Identification of changing precipitation extremes and attribution to atmopsheric, oceanic and climatic changes
Lead Research Organisation:
University of East Anglia
Department Name: Environmental Sciences
Abstract
Some of the most critical impacts of climate change will probably occur due to changes in the extremes of the hydrological cycle (droughts and floods), yet the expected changes in future precipitation and its extremes are currently quite uncertain. Scenarios of future change are derived from simulations with global and regional climate models, and our confidence in scenarios of future precipitation extremes rests on our assessment of the reliability of those models. We propose to evaluate these models by careful comparison of their simulations with observed variations in extreme precipitation events. Our comparisons will go far beyond simple comparisons of the statistics of simulated and observed events, but will in addition assess the linkages between atmospheric circulation variability (wind speeds and directions, stability, convergence and uplift), atmospheric humidity, and resulting precipitation extremes in both models and the real world. We will then extend the assessment to consider whether including changes in greenhouse gases (and other external climate influences) in the model simulations improves the agreement with changes detected in the observational data.
Organisations
Publications
Agnew M, Goodess C, Jones P And Osborn T
(2009)
Coping with climate change: risk and opportunities for insurers
Maraun D
(2011)
The influence of synoptic airflow on UK daily precipitation extremes. Part II: regional climate model and E-OBS data validation
in Climate Dynamics
Maraun D
(2009)
The influence of synoptic airflow on UK daily precipitation extremes. Part I: Observed spatio-temporal relationships
in Climate Dynamics
Maraun D
(2009)
The annual cycle of heavy precipitation across the United Kingdom: a model based on extreme value statistics THE ANNUAL CYCLE OF HEAVY PRECIPITATION ACROSS THE UNITED KINGDOM
in International Journal of Climatology
Maraun D
(2008)
United Kingdom daily precipitation intensity: improved early data, error estimates and an update from 2000 to 2006 UNITED KINGDOM DAILY PRECIPITATION INTENSITY
in International Journal of Climatology
Osborn T
(2008)
Reply by Tim Osborn
in Weather
Pope R
(2014)
The influence of synoptic weather regimes on UK air quality: analysis of satellite column NO 2
in Atmospheric Science Letters
Rust H
(2009)
Modelling seasonality in extreme precipitation A UK case study
in The European Physical Journal Special Topics
| Description | Our project focussed on describing and explaining the changing occurrence of heavy or extreme precipitation over the UK that is evident in daily raingauge measurements over recent decades. We defined "heavy" precipitation events as those highest daily rainfall totals that are sufficient to contribute around 10% of the total recorded rainfall (typically between 0.5% and 1% of highest daily rainfall totals are sufficient to provide 10% of the total recorded rainfall). For "extreme" daily precipitation, we used extreme value theory to estimate the magnitude of the daily rainfall totals that might be expected to occur with a return period of, for example, 10 years. We analysed observations from a set of 689 raingauges covering almost the whole UK and with records varying in length from over 100 years down to around 30 years. We investigated the links between the occurrence of extreme daily rainfall amounts and geographic location, time of the year and the atmospheric circulation pattern. Our main findings include: (i) When viewed across the whole dataset, a trend towards an increased contribution from heavy rainfall events is apparent over the period from 1900 to 2006 in autumn, spring and especially in winter. We also assessed the uncertainty in interpreting these results as being representative of the UK as a whole, which arises because the coverage is incomplete especially in the early decades of the 20th century. (ii) Results for the summer season showed strong multi-decadal variability, but little evidence for any underlying increases or decreases in heavy rainfall. (iii) The spatial patterns of the annual cycle of precipitation extremes are linked to the changing contributions of convective, frontal and orographic rainfall and provide a useful test of regional climate model simulations (i.e., to evaluate whether these models can correctly simulate the dominance of intense precipitation during late summer in SE England, compared to more intense extremes in late autumn or winter over the mountains of NW UK. (iv) Changing atmospheric circulation patterns (e.g., more westerly winds during winter) can explain a significant fraction of the variability in extreme precipitation on seasonal to decadal time scales, though in many cases the changes evident on longer time scales are not explained by changes in atmospheric circulation. (v) We have evaluated the ability of regional climate models (that are used to develop future climate scenarios) to simulate the links between atmospheric circulation and extreme UK rainfall. In most cases, there is some similarity in the patterns of how extreme rainfall amounts are influenced by atmospheric circulation (e.g. flow direction and strength of flow, cyclones and anticyclones) simulated by climate models and identified in the observed data. |