PhD defence Joep Schyns

Sustainable and efficient allocation of limited blue and green water resources 

Joep Schyns is a PhD-student in the Water Engineering and Management (WEM) research Group. His supervisor is Professor Arjen Hoekstra from the Faculty Engineering Technology.

Freshwater stems from precipitation over land, which differentiates into a blue water flow (groundwater and surface water) and a green water flow (evaporation). Both flows are partially allocated to serve the economy, resulting in blue and green water footprints (WF). There are maximum sustainable levels to the blue and green WF, since rainfall is limited and part of the flows need to be reserved for aquatic and terrestrial biodiversity. Water scarcity, the degree to which the actual approaches the maximum sustainable WF, is becoming increasingly important due to increasing water consumption but limited water availability. The goal of this research is to broaden the discourse on freshwater scarcity in two respects. First, by assessing how Water Footprint Assessment (WFA) for a country can contribute to more sustainable and efficient allocation of blue water resources. Second, by assessing the allocation of the world’s green water resources with respect to maximum sustainable levels.

This research has shown that national policies for sustainable and efficient use of blue water resources can be enriched by WFA. First, WFA feeds discussion on whether water is efficiently allocated, by showing the WF of end-purposes and the associated economic value. Second, WFA can provide enriching insights in pressures on blue water resources, by assessing the ratio of the actual to the maximum sustainable blue WF in a river basin at a monthly resolution and by quantifying the role of water pollution through assessment of the grey WF. Third, WFA reveals options to reduce water demand by changing production and consumption patterns, which can lead to significant savings compared to traditional measures considered in water management. Fourth, WFA emphasizes the risks of being dependent on water resources outside the country’s borders when virtual water imports are placed in the context of water scarcity in the exporting nations. Furthermore, this research has shown that, to date, green water scarcity did not receive the attention it deserves. It is found that green water is scarcer than blue water in 91 out of 163 countries, and that humanity is closer to the planetary boundary for green water (56% appropriation) than for blue water (27-54% appropriation). Globally, 18% of the green WF is in areas to be reserved for nature. By quantifying the limits to green water availability, the main source of water to produce food, feed, fibre, timber and bio-energy, this research emphasizes the critical role green water has to play in the discourse on freshwater scarcity.