Spatial gridding of daily maximum and minimum temperatures in Europe

We developed an operationally applicable land-only daily high-resolution (5 km 9 5 km) gridding method for station observations of minimum and maximum 2 m temperature (T-min/T-max) for Europe (WMO region VI). The method involves two major steps: (1) the generation of climatological T-min/T-max maps for each month of the year using block regression kriging, which considers the spatial variation explained by applied predictors; and (2) interpolation of transformed daily anomalies using block kriging, and combination of the resulting anomaly maps with climatological maps. To account for heterogeneous climatic conditions in the estimation of the statistical parameters, these steps were applied independently in overlapping climatic subregions, followed by an additional spatial merging step. Uncertainties in the gridded maps and the derived error maps were quantified: (a) by cross-validation; and (b) comparison with the T-min/T-max maps estimated in two regions having very dense temperature observation networks. The main advantages of the method are the high quality of the daily maps of T-min/T-max, the calculation of daily error maps and computational efficiency.