Lagrangean analysis of convective cells under climate change

Precipitation is typically analysed from an Eulerian perspective, in which rainfall is considered at a fixed location. Lagrangean analysis of precipitation represents an alternative approach. Here, precipitation objects – for example, convective cells – are identified in a precipitation field and are then tracked through space and time, allowing object properties over the whole life of a convective cell to be collected. For the study of precipitation under climate change, this approach may offer additional insights into the mechanisms by which precipitation increases or decreases; for example, changes in cell lifetime or areal extent.

In this study, we analyse the climate-change response of convective cells’ properties by combining Lagrangean tracking with the pseudo global warming (PGW) modelling approach. A 14-day period of unusually high convective activity over central Europe is first simulated under observed conditions in an 18-member ensemble with the COSMO-CLM at convection-permitting resolution (2.8 km). The ensemble is then re-simulated under PGW conditions, created by modifying the initial and boundary conditions based on an RCP8.5 end-of-century scenario. All convective objects are then systematically tracked through space and time. Here we present the response to warming of the convective cell characteristics for the study period, and explore the variability of these changes across the full distribution of objects. Cell characteristics considered include cell area, intensity, volume, lifetime and distance travelled.