Same Pressure, Different Outcomes? Land-System Change and the Divergence of Water Quality in São Paulo State (Brazil) and Europe

Abstract Evidence that land-use change degrades surface water comes almost entirely from single-jurisdiction studies, which cannot ask whether the same land-system pressure is associated with the same water-quality outcome elsewhere. This study combines 41 years of annual MapBiomas land-cover data for six monitored water-management units (UGRHIs) in São Paulo State, Brazil, with a harmonised land-cover and water-quality panel for 179 European NUTS2 regions (LUCAS, cross-checked against Corine Land Cover for 2018, $$r=0.92$$ ). A within/between panel decomposition shows that within-unit increases in artificial land share are associated with lower nitrate (NO 3 –N) in São Paulo ( $$\beta =-0.210$$ standard deviations per percentage point, mixed-model $$p<0.001$$ ) and essentially unrelated to nitrate in Europe ( $$\beta =0.004$$ , 95% CI $$-0.026$$ to 0.034). The São Paulo estimate is stable across data-handling choices and precipitation adjustment, but it is not significant under cluster-robust or wild-cluster-bootstrap inference with six clusters ( $$p=0.23$$ and 0.43) or under a time-series-preserving permutation test ( $$p=0.30$$ ); it disappears when one unit is omitted, when unit-specific trends are allowed, and when land cover is measured over each station’s upstream drainage area ( $$\beta =-0.027$$ ). Biochemical oxygen demand and total phosphorus show no reliable within-unit differences, turbidity is associated with land use only in an exploratory model and not under few-cluster inference, and lead was excluded because its decline coincides with Brazil’s leaded-gasoline phase-out. The associations therefore differ across these monitored samples at the scale of management units, but their robustness and causes remain uncertain; differences in wastewater treatment are a plausible but untested explanation.