Researchers have launched a health check of India’s water ecosystems from space. A new study shows that nearly 100 of the country’s largest wetlands are seeing a significant decline in vital aquatic plants. Using high-resolution satellite data and computer modelling, a research team from the Space Applications Centre-ISRO, Gujarat University, the Indian Institute of Remote Sensing, and the Indian Institute of Space Science and Technology has developed a new way to track the pulse of 500 major wetlands across the nation. The study warns that changing rainfall and rising temperatures are directly altering the growth of underwater and floating vegetation, which could have serious consequences for biodiversity and water quality.
Wetlands are often called the ‘kidneys of the landscape’ because they filter pollutants, prevent floods, and provide homes for countless species. However, monitoring them on the ground is notoriously difficult because they are often vast and hard to access. To solve this, the researchers turned to the European Space Agency’s Sentinel-2 satellites. These eyes in the sky capture multispectral data, measuring light at multiple wavelengths. Because different types of plants reflect light in unique ways, called a spectral signature, the team could distinguish between plants that grow entirely underwater, those that float on the surface, and emergent plants like reeds that poke out of the water.
The team built a classification tree model, a digital flowchart that classifies pixels by asking a series of Yes or No questions about the light reflected from a single pixel of the satellite image. For example, if a pixel shows a high level of moisture but very little green light, the model identifies it as open water. If the light signature shows the specific pattern of a vertical leaf structure, it categorises it as emergent vegetation. This method proved incredibly accurate, correctly identifying submerged plants 94% of the time. By processing years of these images in Google Earth Engine, the team observed how these plants grew and shrank across different seasons and years.
The most alarming discovery was a widespread shrinking of plant life. Of the 500 wetlands studied, significant declines were found in 88 wetlands for submerged plants (those underwater), 78 for floating plants, and 86 for emergent plants (reeds and grasses). This indicates that many of India’s most important water bodies are under severe environmental stress.
They also discovered that rainfall is the biggest driver of wetland health. In many areas, a delayed monsoon means delayed green-up of the water, which measures the amount of vegetation growing in the water. In central and southern India, the decline in submerged vegetation was particularly concerning, likely linked to human activities such as drawing too much water for farming or pollution, which made the water too cloudy for sunlight to reach the bottom. The research also showed that different plants have different preferred seasons. Most submerged plants reached their peak during the pre-monsoon (drier) months when the water was clearer and shallower. In contrast, floating and reed-like plants became most dominant during the post-monsoon period, after the rains had filled the basins and brought in new nutrients.
The new approach developed in the study provides a view of the sequence of events rather than single snapshots, showing how wetlands from the cold Himalayas to the tropical Western Ghats are changing simultaneously. Knowing exactly which wetlands are shrinking in real time, the government and local communities can take targeted action to save them. Protecting these plants is about ensuring clean water, protecting homes from flooding, safeguarding biodivrersity and maintaining the delicate balance of our environment amid rapid climate change.
