National-scale assessment of salt-affected areas in Portugal: Learning from legacy data to establish a framework for comprehensive monitoring and management

Developing efficient, cost-effective frameworks to assess the spatial and temporal distribution of salt-affected areas at multiple scales is essential for effective soil management. This study enhanced the Portuguese INFOSOLO soil information system by incorporating legacy data on soil salinization and sodification from 1979 to 2020. National-scale soil maps were then generated using geostatistical stochastic sequential simulation. Soil salinity was mapped based on electrical conductivity data from soil saturation paste extracts of topsoil samples collected in 2015 and 2018, while soil sodicity was mapped using the full coverage of exchangeable sodium percentage data across multiple soil layers. The resulting maps effectively captured significant salinization and sodification trends across Portugal, identifying both natural and human-induced hotspots of salinity and sodicity. However, they did not fully represent the extent of highly saline and sodic areas. Given the absence of a comprehensive monitoring framework for soil salinity and sodicity in Portugal, these findings highlight the necessity of establishing targeted monitoring efforts in identified high-risk areas. Consequently, a well-designed framework is proposed to monitor soil salinity and sodicity in Portugal's most sensitive regions, particularly important in light of intensified agricultural activities and increasing water scarcity driven by climate change.