steeneveld@wur.nl

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