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Paleoenvironmental Changes during the Last 4000 yr in the Tigray, Northern Ethiopia
- Maria J. Machado, Alfredo Pérez-González, Gerardo Benito
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- Journal:
- Quaternary Research / Volume 49 / Issue 3 / May 1998
- Published online by Cambridge University Press:
- 20 January 2017, pp. 312-321
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In the Tigray region at the northern Ethiopian Highlands, paleoenvironmental reconstruction based on several infilled valley deposit sequences suggests that the past 4000 yr comprised three major wetter periods (ca. 4000–3500 yr B.P., 2500–1500 yr B.P., and 1000–960 yr B.P.), during which soils were formed, and two degradation episodes (ca. 3500–2500 yr B.P. and 1500–1000 yr B.P.), during which there was an increase of sediment yield from the slopes into the valleys. For the past 1000 yr, and in particular since the early 17th century, stratigraphic records together with historic chronicles suggest increasing aridity. Although difficulties arise in distinguishing between natural and human impacts, particularly in a region with a long established agricultural background, stratigraphical and proxy paleoclimatic data have indicated climate as the main controlling factor responsible for the environmental changes in the Tigray.
Chapter 4 - Changes in Impacts of Climate Extremes: Human Systems and Ecosystems
- from Section III
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- By John Handmer, Yasushi Honda, Zbigniew W. Kundzewicz, Nigel Arnell, Gerardo Benito, Jerry Hatfield, Ismail Fadl Mohamed, Pascal Peduzzi, Shaohong Wu, Boris Sherstyukov, Kiyoshi Takahashi, Zheng Yan, Sebastian Vicuna, Avelino Suarez, Amjad Abdulla, Laurens M. Bouwer, John Campbell, Masahiro Hashizume, Fred Hattermann, Robert Heilmayr, Adriana Keating, Monique Ladds, Katharine J. Mach, Michael D. Mastrandrea, Reinhard Mechler, Carlos Nobre, Apurva Sanghi, James Screen, Joel Smith, Adonis Velegrakis, Walter Vergara, Anya M. Waite, Jason Westrich, Joshua Whittaker, Yin Yunhe, Hiroya Yamano
- Edited by Christopher B. Field, Vicente Barros, Thomas F. Stocker, Qin Dahe
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- Book:
- Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation
- Published online:
- 05 August 2012
- Print publication:
- 28 May 2012, pp 231-290
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Summary
Executive Summary
Extreme impacts can result from extreme weather and climate events, but can also occur without extreme events. This chapter examines two broad categories of impacts on human and ecological systems, both of which are influenced by changes in climate, vulnerability, and exposure: first, the chapter primarily focuses on impacts that result from extreme weather and climate events, and second, it also considers extreme impacts that are triggered by less-than-extreme weather or climate events. These two categories of impacts are examined across sectors, systems, and regions. Extreme events can have positive as well as negative impacts on ecosystems and human activities.
Economic losses from weather- and climate-related disasters have increased, but with large spatial and interannual variability (high confidence, based on high agreement, medium evidence). Global weather- and climate-related disaster losses reported over the last few decades reflect mainly monetized direct damages to assets, and are unequally distributed. Estimates of annual losses have ranged since 1980 from a few US$ billion to above 200 billion (in 2010 dollars), with the highest value for 2005 (the year of Hurricane Katrina). In the period 2000 to 2008, Asia experienced the highest number of weather- and climate-related disasters. The Americas suffered the most economic loss, accounting for the highest proportion (54.6%) of total loss, followed by Asia (27.5%) and Europe (15.9%). Africa accounted for only 0.6% of global economic losses. Loss estimates are lower bound estimates because many impacts, such as loss of human lives, cultural heritage, and ecosystem services, are difficult to value and monetize, and thus they are poorly reflected in estimates of losses. [4.5.1, 4.5.3.3, 4.5.4.1]
Chapter 3 - Changes in Climate Extremes and their Impacts on the Natural Physical Environment
- from Section III
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- By Sonia I. Seneviratne, Neville Nicholls, David Easterling, Clare M. Goodess, Shinjiro Kanae, James Kossin, Yali Luo, Jose Marengo, Kathleen McInnes, Mohammad Rahimi, Markus Reichstein, Asgeir Sorteberg, Carolina Vera, Xuebin Zhang, Matilde Rusticucci, Vladimir Semenov, Lisa V. Alexander, Simon Allen, Gerardo Benito, Tereza Cavazos, John Clague, Declan Conway, Paul M. Della-Marta, Markus Gerber, Sunling Gong, B. N. Goswami, Mark Hemer, Christian Huggel, Bart van den Hurk, Viatcheslav V. Kharin, Akio Kitoh, Albert M.G. Klein Tank, Guilong Li, Simon Mason, William McGuire, Geert Jan van Oldenborgh, Boris Orlowsky, Sharon Smith, Wassila Thiaw, Adonis Velegrakis, Pascal Yiou, Tingjun Zhang, Tianjun Zhou, Francis W. Zwiers
- Edited by Christopher B. Field, Vicente Barros, Thomas F. Stocker, Qin Dahe
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- Book:
- Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation
- Published online:
- 05 August 2012
- Print publication:
- 28 May 2012, pp 109-230
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Summary
Executive Summary
This chapter addresses changes in weather and climate events relevant to extreme impacts and disasters. An extreme (weather or climate) event is generally defined as the occurrence of a value of a weather or climate variable above (or below) a threshold value near the upper (or lower) ends (‘tails’) of the range of observed values of the variable. Some climate extremes (e.g., droughts, floods) may be the result of an accumulation of weather or climate events that are, individually, not extreme themselves (though their accumulation is extreme). As well, weather or climate events, even if not extreme in a statistical sense, can still lead to extreme conditions or impacts, either by crossing a critical threshold in a social, ecological, or physical system, or by occurring simultaneously with other events. A weather system such as a tropical cyclone can have an extreme impact, depending on where and when it approaches landfall, even if the specific cyclone is not extreme relative to other tropical cyclones. Conversely, not all extremes necessarily lead to serious impacts. [3.1]
Many weather and climate extremes are the result of natural climate variability (including phenomena such as El Niño), and natural decadal or multi-decadal variations in the climate provide the backdrop for anthropogenic climate changes. Even if there were no anthropogenic changes in climate, a wide variety of natural weather and climate extremes would still occur. [3.1]
A changing climate leads to changes in the frequency, intensity, spatial extent, duration, and timing of weather and climate extremes, and can result in unprecedented extremes. Changes in extremes can also be directly related to changes in mean climate, because mean future conditions in some variables are projected to lie within the tails of present-day conditions. Nevertheless, changes in extremes of a climate or weather variable are not always related in a simple way to changes in the mean of the same variable, and in some cases can be of opposite sign to a change in the mean of the variable. Changes in phenomena such as the El Nino-Southern Oscillation or monsoons could affect the frequency and intensity of extremes in several regions simultaneously. [3.1]
10 - Flood hazards: the context of fluvial geomorphology
- Edited by Irasema Alcántara-Ayala, Andrew S. Goudie, St Cross College, Oxford
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- Book:
- Geomorphological Hazards and Disaster Prevention
- Published online:
- 10 January 2011
- Print publication:
- 04 March 2010, pp 111-128
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Summary
Introduction
River flooding occurs as high water inundates the adjacent floodplain, and is controlled by a combination of discreet processes operating at local and watershed scales. A floodplain is the relatively flat alluvial landform adjacent to a river that is more or less related to the modern flood regime (Wolman and Leopold,1957; Nanson and Croke, 1992; Knighton, 1998; Bridge, 2003). Most floods are natural events vital to river and floodplain geomorphological (Leopold et al., 1964) and ecosystem processes (Hupp 1988; Junk et al., 1989; Thoms, 2003). When humans are impacted, however, floods become “natural disasters” (Figure 10.1). For thousands of years floods have been among the most common and severe natural disasters on Earth, in terms of economic damage and loss of life.
Floods in most river basins are caused by excessive rainfall generated by a variety of atmospheric mechanisms (Smith and Ward, 1988; Slade and Patton, 2002). In cold-winter regions, large floods can be generated from snow/ice melt, particularly in combination with rainfall, while along coastal-draining rivers extensive flooding may be associated with storm surge events. Floods are also generated from catastrophic failure of artificial (reservoirs) and natural lakes, a category that includes dams created by ice, glacial moraines, volcanic lava flows, and landslides (Costa, 1988). Flood hazard refers to the potential of a given flood to threaten human life and property (Smith, 1996).