The Portuguese National Roadmap for Adaptation 2100: from regional climate simulations to economic costs and adaptation

As warming and drying future conditions may significantly affect the human and natural environment in the Mediterranean, the climate risks and vulnerabilities assessments are key to support adaptation strategies. In this context, the Portuguese National Roadmap for Adaptation 2100 (RNA2100) aimed at providing scientific support to adaptation  policy exercises by (1) identifying and characterising climate change impacts on the most vulnerable domains in Portugal Mainland; (2) characterising socioeconomic impacts on different territorial scales and assess financial needs; and (3) contributing to the implementation of a National Spatial Planning Policy Programme. The most vulnerable domains focused by the RNA2100 include the coastal regions, water resources/agroforestry and wildfires. The RNA2100 followed three stages: regional climate scenarization, biophysical impacts for a number of sectors and hazards, and the economic analysis of selected impacts. The future projected climate for Portugal was characterized using a weighted multi-model multi-variable ensemble based on the EURO-CORDEX Phase I simulations, produced at 12 km resolution. One historical present climate period (1971-2000) and three future periods (2011-2040, 2041-2070, 2071-2100), under three different scenarios (RCP2.6, RCP4.5 and RCP8.5), were considered. The biophysical impact modelling was performed for four climate impact sectors: coastal erosion and flooding, forest fires, water and agroforestry systems.

Climate change poses a significant threat to water resources and agroforestry in mainland Portugal. Southern regions, particularly beyond the Tagus River, will face more significant impacts, with the Water Exploitation Index plus (WEI+) potentially increasing by up to +99 percentage points under RCP8.5 or around +22 points under RCP4.5. Without adaptation, economic losses in crop yields could reach €426 million annually under the moderate mitigation scenario and approach €670 million under the high emissions scenario. Even meeting Paris Agreement targets could still result in yearly losses of €172 million by 2100. The discourse on climate adaptation and wildfire management in the five NUTS II regions emphasizes the importance of multifaceted strategies in confronting the escalating threat of wildfires exacerbated by climate change. The results emphasize the pivotal role of awareness initiatives with coercive measures to effectively reduce ignitions and mitigate projected losses (saving from 290,000 euros/year in A.M.L. to 88 million euros/year in Centro). Portuguese coastal areas are extensively vulnerable to climate change impacts, with projections showing up to 587 km² (RCP4.5) and 604 km² (RCP8.5) of vulnerable coastlines by the end of the 21st century. Adaptation is overall recommended at national scale, despite the different results yielded by the cost-benefit analysis, depending on the region. Total inaction costs (without adaptation) are projected to surpass 12000 million € (RCP4.5) and 14000 million € (RCP8.5) until 2100, in contrast with approximately 5000 million € (for both scenarios) of expected adaptation costs.

Acknowledgements

This work is supported by the Portuguese Fundação para a Ciência e Tecnologia, FCT, I.P./MCTES through national funds (PIDDAC):  UID/50019/2025 and LA/P/0068/2020 https://doi.org/10.54499/LA/P/0068/2020).