Having been talking a lot at a
huge, global scale, it’s time to turn things on their head and focus in on the
national scale. Dear old blighty (the UK, for the uninitiated) naturally has
large banks of hydrological research, given the strength of our academia. The
question is, what is going to happen to river flow, runoff and flooding in the
future? Will we still be able to sit near the local river in driving rain on a ‘summers’
day, eat poor quality ice cream and have a family argument?
In the early 2000s, Defra advised
that research in the UK should take account of possible climate change by
modelling a 20% increase in peak flows in the next 50 years. Back in 2004,
Reynard, et al. (2004) carried out hydrological modelling using UKCIP02 climate
scenarios (UKCIP09 are now the most recent) and concluded that all but the most
extreme increases in flow across major catchments in the UK would be within
this 20% boundary. This would suggest the 20% peak flow increase is a useful precautionary
value in the face of great uncertainty of the effect of climate change on river
flow. Kay, et al. (2009) identify the variety of sources of uncertainty in
hydrological prediction: future greenhouse gas emissions; Global Climate Model
(GCM) structure; downscaling from global to regional model level; the structure
and parameterisation of hydrological models, and the natural internal
variability of climate. Clearly, this is not an easy process with any level of
great surety. Both Kay, et al. (2009) and Prudhomme, et al. (2003)
concur that the largest uncertainties are attributed to the type of GCM that is
used, suggesting predictions for the future should be made using a variety of
GCMs under a range of climate scenarios.
With respect to likely
effects of climate change on rivers in the UK, Wilby, et al. (2008) suggest a
connection between the seasonality of flood and the seasonality of climate in
larger catchments; the peak of annual rainfall is followed by annual peak of
discharge, as with the River Thames. For smaller catchments, large flow events
tend to be more flashy in nature and occur directly after the heaviest rain,
whatever time of the year – future changes in precipitation intensity could
have implications for flows and flash flooding in such catchments. Prudhomme,et al. (2003) model the largest increases of peak flow in the UK (using a variety of
GCMs) to be in northern England and Scotland, with a 0.13% increase
in flood magnitude each year, compared to 0.04-0.05% in southern catchments of
England. While some of this may be related to catchment morphology, there is a
clear geographical signal of climate change across the country.
After all the global
scale examination, we see that even an island as small as the UK will likely be
differentially affected by changes in discharge and flood magnitude as a result
of climatic change. At least we’ll still have the weather to moan about.
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