Assessing groundwater nitrate hotspot mitigation through management scenarios and AI-based risk prediction across Europe under climate change

Groundwater nitrate contamination remains a persistent challenge across Europe, despite decades of regulation and monitoring. Although nitrate pollution is commonly framed as a diffuse agricultural pressure, exceedance patterns are spatially structured and strongly associated with management intensity. This supports a management-relevant modelling pathway: risk mapping can be extended into scenario-based evaluation of mitigation strategies, enabling spatial prioritization and transparent comparison of intervention options. In this study we present a management-focused scenario framework to quantify future changes in groundwater nitrate hotspot risk across Europe on a harmonized grid. Groundwater nitrate monitoring data are linked to land-use composition predictors (fractions of cropland, grassland, forest, wetlands, and impervious surfaces), alongside regional landscape descriptors and climate–hydrological covariates. Model outputs are provided as (i) a continuous probability of hotspot occurrence and (ii) a binary hotspot classification defined by exceedance of the drinking-water nitrate threshold. To improve continental transferability and reduce over-optimistic performance from spatial autocorrelation, model development and evaluation rely on spatial cross-validation and region-based holdouts. The predictive core is an AI-based ensemble designed to capture nonlinear interactions between land systems, hydroclimate, and nitrate outcomes. Management scenarios include: (1) cropland reallocation to grassland/forest to represent extensification and protection-zone land-use transitions; (2) wetland restoration to increase landscape retention and reduce leaching susceptibility; (3) fertilizer-pressure reduction implemented as proportional decreases in agricultural nitrogen intensity. For each strategy, we compare uniform implementation against risk-based targeting applied only in high-probability hotspot cells. Finally, all scenarios are evaluated under 2050 climate conditions (multi-scenario climate projections), allowing assessment of mitigation robustness under altered recharge regimes and climate-driven changes in leaching potential. The framework provides an operational route from EU-scale monitoring to management-ready, climate-aware decision support for prioritizing groundwater nitrate mitigation across Europe.