Rivers as an underestimated source of greenhouse gases
Rivers around the world are under severe stress: they are warming, losing oxygen, and consequently emitting increasing amounts of greenhouse gases. Dr. Ricky Mwangada Mwanake, Dr. Elizabeth Gachibu Wangari and Dr. Ralf Kiese have now quantified these global trends over a period of two decades. Their findings show that rising temperatures and changes in human land use are fundamentally altering river systems—with serious consequences for the climate.
Rivers are habitats, sources of water, and shape entire cultural regions. The local consequences are correspondingly negative when agriculture and industry burden river systems. “Rivers also have a significant influence on the global climate system,” says Dr. Ralf Kiese of the Institute for Meteorology and Climate Research – Atmospheric Environmental Research (IMKIFU), the Alpine Campus of KIT in Garmisch-Partenkirchen. “We are increasingly observing that rivers are becoming a significant source of greenhouse gases.” The primary cause is microbial biogeochemical processes: When organic carbon and nutrients from agriculture or wastewater enter rivers, they are converted there into carbon dioxide, nitrous oxide, and methane—greenhouse gases that then exert their effects in the atmosphere.
Machine learning fills in missing data
To quantify these developments on a global scale for the first time, the researchers combined measurement data with satellite observations and machine learning methods. Their analysis was based on water parameter data from over 1,000 river sites. They linked this data with globally available satellite information on vegetation, radiation, and topography. The models learned how these environmental factors affect water temperature, oxygen content, and the accumulation of greenhouse gas concentrations. The researchers then applied these relationships to more than 5,000 additional watersheds worldwide, thereby reconstructing consistent time series from 2002 to 2022 for the first time—including for regions without measurement data.
The analyses reveal clear global trends: rivers are warming, losing oxygen, and becoming increasingly saturated with greenhouse gases. “On average, the oxygen content is decreasing by 0.058 milligrams per liter per decade—significantly faster than in lakes and oceans. At the same time, emissions of carbon dioxide, methane, and nitrous oxide are rising,” says Dr. Ricky Mwanake of IMKIFU, who played a key role in conducting the calculations. “Overall, we estimate the additional anthropogenic emissions from rivers to be approximately 1.5 billion tons of CO₂ equivalent during the study period from 2002 to 2022. These additional emissions had not been accounted for in current global greenhouse gas budgets.”
Climate change and land use are driving up emissions
Particularly rapid changes are occurring in regions experiencing increased agricultural use and urbanization. There, rising water temperatures are compounded by increased inputs of nutrients and organic carbon. Accelerated microbial processes create hotspots where these pressures reinforce each other and greenhouse gases accumulate in the water. As a result, rivers can become particularly significant sources of greenhouse gas emissions. “If we succeed in reducing these nutrient inputs and better protecting rivers, this effect can be reversed,” says Mwanake. “Thus, protecting rivers is always also active climate protection.”
Original publication
Ricky Mwangada Mwanake, Elizabeth Gachibu Wangari, Ralf Kiese: Rising Global Riverine Deoxygenation Rates and GHG Emissions Driven by the Synergistic Effects of Warming and Anthropogenic Land Use Expansion, Global Change Biology, 2026 DOI: 10.1111/gcb.70828