Croatian high-resolution monthly gridded dataset of homogenised surface air temperature

Homogenised climatological series and gridded data are the basis for climate monitoring and climate change detection. Considering this, monthly mean temperatures from 122 Croatian stations were homogenised, and high-resolution monthly gridded data were developed for the 1981–2018 period. Homogenisation needs to be performed on stations from the same climate region; therefore, hierarchical clustering is introduced to define those climate regions in Croatia. The breaks of homogeneity were detected by the standard normal homogeneity test on 54 stations. Regression kriging was applied to produce monthly grids for each month in the analysed period. The quality of the interpolation assessed by leave-one-out cross-validation resulted in a root mean square error of 0.7 °C. The quality of spatial interpolation is supplemented with normalised error maps. The derived homogenised station data and monthly grids are necessary for national climate monitoring, the production of climate normals and the estimation of trends. After 1999, average annual anomalies from the 30-year climate standard normal 1981–2010 were positive and up to 1.4 °C warmer than the average and only occasionally negative. The measured amount, sign and significance of the trend were accurately captured on the trend maps calculated from the monthly maps. Significant strong warming was observed and mapped over the entire Croatian territory in April, June, July, August and November. It was stronger inland than on the coast. Annual trends were significant and ranged from 0.3 °C/decade to 0.7 °C/decade. There was no observational evidence of enhanced elevation-dependent warming over elevations from 750 to 1594 m.