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Monitoring of glaciers worldwide has shown that almost all of them experienced considerable loss of volume in the last century, and especially the last decades. And for the next future there is no sudden turn to be expected.
This raised some concern, especially considering the role that glaciers have in the hydrologic circle of mountain ranges. Glaciers act as storage; they collect and hold back precipitation during winter, and release it during spring and summer, smoothing the average discharge of a catchment area.
Common scenario's stated that the melting of glaciers would diminish the amount of water for agriculture use, and also potable water, causing droughts that could influence up to 2 billion people (mainly Himalaya-area and China). However such statements are inferred often only by considering the human population in a certain catchment area, and thus overestimated.
The importance of glaciers for humans however depends on various climatic and geographic variables. Not only matters how much people live in a catchment area, but also when glaciers release the stored water in relation to the annual precipitation.
In the Himalaya the main discharge occurs during spring and summer, when anyway the monsoon brings great amounts of water. The impact of reduced glacier discharge in this example on humans is therefore low.
In contrast in the region of the Aral Sea the main precipitation peak is during winter, and the glaciers release the water during summer drought. Here the role of glaciers for local communities is essential.
These first results will help to put the discharge reduction in the correct regional scale, point out regions were this discharge shortage can became a major problem and where mitigation strategies must be considered in the future.
This raised some concern, especially considering the role that glaciers have in the hydrologic circle of mountain ranges. Glaciers act as storage; they collect and hold back precipitation during winter, and release it during spring and summer, smoothing the average discharge of a catchment area.
Common scenario's stated that the melting of glaciers would diminish the amount of water for agriculture use, and also potable water, causing droughts that could influence up to 2 billion people (mainly Himalaya-area and China). However such statements are inferred often only by considering the human population in a certain catchment area, and thus overestimated.
The importance of glaciers for humans however depends on various climatic and geographic variables. Not only matters how much people live in a catchment area, but also when glaciers release the stored water in relation to the annual precipitation.
In the Himalaya the main discharge occurs during spring and summer, when anyway the monsoon brings great amounts of water. The impact of reduced glacier discharge in this example on humans is therefore low.
In contrast in the region of the Aral Sea the main precipitation peak is during winter, and the glaciers release the water during summer drought. Here the role of glaciers for local communities is essential.
These first results will help to put the discharge reduction in the correct regional scale, point out regions were this discharge shortage can became a major problem and where mitigation strategies must be considered in the future.
Fig.1. The map by KASER et al. 2010 (click to enlarge) summarizes the results for the various analysed catchment areas with glaciers, the grey bars represent the Population Impact Factor, a factor that encompass the amount and time when glaciers contribute to the demand of population in relation to the annual precipitation.High grey bars shows that glaciers provide water when it is needed most, low bars shows that the discharge of glaciers occurs during wet periods, when their contribution is less important.
Bibliography:
KASER, G.; GROßHAUSER, M. & MARZEION, B. (2010): Contribution potential of glaciers to water availability in different climate regimes. PNAS November 8, 2010; Published online before print DOI: 10.1073/pnas.1008162107
I wonder how glacial damming in the Himalaya would affect the people of the Bengal Basin. Is it possible that we could see flood bursts as the glaciers retreated?
ReplyDeleteIt’s an intriguing question, I tried to summarize some cases of glacial lake outburst here:
ReplyDeletehttp://historyofgeology.blogspot.com/2011/01/glacier-outburst-floods-threat.html
– such events are surely a danger in the valleys, were the discharge is canalized and depending from the released volume they can travel for more then 200 kilometres, this would be at least enough to reach the border of the Himalaya.
A second possible effect of the glacier change on flood probability in the lowlands would be the loss of storage capacity of the glaciers.
In the Alps this phenomena is observable, when the discharge of glaciers increase due increase in temperature, rivers can reach their transport capacity early in the spring and especially in summer, supplementary precipitation can so much faster cause floods, inundations or debris flows.
ReplyDeleteVery interesting info!Perfect just what I was looking for!