## 1 Introduction  
Air temperature has a significant impact on health, environment, agriculture, society, and economy. Variability, extremes, and trends have been extensively investigated, based on daily, monthly, or annual data in Portugal [1; 2; 3; 4]. However, studies based on hourly data are not currently available. In effect, hourly data provides a much more accurate picture of the thermal conditions at a given location or region, also contributing to improving our understanding of climatic patterns and regimes. This kind of information is very useful for assessing climatic conditions and suitability of a given region for growing specific crops or forest species. This is particularly relevant for mainland Portugal, where temperature is spatially heterogeneous, showing strong spatial gradients. In addition, there is a strong seasonality and large inter-annual variability in precipitation and temperature across the territory [3]. Mainland Portugal is located in the transitional region between the sub-tropical anticyclone and the sub-polar low-pressure systems [2], therefore its climate is influenced by the alternation of anticyclones and depression systems. However, locally the climate is also greatly influenced by the complex orography, latitude, and proximity of the Atlantic Ocean [5; 6]. In fact, mainland Portugal presents large orographic heterogeneities, being more mountainous in the northern region (where maximum terrain elevation reaches 1993 m a.s.l.) than in its southern part (Figure 1a). These heterogeneities play a key role on the precipitation distribution [4] and on temperature pattern (Figure 1). With a predominantly mild Mediterranean climate [2], Portuguese climates feature typical warm and dry summers and cool and rainy autumn-winter periods, but with large inter-annual variability and seasonal irregularity. The annual mean temperature varies between about 9 \({}^{\circ}\)C, in the north and central mountains, to approximately 18 \({}^{\circ}\)C in the southern coast and inner Alentejo (Figure 1c). The territory is administratively organized in NUTS (Nomenclature of Territorial Units for Statistics) level 2 (Figure 1a) and NUTS level 3 divisions (Figure 1b). These units will be used herein to summarize information on the prevailing thermal conditions throughout the country. It is widely accepted that the two dominant global climatic drivers of plant distribution are temperature and water availability [5]. The plant growth and development is dependent upon the temperature surrounding the plant and each species has a specific temperature range, commonly characterized by a thermal optimum, minimum, and maximum thermal limits [6]. For fruit species, a certain heat accumulation is essential for adequate growth, physiological development and to obtain ripe fruits [7; 8]. Many woody plant species growing in temperate climates also require a certain amount of exposure to cold temperatures to break winter dormancy and prepare to springtime warming [9]. Several studies have combined heat and chill indices for studying thermal requirements of different fruit species [10; 11; 12; 13; 14; 15; 16]. [PERSON], [PERSON], and [PERSON] [7] evaluated the thermal growing conditions of fruit  
Figure 1: (**a**) Terrain elevation of mainland Portugal and location of the 63 selected meteorological stations. (**b**) Geographical borders of the 23 NUTS (Nomenclature of Territorial Units for Statistics) level 3 (see the list for their designations). (**c**) Annual mean air temperature for mainland Portugal during the period of 2000–2018. species in mainland Portugal using two bioclimatic indices: growing degree hours and chilling portions. These two indices were estimated based on gridded daily mean temperatures. With its large range of climates, Portugal produces various types of fruits and crops. Agricultural soils cover more than 35% of the total area of Portugal [17]. Grapevines and olive trees are the fruit crops that occupy the largest area, of 178,770 ha and 361,483 ha, respectively [18].