Effects of increasing spatial resolution towards convection permitting scales in the Mediterranean area

Similarly to weather forecasting techniques, climate projections also aim to achieve very high spatial and temporal resolutions, which are needed both as inputs to impact models and to perform reliable risk assessment studies. This is all the more true for the Mediterranean region and the Italian territory in particular, whose heterogeneous and complex morphology do affect the local climate (highly sensitive to global warming), making this area particularly vulnerable to hydrogeological risks, such as heavy rainfall, landslides and flooding with serious losses of both human lives and economic. We present the results of downscaling CMIP6 global climate projections to local scales for the Mediterranean and Italian regions, aiming to produce high-resolution climate information for assessing climate change signals, with a particular focus on small-scale phenomena and extreme events. We performed hindcast (i.e. ERA5-driven) and historical simulations (driven by the MPI-ESM1-2-HR model) to simulate the present (1980-2014) and future (2014-2100) climate under three different emission scenarios (SSP1-2.6, SSP2-4.5, SSP5-8.5). For each experiment, we used a double nesting approach to downscale global data first to a regional domain, covering the whole of Europe (EURO-CORDEX domain) with a spatial resolution of 15 km, and subsequently to a fine spatial scale domain centered over Italy and the north-western Mediterranean with a resolution of 5 km, (i.e. close to the convection permitting limit resolution).  We explore the effects of pushing the resolution to km-scale while still falling within the so-called “gray zone” (5-10 km), where deep convection can still be insufficiently resolved and a parameterization of the deep convection is still needed to fully represent it. We present the analysis of the most relevant Essential Climate Variables (ECVs), and the statistics of extreme events for both the current climate and for end of the century scenarios. Results highlight that the gray-zone model in the configuration here implemented mimics the behavior of a convection permitting model and improves the representation of the mean precipitation field over the entire domain. This improvement is also detectable for heavy precipitation, represented through high percentile of daily precipitation (p95 – p99). We show the multi-scenario projection of the climate signal for both the simulations on the common domain.

This study was carried out within: RETURN Extended Partnership and received funding from the European Union Next-GenerationEU (National Recovery and Resilience Plan – NRRP, Mission 4, Component 2, Investment 1.3 – D.D. 1243 2/8/2022, PE0000005);

ICSC Italian Research Center on High-Performance Computing, Big Data and Quantum Computing and received funding from the European Union Next-GenerationEU (National Recovery and Resilience Plan – NRRP, Mission 4, Component 2, Investment 1.4 – D.D: 3138 16/12/2021, CN00000013)