Climate Change and the European Water Dimension - Agri ...

V.B.5. Climate change and droughts
Global warming is predicted to cause significant changes to the world’s climate, but
uncertainties remain about the precise nature of these changes. This is particularly
true with regard to possible changes at a regional level and to extremes, such as
prolonged periods of low rainfall. It is precisely the changes in these climate
extremes that will have a direct impact on the frequency and severity (in space and
time) of drought episodes across Europe.
The latest climate change scenarios from the various groups modeling the global
climate response to increased concentrations of greenhouse suggest significant
summer drying across many parts of Europe, particularly in the Mediterranean basin
with more hot days and heat waves very likely across most land areas (IPCC, 2001).
These scenarios also suggest decreases in rainfall in some areas for spring and
autumn and an increased variability in the amount of winter rainfall. Combining these
patterns of change leads to an assertion that over the next 100 years Europe is likely
to suffer more frequent meteorological drought conditions, especially in the south.
Furthermore, the scenarios mean that these events might manifest themselves either
as short but extreme single season droughts (such as the hot summer of 2003) or
longer-term, multi-season droughts, and they might be local or widespread in nature.
A comprehensive framework for reducing Europe’s vulnerability to droughts is
essential in preparing for conditions of increasing drought frequency and severity
With generally elevated temperatures (scenarios suggest that summer temperatures
might be, on average, anything between 2 and 6ºC higher than the present day)
these rainfall deficits are likely to be accompanied by higher evaporative demand
leading also to the potential for severe hydrological drought. Despite the
uncertainty surrounding these climate scenarios it is vital that water resource
planners across Europe begin to think about their potential vulnerability to changes in
climate as described above. For example, in the UK the water industry have been
addressing the issue of incorporating climate change scenarios into their long-term
water resource plans, including some specific low probability but high consequence
extreme scenarios. The current method evaluates the climate change impacts using
reference scenarios developed by the UK Climate Impact Programme, known as the
UKCIP02 scenarios. These scenarios are applied using a simple perturbation
method whereby the observed series of climatic inputs to a hydrological model are
changed proportionally according to the UKCIP02 monthly factors.
However, more sophisticated techniques are now available which express climatic
changes simulated by Global Climate Models (GCMs) at hydrologically appropriate
time and space scales. These techniques include statistical and dynamic methods
such as the use of output from Regional Climate Model (RCMs). There remains
much uncertainty surrounding future climate change scenarios. These uncertainties
may be derived from assumptions about the future socio-economic trends leading to
certain greenhouse gas emissions pathways, through to uncertainties in how localscale,
high intensity, short duration rainfall events might change. While it is true to
say that many of the GCMs are converging in terms of their predictions for global
average temperature change, there remain serious discrepancies (in terms of
direction of potential change as well as the magnitude) in the scenarios of change in
extreme rainfall events. Hence, the choice of GCM within a climate change impact
assessment is thought to be the largest single source of uncertainty (Jenkins and
Lowe, 2003, Prudhome et al., 2003, Reynard and Young, 2003). Future analysis of
climate change impacts should therefore use the output from a range of GCMs
(IPCC, 2001).
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