Statistical analysis and attribution of impact relevant climate extremes (Webinar)

UK Climate Resilience Programme webinar series

23 September 2020

Speakers: Simon Brown / Daniel Cotterill (Met Office), stakeholder response by Tom Butcher (Met Office business group)

Chair: Suraje Dessai

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Abstract (Simon Brown)

Heatwaves can have substantial detrimental impacts to many sectors including health, agriculture, transport and industry, yet each sector and vulnerability can have its own specific sensitivity to heatwaves, such as heatwave threshold definition, maximum temperature, mean temperature or duration.  This has lead to a plethora of heatwave definitions and studies that are difficult to compare or synthesise into a holistic picture of future heatwave risk.  Stratifying observed  heatwaves with regard to duration and temperature, or those from climate models, also severely compromises the derivation of their likelihoods of occurrence due to insufficient number of events, but this is required information for risk mitigation.

I present a different approach to this problem consisting of a statistical model that can accurately simulate the upper tail of all daily temperatures from which heatwave metrics of choice can be extracted and probabilities calculated through repeated sampling.  This daily temperature simulator captures the annual cycle, climate change effects and the extremal temporal dependence of persistent periods of hot daily temperatures. Whilst providing precise estimates of probabilities this approach also provides event sets of heatwaves, including those yet to be observed, with a range of characteristics, which may be useful to applications for which the temporal evolution of a heatwave is important, such as the internal temperature of buildings during prolonged heatwaves.

Abstract (Daniel Cotterill)

The UK has seen many flooding events over the start of the 21st century occurring after extreme rainfall events. This project looks at extreme daily totals on a UK-wide scale through a new index and the UKCP18 climate projections. Here we look at Autumn in the light of the 2019 November flooding in South Yorkshire which saw one fatality, at least 500 properties flooded and 1200 households evacuated. Observations show that the frequency of extreme daily precipitation in the form of the new index has already increased by 60% in the UK in late Autumn between the beginning of the 20th and 21st centuries and are set to increase exponentially between 2019 and 2080. Future work in collaboration with the Flood Forecasting Centre will examine how river flows are changing for the UK. This will allow for examination of metrics such as river levels allowing for the quantification of climate risk for river flooding at a regional level.


Simon Brown joined the Met Office’s Hadley Centre in 1996 and has been working in climate research ever since, apart from a two year secondment to DEFRA as an embedded scientist providing climate science advice directly to policymakers.  Simon has focussed on climate and weather extremes for a number of years particularly the future prediction of very rare events from a probabilistic perspective leading to the first, soon to be released, UKCP extremes products.  Simon’s current interest is developing tools to correctly account for the spatial and temporal extremal dependence present in weather hazards so that accurate probabilities of extreme events are calculated now and in the future.

Daniel Cotterill is a Climate Scientist at the UK Met Office working in detection and attribution. His work mainly focuses on the impact climate change is having on extreme precipitation and heatwaves by using statistical methods to analyse climate observations and climate model data.

Tom Butcher leads the Met Office’s team of scientists and scientific consultants who work with industry to solve critical weather and climate related problems and provide advice weather and climate expert advice across industry sectors.  His areas of expertise include: energy; offshore oil & gas; surface transport; aviation; water; retail; infrastructure.  He leads and develops strategic partnerships to understand complex requirements, design solutions, and ultimately deliver valuable customer outcomes. Tom has been working with the Met Office, World Meteorological Organisation and Australian Bureau of Meteorology since 2002.

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