Assessment of Growing Thermal Conditions of Main Fruit Species in Portugal Based on Hourly Records from a Weather Station Network

Thermal conditions in mainland Portugal were evaluated using a new hourly database over the recent period of 2000-2018 (19 years). The number of hours within each different temperature interval was calculated from the long-term means of the hourly temperatures of a network of 63 meteorological stations. A geostatistical approach, using elevation, distance to coastline and latitude, was subsequently applied to provide gridded patterns at a high spatial resolution (1 km grid spacing). Eight fruit species (almond tree, carob tree, chestnut tree, citrus fruits, cork oaks, holm oaks, olive trees, and grapevines) were selected to assess their hourly thermal growing conditions. The results highlight the strong spatial variability of temperature levels in mainland Portugal, providing new insights into their spatial distribution. The number of hours in the year with cool conditions (4-12 degrees C) is higher in the northern-central regions, mainly in mountainous areas. Additionally, the number of hours in the year with temperate conditions (12-20 degrees C) emphasizes the importance of the distance to the coastline (maritime influence). The warm conditions (20-28 degrees C) are most prevalent in the south of the country and in the Douro valley, whereas the very warm conditions (number of hours with temperature between 28-36 degrees C) are essentially restricted to inner-southern Portugal and to the upper Douro valley. This study also reveals, with high accuracy, the thermal growing conditions of main fruit species in mainland Portugal, giving particular emphasis to olive trees and grapevines. These findings may help decision support systems providing more reliable and accurate guidelines to stakeholders, decision-makers, and farmers. The main maps are available in a widely used file format (shapefile), thus allowing their application to a wide range of other areas of interest.