Satellites reveal hotspots of change in the extent of global rivers

Rivers are one of the most dynamic components of the water cycle on Earth and play an important role in the development of human societies, ecosystem sustainability, and regional climate. However, its natural balance is threatened by human disturbances and constant climate change, as evidenced by changes in the extent of the rivers over recent decades.

In order to better understand behind these changes, researchers led by Professor Song Chunqiao of the Nanjing Institute of Geography and Lake Sciences of the Chinese Academy of Sciences and their collaborators from China and the United States analyzed variations in water extent using four decades. The value of Landsat images in order to attribute recent changes in river systems globally to morphological dynamics or hydrological signals.

The study has been published in Nature Communications On March 22nd.

To estimate and interpret multi-decadal changes in river extent at large spatial scales, researchers used information from two major recent surface water databases: the Surface Water and Ocean River Database (SWORD) and the Global Surface Water Database. (GSW) database.

They compiled a new reservoir inventory to determine the arrival of a new reservoir type river (Type-R). The remaining riverine changes at the basin level were classified into two types—morphological dynamics (type-M) and hydrological signals (type-H)—using a machine learning classification approach.

“We provide the first-ever attribution of different types of river extension changes on a global scale,” said Professor Song.

The results showed that changes based on morphological dynamics prevailed in about 20% of the global river area. In this type of river basin, high rates of narrowing and widening are observed along different banks of the river’s tributaries, which are associated with meandering, braided, branching or roving river channels – all variations of flow regimes.

Globally, dam construction has emerged as a major contributor to river widening. “The new dams, most of which are oblique in Asia and South America, have contributed 32% of the river’s widening,” said Professor Qi Linghong, lead author of the study.

Changes attributed to hydrological signals were detected in contrasting hotspots, including regions characterized by prominent river widening in alpine and arctic regions and narrowing of arid or semi-arid interiors. “These phenomena were driven by different trends in climate forcing, cryosphere response to warming, and human water management,” said Wu Qianhan, a NIGLAS student and another lead author of the study.

The study provides global-scale but spatially-accurate guidance for prioritizing future river protection and restoration efforts under the United Nations 2030 Agenda for Sustainable Development, which calls for international action to track the spatial extent and condition of water-related ecosystems.