Thermal severity on brazilian lettuce crops under two global climate change scenarios.

Lettuce (Lactuca sativa L.) is one of the most produced and consumed vegetables in Brazil. As a crop of Mediterranean origin and therefore adapted to cool and/or mild climates, it is strongly affected by high temperatures. Morphophysiological disorders such as premature bolting and tipburn are examples of these impacts. Such problems are expected to worsen under projected scenarios of global warming and climate change. Therefore, this study aimed to assess the vulnerability of Brazilian lettuce production to two global climate change scenarios (RCP 4.5 and RCP 8.5) throughout the 21st century, using the regional climate model ETA-HadGEM2-ES, as well as the impacts of what we defined here as the Thermal Severity Index, calculated by summing the vulnerability indices of mean temperature and maximum temperature. Projections of mean temperature (Tmean) and maximum temperature (Tmax) were analyzed for the four seasons of the year, generating thematic maps of climate vulnerability and the Thermal Severity Index (IS), which integrates both variables. The results indicate a generalized warming trend, more pronounced under the RCP 8.5 scenario, with significant impacts on lettuce production, especially in the Central-West, Northeast, and Northern regions. Impacts will be greatest during summer and spring. By the end of the century, in both scenarios, almost the entire country, across all seasons, will present high to very high IS values. Only the Southern region and parts of mountainous areas showed high suitability for lettuce cultivation. The urgent adoption of climate change adaptation strategies and improvements in production system resilience is therefore necessary. As lettuce cultivation is highly associated with family farming—largely neglected in current climate change actions, this also becomes a matter of climate justice.