From Weather to Climate: Using Medium-Range Forecasts to Quantify Long-Term Trends in Extreme Events

The frequency and intensity of some extreme weather events, such as heatwaves,
are increasing due to climate change, with significant implications for socio-economic
sectors globally. This study focuses on the question of how we quantify the rate at
which the probability of these severe events is changing, enhancing our ability to
support effective adaptation strategies and deepen our understanding of climate
change’s diverse impacts on different regions and populations. Our initial case
study uses the ECMWF’s Reforecast dataset to analyse trends and the evolving
risk of extreme high summer temperatures in the Pacific Northwest. We specifi-
cally explore the relationship between the probability of exceeding climatological
temperature thresholds and local, regional, and global temperature changes. We
identify a consistent relationship, statistically significant in the case of local and
regional trends, allowing large-scale temperature trend information to be used to
provide an estimate of a risk-doubling time to complement other approaches. Our
results indicate that regional and local rising temperatures significantly elevate
the likelihood of extreme weather events, highlighting the growing risk associated
with climate change. Our evaluation confirms the ECMWF Reforecast data as a
reliable model to use as a potential source for such analyses, although limited by
the relatively short (20-year) length of the dataset.