Regional Changes In Precipitation In Europe Under An Increased GHG Scenario - AGU

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Subject: Regional Changes In Precipitation In Europe Under An Increased GHG Scenario - AGU
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Regional changes in precipitation in Europe under an increased greenhouse emissions scenario
F. J. Tapiador, E. Sánchez, and M. A. Gaertner
Instituto de Ciencias Ambientales, Facultad de Ciencias del Medio Ambiente, Universidad de Castilla-La Mancha,
Toledo, Spain

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<5> Here we have used eight regional climate models (RCM) to compare present climate and increased greenhouse gases (GHG) scenario simulations using PDFs. The models are the HIRHAM, CHRM, HadRM3H, REMO, PROMES, RACMO, CLM and RCAO models, described in detail in . As in , we have chosen the 2070–2100 period since the expected changes will be more apparent by the end of the 21st century than in the immediate future. The rationale of selecting a multimodel ensemble is to allow for variability arising from different parameterizations. This approach differs from weather or seasonal forecasting where sensitivity to initial conditions (SIC hereinafter) is a major concern . In climate simulations SIC is comparatively small to the effects of the parameterizations and their dynamical cores .

<6> For any numerical future-climate simulation to be consistent, two conditions have to be met. First, simulated PDFs for present climate have to be as close as possible to measured PDFs . Secondly, different simulations have to agree as much as possible , indicating a highly-predictable state. If these two necessary conditions are met, confidence growths in the models being capable of simulating future climate under a prescribed scenario.

<7> Having met those requirements in our simulations (section 3.1), what we find are noticeable departures from the present climate precipitation climatologies in the future, for all the regions under scrutiny. These new results suggest that under the A2 scenario the Mediterranean precipitation climatology (long dry season) will strengthen in those areas currently Mediterranean; and that traditionally Atlantic-type areas will change its character toward a Mediterranean precipitation climatology, characterized by an exponential PDF shape. The net result of this change will be an increase in the hydrometeorological extremes affecting Europe, though notable regional differences appear.

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Figure 2. Normalized frequency distribution (PDF) of monthly precipitation for the control run (frequency average, red; two-sigma interval, light red), and for CRU (validation data, black line). X-axis unit is mm month−1; y-axis represents frequencies. Enhanced EPS <304 KB>


Figure 3. Same as Figure 2, but for A2 scenario, compared with mean CT results. Enhanced EPS <303 KB>


Figure 4. Changes in the statistics used to characterize the PDF (mean, standard deviation, coefficient of variation, asymmetry, kurtosis; and the 25th, 50th, 75th, and 90th percentiles) between A2 and present climate conditions. Boxes indicate one standard deviation between the eight RCMs, whiskers the 5–95% percentile interval, and asterisks the extreme values. Enhanced EPS <1.3 MB>

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18] Figure 4, seen as a whole, suggests that the overall change is related with the lower mean monthly rainfall in the Mediterranean regions, but with larger standard deviation and kurtosis. The increase in the 90th percentile points up to an overall increase in very high monthly precipitation in Europe, albeit there are large regional differences, as Figure 4 illustrates. In Figure 4, Italy, the British Isles, the Alps, Central and Eastern Europe, and France present increased values of high monthly accumulated precipitation. The case of the British Isles shows that a balance might happen (there is just a slight variation in the mean) even if the extremes greatly vary. This case is also important because the simulations and CRU data (Figure 2) presents an impressive agreement for this region. Thus, it is reasonable to assume that our future climate simulations will provide a very good approximation of the A2 scenario climate here. Given the atmospheric dynamics at such latitudes, the results are indicative of more frequent and/or stronger cyclones. This will result in increased erosion, hydric stress for vegetation and hydrometeorological risks.

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