Attribution of seasonally relevant winter and spring climate indices in Hungary

Although anthropogenic global warming is well-known within the scientific community, the public is still not certain how to associate specific local weather and climate events to this issue. Therefore, it is essential to raise public awareness by providing sound and readily understood scientific information, and to explain how humans contribute to specific (extreme) events. Although a few case studies for past high-impact weather events were assessed in Hungary, a systematic analysis of long-term past and future trends of these indices is missing, and their linkage to anthropogenic activity has not been addressed at all. Our attribution project (started in September 2021) aims to fill this gap in Hungary: the results of the analysis of seasonally relevant indices are published in each season at the time of an (extreme) event occurrence. The dissemination is done via an already established Hungarian platform (https://masfelfok.hu/) reaching the public with readily understood climate change information through their broad media coverage and a large social media network.

The assessments are prepared within the project using several data sources: (1) an ensemble of CMIP6 global climate model simulations of both natural-only forcings and historical runs, (2) an ensemble of regional climate model simulations from Euro-CORDEX, including both RCP4.5 and RCP8.5 scenarios, (3) a fine-resolution, homogenized observation-based gridded data for Hungary, (4) the ERA5 reanalysis. We address seasonally relevant extreme and compound events, and the attribution of pre-selected indices to anthropogenic activity through their intensity, duration, and frequency changes. For instance, frost days, annual temperature minima and return values, snowfall and heavy snowfall days are evaluated for winter, while the start of vegetation period, late frost, dry and heavy precipitation days for spring, as they are of most public interest. Furthermore, we determine how many seasonal record low/record high breakings happen and how large area within the domain is affected.

Preliminary winter results suggest that the decrease of frost days in Hungary is clearly due to anthropogenic activity, while it is not the case for the annual minimum temperatures but will be in the future. No significant decrease has been detected for the snowfall and heavy snowfall days, and the effects of anthropogenic activity on these indices will only occur following the pessimistic future scenario.