Extreme Events
Sonia Barbey & Xiaoyu Liu
The associations which come to mind when hearing the term “extreme event” are numerous and quite equivocal. “Extreme event” usually refers a happening or action of the greatest possible degree, extent or intensity i.e. one may substitute the term “event” for others to make new terms such as "extreme cold"; "extreme caution"; "extreme pleasure", “extreme sports”, “extreme danger” etc… We may also associate extremities with danger, fear or caution.
As in the examples stated above, “Eextreme events” may be climatic. In fact, in climatology, extreme events can be seen as being the highest or the lowest value of a climatic element observed, in a particular location, during a specific time frame or during specific period.
However one of the most pragmatic yet tolerant explanations has come across so far:
“There are a number of ways extreme climate events can be defined, such as extreme daily temperatures, extreme daily rainfall amounts, large areas experiencing unusually warm monthly temperatures, or even storm events such as hurricanes. Extreme events can also be defined by the impact an event has on society. That may involve excessive loss of life, excessive economic or monetary losses or both.” (Easterling et al 2000)
If this value was the greatest of all the recorded extremes it would be considered the absolute extreme.
In this overview of Extreme events we will be consulting literature composed of scientific articles as well as lay magazine articles. We will than assess what information these articles give us about extreme events. Finally, we will outline the 3 main points we find most crucial to our topic, “Extreme Events”.
Observed variability and trends in extreme climate events: A brief review
DR Easterling et al
This article is a great way into extreme events. It explains some of the main events and some of the difficulties scientists are having with them. It explains that in order to create better models we need more international cooperation in order to get better data. However, it outlines that this is getting increasingly difficult. It shows on a global scale how extreme events are very present in some areas and not in others.
“Heavy precipitation and high streamflow in the contiguous United States: Trends in the twentieth century”
Groisman et al.
This article is an extensive study of some of the repercussions of the changes in precipitation in the United States. It suggests that these extreme precipitation events (which they have found to be increasing to at a statistically significant level 95%) may have repercussions on streamflow. However due to the multiple contributors of streamflow and the fact that “precipitation is not routinely monitored within the U.S. streamflow network” For this reason they cannot generalize their results to the entire US., Rrather they split the results in the eastern US where their data strongly supports a relationship between maximum streamflow and heavy precipitation events. For the western US snowmelt has been occurring earlier, and is thus a major contributor to maximum streamflow and thus it is difficult to extricate precipitation from streamflow in these parts. In Central US the data is too sparse to make any claims. This is an interesting article because it looks not only at the extreme precipitation events but at what is MEANS to have increased precipitation in certain areas. One may derive other repercussions from these increased extreme events; this paper is an illustration of how one may do this, with streamflow.
Quantifying the risk of extreme seasonal precipitation events in a changing climate Palmer et al.
This article looks at the chance of having more extreme events in England and Bangladesh. Once they examine this (In parts of the UK, precipitation will increase by factor of 5 over the next 50-100 years and similar results were found for Bangladesh) they try to give an economic value to their probabilistic projections. They finally discuss how these extreme events would benefit from being included into more general climate models although the scales of these models are quite different. They claim that inclusion of these extreme climate events would help us determine and define “future computational requirements for the climate change problem”
Increasing risk of great floods in a changing climate
Milly et al.
This paper examines increased flood risk due to extreme precipitation events due to anthropogenic sources. The paper looks at the flood increase in the 20th century. They do find that “The 100 year flood was exceeded 21 times in our observational record of 20166 station-years. Flood events were concentrated in the latter half of the record: half the observations were made after 1953 and 16 of the flood events occurred after 1953”. In effect due to increased anthropogenic activities and emissions one could assume that these events are linked, at least enough to say that flood risk is associated with radiatively forced climate change. The significance of their results is “tentative”. They end up suggesting more stream gouging programs and more tropical hydroclimate simulations.
Climate change scenarios for the US National Assessment.
MacCracken et al.
This article has more of an agenda. It looks at and assesses climate projections in order to establish whether they can be taken into account by the USNA to provide “the nation” with what?. It explains what it looks for in models and how much significance is needed for them to be significant. It also extracts what they call “key findings”. These 10 points summarize what has been looked at, what can be expected and what requires vigilant preparation due to climate change. In terms of extreme events, this article is useful because it underlines that we still need to include extreme events and non linearitiessuch as “10 year drought in California”. Overall it explains why and how models are used and underline their strengths and weaknesses, supplementing their predictions with other factors such as “historical trends, physical and biological relationships […]”
Global Hydrological Cycles and World Water Resources” Taikan Oki and Shinjiro Kanae Science in www.sciencemag.org August 2006
This article states that climate change due to anthropogenic sources will affect hydrological cycles. However, it stresses that the extent to which this effect will take place is highly uncertain due to the high variability of extreme events, however, some of the ways in which hydrological cycles will be affected have been assessed: temperatures will affect snowmelt, water rise will salinate aquifers, and precipitation will increase, amongst many other changes.
“Water Supply Chapter 6” David Major and Richard Goldberg
This is more of a policy related article. But it outlines some of the difficulties we encounter when having to prepare for extreme events in terms of water resources and changing precipitation patterns.
The five year forecast November 27, 2006 issue of New York Magazine
Clive Thompson
This article is an interesting lay article. It outlines how climate events are heavily interlinked, with each other and with other disciplines. For example we thank El Nino events for “extremely mild” winters and fewer hurricanes. It is also interesting that climate events are linked to many other issues such as economy, making it a “meaty” article for many people, not just people interested in climate.
Extreme Events Examples:
Heat Waves:
Definition:
Hot sustained temperatures have been known to produce notable impacts on human mortality, regional economies and ecosystems.
Pattern:
A global coupled climate model Parallel Climate Model (PCM) shows that there is a distinct geographic pattern to future changes in heat waves. Model results for areas of Europe and North America, associated with the severe heat waves in Chicago in 1995 and Paris in 2003, show that future heat waves in these areas will become more intense, more frequent, and longer lasting in the second half of the 21st century. Observations and the model show that present-day heat waves over Europe and North America coincide with a specific atmospheric circulation pattern that is intensified by ongoing increases in greenhouse gases, indicating that it will produce more severe heat waves in those regions in the future.
Physical Mechanism:
Heat waves are generally associated with specific atmospheric circulation patterns represented by semi-stationary 500-hPa positive height anomalies that dynamically produce subsidence, clear skies, light winds, warm-air advection, and prolonged hot conditions at the surface. The 500-hPa height anomalies are most strongly related to positive warm season precipitation anomalies over the Indian monsoon region and associated positive convective heating anomalies that drive mid-latitude teleconnection patterns in response to anomalous tropical convective heating in future climate.
Hydrological Cycle Change
There is evidence that precipitation extremes, particularly heavy rainfall events, are increasing in the United States and Australia, also suggesting an enhanced hydrologic cycle as the planet warms.
There is some evidence for an increase in intense rainfall events (United States, tropical Australia, Japan, and Mexico), but analyses are far from complete and subject to many discontinuities in the record. The strongest increases in extreme precipitation are documented in the United States and in Australia. The extreme precipitation amounts are increasing, in some areas by as much as 12%. However, for many areas this is being offset by decreases in more moderate events, and in other areas of the country (e.g., the Northwest, Southeast, and Northeast) both amounts are increasing. Such an increase, at least in the United States, has been supported by an observed increase in water vapor and total precipitation. Changes have not been detected in the year-to-year or season-to-season variability of snow extent during the satellite era.
Temperature
Interannual temperature variability has not changed significantly over the past century. However, on shorter timescales and higher frequencies however, e.g., days to a week, there is some evidence for a decrease in temperature variability across much of the Northern Hemisphere. Related to the decrease in high-frequency temperature variability, there has been a tendency for fewer low-temperature extremes and a reduction in the number of freezes in disparate locations such as the northeastern United States and Queensland, Australia.
Summary
What evidence exists from past/current observations?
In many of the articles it is stated that anthropogenic contributions to GHGs have had an impact on extreme events. This has been outlined in the works concerning water management, the five year forecast, flood risk as well as streamflow increase. The twentieth century has wit ????
What do model simulations of past/present indicate?
It is very difficult to model extreme events but the forecasts indicate done by Milly in terms of predicting floods suggest extreme events will happen more and more frequently. However most authors are hoping that extreme events will be given a bigger place in future climate models.
What are the models suggesting for the future, and what are the assumptions in those projections?
The assumptions are that our emissions of GHGs will remain the same. Thus there could be some good news in store if we can manage to harness some of them.
The assumptions are that
What are the principal uncertainties in the scientific evidence and in the forecasts?
The emissions are uncertain; hopefully we will be seeing some changes. Also the extreme variability of extreme events makes it difficult for them to be predicted and difficult to incorporate in to the climate models.
3 points
1) Extreme events have been closely linked to GHG emissions
2) Extreme events are very variable and are difficult to model
3) Extreme events have many repercussions and impacts. We need to get prepared even we cannot model it very well.
Bibliography
§ Observed variability and trends in extreme climate events: A brief review
DR Easterling, JL Evans, PY Groisman, TR Karl, KE … - Bulletin of the American Meteorological Society, 2000 - agci.org
§ Easterling, DR and co-authors, 2000. Observed climate variability and change of relevance to the biosphere. Journal of Geophysical Research-Atmos., 105 (D15): 20101-20114.
§ Meehl, GA and C. Tebaldi, 2004. More intense, more frequent, and longer lasting heat waves in the 21st century. Science, 305 (5686): 994-997.
§ Stott, PA, DA Stone and MR Allen, 2004. Human contribution to the European heat wave of 2003. Nature, 432 (7017): 610-614.
§ Groisman, PY and co-authors, 2004. Contemporary changes of the hydrological cycle over the contiguous United States: Trends derived from in situ observations. Journal of Hydrometeorology, 5 (1): 64-85.
§ Groisman, PY, WE Knight and TR Karl, 2001. Heavy precipitation and high streamflow in the contiguous United States: Trends in the twentieth century. Journal of Climate, 82 (2): 219-246.
§ Palmer, TN and J Raisanen, 2002. Quantifying the risk of extreme seasonal precipitation events in a changing climate, Nature, 415: 512-514.
§ Milly, PCD and co-authors, 2002. Increasing risk of great floods in a changing climate, Nature, 415: 514-517.
§ MacCracken, MC and co-authors, 2003. Climate change scenarios for the US National Assessment. Bulletin of the American Meteorological Society, 84 (12): 1711-+.
§ Major, D. and R. Goldberg. 2001. Water Supply. In: Rosenzweig, C. and W.D. Solecki (Eds.) 2001. Climate Change and a Global City: The Potential Consequences of Climate Variability and Change – Metro East Coast. New York: Columbia Earth Institute. p. 87-101.
§ Taikan Oki and Shinjiro Kanae Science in www.sciencemag.org August 2006 Global Hydrological Cycles and World Water Resources”