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Future Forests May Frustrate Future Floods
Reynard, N.S., Prudhomme, C. and Crooks, S.M.  2001.  The flood characteristics of large UK rivers: Potential effects of changing climate and land use.  Climatic Change 48: 343-359.

What was done
The authors used a continuous flow simulation model to assess the impacts of potential climate and land use changes on flood regimes of the UK's Severn and Thames Rivers.  The climate changes employed in the study were similar to those calculated by the UK Met. Office's Hadley Centre for Climate Prediction, which was a major contributor to the most recent IPCC report.

What was learned
By the year 2050, the flow simulation model suggests that the predicted climate changes will have increased the magnitude of 50-year floods on the Severn River by 20%, while 50-year floods on the Thames will be 16% larger.  The authors also investigated the impact of what they call "an extreme scenario" of land use change, wherein forest cover increases to 50% of the rivers' catchment areas.  In the final sentence of their paper, they note that this increase in forest cover "acts in the opposite direction to the climate changes and under some scenarios is large enough to fully compensate for the shifts due to climate."

What it means
Although the authors refer to the projected increase in forest area as "an extreme scenario," the projected climate change they utilize is equally, if not more, extreme, suggesting that in the real world the competition between the likely much-reduced magnitudes of both phenomena may indeed cancel each other, leaving the river flows essentially unaltered.  Also, there are two unmentioned factors that could come into play to make the projected increase in forest area not as extreme as the authors might think it to be.

First, there is the likelihood that if forests are deemed to be important carbon sinks, which they are, and national governments begin to employ them as such, the UK may well promote the development of new forests on much of the land in question.  Second, there is the likelihood that as the air's CO2 content continues to rise, there will be a great natural impetus for forests to grow in areas where grasses now dominate the landscape (see Trees (Range Expansions) in our Subject Index).  Hence, it is even possible there could be a decrease in the magnitudes of large floods on the Severn and Thames Rivers by the time 2050 rolls around.

And what could happen to those rivers in this regard could happen elsewhere around the world as well.