Projected Bioclimatic Changes in Portugal: Assessing Maize Future Suitability

In Portugal, maize is a major crop, occupying about 40% of the cereals area. The present study aimed to assess future bioclimatic conditions that could affect maize production in Portugal. For this purpose, a set of indicators was selected including dry spells (DSs) and the aridity index (AI). Two additional indicators were included, one related to the soil water reservoir available for maize (RAW) and the other related to the maize thermal unit (MTU), which were designed to assess the suitability of land for growing different varieties of maize. The analysis focused on historical (1971–2000) and future (2011–2070; 2041–2070; 2071–2100) climate scenarios (RCP4.5 and RCP8.5) using a four-member ensemble of global climate models. The results for the more distant and severe scenario suggest that there will be an overall increasing tendency in the AI, i.e., higher aridity, namely in the southern part of Portugal compared to the north (0.65 vs. 0.45). The soils in the south are characterized by a lower average RAW (<35 mm) than in the north (>50 mm), which leads to a lower irrigation frequency requirement in the north. As a result of the increased MTU, maize production will shift, allowing for varieties with higher thermal requirements and the conversion of areas traditionally used for silage maize to grain maize production areas. Adaptation measures to improve the climate resilience of maize are discussed.