High-Resolution Climate Projections for Ireland – a Multi-Model Ensemble Approach

This project involves simulating climate change in Ireland at high spatial resolution using Regional Climate Models (RCMs). The periods 1975-2005 and 2020-2100 are simulated. The boundary data are provided by a separate EPA-funded project (PI: Paul Nolan, ICHEC/Met Éireann) which involves running EC-Earth global simulations and contributing towards the CMIP6 project. The RCMs are run at high spatial resolution, ~3.8km, thus allowing a better evaluation of the local effects of climate change in Ireland. To account for the uncertainty in future emissions, all IPCC RCP (2.6, 4.5, 6.0 & 8.5) emission scenarios are used to simulate the future climate. Through the ensemble approach, the uncertainty in the RCM projections can be partially quantified, thus providing a measure of confidence in the predictions.  

Numerous studies show that coupled atmosphere-ocean-wave models simulations result in a more accurate representation of the climate, particularly in coastal regions. For example, storm and rainfall events are more accurately simulated if the RCMs are coupled to an ocean model. In addition, these simulations provide projections of the ocean and wave climate of Ireland. A number of RCM simulations will be repeated using the COAWST (WRF, ROMS and SWAN) coupled atmosphere-ocean-wave climate model.

Running such a large ensemble of high resolution climate models is a substantial computational task and requires extensive use of the ICHEC supercomputer systems.

The research will consolidate and greatly expand on previous EPA-funded climate change research carried out by ICHEC. Findings from this study indicate that by the middle of this century:

Temperature:

  • Mean annual temperatures will increase by 1–1.6°C, with the largest increases seen in the east of the country.
  • Hot days will get warmer by 0.7-2.6°C compared with the baseline period (see Figure 1).
  • Cold nights will get warmer by 1.1-3.1°C.
  • Averaged over the whole country, the number of frost days is projected to decrease by over 50%.
  • The average length of the growing season will increase by over 35 days per year (see Figure 2).

 

climate projections, extreme heat
Figure 1. Projected changes in the top 5% of maximum daytime summer temperatures for the medium-low and high emission scenarios. In each case, the future period 2041-2060 is compared with the past period 1981-2000. The numbers included on each plot are the minimum and maximum increases, displayed at its location.

 

 

Climate Change effects on agriculture in Ireland
Figure 2. “Likely” increase in the length of the growing season (days per year). (a) Medium-low emission scenario; (b) high-emission scenario. In each case, the future period 2041–2060 is compared with the past period 1981–2000.

 

Precipitation:

  • Significant decreases in mean annual, spring and summer precipitation amounts by mid-century are likely (Figure 3).
  • Heavy rainfall events will increase in winter and autumn.

 

Climate Change, Rainfall Ireland
Figure 3. Projected mean ensemble change (%) in annual precipitation for the medium-to-low and high emission ensemble scenario. In each case, the future period 2041–2060 is compared with the past period 1981–2000. The numbers included on each plot are the minimum and maximum changes, displayed at their locations.

 

Climate Change & Storm Tracks, Ireland

Wind Energy & Extreme Events

  • The energy content of the wind is projected to decrease during spring, summer and autumn. The projected decreases are largest for summer, with values ranging from 3% to 15%.
  • Storms affecting Ireland will decrease in frequency, but increase in intensity, with increased risk of damage (see Figure 4).  As extreme storm events are rare, the storm-tracking research is currently being extended to focus on analysing a larger ensemble, thus allowing a robust statistical analysis of extreme storm track projections
  • Increase in number of heatwaves by mid-century (See Figure 5)

 

Climate Change Heat Waves, Ireland
Figure 5. “Likely” increase in the number of heat waves events over the 20-year period 2041-2060. (a) Medium- to low-emission scenario; (b) high-emission scenario. In each case, the future period 2041–2060 is compared with the past period 1981–2000. The numbers included on each plot are the minimum and maximum increases, displayed at their locations.

The project outputs have contributed towards numerous national studies in diverse areas such as flooding mitigation, agriculture and renewable energy.

Current Regional Climte Modelling Research:

An ensemble of downscaled RCM simulations is currently running for the period 1975-2100. This research will greatly enhance and improve the high-resolutions climate projection dataset for Ireland (presented above). An overview and progress of these simulations are outlined in Table 1. An overview of the archived fields is presented in Table 2.

Preliminary RCM projection results are presented below. The following downscaled simulations of Table 1 were used to provide an initial assessment of regional climate change; COSMO5-ECEarth (4km resolution), COSMO5-MPI-ESM-LR (4km), COSMO5-CNRM-CM5 (4km), COSMO5-HadGEM2-ES (4km) and COSMO5-MIROC5 (4km). These results will be regularly updated as the simulations of Table 1 complete. The results (to-date) are summarised as follows:

  • Temperature projections show a clear west-to-east temperature gradient, with the largest increase in the east. This trend is consistent with previous studies and with all RCPs, RCM-GCM simulations and time periods assessed to-date (see Figure 6). Projections of daily minimum and maximum temperature are similar.
  • Rainfall is projected to increase during winter and autumn and decrease during summer (see Figure 7). Again this is consistent with previous research. To-date, results show a north-west to south-east trend in the rainfall projections. However, more work is required before any regional details can be assigned with confidence to the rainfall projections.
  • Wind Speeds are projected to decrease during spring and summer (see Figure 8). Small increased are noted for winter but more work and simulations are required as there exists some disagreement between RCMs.

 

Table 1. Outline of RCM simulations. Green shading: these simulations have been completed as part of a previous EPA project authored by the PI [1] (project 159). These particular simulations will be analysed as part of the current research as the resolution is comparable to the newer simulations. All lower resolutions simulations of previous research will be archived. Blue shading: Downscaled CMIP5 simulations complete or currently running on ICHEC, ECMWF and PRACE supercomputers. Red Shading: Downscaled CMIP6 simulations which will commence during July 2018 and run in parallel with the CMIP6 EC-Earth simulations.
*COAWST is a coupled atmosphere (WRF), ocean (ROMS) and wave model (SWAN/WAVEWATCH3) model
**Pre-processing scripts prepared and simulations tested. Will start if CMIP6 is further delayed.

 

Table 2. Archived data of the RCM simulations. With the exception of the daily and monthly data, all variables are archived at three-hour intervals.

 

Figure 6. Preliminary RCM Ensemble Projections of 2m Temperature. All RCM ensemble members were run with 4km grid spacing. In each case, the future 30-year period is compared with the past period 1976-2005. The numbers included on each plot are the minimum and maximum projected changes, displayed at their locations.

 

Figure 7. Preliminary  RCM Ensemble Projections of Winter Rainfall (%). All RCM ensemble members were run with 4km grid spacing. In each case, the future 30-year period is compared with the past period 1976-2005. The numbers included on each plot are the minimum and maximum projected changes, displayed at their locations.

 

Figure 8. RCM Ensemble Projections of Summer 10m Wind Speed (%). All RCM ensemble members were run with 4km grid spacing. In each case, the future 30-year period is compared with the past period 1976-2005. The numbers included on each plot are the minimum and maximum projected changes, displayed at their locations.

 

If you are interested in learning more about the project or accessing the datasets, please contact paul.nolan@ichec.ie