Abstract
Abstract. Although hydrologic models provide hypothesis testing of complex dynamics occurring at catchments, freshwater quality modeling is still incipient at many subtropical headwaters. In Brazil, a few modeling studies assess freshwater nutrients, limiting policies on hydrologic ecosystem services. This paper aims to compare freshwater quality scenarios under different land-use and land-cover (LULC) change, one of them related to ecosystem-based adaptation (EbA), in Brazilian headwaters. Using the spatially semi-distributed Soil and Water Assessment Tool (SWAT) model, nitrate, total phosphorous (TP) and sediment were modeled in catchments ranging from 7.2 to 1037 km2. These headwaters were eligible areas of the Brazilian payment for ecosystem services (PES) projects in the Cantareira water supply system, which had supplied water to 9 million people in the São Paulo metropolitan region (SPMR). We considered SWAT modeling of three LULC scenarios: (i) recent past scenario (S1), with historical LULC in 1990; (ii) current land-use scenario (S2), with LULC for the period 2010–2015 with field validation; and (iii) future land-use scenario with PES (S2 + EbA). This latter scenario proposed forest cover restoration through EbA following the river basin plan by 2035. These three LULC scenarios were tested with a selected record of rainfall and evapotranspiration observed in 2006–2014, with the occurrence of extreme droughts. To assess hydrologic services, we proposed the hydrologic service index (HSI), as a new composite metric comparing water pollution levels (WPL) for reference catchments, related to the grey water footprint (greyWF) and water yield. On the one hand, water quality simulations allowed for the regionalization of greyWF at spatial scales under LULC scenarios. According to the critical threshold, HSI identified areas as less or more sustainable catchments. On the other hand, conservation practices simulated through the S2 + EbA scenario envisaged not only additional and viable best management practices (BMP), but also preventive decision-making at the headwaters of water supply systems.
Highlights
Basin plans comprise the main management tool and they plan sustainable use of water resources in both spatial and temporal scales
Since in the region the restoration of riparian forests is mostly due to Water-payment for ecosystem services (PES) projects, which was recognized as an ecosystembased adaptation, we identify the third scenario as S2 + ecosystem-based adaptation (EbA)
The water–forest system interaction is a classic issue in hydrology, the impacts of vegetation on qualitative and quantitative aspects of water resources need to be better understood
Summary
Basin plans comprise the main management tool and they plan sustainable use of water resources in both spatial and temporal scales. River plans are based on accurate data on actual water availability per basin, taking into account water needs for humans, environmental water requirements and the basin’s ability to assimilate pollution (Mekonnen et al, 2015). Adaptive management options such as ecosystem-based adaptation (EbA; see CBD, 2010; BFN/GIZ, 2013) and the water footprint (WF) (Hoekstra and Chapagain, 2008; Hoekstra and Mekonnen, 2012) have rarely been incorporated into Brazilian basin plans. This study, titled Estudio Nacional del Agua (Colombia, Instituto de Hidrología, Meteorología y Estudios Ambientales, 2014), was not included in the national water management plan, the strategic plan of the Magdalena– Cauca basin incorporates the grey water footprint (greyWF) to assess agriculture pollution (Colombia, 2014). In Brazil, a glossary of terms released by the Brazilian National Water Agency (ANA, 2015) includes the concept of WF to support water resources management
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