Climate Warming, Extreme Events, and Landscape Stability: Impact upon landscape and fluvial processes

Geological hazards are often very narrowly defined, and primarily at large scale magnitudes, e.g., earthquakes, volcanic eruptions, or tsunamis. However, it is the smaller scale geological events that have just as great an impact upon the earth, and its people, that are now becoming more and more frequent in their occurrence. Why? Because they are linked to changing climate, and as the degree and rate of climate change increases these events will multiply, and become just as destructive as the more massive events, especially when their cumulative impact is compounded. It is not simply global warming that is the problem, but the destabilizing impact that it has upon geological processes either directly or indirectly. Global warming impacts the earth’s surface and its plant, animal and human inhabitants primarily through its global impact upon changing temperature, moisture and wind conditions. Temperature variations affect global weather patterns and changes the supply of moisture, its annual timing, and the nature of its delivery, i.e., changing the force which rain impacts the ground surface. It causes drought, and through thunder storms, fires. This results in the removal of the protective vegetation covering, which would normally reduce the impact of rain upon the ground surface. Unprotected ground is then exposed to torrential rains, which will increase surface runoff and stream velocity, accelerating stream incision and head-ward erosion of streams. It also causes debris flows, especially if subsurface layers of soil have been indurated by the action of drought or fire, and the top soil has become saturated. The water-rich layer of sediment perched upon the indurated layer of soil, will result in large-scale slope failure with massive, destructive landslides. This is accentuated by the geology of the sediments being affected. In such landslides human activity becomes a critical factor as well. Bad agricultural practices, such as farming of high angle slopes, incorrect plowing patterns, and removing of surface stubble, through field burning or plowing under of stubble (which could protect the ground from the direct impact of torrential rains, reduce the speed of surface runoff, and aid in infiltration of rainfall into the groundwater table) all exacerbate the possibility of landslides. In addition, people become a contributing factor to global warming through traditional field burning, which adds huge amounts of carbon to the atmosphere, raising atmospheric temperatures and accelerating both the rate and magnitude of global warming. Smoke from crop burning also causes humanrespiratory problems. Global warming, by heating the oceans and atmosphere, changes the global position of high and low pressure systems. This results in changes in wind patterns (directions), and seasonal strength, affecting aeolian activity. It can initiate large-scale deflation of newly exposed or stream-deposited sediments, and result in the trans-location of massive amounts of sediments. Changes in winds will also result in the destabilization and reactivation of already extant aeolian features. Redistribution of surficial deposits will result in changes in the albedo of the earth’s surface and affect the solar insolation of the earth and its heat budget. Increased global temperature will accelerate the melting not only of Arctic and Antarctic ice sheets, but of mountain glaciers, many of which have already disappeared. The often catastrophic release of huge amounts of water often results in highly-destructive flooding and debris flows in the drainages that are fed by the mountain glaciers. The sediment clouded waters that eventually enter the sea results in the death of marine life, and the disruption of migration patterns as well. Eventually rising sea level will disrupt not only the oceanic ecosystem, but destroy coastal marine habitats, force a major segment of human population out of coastal areas.These changes can be of small scale and occur incrementally, or they can be of great magnitude, and occur rapidly. In either case, global warming is a prime mover in geological hazards.

کلیدواژه ها:

Geological Hazards ، Global Warming ، Precipitation Change ، Wind Pattern Change ، Surfacial Processes ، Glacial Melt