Preparation of Tailored Climate Projection Analyses for Climate Change Adaptation in Slovenia

Following the catastrophic floods that struck Slovenia in 2023, public awareness of the impacts of climate change has significantly increased. As a result, there is growing demand for information on future climate extremes—particularly changes in extreme precipitation, and to a lesser extent, extreme temperatures. The majority of these requests come from engineers who need to design climate-resilient infrastructure. More recently, municipalities—either individually or as regional consortia—have also begun seeking assessments of their resilience to future climate change.

In 2016, the Slovenian Environment Agency (ARSO) launched the project Assessment of Climate Change by the End of the 21st Century, analysing regional climate model outputs from the Euro-CORDEX project. The analysis included three Representative Concentration Pathways (RCPs): RCP2.6, RCP4.5, and RCP8.5. For each scenario, we evaluated an ensemble of models to calculate projected changes and their statistical robustness for various climate variables, focusing on future 30-year periods relative to the 1981–2010 reference period. For temperature and precipitation, we also assessed trends in extremes using the Generalized Extreme Value (GEV) distribution.

Trends in annual maximum values were used to estimate changes in extreme one-day precipitation and temperature (both maximum and minimum), based on the GEV location parameter. However, we found that one-day precipitation trends tend to underestimate the changes in shorter-duration events (e.g., 5–30 minutes). To better estimate changes in sub-daily extreme rainfall, we now derive trends from mean temperature changes and apply the Clausius–Clapeyron relation. These temperature trends are calculated from annual averages using simple linear regression, rather than from extremes or GEV analysis.

When users request an analysis, they typically provide location coordinates, a future target year, and a preferred RCP scenario. Most analyses are focused on projections to 2050 under RCP4.5, though some users request longer-term assessments under RCP8.5. For temperature, the most common request is the projected change in the 50-year return level of maximum temperature. For precipitation, users frequently request 100-year return levels for one-day and sub-daily extreme rainfall (e.g., 5, 10, 15, 20, 30 minutes). Present-day conditions are derived from meteorological station data interpolated to a ~1 km grid. We then apply model climate trends to these current extremes to estimate future values.

Approximately 90 % of requests involve extreme precipitation projections, followed by 7 % for municipal or regional climate impact assessments, and the remaining 3 % for extreme temperature projections.