## 3 Results
### Distribution of Temperature Intervals
After applying the geostatistical interpolation approach described above, the maps of Figure 4 highlight the strong spatial variability of temperatures in mainland Portugal, also showing spatially coherent patterns. The annual number of hours with temperature between 4-8 \({}^{\circ}\)C (NH 4-8 \({}^{\circ}\)C) occurred along the southern and western coasts and maximum values in the mountainous areas and in the northeast. The NH 4-8 \({}^{\circ}\)C ranges from approximately 38% in Serra-da-Estrela to 3% in the Algarve coast. The NH 8-12 \({}^{\circ}\)C ranges from 13% to 21% in the southern part and presents values above 20% in the northern part, with a maximum in the northwestern quadrant (Figure 4b). Figure 3: Multivariate linear regression coefficients of the three selected regressors (latitude, elevation, and distance to coastline), along with their corresponding 95% confidence intervals. Figure 4: _Cont._  
The maps with the number of hours with temperature between 12-16 \({}^{\circ}\)C and 16-20 \({}^{\circ}\)C (Figure 4c,d) essentially highlight the continentality effect (distance to the coastline), particularly in the former interval, with higher percentage along the coast, as these temperatures are close to the sea surface temperatures. The NH 20-24 \({}^{\circ}\)C ranges from about 15% in south to about 6% in the mountains of the north and centre of the country. The NH 24-28 \({}^{\circ}\)C ranges from less than 2% in the Serra da Estrela to about 11% in the southeast, Tagus valley and the inner Douro valley. The NH 28-32 \({}^{\circ}\)C varies from roughly 0% to 7%, with a clear gradient from the northwest to the southeast. The NH 32-36 \({}^{\circ}\)C shows a similar pattern, but with generally lower percentage and an enhanced contrast (Figure 4h). Figure 4: Relative number of hours in the year (in %) by different temperature intervals: (**a**) 4–8 \({}^{\circ}\)C, (**b**) 8–12 \({}^{\circ}\)C, (**c**) 12–16 \({}^{\circ}\)C, (**d**) 16–20 \({}^{\circ}\)C, (**e**) 20–24 \({}^{\circ}\)C, (**f**) 24–28 \({}^{\circ}\)C, (**g**) 28–32 \({}^{\circ}\)C, (**h**) 32–36 \({}^{\circ}\)C, over mainland Portugal, for the period of 2000–2018 after applying the geostatistical interpolation (cf. Figure 1b for designations of mapped NUTS level 3). For the sake of succinctness, the previous eight classes were grouped into the following four thermal categories: cool (4-12 \({}^{\circ}\)C), temperate (12-20 \({}^{\circ}\)C), warm (20-28 \({}^{\circ}\)C), and very warm (28-36 \({}^{\circ}\)C) (Figure 5). Although this categorization is empirical, it reflects the main climatic conditions occurring in the country, the regional heterogeneities and the share of each category to the local climate. This information may be very useful to accurately and briefly classify local thermal conditions. The number of hours in the year with cool (4-12 \({}^{\circ}\)C) conditions ranges from approximately 65% in Serra da Estrela to 18% in the south of Portugal. The number of hours in the year with temperate (12-20 \({}^{\circ}\)C) conditions highlights the continentality effect (distance to the coastline), with much lower percentage over inner regions, mostly in the northeast. Along the coast, more than 50% of the hours of the year, on average, have temperate temperatures between 12 \({}^{\circ}\)C and 20 \({}^{\circ}\)C. On average, the number of hours of the year with warm conditions (20-28 \({}^{\circ}\)C) varies between 8% at the highest mountain to 25% in Alentejo and Algarve regions. Finally, the very warm conditions (number of hours with temperature between 28-36 \({}^{\circ}\)C) are essentially restricted to inner southern Portugal and to the upper Douro valley (Figure 5d). Figure 5: Typical relative number of hours during a year (in %) with (**a**) cool (4-12 \({}^{\circ}\)C), (**b**) temperate (12–20 \({}^{\circ}\)C), (**c**) warm (20–28 \({}^{\circ}\)C), and (**d**) very warm (28–36 \({}^{\circ}\)C) conditions over mainland Portugal, for the period of 2000–2018 (cf. Figure 1b for designations of mapped NUTS level 3).