Evaluation of HCLIM convection-permitting climate simulations over Croatia

Croatia’s location, complex coastal orography and strong thermal contrasts with the Adriatic Sea in autumn make this region particularly prone to extreme mesoscale phenomena, including downslope windstorms, thunderstorms, mesoscale convective systems, orographic precipitation and waterspouts. Numerous studies have shown the benefits of convection‑permitting climate models for simulating such extreme events, especially heavy precipitation events. The HARMONIE‑Climate (HCLIM) regional climate model, a state‑of‑the‑art convection‑permitting model, has proven applicable across many regions, providing satisfactory evaluation results and realistically reproducing sub‑daily precipitation statistics and mesoscale precipitation structures. This study aims to assess whether HCLIM can realistically simulate the climatology over Croatia, with a particular focus on precipitation and precipitation extremes.

HCLIM is run for a ten-year period, from 2010 to 2020, with a one-year spin-up time and two nested domains with horizontal grid spacings of 12 km and 3 km. The 12 km simulations are driven at the lateral boundaries by the ERA5 reanalysis. We utilise the flexibility of HCLIM by analysing the performance of two different model configurations. First, we run the 12 km simulations using both the ALADIN physics (hydrostatic dynamical core and parametrised deep convection) and the AROME physics (non-hydrostatic dynamical core without deep convection parameterisation). Second, these two simulations provide the input for two corresponding AROME simulations at 3 km. As observational references, we use E-OBS, a daily gridded dataset at 0.1° horizontal resolution, the sub-daily regional reanalysis CERRA at 5.5 km resolution, and hourly precipitation observations from approximately 40 automatic weather stations in Croatia. We evaluate daily precipitation, temperature, wind, relative humidity and mean sea level pressure, and, given our focus on precipitation, several heavy and extreme precipitation indices, with particular emphasis on hourly precipitation over several specific subregions. Generally, HCLIM simulations realistically reproduce the spatial patterns of precipitation across Croatia. The finer-scale runs at 3 km outperform the coarser 12 km runs by exhibiting smaller biases and better capturing precipitation intensities, frequencies and mesoscale structures.