Climpact2 and regional climate models

Transcription

1 Climpact2 and regional climate models David Hein-Griggs Scientific Software Engineer 18 th February 2016

2 What is the Climate System??

3 What is the Climate System? Comprises the atmosphere, hydrosphere, cryosphere, surface lithosphere (land surface) and biosphere. These elements all determine the state and dynamics of Earth s climate WMO 2015 Climate refers to the state of the climate system as a whole including a statistical description of its variations.

4 Components of the climate system

5 Weather vs. Climate Climate is what we expect, weather is what we get (1887) Climate = Average weather and its variability over a period of time, ranging from months to millions of years. WMO Quantifies climate over a 30-year average period. Observations create the 30 year climate baseline, which new observations and climatic trends are measured against. Climate refers to the state of the climate system as a whole, including a statistical description of its variations.

6 Natural variability of climate External forcings: Solar radiation Volcanic eruptions = aerosol emission Earth s orbit Milankovitch cycles Internal climate variability: ENSO NAO and other leading modes of variability

7 Human-induced climate variations 1. Perturbations of the atmospheric composition : The enhanced greenhouse effect Aerosol direct effect (scattering of incoming solar radiation) Aerosol indirect effect (affecting the radiative properties of clouds) 2. Land-use change (agriculture, deforestation, reforestation, afforestation, urbanisation, traffic, )

8 Global temperature rising? C Global Slowdown Reduced uncertainty as observation equipment has improved The Met Office says Yes. National Climatic Data Center (NCDC) says Yes. NASA Goddard Institute for Space Studies (GISS) says Yes.

9 So are the observed changes due to Natural Climate Variations? +

10 Human + Natural Variations Fits the Trend

11 How do we quantify the response of the climate to a change in the system? The response of the climate system to these forcing agents is complicated by: 1. feedbacks 2. the non-linearity of many processes 3. different response times of the different components to a given perturbation The only means available to calculate the response is by using numerical models of the climate system.

12 Climate models are a large set of equations describing the physical and chemical processes occurring in the atmosphere, oceans, land surface, cryosphere and the biosphere =

13 Equations solved in grid-cells of a large global grid

14 Development of Climate models

15 Representative Concentration Pathways (RCPs) Based on principle of additional +ve radiative forcing Business as usual 2 C by C by C Stabilisation scenarios +1.5 C +2 C Mitigation Scenario Fuss et al. 2014

16 Climate Models A numerical representation of the climate system that is based on the physical, chemical, and biological properties (IPCC 2014 ) SWCSC 2012

17 Crown copyright Met Office Resolution is important (example)

18 Crown copyright Met Office Resolution is important (example)

19 We need to downscale!

20 Statistical Downscaling? Statistical downscaling makes many assumptions which may not be true for the future. Dynamical downscaling takes longer, but it is more defendable scientifically. Dynamical downscalers often consider statistical downscaling to be witchcraft.

21 What is a Regional Climate Model? RCM = Climate model for regional purpose Covers a limited area of the globe Includes (at least) the atmosphere and land surface components of the climate system

22 One way nesting RCMs are driven at the boundaries by GCM or observed data Lateral (side) and bottom (sea surface) LAMs are highly dependent on their boundary conditions and cannot exist without them

23 RCMs simulate current climate more realistically Patterns of present-day winter precipitation over Great Britain

24 Represent smaller islands Projected changes in summer surface air temperature between present day and the end of the 21st century.

25 Resolve intense mesoscale systems A tropical cyclone is evident in the RCM (right) but not in the GCM

26 Describe daily extremes more accurately Frequency of winter days over the Alps with different daily rainfall thresholds. RCM and Observations aggregated at GCM scale

27 Added value from using RCMs Using GCMs alone to assess changes in extremes will often miss the influence of regional dynamics By running RCMs, we re able to better detect the influence of complex topography and regional characteristics on extremes Fig 5. from Frei et al., 2006

28 A chain of separate models Global Climate Model Regional Climate Model Impacts Models

29 The PRECIS user interface

30 PRECIS Graphical User Interface Map of Region Run Monitor Choice of model domain and resolution Stop Fine scale configurations to region RCM, GCM/ Reanalysis and scenario Output data configurations Experiment start date and run length (with spin-up)

31 Surface configuration: Land-sea mask editing The land-sea mask is important The influences of land and sea on climate are very different The default land-sea mask may contain inaccuracies due to the rotation and regridding of the fractional source data Sometimes better to be set as land

32 Surface configuration: Topographic height Can specify the topographic height of individual grid boxes

33 Station data vs.. Gridded data David and Victoria Beckham have just purchased a 27 million pound country house in England. David wants to know if he needs to adapt his house for climate change, so he runs PRECIS over the UK. When the models finish he then extracts the grid box his house is in and starts performing analysis on the data for that grid box. What s wrong with his method? Crown copyright Met Office

34 Station data vs. Gridded data Compare like with like Data only have skill at spatial scales resolved by their grids The grid box data values are an area average for the full area. They are not point data and therefore not directly comparable with single point time series. Crown copyright Met Office

35 Example 4: Individual station vs.. area averages 26 stations in a 25km 25km area (black bars) and their area averages, (red bars). The area average (c.f. model grid box output) is considerably and inconsistently different to most individual stations Crown copyright Met Office

36 Case Study: Climpact2 analysing PRECIS output data The great thing about Climpact2 (thank you Nicholas) is that in addition to analysis of point observations, it can also ingest gridded data from climate models. I ran two PRECIS experiments for the case study over a 25km Eastern Caribbean region. One experiment downscaled from the HadGEM2-ES GCM (a CMIP5 model) using historical GHG values and a second from HadGEM2-ES RCP 8.5.

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38 Case Study: Climpact2 analysing PRECIS output data The raw output data from the experiments has to be processed to be Climpact2 ready. That means regridding, changing the units (to Celsius / millimetres per day), conversion to NetCDF data format, and more

39 Case Study: Climpact2 analysing PRECIS output data When the PRECIS data was in the right format, I edited a file in the climpact2-master directory: climpact2.wrapper.r I made changes to this file to the names of my variables (e.g. Air_temperature instead of Tmax) and to the input file names.

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41 Case Study: Climpact2 analysing PRECIS output data I then ran Climpact2.wrapper.r inputting the baseline data and writing out a quantiles file. Next I ran Climpact2.wrapper.r inputting the future projections data and the quantiles file. Climpact2 ran and produced output NetCDF files. The files are NOT presented as results, but just to show a small range of what is produced. There s still work to be done testing and checking the system. This is a very early prototype.

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48 Next Steps The system needs further testing before official release. If you want to use Climpact2 to analyse regional climate data, you can either generate data yourself with an RCM (including PRECIS) or download data from online repositories, e.g.: (currently down)

49 Questions?