Around the world, more and more people are living near streams and rivers. However, until now, no one has made a detailed, global analysis of human settlement near flowing water over time. Ceola et al. propose a new way to do just that, using nighttime satellite photos of artificial light sources.
People who live near flowing water alter the environment through water use and pollution. In turn, streams affect nearby residents. For example, researchers have linked increased population density near water to increased flood risk and overuse of water resources. These effects aren’t just local—the cumulative impact of local activities like irrigation contributes to global water stress. Analyzing local human distribution near streams and rivers worldwide is critical to improving scientific understanding of the global human impact on water resources. Nighttime satellite imagery could be the key.
The researchers looked at satellite imagery collected by the U.S. Air Force Weather Agency under the Defense Meteorological Satellite Program. Artificial light sources that show up in these photos reveal human settlements and economic activity. The scientists analyzed the photos alongside high-resolution U.S. Geological Survey maps, focusing on data from 1992 through 2013. They calculated human distribution near rivers in 175 study regions of varying sizes.
The team found that during the study period, human presence near rivers increased globally. However, trends in population density at different distances from flowing water varied between study regions. The data also showed how social conflicts and economic crises affected populations near rivers in Syria, Afghanistan, Moldova, and Ukraine.
The results support the use of night lights to analyze population distribution along rivers over time—at the global scale, as well as among continents and countries. This project is the first in what could become a rich new area of study, using nighttime lights to help monitor global human impact on water. It builds on the group’s previous research, which used nocturnal satellite photos to show that floods cause greater economic damage in brighter areas.
Nighttime satellite imagery is just one of a new generation of fine-scale data sets (like Landsat) that could give new perspectives on global water resources management. The authors call for a new approach to water science that fully realizes the potential of these novel data sets. (Water Resources Research, doi:10.1002/2015WR017482, 2015)
—Sarah Stanley, Freelance Writer
Citation: Stanley, S., (2015), Night lights illuminate human presence near rivers, Eos, 96, doi:10.1029/2015EO037619. Published on 20 October 2015.