Severe winter chill decline impacts Tunisian fruit and nut orchards

Abstract

Future warming predicted for Tunisia may reduce winter chill and affect the production of tree fruits and nuts, one of the key sectors of the country’s economy. To assess past and future chill availability, we used weather records from 1973 to 2019 to simulate historic and future chill for 20 weather stations (16 from Tunisia, 3 from Algeria and 1 from Libya) by generating 6 past scenarios and 72 future scenarios for 2041–2070 and for 2071–2100, for two Representative Concentration Pathways (RCP4.5 and RCP8.5). We selected three future scenarios representing optimistic, intermediate, and pessimistic outlooks. Safe Winter Chill (SWC; in Chill Portions) was calculated using the Dynamic Model based on data for 100 winter seasons produced with a weather generator. SWC was then mapped for the whole country. Chilling requirements for typical Mediterranean fruit species (almond, pistachio, and peach cultivars) were compared with future SWC to select the best adapted fruit species, and cultivars within species, for each region. Our findings revealed severe SWC decline in the recent past. This decline will continue in the course of the twenty-first century. At the end of the century, we expect few of the studied species and cultivars to be able to fulfill their chilling requirements. By that time, only almonds may remain viable, whereas pistachios and peaches may experience alarming chill shortfalls. While our findings paint a grim picture for Tunisia’s orchards, they also allow insights for many other important fruit-growing regions with Mediterranean climate.