Temperature trends in olive growing season in producing areas of Extremadura (Spain)

The olive tree is mainly cultivated in the temperate zones of the Mediterranean area. Temperature is the main factor to evaluate the climatic suitability for olive cultivation. The study of the spatial and temporal variations of temperatures in a territory is necessary to define the most appropriate areas for production, as well as to evaluate different varieties. Extremadura has more than 269,000 ha of olive trees with a production of 884,960 tonnes, the third-largest surface area, and the second-largest olive-growing production in Spain. In this study the number of olive active days (OAD), the growing degree-days (GDD), and the average temperature of the olive growing period (OGST) index are analysed. The active days for the olive tree have been defined as those in which the average daily temperatures are above 14.4 °C between April and October. The minimum and maximum daily temperatures, from the meteorological data base of the Spanish government (AEMET), located in the main olive growing areas have been used, considering a period from 1991 to 2020. Mann-Kendal test and Sen's slope have been used to determine trends and their magnitude. The results show 200 active days per year, between 185 in Ibores and 215 in Vegas del Guadiana. The mean GDD value was 1514°C, varying between 1363°C in the Ibores area and 1685°C in La Serena whith a significant increasing trend in five areas. Growing degree-days have increased by an average of 4.9°C per year. The mean OGST value was 22.0°C, varying between 21.7°C in the Logrosan-Guadalupe area and 22.4°C in La Siberia. It has also shown a significant increasing trend in the index in four areas. Temperatures in the olive tree growth period have increased by an average of 0.21°C per decade, which represents an average increase of 0.67°C between 1991 and 2020.

Keywords: olive, active days, degree-days, temperature, trends, Spain.