Spatio-temporal analysis of extreme winter temperatures in Ireland

TL;DR

This study analyzes extreme winter temperatures in Ireland from 1950 to 2022, revealing decreasing frequency and magnitude of cold extremes, with winters warming faster than summers, using advanced statistical models for non-stationarity and spatial extremes.

Contribution

It introduces a comprehensive spatio-temporal modeling approach for extreme winter minima, incorporating non-stationarities and novel risk functions, and compares climate model covariates for extreme and non-extreme events.

Findings

Frequency of extreme cold events decreasing

Magnitude of extreme winter minima decreasing

Winter warming rate exceeds summer warming rate

Abstract

We analyse extreme daily minimum temperatures in winter months over the island of Ireland from 1950-2022. We model the marginal distributions of extreme winter minima using a generalised Pareto distribution (GPD), capturing temporal and spatial non-stationarities in the parameters of the GPD. We investigate two independent temporal non-stationarities in extreme winter minima. We model the long-term trend in magnitude of extreme winter minima as well as short-term, large fluctuations in magnitude caused by anomalous behaviour of the jet stream. We measure magnitudes of spatial events with a carefully chosen risk function and fit an r-Pareto process to extreme events exceeding a high-risk threshold. Our analysis is based on synoptic data observations courtesy of Met \'Eireann and the Met Office. We show that the frequency of extreme cold winter events is decreasing over the study period. The magnitude of extreme winter events is also decreasing, indicating that winters are warming, and apparently warming at a faster rate than extreme summer temperatures. We also show that extremely cold winter temperatures are warming at a faster rate than non-extreme winter temperatures. We find that a climate model output previously shown to be informative as a covariate for modelling extremely warm summer temperatures is less effective as a covariate for extremely cold winter temperatures. However, we show that the climate model is useful for informing a non-extreme temperature model.