Nitrogen pollution to triple scarcity in river sub-basins worldwide

Water scarcity is exacerbated by declining water quality in numerous regions, and the situation is expected to worsen in the years to come, a new report underlined. 

A significant factor contributing to this crisis is nitrogen pollution in rivers, a concern that emerged in 2010 and is anticipated to persist until 2050, the findings showed. The global impact of future nitrogen pollution is alarming, with the number of sub-basins experiencing water scarcity expected to triple.

A recent study, published on February 6, 2024 in Nature Communications highlighted that an additional 40 million square kilometres of river basin area and three billion more people may face water scarcity in 2050 than previously estimated. 

The study introduces the term “clean-water scarcity” and provides a comprehensive assessment considering both water quantity and quality. This assessment, based on global nitrogen pollution and incorporating various climatic and socio-economic scenarios, reveals a more dire situation than previous evaluations.

Comparing the clean-water scarcity assessment to the traditional water scarcity assessment based solely on quantity, the number of sub-basins facing severe scarcity doubled in 2010 and is projected to potentially triple by 2050. Water pollution, particularly nitrogen pollution, played a significant role in aggravating water scarcity in 2,000 sub-basins worldwide.

In 2010, 984 sub-basins were deemed water scarce based on quantity alone, while 2,517 sub-basins faced scarcity due to both quantity and quality. This number is anticipated to increase to 3,061 sub-basins in the worst-case scenario in 2050, as outlined in the study. This alarming projection indicates a more than doubling of the global area and population affected by severe water scarcity.

When considering only water quantity, the study estimated that 45 per cent of the global population lived in areas with severe water scarcity in 2010. However, when water quality is factored in, this estimate rose to 80 per cent. 

Future clean-water scarcity hotspots were identified in China, India, Europe, North America, and potentially Central Africa in the worst-case scenario, each with unique challenges requiring targeted solutions.

Nitrogen losses in rivers can stem from various sources, including human waste, agricultural practices and fertiliser applications. In the worst-case scenario, sewage is projected to become the dominant source of nitrogen pollution in rivers due to rapid urbanisation and inadequate wastewater treatment infrastructure.

India, for instance, experiences nitrogen pollution primarily from agriculture in the first two climate scenarios, but sewage is projected to surpass agriculture as the main source in the worst-case scenario.

A similar trend was observed for Africa, where both agriculture and sewage contribute to nitrogen pollution, but sewage was projected to be the main source in the worst-case scenario.

The study underscored the urgency of addressing water quality in future water management policies to align with Sustainable Development Goals. 

In India, the State of India’s Environment Report 2023 indicated a concerning deviation from the Sustainable Development Goals (SDG), particularly SDG 6 (clean water and sanitation) in 15 states.

The impact of Shared Socioeconomic Pathways — climate change scenarios projecting global socioeconomic changes up to 2100 — further emphasises the need for proactive measures. 

A previous analysis by the Centre for Science and Environment and Down To Earth magazine in 2016 revealed unsafe disposal practices of excreta in Indian cities, with 78 per cent of sewage remaining untreated.

Mitigation strategies addressing water pollution require increased attention, as low water quality emerges as a critical or even dominant factor contributing to water scarcity in many river basins. Controlling nitrogen pollution is identified as a challenging yet imperative aspect of these strategies.