EGU2020-6247
https://doi.org/10.5194/egusphere-egu2020-6247
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Possible Effects of Climate Change on New Zealand Design Wind Speeds

Amir Ali Safaei Pirooz1, Richard G.J. Flay2, Richard Turner3, and Cesar Azorin-Molina4,5
Amir Ali Safaei Pirooz et al.
  • 1Department of Mechanical Engineering, The University of Auckland, Auckland, New Zealand (asaf433@aucklanduni.ac.nz)
  • 2Department of Mechanical Engineering, The University of Auckland, Auckland, New Zealand (r.flay@auckland.ac.nz )
  • 3NIWA, Wellington, New Zealand (richard.Turner@niwa.co.nz )
  • 4Centro de Investigaciones sobre Desertificación – Spanish National Research Council (CIDE-CSIC), Moncada (Valencia), Spain (cesar.azorin@uv.es)
  • 5Regional Climate Group, Department of Earth Sciences, University of Gothenburg, Gothenburg, Sweden (cesar.azorin@uv.es)

The climate is changing, and as a result, the Earth could experience more severe extreme weather events. Growing interest and concern about the effects of climate change on cities, infrastructures and people’s lives raises the question “how are design wind speeds influenced by different climate change scenarios?”. This study aims at (i) analysing the gust wind records of four meteorological stations across New Zealand for the period 1972-2017; (ii) investigating whether or not the long-term wind gust series have changed significantly; and (iii) how these changes can be considered in the estimation of design wind speeds to ensure the safety and reliability of the future structures.

Historical hourly and daily gust wind speed series recorded at the four selected stations were subjected to a robust quality control and homogenisation protocol to ensure all the artificial inhomogeneities resulting from factors like station relocations, anemometer height changes, instrumentation malfunctions, instrumentation changes, different sampling intervals, and observation environment changes, have been eliminated prior to any subsequent analyses. Then, annual and seasonal trends in both magnitudes and frequencies of the extreme winds were evaluated as to whether the observed trends are statistically significant or not by calculating p-values. From the derived gust trends, some recommendations are proposed for consideration in regard to revising the design wind speeds for calculating the wind loads on structures. In addition, the findings of the study are compared with gust wind speed trends in several other countries and also with IPCC 5th assessment projections for New Zealand [1].

The main findings of this research are summarised as follows:

  • The magnitude and frequency of wind gust showed negative (significant for some stations and seasons) trends.
  • This result suggests that at this stage no extra multiplier is required to be applied to the New Zealand design wind speeds.
  • Additional analyses of the long-term wind gust trends at more stations across New Zealand are needed.

 

Reference

[1] Ministry for the Environment 2018. Climate Change Projections for New Zealand: Atmosphere Projections Based on Simulations from the IPCC Fifth Assessment, 2nd Edition. Wellington: Ministry for the Environment.

How to cite: Safaei Pirooz, A. A., Flay, R. G. J., Turner, R., and Azorin-Molina, C.: Possible Effects of Climate Change on New Zealand Design Wind Speeds, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6247, https://doi.org/10.5194/egusphere-egu2020-6247, 2020

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  • CC1: Comment on EGU2020-6247, Linda van Garderen, 05 May 2020

    Thank you for this very interesting presentation!

    I am intreged by your thorough method for homogenizing the windrecords. However, I was a bit surprised about the windtunnel tests. As I understand it from  you text, the actually measurement devises from location were tested in the windtunnel? Not only would that cause in inhomogenius moment in present measurements due to moving the actual devise around, it would only help for the time this device was in operation. You show results from 1970 onward, which means the devices have been updated several times. Would the windtunnel test for the last device in use not increase the inhomogenity as the older devices cannot be tested like this?

    Did the windtunnel test bring you much more information than what was available through the producer of the devices, as they normally calibrate each device?

    You show that your results are different from IPCC, could this be because of the more homogenius data you now have or may there be a different reason?  Is there literature available after IPCC that backs your results up or are your results truly a stand alone?

    Again, thank you very much for your presentation!

    Linda

    • AC1: Reply to CC1, Amir Ali Safaei Pirooz, 05 May 2020

      Dear Linda, 

      Thank you so much for your interest in our work and your comment on our poster. 

      Regarding the wind-tunnel tests: 

      Firstly, the purpose of the wind-tunnel tests was not to check the calibration or the quality of the sensor. But, we carried out these tests to assess the differences caused in wind speed time series due to changes in instrumentations (from old, heavy sensors to new Automatic Weather Stations (AWS) with light cup anemometers) and also change in the signal processing and gust duration. Before the implementation of AWS, the gust duration was only a function of the sensor and recording device, which for New Zealand (i.e. Munro MKII anemometer and chart recorder), the gust duration was around 1 second. However, after the implementation of AWS, the WMO-recommended 3-sec gust duration was adopted at most stations across the world. These changes (as shown in Fig. 1 in the poster) resulted in a significant breakpoint in wind speed time series. 

      Therefore, we conducted the wind-tunnel tests to investigate how much difference was caused by both changes in instruments and also gust duration. We found a set of correction factors that allow us to convert gust measurements with a certain gust duration (for example, 1-sec) to equivalent 3-sec gust duration measurements. 

      Also, we did not take the actual anemometer from the station, which is operating at the moment. However, we used the same type and model, which the MetService and NIWA provided us with from their workshops. 

       

      Regarding the discrepancies between our results and IPCC, the recent IPCC report (cited in the poster) that we have for New Zealand seems that no homogenisation was applied for data used in the IPCC report. Therefore, homogeneity could explain part of the difference. In addition, for the current study, we only used 4 stations. However, now we have homogenised data for 52 stations across New Zealand, and currently, we are analysing them. The new analyses will hopefully give us more insight about the accuracy and validity of our results.

       

      If you are interested, you can find more details about our tests and gust durations in our recent papers: 

      - Turner, R., Safaei Pirooz, A. A., Flay, R. G. J., Moore, S. and Revell, M. (2019) ‘Use of High-Resolution Numerical Models and Statistical Approaches to Understand New Zealand Historical Wind Speed and Gust Climatologies’ Journal of Applied Meteorology and Climatology, Vol. 58: 1195-1218 DOI: https://doi.org/10.1175/JAMC-D-18-0347.1

      - Safaei Pirooz, A. A., and Flay, R. G. J. (2018) ‘Response characteristics of anemometers used in New Zealand’ in: The 19th Australasian Wind Engineering Society Workshop, 4-6 April, 2018, Torquay, Victoria.
      https://www.researchgate.net/publication/324271921_Response_Characteristics_of_Anemometers_Used_in_New_Zealand

      - Safaei Pirooz AA, Flay RGJ, Turner R, Azorin-Molina C (2019) Effects of climate change on New Zealand design wind speeds. Natl Emerg Response 32(2):14-20 https://search.informit.com.au/documentSummary;dn=612564634929911;res=IELHEA 


      Also, we have another poster in EGU2020, which explains our wind-tunnel tests and issues with changes in anemometers and gust durations: 


      https://meetingorganizer.copernicus.org/EGU2020/EGU2020-12298.html
      https://presentations.copernicus.org/EGU2020/EGU2020-12298_presentation.pdf

       

      Should you have any questions about our papers/results, please feel free to contact me at asaf433@aucklanduni.ac.nz

       

      Kind regards,

      Amir A.S. Pirooz

      • CC2: Reply to AC1, Linda van Garderen, 05 May 2020

        Thank you very much for the elaborate answer. That clarifies a lot!

        Linda

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