Green and blue water demand from large-scale land acquisitions in Africa.

In the last decade, more than 22 million ha of land have been contracted to large-scale land acquisitions in Africa, leading to increased pressures, competition, and conflicts over freshwater resources. Currently, 3% of contracted land is in production, for which we model site-specific water demands to indicate where freshwater appropriation might pose high socioenvironmental challenges. We use the dynamic global vegetation model Lund-Potsdam-Jena managed Land to simulate green (precipitation stored in soils and consumed by plants through evapotranspiration) and blue (extracted from rivers, lakes, aquifers, and dams) water demand and crop yields for seven irrigation scenarios, and compare these data with two baseline scenarios of staple crops representing previous water demand. We find that most land acquisitions are planted with crops that demand large volumes of water (>9,000 m3⋅ha-1) like sugarcane, jatropha, and eucalyptus, and that staple crops have lower water requirements (<7,000 m3⋅ha-1). Blue water demand varies with irrigation system, crop choice, and climate. Even if the most efficient irrigation systems were implemented, 18% of the land acquisitions, totaling 91,000 ha, would still require more than 50% of water from blue water sources. These hotspots indicate areas at risk for transgressing regional constraints for freshwater use as a result of overconsumption of blue water, where socioenvironmental systems might face increased conflicts and tensions over water resources.

Mapping and quantifying perceptions of environmental change in Kilombero Valley, Tanzania.

Large-scale land acquisitions are a critical driver of global socio-environmental change, in particular in the Global South. This study aims to investigate drivers, impacts and feedbacks of environmental change in Kilombero Valley, Tanzania, a region in rapid societal and environmental transformation. We use land cover classifications to map and quantify land cover changes from 1990 to 2016, and compare these with local perceptions of change from fieldwork conducted in 2015 and 2016. The land change detection clearly shows farmland expansion over the wetlands, which is in line with local perceptions, but fails to detect changes in forest cover, which contradicts local perceptions that proclaim rapid deforestation over the past decade. In order to move towards more inclusive sustainable development, there is a need to break the power asymmetries between agribusinesses and local farmers. Our approach posits that policies of importing regions and countries where land is leased need to be strengthened to make sure that agribusinesses establish farms that are consistent with local and domestic needs. Such policies should not only be informed by assessments of environmental change, but also be guided by local knowledge, needs and future aspirations.