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12 - Temperate forests and rangelands
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- By Roy C. Sidle, Appalachian State University, Tim P. Burt, Durham University
- Edited by Olav Slaymaker, University of British Columbia, Vancouver, Thomas Spencer, University of Cambridge, Christine Embleton-Hamann, Universität Wien, Austria
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- Book:
- Geomorphology and Global Environmental Change
- Published online:
- 05 July 2015
- Print publication:
- 02 July 2009, pp 321-343
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- Chapter
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Summary
Introduction
12.1.1 Hydrological and geomorphic processes in temperate forests and rangelands
Long-term experiments in forest hydrology, often using the paired catchment approach, have shown the striking dependence of stream flow volume on type of vegetation cover. The main change following forest clearance is an increase in storm flow volume on the falling limb of the storm hydrograph; as volumes of storm runoff from many headwater catchments converge lower down the stream network, extensive and serious flooding of lowlands can occur. These problems are exacerbated by the land degradation that follows clearcutting of forest and it is this land degradation and its catastrophic consequences through mass movements which form the core of this chapter.
Landslides are one of the major geomorphic processes affected by land use and climate change in mid-latitude temperate forests and rangelands. Inherent in these discussions are potential changes in hydrological processes that either drive or influence landslides, as well as issues such as land degradation. Landslides are typically episodic and not only impact stream channels and decrease site productivity, but also represent formidable hazards to humans and property. Surficial or slow-moving landslides contribute sediment to streams, decrease site productivity and may damage property, but do not typically endanger people (Sidle and Ochiai, 2006).
Mid-latitude forest and rangeland ecosystems are constantly changing as the result of human activities, movement of population sectors, climate change, and most recently a surge in information technology. This last development is important because it affects public perception of these geomorphic changes and hazards. Given the current easy access to such information, it is imperative that scientists, land managers and planners provide accurate, rational and timely information and assessments on environmental change issues to the public (Sorensen, 2000). Neither apocalyptic nor ‘business as usual’ scenarios of climate change and forest land use are in the best public interest.
4 - Rivers
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- By Michael Church, University of British Columbia, Vancouver, Tim P. Burt, Durham University, Victor J. Galay, Northwest Hydraulic Consultants Ltd, G. Mathias Kondolf, University of California
- Edited by Olav Slaymaker, University of British Columbia, Vancouver, Thomas Spencer, University of Cambridge, Christine Embleton-Hamann, Universität Wien, Austria
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- Book:
- Geomorphology and Global Environmental Change
- Published online:
- 05 July 2015
- Print publication:
- 02 July 2009, pp 98-129
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- Chapter
- Export citation
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Summary
Introduction
Water plays a key role in the transfer of mass and energy within the Earth system. Incoming solar radiation drives evaporation of about 434 000 km3 a–1 from the ocean surface and 71 000 km3 a–1 from the land surface, while precipitation delivers about 398 000 km3 a–1 of water to the ocean and 107 000 km3 a–1 to the land surface. The balance is redressed through the flow of 36 000 km3 a–1 of water from the land to the oceans via rivers (data in Berner and Berner, 1996). Environmental change affecting any of these water transfers produces changes in runoff and river flows, hence in the rivers themselves.
Changing climate is intensifying the global hydrological cycle, leading to significant changes in precipitation, runoff and evapotranspiration (Huntington, 2006; Bates et al., 2008; see also Chapter 1). Intensification of the hydrological cycle is likely to mean an increase in hydrological extremes (IPCC, 2001). Changes in the frequency distribution of precipitation alter water flows and water availability in the surface environment leading, in turn, to a change in river regimes.
These factors are superimposed upon the effects of human actions associated with land use and with the attempt to control water for various uses that have directly changed river channels and the quality of water flowing in them. Land surface condition mediates quantity of water and the amount and calibre of sediment delivered to rivers which, in turn, influences river sedimentation, morphology and stability. Humans also manipulate the terrestrial hydrological cycle deliberately by construction of reservoirs, abstractions of water for human use, and discharges of water into river courses. Moreover, we directly modify watercourses by realigning them, by river ‘training’ works, by dredging, by fixing banks and building dykes.