In a paper just published in Lancet Planetary Health, researchers use a global hydrological model to estimate the population at risk of facing water stress if we are to ensure the survival of ecosystems and thus the fundamental services they provide to us. The results indicate that significant proportions of the global population are at risk, so it is critical that we find strategies to ensure the balance of water resources between us and ecosystems.
Do we have enough water to ensure everyone gets the amount they need, while also ensuring ecosystems get enough? This is, in general terms, the question that a study just published in The Lancet Planetary Health, led by researchers of the Joint Research Centre (JRC) of the European Commission; among the authors there is Lorenzo Alfieri, researcher of our Hydrology and Hydraulics Department.
Using a global hydrological model that allows to investigate together all the rivers of the planet, the authors have tried to make estimates. Their results show that, if enough water is ensured for the well-being of ecosystems, significant percentages of the world’s population will face water stress (and vice versa).
These results are not encouraging, all the more so given that in many respects they may represent underestimates of the problem, which could worsen primarily due to global population growth and the potential adverse effects of climate change. However, they are essential data for the development of strategies to help mitigate the problem and achieve the sixth of the Sustainable Development Goals of the 2030 Agenda: Ensuring the availability and sustainable management of water and sanitation for all.
Water in rivers, for humans and ecosystems
In the last century, the global demand for water has been increasing, both because of the increase in the population of the planet and because of the increased use of water for agricultural, industrial, energy production, livestock and so on. The lack of this resource represents a threat to the population, aggravated by the possible effect of climate change on the availability of water resources. But water is not, of course, essential only for human activities: it is the basis of life and welfare of many other species, animals and plants, and ecosystems in which they live and of which they are part. Because ecosystems provide us with a vast array of services, ours and their wellbeing are linked by a double thread, and it is increasingly important to understand how to balance the water needs of both.
The new study is dedicated to this problem: “We compared the global anthropogenic water demands with an indicator called environmental flows (EFs), which actually represents the water that rivers must have to ensure the survival of ecosystems”, says Lorenzo Alfieri. “EFs are not easy to estimate and in the scientific literature there are several. In our study, we employed three of the most commonly used and accepted ones”. This approach allowed the researchers to create different scenarios – in other words, to try to figure out how much water resource would remain available for our needs depending on whether ecosystems needed more or less water.
The data were used in the LISFLOOD global hydrologic model, whereby the authors of the study calculated how much water would be available without anthropogenic presence over the period 1980-2018; they then used this estimate to calculate what the balance would be by adding human use (using 2010 data).
Water stress estimates
“Our estimates show that between 32% and 46% of the world’s population would face water stress, i.e., where there is insufficient water available to meet their needs, for at least one month per year. The percentage varies depending on the minimum vital runoff considered: if we apply a very precautionary EF, i.e. that provides a greater amount of water for the survival of ecosystems, in fact, less will remain for anthropogenic use,” says Alfieri. “Asia would be the region most affected by the phenomenon: we calculated that about 80% of the people who would face water stress live in this continent, and in particular in India, Pakistan and China”.
The data obtained by the researchers represent in a sense a snapshot of a specific period; this also means that, in reality, they may be underestimates compared to those that could be obtained with today’s data: the population, in fact, has been increasing over the years, and with it the demand for water. It will be necessary to conduct further studies to take into account socio-demographic projections and also to try to understand how climate change may affect the availability of water resources. In addition, the paper’s authors write, it will be important to supplement the assessment with estimates performed at the local and regional levels.
“In general, however, these results provide a very clear indication for future strategies: it will be necessary a great effort to ensure a balance between the demand for water for anthropogenic use, so as to avoid that a substantial part of the population faces conditions of water stress, and that necessary to ensure the survival of ecosystems,” concludes the researcher. “On the other hand, the importance of this goal is also already recognized in the 2030 Agenda, and in particular by target 6.4, which aims to reduce people facing water stress conditions”.
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