Limiares de aquecimento global (1,5–4 °C) e impactos na disponibilidade hídrica e na produtividade dos plantios de eucalipto baseados em modelos climáticos do CMIP6

Abstract

Eucalyptus spp. plantations face increasing risks as a result of climate change, particularly due to reductions in water availability and changes in productivity. Considering the current commitments established under the Paris Agreement may be insufficient to limit global warming to 1.5 °C and below 2 °C relative to pre-industrial levels either, it becomes essential to assess the impacts associated with these thresholds, as well as with higher thresholds such as 3 °C and 4 °C. In this context, this thesis was divided into two chapters, with the following aims: i) to determine the spatial patterns of four global warming levels (1.5, 2, 3, and 4 °C) relative to pre-industrial period; ii) to assess the impacts of these thresholds on actual evapotranspiration (AE), water surplus (WS), water deficit (WD), and the viability of eucalyptus plantations at the global scale, using multiple climate models from the NASA Earth Exchange Global Daily Downscaled Projections (NEX-GDDP-CMIP6) dataset (Chapter I); iii) to identify the spatial patterns of key variables related to eucalyptus productivity under the four global warming levels compared to the control period; and iv) to assess the impacts of these thresholds on accumulated potential productivity (APP) and accumulated attainable productivity (AAP) of eucalyptus in South America, also based on NEX-GDDP-CMIP6 climate models (Chapter II). For this purpose, climate model data from the Coupled Model Intercomparison Project Phase 6 and the NEX-GDDP-CMIP6 were used, considering the SSP2-4.5 and SSP5-8.5 scenarios. Initially, the years in which each global warming threshold was reached were determined, and subsequently, water availability and productivity (potential and attainable) were calculated using the Agroecological Zone Model of the Food and Agriculture Organization (AZM-FAO) associated with each threshold. The results indicate additional increases in air temperature ranging from +0.5 °C to +3 °C across various regions worldwide, associated with heterogeneous patterns of annual precipitation (±150 mm year⁻¹), directly affecting water availability. Increases in crop evapotranspiration, AE, and WD, as well as reductions in WS, were observed, particularly over Brazil, South Africa, southern Europe (Spain and Portugal), India, Thailand, and Australia. As consequence, the viability of eucalyptus plantations may be compromised by 30% to 89%, depending on the region. Regarding productivity, APP showed increases in southern South America, ranging from +25 to +75 m³ ha⁻¹. In contrast, reductions between −25 and −75 m³ ha⁻¹, especially under the 3 °C and 4 °C warming levels, predominated across much of Brazil, northern Paraguay, eastern Bolivia, and northern regions of the continent. More pronounced reductions were observed for AAP, with decreases ranging from −25 to −150 m³ ha⁻¹ and productivity losses of up to 80%, particularly under the 3 °C and 4 °C, affecting large areas of Brazil, Argentina, Bolivia, western Peru, and the northern part of the continent. The findings of both chapters highlight the intensification of plantation vulnerabilities under higher global warming levels and reinforce the need for targeted adaptation strategies. These include selecting genotypes more tolerant to thermal and water stress, adjusting silvicultural management practices such as optimizing spacing and stocking, more frequent thinning and pruning, adopting soil-water conservation practices, and production diversification through agroforestry systems.