Extreme events and risk assessment

extremes-ID-10024304Hurricanes, storms, droughts and floods are among the most spectacular and dramatic features of the climate system. Those extreme events occur on a wide range of timescales, ranging from a few hours for some severe storms to years or decades for persistent droughts. They strongly impact the natural systems and the human societies and even the short duration events can lead a long term imprint in the environment.

The extreme events are in most cases relatively rare, and consequently the instrumental period has a too short duration to provide an adequate sampling and characterization. A robust risk assessment of their probability is thus only possible by extending the data series using natural archives that record the occurrence and impact of past extreme events at natural scales.

This integrated activity is focused on the documentation of the occurrence and the understanding of the mechanisms at the origin of past climatic and ecological extreme events. A quantitative approach is expected in order to obtain robust probability estimates based on long term series that can be compared directly to their equivalent derived from instrumental data. These efforts are directly relevant to risk assessment.


Natural archives provide many records of past extreme events over a wide range of climate and environmental conditions, in particular for floods, droughts and storms. The goals of this integrated activity are to reinforce the coordination between existing research lines, to stimulate new analysis and to facilitate the transfer of relevant information to potential users.

Those objectives can be articulated around the following questions:

- For which type of event and which periods could we provide robust statistics of extremes based on paleodata?

- What is the impact of extreme events on ecosystems and what is their resilience to such events?

- What is the impact of changes in the mean state on the probability of occurrence and the intensity of extreme events?

- Are the current models able to reproduce the observed properties of extreme events as well as the links between large-scale drivers and the regional to local scale triggers or amplification mechanisms?

- How should we present research results so that they can be easily used by scientists working on the instrumental period and specialists of risk assessment?

PAGES working groups involved in extremes

1. GPWG2: The Global Paleofire Working Group promotes the collection and analysis of charcoal data from all around the world via the Global Charcoal Database (GCD), which currently contains over 1000 records. Global and regional syntheses enable the examination of broad-scale patterns in paleofire activity, creating a framework for exploring the linkages among fire, humans, climate and vegetation, together with the evaluation of fire model simulations. The database is continuously growing and can be now used to explore the occurrence and spatial distribution of severe fire events in the past ("Megafires"), the synchronicity with extreme climatic drivers such as droughts, and its cascading effects for ecosystems processes.

2. Floods: The Floods Working Group (FWG) brings together all the scientific communities reconstructing past floods (historians, geologists, geographers, etc.) and those studying current and future floods (hydrologists, modelers, statisticians, etc.) in order to coordinate, synthesize and promote data and results on the natural variability of floods. The overall goals of the FWG are i) providing regional to global analyses of the natural flood variability with a particular focus on the most extreme events and ii) promoting and disseminating historical and paleoflood science data at different levels, i.e. academic, engineers and stakeholders.

3. VICS: The Volcanic Impacts on Climate and Society working group (VICS) supports research focused on reconstructing the history of past explosive volcanism to better understand how the climate system responds to changes in radiative forcing and how societies have been impacted by and responded to the resulting climatic shocks. Major volcanic eruptions have been an important driver of extreme climate events in the past, causing the majority of hemispheric-scale extreme cold periods over the past 1500 years, on both annual and decadal time scales (Sigl et al. 2015). Furthermore, volcanic eruptions are increasingly being understood as a driver of large-scale changes in the hydrological cycle, driving tropical Monsoon failures (Oman et al. 2006), and extreme regional-scale rainfall and flood events (Brázdil et al. 2016). Volcanically-driven extreme climate anomalies have also influenced past societies, from direct impacts upon agricultural production, to triggering social crises and inducing a range of political and cultural responses (Huhtamaa and Helama 2017; Toohey et al. 2016).

4. EcoRe3: The Resistance, Recovery and Resilience in Long-term Ecological Systems working group (EcoRe3) aims to understand why some ecosystems may be more resilient to an environmental disturbance (i.e. extreme events) than others using the proxy information preserved in sediments. The first workshop in 2017 aimed to identify a new set of approaches for (i) detecting abrupt changes in pollen data, and then (ii) quantifying components of resilience (i.e. the resistance and the rates of recovery) to characterise the responses to these disturbances. Work is currently ongoing to consolidate these methods, with the goal to apply them to a number of high resolution palaeoecological sequences so that the responses between different ecosystems can be compared. In May 2018 there will be a second workshop which aims to investigate how we can use biological traits to explain differences in resilience (through rates of recovery and resistance) in paleoecological data. The goal will be to develop a new set of standardised, transferable approaches that will enable components of resilience across a range of biomes representing a range of timescales.

5. 2k Network: The 2k Network seeks to understand the mechanisms driving climate variability on interannual to centennial timescales, reduce uncertainties in the interpretation of observations imprinted in paleoclimatic archives and analyse agreement between reconstructions and climate-model simulations over the past 2000 years. This period is critical for identifying extreme events since it contains a vast amount of paleoclimatic data to extent the period covered by instrumental data and the past millennium is also a standard period for simulations performed in the framework of the Paleoclimate Model Intercomparison Project (PMIP) (Jungclaus et al. 2017). Several studies have been performed on droughts (Cook et al. 2015), severe storms (van der Schrier and Groenland 2017), heat waves (Luterbacher et al. 2016) over the past 2000 years, which is further widening the recent past perspective of extreme events.


Brázdil, R., Řezníčková, L., Valášek, H., Dolák, L. and Kotyza, O.: Climatic effects and impacts of the 1815 eruption of Mount Tambora in the Czech Lands, Clim. Past, 12(6), 1361–1374, doi:10.5194/cp-12-1361-2016, 2016.
Cook E. et al.: Old World megadroughts and pluvials during the Common Era. Sci. Adv. 2015;1:e1500561, 2015.
Huhtamaa, H. and Helama, S.: Distant impact: tropical volcanic eruptions and climate-driven agricultural crises in seventeenth-century Ostrobothnia, Finland, J. Hist. Geogr., 57, 40–51, doi:10.1016/j.jhg.2017.05.011, 2017.
Jungclaus J. et al.: The PMIP4 contribution to CMIP6 – Part 3: the Last Millennium, Scientific Objective and Experimental Design for the PMIP4 past1000 simulations. GMD, doi:10.5194/gmd-2016-278, 2017.
Luterbacher J. et al.: European summer temperatures since Roman times. Environ. Res. Lett. 11, 024001, doi:10.1088/1748-9326/11/2/024001, 2016.
Oman, L., Robock, A., Stenchikov, G. L. and Thordarson, T.: High-latitude eruptions cast shadow over the African monsoon and the flow of the Nile, Geophys. Res. Lett., 33(18), L18711, doi:10.1029/2006GL027665, 2006.
Sigl, M., Winstrup, M., McConnell, J. R., Welten, K. C., Plunkett, G., Ludlow, F., Büntgen, U., Caffee, M., Chellman, N., Dahl-Jensen, D., Fischer, H., Kipfstuhl, S., Kostick, C., Maselli, O. J., Mekhaldi, F., Mulvaney, R., Muscheler, R., Pasteris, D. R., Pilcher, J. R., Salzer, M., Schüpbach, S., Steffensen, J. P., Vinther, B. M. and Woodruff, T. E.: Timing and climate forcing of volcanic eruptions for the past 2,500 years, Nature, 523, 543–549, doi:10.1038/nature14565, 2015.
Toohey, M., Krüger, K., Sigl, M., Stordal, F. and Svensen, H.: Climatic and societal impacts of a volcanic double event at the dawn of the Middle Ages, Clim. Change, 136(3–4), 401–412, doi:10.1007/s10584-016-1648-7, 2016.
Van der Schrier and R. Groenland: A reconstruction of 1 August 1674 thunderstorms over the Low Countries. Nat. Hazards Earth Syst. Sci., 17, 157–170, doi:10.5194/nhess-17-157-2017, 2017.


Past activities

1. Lunchtime session during the OSM, Zaragoza, Spain, 10 May 2017

The goal of this open meeting is to discuss the current research on extreme events in the PAGES community, to identify the activities such as workshops or review papers that would allow a better integration of existing studies and contribute to new developments and to propose actions that would reinforce the visibility and the impact of the scientific results, including for stakeholders.

If you are interested in attending or would like to give a brief overview of some activities related to extreme events during the session, please contact Blas Valero-Garcés and Hugues Goosse (details below).

Read more: http://pastglobalchanges.org/calendar/upcoming/127-pages/1668-extremes-ia-meeting-spain-17

2. Future Earth initiative: Extreme Events and Environments from climate to Society (E3S).

PAGES will join colleagues from the Future Earth research projects and WCRP in this Future Earth initiative addressing extreme events amd their impacts on societies.

Project website: www.e3s-future-earth.eu

The Cross community workshop on Extreme Events and Environments from Climate to Society (E3S) was held in Berlin, Germany, from 14-16 February 2016. Read a Future Earth blog article about the event here.



Blas Valero-Garcés
Hugues Goosse

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Image credit: Courtesy of Evgeni Dinev at FreeDigitalPhotos.net