Amid the tropical Andes of Peru lies the Cordillera Blanca mountains, home to more tropical glaciers than anywhere else on Earth. This range provides water to some 95 million people. Rising temperatures over the last several decades, however, mean its once abundant glaciers are vanishing rapidly. That’s impacting the water supply of downstream communities, which are becoming increasingly dependent on soil moisture.
In an innovative study published in the journal Remote Sensing of Environment, researchers used drones to obtain high-resolution images of the valleys left behind as Cordillera Blanca’s glaciers recede. As the drones pass over these “proglacial valleys,” they can produce highly accurate maps of the soil moisture within the fields, rivers, wetlands, and meadows below.
Historically there has been “very little understanding” of how water circulates in areas like proglacial valleys, Jorge Recharte, director of the Andes program at the Mountain Institute, told GlacierHub.
The study’s lead author, Oliver Wigmore of the University of Colorado, Boulder, said his team’s findings help to improve understanding of proglacial hydrology. “This data … is providing unique insights into the patterns and processes that move and store water within these dynamic proglacial environments,” he said.
This study is the first to apply drone images to the temperature vegetation dryness index (TVDI) method. TVDI demonstrates the relationship between land surface temperature and normalized difference vegetation index (NDVI), which measures an area’s greenness, or density of vegetation, which can then be used to determine soil moisture.
Anais Zimmer, a Ph.D candidate in the department of geography and the environment at the University of Texas, Austin, said the study offered “excellent outcomes on surface and subsurface hydrological processes that could be used at a broader scale and applied to many other sub-disciplines to understand the functioning and the future of alpine ecosystem services.”
The researchers found that soil moisture varied drastically over very short distances. “The unique, high-resolution multispectral drone imagery that we collected has provided an unprecedented snapshot of the spatial variability of surface soil moisture within these systems,” said Wigmore.
Drones are essentially the third generation of technology to be used in scientific research. First were direct measurements, which cannot be accurately generalized over such a variable area. Then came remote sensing using satellites, which provides averaged data over larger areas, but would likely miss any important variability happening on a smaller scale. For this study, researchers used two types of drone-mounted cameras: one to measure greenness, an indicator of plant health, and a second to record temperature.
“[The images] provide excellent tools to establish comparisons between valleys, depending on land use changes and climatic factors,” Zimmer said.
Wigmore and his team conducted their survey in two proglacial valleys in the Cordillera Blanca that were markedly different from each other in terms of precipitation level, glacier extent, land cover, and land use. The researchers found that soil moisture variability across the Cordillera Blanca’s proglacial valleys can be attributed to three criteria: distance from local water supplies; the type and abundance of vegetation; and soil disturbance such as animal grazing.
“We have found that the proglacial valleys in Cordillera Blanca often have substantial groundwater reservoirs that regulate dry season stream flow by storing and gradually releasing wet season precipitation and glacial meltwater,” said Wigmore. He added that knowing the groundwater storage capacity of these valleys could help minimize negative impacts of meltwater decline on downstream communities.
“Research in these high landscapes is key to planning for both local impacts in the short term and whole-watershed impacts in the long term,” Recharte said.
Zimmer emphasized the need for enhanced monitoring, modeling, and case studies that might help to better predict the impact of climate change in mountain communities.
Around the world, many glaciers have already reached peak discharge, which threatens the freshwater supplies of downstream communities. The study by Wigmore and his team not only provides an unprecedented look into the hydrology of proglacial valleys, it also provides a glimmer of hope that not all is lost, at least for now. Their results document the enormous water-storage potential that lies beneath the surface of proglacial valleys, but also highlights the extreme vulnerability of these ecosystems.
Read more on GlacierHub: