The disappearance of natural floodplains is happening rapidly.

When rivers exceed their boundaries, they release fresh water, nutrients, and debris into nearby low-lying areas. These fertile floodplains are appealing for farming and construction, but when humans expand into these regions, the likelihood of floods and harm to wetland ecosystems increases. A recent study published in Scientific Data revealed that 600,000 square kilometers of floodplains have disappeared in the past 27 years.

Raghu Murtugudde, an Earth systems scientist at the Indian Institute of Technology Bombay and the University of Maryland, explained that as progress and expansion take place, both deliberate and accidental encroachments onto floodplains occur. He was not a part of the research team.

A group of researchers created a new worldwide data collection of changes in floodplain development from 1992 to 2019 in order to determine the amount of lost area. This data collection used various sources, such as a map from NASA’s Shuttle Radar Topography Mission, land use maps from the European Space Agency, and maps of major river basin boundaries. The data, which had a 250 meter resolution, provided insight into the specific changes made to each floodplain.

The scientists discovered that individuals have transformed 460,000 square kilometers of floodplain into farmland and expanded by 140,000 square kilometers. This is equivalent to an area bigger than Madagascar.

Adnan Rajib, the lead author of the study and a civil engineer at the University of Texas at Arlington, likened the impact to losing an entire nation.

According to Ellen Wohl, a fluvial geomorphologist from Colorado State University who was not involved in the study, floodplains have traditionally been utilized for human habitation and agriculture. However, these activities can have negative impacts on the floodplain’s ability to offer other important services, such as clean water and flood management.

Previous research had observed an increase in both population and infrastructure development in flood-prone areas globally. However, the extent of this growth compared to non-floodplain regions was unknown. According to Rajib, the latest study revealed that floodplains were 1.75 times more impacted than non-floodplain areas. This data emphasizes the importance of distinguishing floodplains from other landscapes in policy-making, according to his opinion.

Murtugudde stated that the study provides a comprehensive overview of the decline of floodplains, making it valuable for adjusting and managing land use. He also expressed that the extensive scope of the study strengthens the reliability of the results.

Asia experienced the greatest loss of floodplain area. According to Rajib, many Asian nations lack well-established policies and initiatives for protecting floodplains. He also noted that the high population and resulting need for resources such as food, housing, and employment contribute to unplanned development in flood-prone areas. For instance, the recent floods in Delhi, India, which were the most severe in 40 years, were caused by excessive encroachment on floodplains.

Rajib stated that one-third of floodplain wetland losses took place in North America, while Europe accounted for nearly 60% of the urbanization in floodplains worldwide. Wohl emphasized the significance of this study in highlighting the widespread occurrence of floodplain losses globally and providing specific information for different regions.

Mapping Loss

The researchers examined the main changes in six major basins and discovered that there were differences in land use. For instance, in the Great Lakes Basin in North America, urbanization led to the conversion of forested floodplains, while in the Nile Basin, grasslands were transformed into agricultural land. In the Danube River Basin in Europe and the Yangtze River Basin in Asia, there was an increase in agricultural development.

According to Wohl, various types of land use offer distinct habitats and ecosystem benefits, making it crucial to have this information. Alterations in land use can also impact the consequences of floods and the capacity for storing carbon in floodplains.

According to Rajib, individuals involved in United Nations Sustainable Development Goals and policymakers can utilize this data to observe the specific locations and methods of change and use it to inform policy choices. They can determine the causes of change, such as the conversion of agricultural land into urban areas or the transformation of forests into agricultural land. The team of researchers has created and shared tools for other researchers and stakeholders to investigate and examine individual basins. The data can aid in developing policies to prevent or reverse changes to floodplains and investing in restoration efforts to decrease the potential harm to people, their means of living, and the natural surroundings.

Wohl stated that the results of the study underscored and supported previous research. He suggests that the rapid decline of natural floodplains in certain areas should serve as a motivation to preserve and revitalize these floodplain ecosystems.

Deepa Padmanaban is a science writer.

According to Padmanaban (2023), there has been a rapid disappearance of natural floodplains. This information was published in Eos on 18 September 2023, and can be accessed at https://doi.org/10.1029/2023EO230353.

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