Dynamics of carbon-water coupling in the Brazilian Cerrado: A long-term comparison of natural and agricultural systems (1985–2024)

We investigated the evolution of surface-atmosphere interactions in two strategic irrigated agricultural frontiers within the Brazilian Cerrado: The Alto Rio Preto and São Marcos basins. Driven by agricultural expansion, regional landscapes underwent transformations over the last four decades. In Alto Rio Preto, savanna cover decreased from 42% to 30 %, while agriculture expanded to occupy 42% of the basin. In São Marcos, native vegetation retreat was more severe, dropping from 42% to 17%, yielding space to an agricultural matrix that dominates 43% of the total area, with irrigated agriculture already consolidating 10% of the territory. The central objective was to quantify how the replacement of native vegetation with rainfed systems and the subsequent implementation of irrigation altered regional ecosystem carbon and water dynamics. The methodology employed Landsat time series (30 meters) for field-scale vegetation mapping. Gross Primary Productivity (GPP) was estimated using an adapted Light Use Efficiency (LUE) model, and Evapotranspiration (ET) was obtained via the geeSEBAL model. Ecosystem Water Use Efficiency (WUE_eco) was calculated as the ratio of carbon uptake to water loss (GPP/ET). The analysis was stratified into three levels: (i) regional spatiotemporal dynamics; (ii) trends in constant Land Use/Land Cover (LULC) areas; and (iii) impacts in technological transition zones. Regionally, a robust growth trend in GPP was observed, with mean annual values rising to unprecedented levels in both basins. Notably, over the last decade, the extent of high-productivity areas expanded significantly, becoming the dominant landscape feature in the São Marcos Basin. Water consumption followed this dynamic but with distinct regional behaviors: while ET in São Marcos remained stable at elevated levels, Alto Rio Preto underwent a structural shift, marked by a drastic reduction in low-consumption areas and a transition toward a regime of higher mean evapotranspiration. Consequently, mean annual WUE_eco in both basins rose from <1.0 to >2.0 gC/mm, indicating that carbon uptake increments proportionally outpaced ET rates. The analysis of constant land use areas revealed distinct intensification strategies. Although forests maintained the highest absolute GPP and ET averages, anthropogenic systems showed the highest acceleration rates. The São Marcos basin was distinguished by the efficiency of rainfed agriculture, recording the highest relative productivity leap (+169%) while operating with stable water consumption, culminating in a 189% rise in WUE_eco. In technological transition areas (rainfed to irrigated), the year 2000 marked a clear inflection point. From this date onwards, transition areas consistently outperformed rainfed GPP. Post-2010, WUE_eco values converged between irrigated and rainfed areas, suggesting technical maturity. It is concluded that agricultural modernization has established a new regional paradigm: cultivated systems have attained water use efficiency levels that significantly contrast with historical baselines, resulting in a highly productive landscape that maintains resilience despite the extensive replacement of native vegetation.