Abstract
Modelling the rare but high-impact Mediterranean Heavy Precipitation Events (HPEs) at climate scale remains a largely open scientific challenge. The issue is adressed here by running a 38-year-long continuous simulation of the CNRM-AROME Convection-Permitting Regional Climate Model (CP-RCM) at a 2.5 km horizontal resolution and over a large pan-Alpine domain. First, the simulation is evaluated through a basic Eulerian statistical approach via a comparison with selected high spatial and temporal resolution observational datasets. Northwestern Mediterranean fall extreme precipitation is correctly represented by CNRM-AROME at a daily scale and even better at an hourly scale, in terms of location, intensity, frequency and interannual variability, despite an underestimation of daily and hourly highest intensities above 200 mm/day and 40 mm/h, respectively. A comparison of the CP-RCM with its forcing convection-parameterised 12.5 km Regional Climate Model (RCM) demonstrates a clear added value for the CP-RCM, confirming previous studies. Secondly, an object-oriented Lagrangian approach is proposed with the implementation of a precipitating system detection and tracking algorithm, applied to the model and the reference COMEPHORE precipitation dataset for twenty fall seasons. Using French Mediterranean HPEs as objects, CNRM-AROME’s ability to represent the main characteristics of fall convective systems and tracks is highlighted in terms of number, intensity, area, duration, velocity and severity. Further, the model is able to simulate long-lasting and severe extreme fall events similar to observations. However, it fails to reproduce the precipitating systems and tracks with the highest intensities (maximum intensities above 40 mm/h) well, and the model’s tendency to overestimate the cell size increases with intensity.
Highlights
The northwestern Mediterranean is affected by Heavy Precipitation Events (HPEs), mainly during the fall season (Ducrocq et al 2008; Nuissier et al 2008, 2011)
We show that the CNRM-ALADIN 12.5 km Regional Climate Model (RCM), unlike the Convection-Permitting Regional Climate Model (CP-RCM), is not able to reproduce realistic location and intensity values for extreme precipitation, and clearly underestimates the number of heavy precipitation events
As CNRMALADIN is not able to produce realistic precipitating systems, the tracking method will not be applied to this model
Summary
The northwestern Mediterranean is affected by Heavy Precipitation Events (HPEs), mainly during the fall season (Ducrocq et al 2008; Nuissier et al 2008, 2011). Since the late 1980s, the climate modelling community’s solution has been to increase the resolution in specific regions and implement Regional Climate Models (RCMs) (Giorgi and Bates 1989; Giorgi 2019) with a current resolution of 50 km up to 12 km The use of these high-resolution limited area models provides a clear added value compared to 150 km GCMs, especially for precipitation (Déqué and Somot 2008; Ruti et al 2016; Prein et al 2016; Fantini et al 2018). The resolution remains too coarse to represent the fine scale processes involved in the triggering of sub-daily precipitation (Berg et al 2019) and convective phenomena correctly It limits confidence in the expected evolution of extreme precipitation in the context of climate change (Bony et al 2015)
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