Evaluation of historical and future thermal conditions for almond trees in north-eastern Portugal

The Tras-os-Montes agrarian region (TM; north-eastern Portugal) is a traditionally growing area of almond trees. However, climate change may significantly alter the current growing conditions and threaten sustainability. Chilling and forcing conditions in TM are assessed herein, also considering different varietal phenological timings. The dynamic model/chill portions (CP) and chilling hour (CH) models are used to assess the chilling phase. For the forcing phase, growing degree hours (GDH) and growing degree days (GDD) models are selected, hinting at differences between simpler (CH and GDD) and more complex models (CP and GDH). Furthermore, the climate change projections for these models are assessed. The models are computed using daily temperatures for baseline (Iberia01, 1971-2015) and two future periods (EURO-CORDEX: medium-term, 2041-2060, and long-term, 2061-2080), following two anthropogenic forcing scenarios (RCP4.5 and RCP8.5). For the future, a five-member ensemble of regional-global climate model chains is used. Projections for CP and CH show decreases, mostly for RCP8.5, whereas projections for GDH and GDD reveal an increase in heat conditions until the beginning of summer. GDH shows that potentially damaging high temperatures during summer, effectively lead to a decrease in heat accumulation for almond trees. CP and GDH, more biologically effective, seem to be more accurate in capturing climate change impacts. For the three varietal groups, the late cultivar may experience a greater reduction of CP and GDH compared to early and mid-season varieties. Nonetheless, the increase in heat forcing should be more detrimental than the decrease in chilling conditions. Although almond production may be compromised in the future, adequate adaptation options are suggested to mitigate future losses of yield/quality and warrant its sustainability.