High-resolution regional modelling of changing extreme precipitation

Meredith, Edmund

Extreme precipitation is of interest because of the often dramatic effects that it can have on society and the environment. In this thesis, high-resolution regional modelling experiments are used to study how climatic changes affect regional precipitation extremes, with a focus on the Black Sea and Mediterranean (BSM) region. The impact of model resolution, in particular at convection-permitting (CP) scales, on the representation of changes in extreme precipitation is also examined. The added value of high-resolution regional models, at up to CP resolution, for reproducing observed extreme precipitation events is established in chapter 3. In chapter 4, the July 2012 precipitation extreme in the Black Sea town of Krymsk is taken as a showcase example for studying the impact of sea surface temperature (SST) increase on convective extremes, and simulated under a range of SST forcings. The crucial role of recent SST increase in the intensity of the event is revealed. A highly nonlinear precipitation response to incremental SST increase suggests that the Black Sea may have exceeded a regional SST threshold. The physical mechanism identified indicates that BSM coastal regions may face abrupt amplifications of convective precipitation under continued SST increase, and illustrates the limitations of thermodynamical bounds for estimating the temperature scaling of convective extremes. The added value of CP models for simulating changes in convective extremes is explored by comparing how the intensity of the Krymsk event responds to increasing SSTs in simulations with explicit and parametrized convection. Compared at the same spatial scale, the strongly nonlinear extreme precipitation response to SST increase in the CP simulations is not evident when convection is parametrized. The physical mechanisms behind the different responses are the focus of chapter 5.

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Meredith, Edmund: High-resolution regional modelling of changing extreme precipitation. 2015.

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