As the source of all life, water is essential to our health, well-being and dignity as well as to the functioning of our ecosystems and societies. Access to water is therefore synonymous with development. However, around the world, water is being overexploited, wasted, and contaminated at unprecedented rates. On the occasion of the 9thWorld Water Forum in Dakar from 21 to 26 March 2022, IRD Le Mag’ is taking a fresh look at the key challenges involved in efforts to sustainably preserve this unique natural resource.
Water, symbolising purity, fertility and life, is one of a kind. It is essential to quench our thirst, wash and refresh ourselves, but also to produce our food, making it vital to our societies. We also need water to generate electricity, sail, make our clothing and manufacture the products we use every day. Yet this precious resource is under threat. While water supplies are being overexploited in many parts of the world, they are taken for granted and wasted in other regions. And despite the existence of ingenious systems for sharing water, human activities lead to the degradation of its quality, to the point of making it unfit for human consumption and agricultural use. Climate change also affects the entire water cycleA natural phenomenon formed by the transfer of water between oceans and continents as it moves through different forms: from precipitation to river water flowing to the ocean and evaporating again to form clouds, beginning a new cycle.. Precipitation has therefore decreased and caused droughts in certain areas, while increasing elsewhere and leading to floods. The threats to this valuable liquid as well as water-related hazards could seriously undermine the Sustainable Development Goals (SDGs) established by the United Nations, particularly in the Global South. There is still much to be done for goal 6 alone, which aims to ensure access to clean water for all by 2030. According to the latest estimates from the United Nations, 2 billion people still did not have access to safe drinking water in their homes in 2020. 771 million still had to travel at least thirty minutes from their home to access safe water. Worse still, over one hundred million people drink untreated, poor-quality water (pathogens, pollution). In light of this bleak report, there is an urgent need to manage this resource more sustainably with the aim of counteracting this universal water crisis exacerbated by an ever-growing global population and a changing climate.
Researchers in pursuit of blue gold
The blue planet. There is so much water covering the Earth’s surface that it appears blue from space. Nearly three-quarters of the Earth’s surface is covered with water. Liquid in the ocean, seas, lakes and ponds, rivers and streams, and also in the soil. It also exists in the form of ice and snow, in glaciers, sea ice, ice caps and at the top of some mountains.
Yet only 2.8% of all of this water – 1.4 billion km3 – is fresh and less than 1% is directly exploitable on the surface or in water tablesWater reserves, also known as aquifers, located beneath the Earth’s surface . Simply put, fresh water is relatively scarce. Several generations of hydrologists have therefore sought to quantify water resources in the field by measuring the streamflow and depths of rivers, assessing the surfaces of inland seas and lakes, and conducting soil investigations in search of groundwater reserves. “This data is essential in understanding every aspect of the hydrological cycle,” says hydroclimatologist Fabrice Papa, Director of Research at UMR LEGOS. The in-depth knowledge of water resources provided by these measurements facilitates better management. Once we know the volume of water retained by dams, for example, we can allocate it according to domestic, agricultural and industrial needs. This data is equally valuable in responding to floods and trying to prevent them. Yet it is sometimes difficult to acquire, especially in areas with difficult access, such as intertropical and polar regions, or in areas where insecurity prevails (war, terrorism). In the past thirty years, satellites have been used to supplement or fill in gaps in field measurements from space.
Water as seen from space
“Spatial hydrology is a fabulous tool for obtaining large-scale data because it multiplies observation points,” Fabrice Papa explains. Depending on the instruments available on board the satellites, it is possible to assess precipitation, determine the levels and extent of surface waters, or the quantity of water on the continents. “These measurements support concrete research issues,” he says. By combining data from several satellites, we were able to show that Lake Chad no longer dries up as was the case in the 1970s and 1980s. On the contrary, its surface and storage capacity has increased since 2003.” These findings provide perspective on plans to divert the Ubangi River, a tributary of the Congo River, in order to supply water to this isolated oasis in the heart of the Sahara.
Satellites not only support research on bodies of water, they also contribute to the study of hydroclimatic variability in large river basins, one of Fabrice Papa’s favourite topics. “Together with our French and Brazilian colleagues, we used satellite data to assess variations in the quantity of water contained in water tables in the Amazon basin. That is a first!” The researcher has now focused on the Congo Basin, which spans nearly four million square kilometres in ten countries and includes some 25,000 kilometres of waterways. “It is the second largest river basin in the world after the Amazon basin, but only a dozen measurement stations are operational,” says the hydroclimatologist. “Very little data is available on the current streamflow and it is therefore impossible to predict future changes.” To remedy this situation, Agence Française de Développement (AFD) has joined together with the International Commission of the Congo-Ubangui-Sangha Basin (CICOS) and the National Centre for Space Studies (CNES) to establish a project using satellite data to conduct the hydrological monitoring of this huge basin covered with tropical forests that are difficult to access. “The satellites will allow us to obtain 2,300 measurement points on the river in real time,” says the researcher. In addition to providing a better picture of the basin’s hydrological system, the data generated could also be used to create decision support tools for navigability and resource management.
SWOT: a game changer for spatial hydrology
SWOT, which stands for Surface Water and Ocean Topography, grew out of a collaboration between NASA and France’s National Centre for Space Studies (CNES). This space mission promises to revolutionise hydrology as we know it. “The scientific community is eagerly awaiting its launch at the end of 2022. SWOT will be the first satellite dedicated to studying surface water,” says Fabrice Papa, who is a member of the project’s scientific team and coordinator of the working group devoted to river hydrology. “Using an altimeter that can observe wide surfaces with very fine spatial resolution of about 100 metres, SWOT will be able to identify spatiotemporal variations in continental water levels, while also determining their dimensions and streamflows, with unparalleled precision.” The countdown to the launch into orbit has begun!
More grist to the research mill
In addition to accessibility challenges, although some hydrological data exists, it is not readily available due to State sovereignty and confidentiality issues, or due to a lack of means. This is particularly true in Africa, which already suffers from a weak network of hydrological measurement stations. The online release of the African Database of Hydrometric Indices (ADHI) in 2020 has helped to mitigate this problem. “This unprecedented reference database for Africa has provided the scientific community with access to current and historical data from 1,500 measurement stations spread across the majority of the African continent,” says Yves Tramblay, a hydrologist at UMR HSM who is in charge of the database. ADHI, constituted by IRD in conjunction with the national services of several African countries, the World Meteorological Organization (WMO) and the Global Runoff Data Centre (GRDC), came as the culmination of collaborative work by several generations of hydrologists, with some measurements dating back to the 1950s. “This data can provide impetus for research issues and contribute to improving hydrological knowledge on the African continent,” the researcher adds. Hosted by DataSuds, the IRD data warehouse, ADHI has already been downloaded by over 2,200 users around the world.
Hydrological data is crucial to gaining a picture of the current level of water resources as well as understanding how they have changed over time and to predict their future in a context of accelerating climate change. This is in fact one of the objectives of the Water Cycle and Climate Change Project (Cycle de l’Eau et Changement Climatique–CECC) which aims to provide scenario forecasts for water resources in the Sahel and the Tropical Andes; two regions where the water cycle is heavily affected by the global temperature rise. “We will use hydrological and meteorological models to simulate future changes in surface water and groundwater in certain areas of these regions up to the year 2100,” says Benjamin Sultan, a climatologist at UMR Espace-DEV. The researchers plan to target the city of Dakar in Senegal, the middle course of Niger River, Lake Titicaca, and the Beni River’s upper basin, located in western Bolivia. The findings from the project launched in July 2021 and financed for four years by AFD and IRD will be made available to decision makers, managers, and the academic world via a web portal. “Decision support tools will also be developed to facilitate the management of hydrological infrastructures and anticipate risks of drought and flooding in these vulnerable regions,” the researcher adds.
Water, Water Everywhere!
Life-giving water can sometimes transform itself into a destructive force. Floods and landslides are both natural disasters caused by excess rainfall. According to the United Nations Office for Disaster Risk Reduction (UNDRR), the number of flood-related disasters has increased 134% since 2000 compared to the previous two decades. And the IPCC forecasts are hardly reassuring. “Even the best-case scenarios suggest an increase in extreme weather events in coming years, including increased rainfall,” says climatologist Benjamin Sultan. He is the author of the IPCC's sixth assessment report, which will be finalised by the end of 2022.
This bleak future has already become a reality in some parts of the world, such as in the Sahel. “In this semi-arid region, cumulative rainfall has increased since the early 2000s. The number of rainy days has remained stable, but the rain has become more intense,” the specialist says. “One of the climate mechanisms at work is the Clausius-Clapeyron relation, which indicates that the maximum amount of water in vapour form increases with the temperature. For each additional degree, the effective water vapour content increases by an average of 7%. This excess humidity in the atmosphere causes more intense rainfall.” The reduction of natural vegetation cover in the Sahel and agricultural intensification have stripped soil bare in many areas. “In the event of intense precipitation, these lands become more susceptible to the formation of slaking crustA compact surface crust formed by the impact of rain drops and the fragmentation of aggregates on the surface layer. The formation of crusts hinders the infiltration of water into the soil and therefore increases runoff; which leads to surface sealing and increases the risk of flooding caused by rainwater runoff,” Benjamin Sultan adds. This results in a long list of consequences for communities, crops, livestock and infrastructure.
More frequent floods
When this intense rain falls on a drainage basinGeographic area that drains all of the water from a river and its tributaries, it can also cause flooding downstream. These floods can sometimes be particularly destructive and deadly (see Box). Between 1950 and 2019, river floods on the African continent affected 82 million people and resulted in approximately 27,000 deaths according to the international database on natural disasters (EM-DAT). However, on closer inspection, it becomes apparent that these figures are unevenly distributed. Nearly three-quarters of deaths have occurred since the 1990s. The ADHI database helps to explain this in part. “Detailed analysis of the hydrological data from nearly 900 measurement stations over this period shows an increase in river floods in West and Southern Africa beginning in the 1980s,” says Yves Tramblay, who supervised this research.
Higher rainfall, caused in particular by a series of rainstorms, plays a major role in increasing the frequency of these extreme events. However, as with runoff floods, changes in land use have exacerbated the risk of floods. “Urban areas, and some agricultural land, do not retain much of the rainwater, which causes rivers to swell,” the hydrologist says. However, additional research by Yves Tramblay, also based on ADHI data, confirms the importance of another factor in the emergence of river floods: soil moisture. “By comparing the seasonality of over 11,000 floods recorded between 1981 and 2018 by around 400 measurement stations on the African continent, we demonstrated that soil moisture is statistically a more dominant factor in triggering floods than maximum annual precipitation.” Water-soaked soil hinders the infiltration of rainwater and leads to runoff. “Of course, without precipitation, there would be no floods, but soil moisture changes the impact of the rainfall and thus the occurrence or absence of floods,” the researcher says.ur.
Anticipating floods in Morocco
River flood forecasting systems in Africa are sorely lacking, yet they could save lives. In the Maghreb, for example “floods have claimed twice as many victims as in Northern Europe in recent decades,” Yves Tramblay says. The steep-sided valleys in the High Atlas mountains of Morocco, like the valley of the Ourika River south of Marrakech, are regularly affected by short-lived but very sudden floods. “The flood of 17 August 1995 is engraved in our memory,” says El Mahdi El Khalki, a research professor in hydrometeorology at Mohammed VI Polytechnic University in Ben Guerir, north of Marrakech. On the evening of that hot summer day, a terrible thunderstorm hit upstream of the Ourika basin, with heavy rainfall causing the river to swell. In about ten minutes, its streamflow increased 30-fold. The flood wave destroyed everything in its path. The toll was high: 289 victims, over 200 hectares of farmland destroyed, over two thousand cattle drowned and damage estimated at approximately US$15 million.
“After this disaster, an alert system was established based on real-time precipitation and streamflow observations. But the current lead time is too short to allow for a response to flash floods like the one in 1995,” says El Mahdi El Khalki, who is currently working to develop a national forecasting system for river flooding. The goal is to be able to predict possible floods 24 to 48 hours in advance. His thesis co-supervised by Mohamed El Mehdi Saidi, a professor at Cady Ayyad University in Marrakech, and Yves Tramblay, has already demonstrated the feasibility of such a system in the Ourika Valley and nearby Rheraya watershed. “After adapting the hydrological and meteorological models to the Moroccan context, we succeeded in simulating the streamflow of these rivers for several floods that occurred in the basins between 2014 and 2016 based on data from Morocco’s National Directorate of Meteorology (DGM),” the researcher says. This work conducted by TREMA, the International Joint Laboratory (LMI) for sustainable water management within watersheds in the Southern Mediterranean region was selected by Morocco’s Special Commission on the Development Model, established by King Mohammed VI, for the theme “Climate Change and Natural Resources: What Responses Should Shape the Morocco of Tomorrow?”
El Mahdi El Khalki, Yves Tramblay, Arnau Amengual, Victor Homar, Romualdo Romero, Mohamed El Mehdi Saidi et Meriem Alaouri, Validation of the AROME, ALADIN and WRF Meteorological Models for Flood Forecasting in Morocco, Water [12(2):437], 6 février 2020 ; doi:10.3390/w12020437
In addition to river floods, tropical storms and cyclones, also called hurricanes and typhoons, are expected to become more severe as a result of climate change. These depressions draw energy from the ocean surface, which is heating up due to global temperature increases. While the IPCC forecasts are less clear-cut in this area than for heavy rainfall estimates, ocean warming could not only give rise to more severe cyclones, it could also cause their paths to reach regions as yet untouched by these cataclysms.
We must therefore anticipate the occurrence of new humanitarian crises in the future like the one in 2019 caused by Tropical Cyclone Idai in Sofala province in Mozambique. On 15th March that year, maximum sustained winds of 205 km/h produced a storm surge of 4.4 metres that swept through the Port of Beira, destroying the city and flooding the surrounding areas up to twenty kilometres inland. The second blow came as the Bùzi et Pungwe, swelling with heavy rainfall from the cyclone, burst their banks on 17 March, further aggravating an already catastrophic situation. The official death toll rose to 602 in Mozambique and nearly 110,000 people were evacuated in the Búzi district alone.
“Although floods are frequent in this region, no plans had been made for a refugee response,” says Uacitissa Mandamule, who is studying issues related to the displacement and resettlement of these victims for her thesis in sociology co-supervised by Valérie Golaz, a demographer at Institut National des Études Démographiques (INED) and Stéphanie Duvail, a Geographer at UMR PALOC. Búzi district has therefore opened thirteen resettlement centres, hosting a total of 6,662 household, including 2,000 in Guara-Guara, a locality about fifteen kilometres upstream of the Bùzi river delta. “These refugees find themselves in a city devoid of economic activities and far from their primary source of livelihood, rice-growing in the floodplain,” the PhD student explains. This population displacement has also led to tension with the residents of Guara-Guara. “The local community was not consulted and have in turn been deprived of resources since the refugees have been resettled on land used for livestock and agriculture.”
During the interviews conducted for her thesis, with support from ITANGO-MOZ, the Young Team Associated with IRD (JEAI) on the governance of natural resources in Mozambique, Uacitissa Mandamule realised that these refugees did not intend to migrate definitively: “They are very attached to their land and have learned to live with the floods by using adaptation strategies.” New agricultural production areas for market gardening, for growing groundnuts and cassava, have been set up on higher ground. They also continue to grow rice in the plain, but with varieties more resistant to flooding. However, the future of these climate refugees remains highly uncertain. New floods, with more death tolls and displaced and resettled people, affected the Bùzi delta in February 2020, and again in 2021 with Cyclone Éloïse, and at the start of 2022 with Tropical Storm Ana.
Some floods are not sudden, violent and cataclysmic. Instead, they occur insidiously. This is the case with flooding from groundwater, which has affected Niamey in Niger. “The first signs of flooding appeared in Dar es Salam district in the mid-1990s,” says Halidou Alassane Hado, a Nigerian PhD student in Hydrogeology who is interested in the different types of floods affecting the capital of Niger. The phenomenon has been growing in recent years. “Today, four districts of the city are affected by this type of flooding year-round. Some houses have literally become waterfront properties,” Halidou Alassane Hado says. The excessive moisture weakens the houses and forces many residents to abandon their property. Some buildings have simply collapsed. Stagnant pools of water on flooded land also contribute to the transmission of diarrhoeal diseases and favour the development of vectors of parasitic diseases, such as malaria.
“Rising water table levels have also contaminated groundwater due to the interrelationship with surface water,” the young researcher explains. His thesis, supervised by Mahaman Moustapha Adamou, a Lecturer in Water and Environmental Engineering at Abdou Moumouni University in Niamey, with logistical and academic support from IRD, has revealed the extent of rising groundwater at different points throughout the city. “By comparing the data reported in the 1960s with measurements made today, we estimate that the water table has risen forty metres in the north-western part of the city.” This has been caused by “the increase in rainfall observed in the past twenty years and the geography of the basin, where clay areas near the surface prevent rainwater from infiltrating deeper in the ground.” The city’s rapid urbanisation and the resulting deforestation are also important factors to consider. “In 1954, Niamey covered only 2.5% of the Gounti Yéna basin, whereas it now covers 87%. During this same period, the vegetation cover dropped from 94 to 7%.” Despite the socioeconomic and health impacts of rising water table levels, local authorities have neglected this issue. “But if nothing is done, it is very likely that other neighbourhoods will be affected in turn,” says Halidou Alassane Hado. However, solutions do exist. “It is possible to drain the groundwater into the Niger River and install pumping stations to dry the pools. In the longer term, restoring Niamey’s green belt by planting hydrophilic tree species would allow some of the rainwater to be absorbed before it reaches the table.”
Much more than water scarcity
While water tables overflow in some areas, water supplies in other regions are running dry. Water withdrawals have more than doubled since 1960, according to the World Resources Institute (WRI). And some countries are withdrawing groundwater at a speed exceeding the rates of renewal for these resources. In 2019, a WRI report based on data from its portal Aqueduct estimated that a quarter of the world’s population lived in areas subject to extremely highwater stress. The most affected regions are North Africa and the area spanning from the Middle East to northwest India. Some specialists even refer to a “thirst diagonal” running from Morocco to China. But the overexploitation of groundwater resources also affects many countries in southern Europe, southern Africa, Chile, and the southern United States. “This invisible crisis has impacts on the entire water cycle and results in the slow drying of the environment, which threatens ecosystems,” says François Molle, a hydrogeographer at UMR G-EAU. Groundwater supports the streamflow of rivers and the sustainability of wetlands. “The overexploitation of groundwater resources also exacerbates challenges in ensuring equitable access to water,” the Water Governance expert explains. When the water supply in shallow aquifers is depleted, deeper holes must be drilled to pump water. This “pumping race” endangers the sustainability of irrigation for the most disadvantaged people, who cannot invest in deep wells. “Unfortunately, neither the countries nor users have succeeded in implementing rules to ensure the sustainability of this resource,” the specialist says. To cap it all, climate change is expected to increase the existing rainfall deficit in the regions most affected by these water shortages. The frequency and duration of droughts have increased 29% since 2000, compared to the previous two decades, according to the United Nations Office for Disaster Risk Reduction (UNDRR).
Bangkok under water
The combined effect of the overexploitation of ground water and climate change is also threatening the resilience of many coastal cities, particularly in South-East Asia. This is the case in Bangkok, a city that is gradually sinking, to the point of being threatened by rising sea levels. “This sinking phenomenon, called subsidence, is caused by the weight of soil and city buildings on sedimentary layers weakened by the massive groundwater extraction,” says Thanawat Bremard, a PhD student with UMR G-EAU and Chulalongkorn University in Bangkok. The Thai capital has developed on the geologically recent part of the Chao Phraya delta, where the sediment is not yet compact.”
Identified in the 1960s, the land subsidence affecting the city worsened in subsequent decades. Subsidence at an average rate of ten centimetres per year was measured in the 1970s and 1980s. “At that time, groundwater was exploited for household use as well as for the city’s economic development, sustained by water-intensive industries: the agri-food, textile and chemical sectors, and manufacturers of electronic components,” says the young researcher whose thesis, supervised by François Molle, deals with urban water governance in Bangkok. In order to limit land subsidence in the city, local authorities have responded with economic measures such as groundwater taxes and the banning of the use of groundwater in the most critical areas. The drinking water distribution system, supplied by Chao Phraya River, has also been expanded and become denser. Dykes and pumps have been set up to control the floods. New land use plans have also helped to relocate industries outside of the city. Today, land subsidence in Bangkok has stabilised at an approximate average rate of one centimetre per year. But Thanawat Bremard doubts this is enough to rule out the threat of floods: “illegal groundwater pumping continues to occur, and inspections are rarely conducted due to a lack of means. The subsidence is therefore continuing inexorably. Furthermore, IPCC’s 6th report estimates that the overall overage sea level in the Gulf of Thailand will rise 40 to 81 centimetres by 2100.” This is enough to raise the spectre of the major floods of 2011, which covered over one-fifth of the city.
A fragile coastline
The situation on the Earth’s surface is hardly more encouraging. In some areas, the over-exploitation of river water has become so intense that some rivers have become intermittent or no longer reach the sea. This is the case for Moulouya River, one of Morocco’s longest rivers, which, hindered by dams and drought, has not emptied into the Mediterranean Sea since the end of 2021. These dams also have an adverse effect on the coastline. “Coasts are in a balance between sediment inputs from rivers and the marine currents that shape the coastline. Yet this coastal balance was broken down by dams that prevent the inflow of river sediments to the coast,” says Gil Mahé, a hydrologist with UMR HSM based at Institut National des Sciences et Technologies de la Mer (INSTM) in Carthage, Tunisia. This hydraulic infrastructure retains coarser sediments in particular, such as sand, which forms the majority of the beaches. Deprived of this alluviumDeposit of sediment carried by rivers, the coasts inevitably become eroded the sea moves further inland.
This phenomenon is particularly prevalent on the coastline of Maghreb countries, which have built many dams in the last 50 years to meet the water needs of a growing urban population, as well as for agricultural irrigation and energy production. “Analysis of sediment cores taken downstream from dams in the Medjerda River shows that this river ceased to carry sand to the coastline of the Gulf of Tunis 40 years ago.” Similar findings were obtained from Moroccan rivers, such as Bou Regreg, which ends in Rabat, and from one of the Maghreb’s largest rivers, Wadi Cheliff, which flows from the Atlas mountains through western Algeria. In this case, a study conducted by the Young Team Associated with IRD from École Nationale Supérieure d’Hydraulique de Blida (JEAI JEENS) showed that dams had intercepted approximately 71% of the total volume of sediment discharged by Wadi Cheliff between 1968 and 2010.
In addition to the increased risk of coastal flooding linked to sea level rise, coastal retreat can lead to significant consequences for coastlines. “In the Gulf of Tunis, for example, coastline retreat in certain areas is as high as twenty metres per year,” says Gil Mahé. The waves have already eroded infrastructures such as the coastal roads, housing and dykes as they continue to gain ground. Sandy beaches may even disappear from the southern coast of the Mediterranean. This is a disaster for the Maghreb countries that derive a significant portion of their income from seaside tourism. The dams’ retention of alluvium also affects marine ecosystems and has an indirect impact on local fishermen, with catches becoming smaller and poorer in quality.
A salty note
Both on the surface and in water tables, the overexploitation of blue gold can lead to soil salinisation, especially in coastal areas. For example, when a river’s streamflow is insufficient, sea water may enter its mouth. The salt front, the boundary between continental freshwater and marine salt water, is gradually moving inland, contaminating soil by diffusion and rendering it unsuitable for agriculture. In addition, the overexploitation of coastal aquifers can lead to an increase in groundwater salinity. “Near the coasts, the fresh water contained in the sedimentary deposits rises above the denser, saline water,” says geochemist Jean-Denis Taupin of UMR HSM, Head of the Joint Laboratory on Stable Water Isotope Analysis (LAMA) in Montpellier. “But massive pumping of freshwater disrupts that balance and can lead to a seawater intrusion in aquifers, which affects the water’s chemical quality and thus its potability.” These phenomena are exacerbated by the rising sea level and are now in danger of undermining the sustainability of certain coastal areas, such as the Bengal Delta.
Irrigation can also contribute to salinisation process, as confirmed by several hydrogeological studies of small watersheds in the Bizerte region in northern Tunisia. “Their groundwater located near the coast can have mineral salt concentrations up to ten times higher than the level recommended by the World Health Organization (WHO). Seawater intrusion was of course the suspected cause of this extremely high salinity,” says Jean-Denis Taupin, who has been studying aquifers in the southern Mediterranean coast for several years. “Yet the precise measurements of coastal aquifer levels ruled out this hypothesis.” What was the source of this salinity threatening the sustainability of agriculture in the region? Extensive chemical analysis finally revealed the agricultural origin of this excessive water mineralisation. “The groundwater in this region is already significantly mineralised due to the local geological conditions. When this water is used for irrigation, part of it is absorbed by plants, while the other part evaporates, leaving the salts behind, either in the soil or in excess water not absorbed by the plants, which returns to the aquifer,” the researcher explains. “This reintegration of irrigation water with a higher salt content over the course of decades lead to greater salinisation of the aquifer.” For these drainage basins, another factor was intensifying this mineralisation: “in the alluvial plains located near the coasts, groundwater levels are so close to the surface that a fraction of the water evaporates naturally, which automatically increases the mineral concentration.” These phenomena could ultimately threaten global food security: approximately 1.5 millions hectares of agricultural land are abandoned each year due to soil salinisation according to the Food and Agriculture Organization of the United Nations (FAO).
A contaminated resource
Water, which is so vital to our existence, is never truly pure. It generally contains many chemical elements, the first of which are mineral salts. “Groundwater salinisation occurs naturally in 95% of cases,” says Jean-Denis Taupin. “The effects of water and carbon dioxide cause the mineral salts contained in the soil to become soluble and are transported to the groundwater. The coastal aquifers in the Maghreb, for example, have a naturally high salt content due to the evaporites present in the superficial geological formations.” In reasonable quantities, most mineral salts do not have a major effect on water quality and potability. Some are even essential to our health. However, certain elements that are relatively common in groundwater can cause health problems. Fluorine, for example, which supports dental health, becomes toxic at high concentrations. “A long-term, low-dose exposure can also lead to skeletal fluorosis, which weakens the bones,” says Jacques Gardon, a physician-epidemiologist at UMR HSM. The regions most affected by this risk are the Middle East, Asia, and Africa, where certain geological basins contain fluorine salts.
Arsenic is another chemical element that naturally exists in high concentrations in some groundwater, such as in Bangladesh, China, India, South America, the United States, Mexico, as well as in France, for example in Lorraine. “Over one hundred million people are affected by arsenic exposure,” the researcher says. He devotes part of his research to studying the health impacts of this metalloidChemical element which has both metallic and non-metallic properties . While some populations seem to have somewhat adapted to this exposure, the health risks associated with the regular consumption of water containing arsenic are well known. “The first signs of exposure are skin lesions that appear on the palms of the hands and the soles of the feet. This exposure can eventually lead to the development of cancer, such as skin cancer in particular, and it also introduces an increased risk of cardiovascular disease and diabetes. Arsenic also affects cognitive development and immunity in infants and children,” the physician explains.
Jacques Gardon has especially observed these clinical signs in the greenstone belt in West Africa, particularly in northern Burkina Faso and Ivory Coast. “The development of artisanal gold mining attracts people seeking new sources of income. In order to meet their increasing need for water, they dig deep wells, without knowing if the water is of good quality.” This geological formation contains many metal sulphides, like arsenopyrite, which releases arsenic into the groundwater and soil when it deteriorates. “In some wells, we recorded concentrations of 1 milligram per litre, which is 100 times higher than the maximum dose recommended by WHO,” the physician says. “This is a true health disaster for these communities who have no awareness of the risks.” Water containing arsenic is clear and has no particular taste or odour. In Burkina Faso alone, 500,000 people are exposed to this naturally contaminated water. Jacques Gardon and his colleagues have been working to expose the danger of this groundwater to the populations concerned, while also identifying the least contaminated wells in order to limit exposure to this invisible poison. “Unfortunately, the current security situation in northern Burkina Faso has prevented us from continuing our research.”
The arsenic risk of artisanal gold mining
The impact of human activities
Humans and human activities are clearly to blame for jeopardising water quality at unprecedented rates. According to the United Nations, over 80% of the world’s wastewater is released into the environment without treatment. This percentage is even as high as 95% in countries without wastewater treatment facilities. The mining sector’s contribution is particularly high. Not only is it water-intensive due to ore processing activities, mines also produce significant quantities of waste that threaten valuable water resources, sometimes for thousands of years to come. Tailings from the mines contain numerous sulphur compounds that produce sulphuric acid when exposed to water and air. “Mine drainage water is very acidic and rich in toxic metal elements. Although it is not consumed by people, it has an enormous environmental impact, especially on aquatic ecosystems, and can contaminate groundwater through surface water pollution,” says Jacques Gardon. Through his project entitled ToxBol, he has studied the impact of polymetallic pollution in Oruro, a mining town in the Bolivian Altiplano. Mercury is another cause for concern. This toxic metal used by gold miners to form an amalgam with gold particles is a significant source of pollution for the atmosphere and rivers, as demonstrated by a study conducted by IRD in the Oyapock River basin in French Guiana.
The entire food chain is then contaminated, putting the health of local communities at risk. “Mercury has significant toxic effects on the nervous systems of exposed miners. And in utero exposure can greatly alter brain development in children,” the physician explains. In addition to mining, other industrial activities, like the petrochemical and textile sectors, also cause groundwater contamination. Not to forget agriculture, another contributor. Pesticide residues and fertilizer, including nitrates and phosphates, find their way into the groundwater. Microplastics are also abundant in rivers, as confirmed by research led by IRD on the Saigon River, and seeps into the aquifers. Domestic wastewater, on the other hand, is a source of what is referred to as emerging contaminants, such as medication, which evade current treatment systems. An international study involving IRD revealed that traces of anti-inflammatory and antiepileptic medication had been found in the surface and underground waters of the Méfou drainage basin, which supplies water to Yaoundé, the capital of Cameroon.
Domestic wastewater can also cause microbiological contamination when untreated. Two billion people use water sources contaminated with faecal matter according to WHO. Yet the contamination of water resources by pathogens is linked to the transmission of numerous diseases, such as diarrhoea, dysentery, cholera, typhoid fever and polio. Also according to WHO, access to safe drinking water and sanitation could prevent over 400,000 deaths each year from diarrhoeal diseases, including nearly 300,000 children under the age of five. But there is still a long way to go. 3.6 billion people did not have home sanitation systems in 2020, according to the United Nations. Some 2.3 billion did not even have basic hand-washing facilities. Worse still, 494 million people continue to defecate outdoors, primarily in sub-Saharan Africa and South-East Asia. Managing sanitation therefore represents an important challenge, especially in the urban centres of developing countries that cannot afford to expand their sanitation networks to cope with a rapidly growing population.
This is the case in Dakar, for example, the capital of Senegal, where the population has more than doubled since the 1990s. “Since the great drought of the 1970s, rural-to-urban migration has contributed to the densification of urban centres, as in Dakar, where people have settled in peripheral areas, without any overall planning or sanitation networks,” says Fatimatou Sall, a geographer and president of the Association of Young Water and Sanitation Professionals in Senegal (AJPEAS). The majority of wastewater is discharged directly into the streets and public spaces before reaching natural environments. On-site sanitation systems have been built in some homes, but the sludge emptying services for these septic tanks are poorly managed. “Due to a lack of wastewater treatment facilities, many manual septic tank cleaners dispose of the sludge through unauthorised dumping or by burying it in wetlands,” the geographer explains. This leads to contaminated of water resources. “The Société Nationale des Eaux du Sénégal (SONES) had to end drilling in the water table in Thiaroye due to this microbiological pollution,” reports Fatimatou Sall, who is coordinating a project to aimed at recovering waste sludge in the Niayes area of Senegal. With technical support from Senegal’s National Sanitation Office (ONAS) and Delvic, a Senegalese company specialised in treating and recovering waste sludge, and financial support from the Public Sanitation Service for Ile-de-France (SIAAP) and the French Water Partnership (FWP), this project led by AJPEAS is working to assess the current management of sludge and wastewater in the Niayes area and analyse their environmental and socioeconomic impacts. This long stretch of coastline from Dakar to Saint Louis is home to abundant fauna and flora. The wetland is also used for market gardening, which has earned it the nickname of Senegal’s “vegetable basket”. Eventually, this project hopes to enhance this fragile ecosystem through nature-based solutions, which are actions aimed at protecting ecosystems in a sustainable manner in order to meet societal challenges, while ensuring human well-being and producing benefits for biodiversity, according to the International Union for the Conservation of Nature (IUCN).
Towards more sustainable water management
Water management efforts face numerous challenges, including population growth, urbanisation, land use change, climate change, and the overexploitation and pollution of resources. Some these challenges can be addressed with nature-based solutions.
For example, “soil and plants can mineralise the organic matter contained in domestic wastewater, just as river banks do naturally,” says Didier Orange, an ecohydrologist at UMR Eco&Sols. The SmartCleanGarden concept is based on this well-known principle of phyto-purification. “Plant bed filter systems offer an ecological, robust and inexpensive solution that eliminate 99.99% of pathogens.” This simply constructed treatment system is formed by a gravel bed that is drained and isolated from the soil in which the plants are planted. Raw wastewater is introduced and distributed at a set rate. Ultraviolet (UV) rays from the sun eliminates pathogens. The water then filters through the gravel, where the organic matter is mineralised before being absorbed by the plants. After bringing the first proofs of concept to Hanoi with support from the Vietnam Academy of Science and Technology (VAST), the SmartCleanGarden consortium partnersare now seeking to improve the effectiveness of these plant bed filter systems, in particular with the O’biom project (French acronym for Optimisation of Plant Bed Filter Systems with Enhanced Biodiversity: Effect on Organic Matter) on the characterisation of the role of biodiversity in the mineralisation of organic matter. “As in natural environments, increased biodiversity improves the effectiveness of the bioremediation and phytopurification offered by plant bed filter systems. Macrofauna, specifically earthworms, and the diversification of the plants used could therefore facilitate the biodegradation of the organic matter in wastewater,” says Didier Orange, the coordinator of this project supported by Labex Centre Méditerranéen de l’Environnement et de la Biodiversité (CeMEB).
Plant bed filter systems is a technical solution that is already operational in urban centres where sanitation networks, and resources, are limited. But the SmartCleanGarden Concept goes beyond the treatment of domestic wastewater. It introduces a paradigm shift: “wastewater should no longer be seen as waste, but as an asset. Not only is it useful, it is also economically profitable and contributes to the ecological transition,” explains Didier Orange. This is also the message that the United Nations sought to convey in 2017 in its annual World Water Development Report. It emphasised the potential of improved wastewater management to generate social, environmental and economic benefits that are essential to sustainable development. “The SmartCleanGarden is a new world solution for locally sanitising wastewater and reusing it on-site to regreen and beautify cities, and even irrigate market gardens in urban and peri-urban areas.” In Dakar, for example, Ecolibri, a socio-environmental NGO, commissioned a Senegalese company, FiltrePlante, to build a plant bed filter system to treat about 10 m3 of wastewater per day. The recovered water is then used to irrigate trees and a market garden.
Saving agricultural water
Irrigation is one of the most water-intensive industries. Irrigated crops are responsible for the majority of agricultural water use, accounting for 70% of global water withdrawals. In arid and semi-arid environments, irrigation is essential to cope with the vagaries of precipitation. By improving land productivity in comparison to rainfed agriculture, it helps provide better pay for farmers. Irrigation is also a key component of global food security: only 20% of cultivated land is irrigated, yet it produces about 40% of agricultural commodities. Globally, and particularly in the Southern Hemisphere, surface irrigation is the predominant system. It generally relies on gravity-flow systems that transport the water to the crops. “These irrigation techniques go hand in hand with a global artificialisation of the environment caused by the construction of dams and canals,” says Jean-Philippe Venot, a geographer at UMR G-EAU. While these infrastructures are clearly necessary, they are also costly and require regular maintenance. In addition, surface irrigation withdraws more water than crops need. To save water, donors and NGOs in particular are calling for the use of other irrigation techniques, such as drip systems. “This micro-irrigation technique can improve the efficiency of the water used per plot as compared to gravity-flow systems and can also limit soil salinisation. However, paradoxically, drip irrigation will likely increase water consumption by making it possible to farm land that could not be cultivated without this technology,” the geographer says. Moreover, “micro-irrigation does not necessarily suit the needs of small farms, particularly those in sub-Saharan Africa, and often goes hand in hand with the promotion of an entrepreneurial agricultural model, which raises equity issues.” The cost of these irrigation systems contributes to a concentration of land among large-scale farmers, thus marginalising small farmers.
These findings have resulted in efforts to rethink irrigation. To assist this reflection, the Agricultural Water Scientific and Technical Committee (COSTEA) was created in 2013 with funding from AFD. “This network for exchange and expertise seeks to enhance knowledge on irrigation in order to make it available to the various stakeholders and decision makers in the countries where AFD operates,” says Jean-Philippe Venot, who is a member of COSTEA’s scientific and technical council. “The goal is to develop more participatory, sustainable and equitable water management practices.” Projects are currently underway in West Africa, the Maghreb, South America and South-East Asia.
For example, in the floodplains of Cambodia, “AFD aims to rehabilitate and build water control infrastructures on ‘preksIrrigation and land drainage canals in the upper Mekong Delta of Cambodia dating back to the colonial period and used for irrigation as well as for fishing, transport, sedimentation, and spate irrigation.’ in Kandal province in the Mekong Delta,” explains the geographer. “However, their impacts on this ecosystem have not been fully assessed.” In addition to agricultural irrigation, these flood zones are also used by fishermen and are home to unique biodiversity. COSTEA’s mission is to characterise the agricultural systems and hydrological networks, while also bringing the various stakeholders together to consider less artificial alternatives than the construction or rehabilitation of water control infrastructures. “The goal is to make environmental and social issues a central focus of these initiatives.”
Is a new water governance possible?
At a global level, water governance efforts face the same obstacles. “Social equity and environmental sustainability issues are far too often neglected in favour of growth and economic development,” says hydrogeographer François Molle. This observation, already highlighted in the 1990s, gave rise to the Integrated Water Resources Management (IWRM) concept. IWRM, which was officially approved at the Rio Earth Summit in 1992, and has since been promoted by donors and NGOs, is based on the idea that water is an integral part of the ecosystem, a natural resource as well as a social and economic good. The integration of all these aspects – environmental, social, economic, and geographical – is therefore necessary in achieving “good” water management. “On paper, everyone agrees with these principles, yet they are often contradictory,” says François Molle. “They are therefore often difficult to implement in the real world, especially in the Global South.” New water laws and watershed management agencies have been established around the world. Yet without the political will, a clear legislative framework and available means, these measures often have little impact on water management practices. “Decisions continue to be based largely on political and/or financial interests.” Only transparent and more horizontal governance, with the participation of all those benefiting from the systems, will succeed in addressing the issues involved in water management.
The water crisis facing humanity appears far from being resolved. Still, researchers are continuing their efforts, in particular by analysing power imbalances in water governance in order to someday offer recommendations. Their mission of sharing knowledge is also paramount, not only among decision makers, but for all those involved, including the youngest citizens (see Box). This is equally true in the academic world, which must continue to strengthen networks of researchers, like those established by the UNESCO FRIEND-Water programme (Flow Regimes from International Experimental and Network Data). “FRIEND allows scientists and water stakeholders from eight major regions of the world (Europe, Asia-Pacific, South America and the Caribbean, the Mediterranean rim, West and Central Africa, the Congo Basin, the Nile Valley and Southern Africa) to receive training and share data and techniques in order to enhance knowledge of water resources,” says Gil Mahé, the current programme representative. “The various regional coordinators also organise events on hydrology, which have been very successful, including for African researchers who, due to economic and visa issues, have little or no access to major international conferences.”
“Phil’eau” workshops: promoting the value of water among young people
The educational “Phil'eau” concept aims to involve the younger generations in water issues by “seeing the world through water”. “This idea of having young people reflect on water issues originated three years ago through collaborative work with Audrey Perez-Fouet, an educator at École Montessori des Leins in Montagnac, in the south of France,” says Jeanne Riaux, an anthropologist at UMR G-EAU. “Together, we created three modules that address water in motion in a way that promotes openness and tolerance, reflecting on the issues related to sharing this resource before focusing on the role water plays in our imaginations.” Currently based in Saint-Louis, Senegal, the anthropologist has offered a series of workshops at several Senegalese schools, with support from the representation of IRD in Dakar, the Network of Scientific Clubs of Senegal (RC2S) and the Institut Français of Saint-Louis and of Dakar. The “Phil'eau” adventure will soon continue in Mauritania and beyond! A teaching kit is currently being prepared in order to provide turnkey materials for teachers who wish to cover this topic with their students.
Research must also address its own weaknesses. “Dialogue between the social sciences and environmental sciences is often non-existent,” says Jeanne Riaux, an anthropologist at UMR G-EAU based in Senegal. In order to re-establish dialogue between disciplines, the researcher introduced the Southern Interdisciplinarities Structural Training Project (PSF) in Senegal and Mauritania. “Through seminars, workshops and times of collective reflection, researchers from all disciplines are questioning their commitments and the means needed to achieve them. By looking at their work in a different light, they begin to ask new and relevant research questions, which are often interdisciplinary in nature.” But the anthropologist would like to go further. “We must move past the borders of the academic world and into society. The dichotomy between local knowledge and scientific knowledge is irrelevant. We all have a certain degree of knowledge about water. Moreover, scientists in general, and hydrologists in particular, produce large amounts of knowledge, yet it is not easy for the various water stakeholders to use. To make this research operational through decision-support tools, hydrologists must become more reflective and engage in discussions with their many non-academic partners.” This is the purpose of the research coordinated by Jeanne Riaux for the Water Cycle and Climate Change (CCEF) project. “This reflective support, first with researchers and later with their civil society partners, aims to help researchers from the CECC project to enable interactions with the non-academic world to shape their research.” This will help to implement sustainability science that better serves decision-makers and communities.