EMS Annual Meeting Abstracts
Vol. 20, EMS2023-313, 2023, updated on 06 Jul 2023
EMS Annual Meeting 2023
© Author(s) 2023. This work is distributed under
the Creative Commons Attribution 4.0 License.

How might the occurrence frequency and intensity of extreme rainfall events in Ireland change in projected future climates?

Enda O'Brien1 and Jingyu Wang2
Enda O'Brien and Jingyu Wang
  • 1Irish Centre for High-End Computing, University of Galway, Ireland (enda.obrien@ichec.ie)
  • 2School of Engineering, University College, Cork, Ireland (JingyuWang@ucc.ie)

Observed data of extreme rainfall occurrence in Ireland are available from approx. 30 stations over periods ranging from about 30 to 70 years.  They are provided as tables of occurrence dates and magnitudes of 9 different metrics, from “r4in15” (4 mm in 15 minutes) to “r30in24h” (30 mm in 24 hours).  These events are too few and too sparse to be treated with non-parametric statistics.  However, they are all “peak over threshold” (POT) events, and so the well-developed theories of POT statistics applies to them.  In particular, the number of such events in any given time period follow a Poisson distribution (which needs only one parameter, the mean), while the exceedances (i.e., magnitudes above threshold) follow a generalized Pareto distribution (which formally needs 3 parameters, but in practise only 2 need to be determined). 

As climate is projected to change in the future, our basic assumption is that the number of POT events (Poisson distribution) will change, while the exceedances (Pareto distributions) will remain the same, only represented by different numbers of samples.  Since the Poisson distribution is determined by just one parameter (the mean), the only quantity needed to fully characterize the nature of future intense rainfall events are projections of the mean of such events. 

Meanwhile, future climate projections (e.g., from CORDEX) are typically available on daily timescales, so the problem reduces to finding a robust relationship, whether physical  (based e.g., on a Clausius-Clapeyron scaling) or statistical (based, e.g., on the tails of frequency distributions)  between each of the 9 intense rainfall metrics and the daily values of standard surface variables under future climate projections.  Different options are explored, and results are shown based on future projections from the TRANSLATE project, as functions of different future emission scenarios. Typically, large increases in the frequency of all 9 metrics are projected regardless of the exact relationship assumed between the intense rainfall events and the frequency distributions of daily precipitation (or temperature).  Results are best shown as frequency distributions rather than single number percentage changes.


How to cite: O'Brien, E. and Wang, J.: How might the occurrence frequency and intensity of extreme rainfall events in Ireland change in projected future climates?, EMS Annual Meeting 2023, Bratislava, Slovakia, 4–8 Sep 2023, EMS2023-313, https://doi.org/10.5194/ems2023-313, 2023.