The Concept & Planning Paper
Olga Zolina, Albert Klein Tank, Francis Zwiers and Siegfried Demuth
Extreme climate events have disastrous impacts on economic and social conditions, resulting in fatalities and monetary losses and affecting the economic stability of many regions. During the last decades, these extreme events (precipitation, flooding, heat waves, dry and wet spells, droughts, cyclone activity, extreme winds, marine storminess and changes in sea level) have grown in intensity and frequency. At the same time, observed and projected changes in the extremes are strongly localized and significantly different from region to region.
IPCC AR4 implies that the intensity of extremes will increase under anthropogenic climate change. Furthermore, changes in extremes may not necessarily go hand in hand with changes of the mean state. The IPCC WGI and WG-II are currently developing a Special Report in “Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation” with the Scoping paper to be developed after the Scoping meeting in Oslo (23-26 March 2009). Regional impacts of weather climate extremes were recently addressed in a number of documents, such as the USGCRP report on extremes, “Weather and Climate Extremes in a Changing Climate (Regions of Focus: North America, Hawaii, Caribbean, and U.S. Pacific Islands),” published as U.S. Climate Change Science Program Synthesis and Assessment Product 3.3 in 2008. The joint CCl/CLIVAR/JCOMM Expert Team (ET) on Climate Change Detection and Indices (ETCCDI) has recently developed comprehensive “Guidelines on Analysis of extremes in a changing climate in support of informed decisions for adaptation” addressing issues of data homogeneity, derivation of the set of indices quantifying extreme events and observed variability of the occurrence and intensity of extremes. Numerous activities overseen by the International Hydrological Programme (IHP) of UNESCO, aiming at water resource management and capacity building, pose additional requirements for accurate estimation of extreme events in a changing climate. Existing water management practices cannot satisfactorily cope with current climate variability and are definitely not capable of managing the impacts of future climate change on water supply, agriculture, energy and aquatic ecosystems.
1.2. Problem areas
Despite unequivocal progress in understanding climate and weather extremes, their estimation is still highly inaccurate. Large uncertainties result from the insufficient quality and sampling of observational data and from inadequate resolution of model simulations. Inadequate quality and resolution of observational and model data makes it difficult to apply advanced statistical methodologies. Furthermore, the same methods applied to the data of different resolutions require different approaches in further analysis. Finally, advanced statistical methodologies for estimation of extremes themselves have not yet been exploited to the full extent and require validation and improvement. This makes difficult effective cross-validation of extremes in observational data and model outputs, including comparisons between estimates derived from observational point data and model outputs. These complications prohibit the efficient use of models for understanding driving mechanisms and the assessment of extremes predictability.
We still poorly understand the spatial aspects of extremes and have trouble overcoming "scaling" problems that make model and observations comparisons difficult for some elements. A fundamental problem of extreme events analysis is so-called "compound events,” where it is often unclear what kinds of pre-conditions lead to extreme outcomes (e.g., a series of successive precipitation events that saturate soil and set the stage for flooding or land slides).
Thus, it is now very timely to organize a Workshop facilitating an open dialogue of climatologists from different areas (meteorology, hydrology, oceanography), data producers (in-situ, satellites, NWP, climate model community) and statisticians. Such a workshop will generate a strategy for the development of the most robust and reliable characteristics of extremes and optimal methodologies for their estimation.
2. Workshop objectives
- Review and assessment of the existing metrics of extreme weather and climate events and identification of their strengths and weaknesses;
- Critical assessment of the variety of methods for estimation of climate extremes and their uncertainties, involving cross-pollination of experience from different areas;
- Assessment of the reliability of representation of different extremes in different data types and model simulations;
- Identification of critical gaps in quantitative estimation of climate and weather extremes in data and model experiments, particularly spatial aspects of extreme events and the nature of the “compound” events;
- Development of the optimal strategy for improving the estimation of climate and weather extremes and their projection in future climate through the implementation of well justified characteristics of extremes and accurate methodologies of their estimation;
- Critical assessment of the synergy between different extremes (e.g. precipitation, temperature and flooding) and of the impacts of extremes.
3. Workshop dates and venue
27-29 September 2010,UNESCO Headquarters, 125 Avenue de Suffren, 75007 Paris, France.
4. Proposed sessions and keynote presentations
- Hydrological extremes (precipitation, flooding and river discharge), including compound hydroclimate extremes
- Extremes in temperature conditions (heat waves, dry spells)
- Extreme tropical and extratropical cyclones and associated wind waves and storm surges
- Methodologies for estimation of extremes
- Risk assessment
4.1. Session Structure
All sessions should accommodate consideration of extremes in observational data and models with keynote talks addressing problems of estimation and representation of extremes in different data types and model outputs.
5. Proposed breakout groups
- Data requirements and availability, including data policy
- Representation of extreme events in climate and operational models, including consideration of scaling and spatial scales of extremes
- Methodologies for estimation of extremes across areas and disciplines