FARMINGTON, N.M. A decadelong federal study says that a drier climate on the Navajo Reservation is causing sand dunes to grow and move, potentially threatening grazing, roads and buildings.

The study by a U.S. Geological Survey geologist found that sand dunes are growing fast and moving more, including old dunes that previously were stable. More than a third of the 27,000-square-mile reservation is covered by sand dunes and sand sheets, and it has experienced varying degrees of drought for the past 15 years.

Geologist Margaret Hiza Redsteer called the Navajo Reservation -- specifically the southwestern portion in Arizona -- "just on the edge of being habitable," the Farmington Daily Times reported. Her work also noted the vulnerability of indigenous people who rely heavily on the land.

"The annual moisture here has historically been just enough to get by," she said . "When there is even a small change, there is a huge effect."

Some of the sand dunes are moving at a rate of 115 feet per year, the report found. Faster migration of active sand dunes and the reactivation of previously immobile dunes can threaten housing, roads and the health of residents.

The study will yield data on diminished vegetation cover and the increasingly arid environment, which threatens livestock, grazing, infrastructure and livelihoods on the reservation. The areas that call for the most alarm are the lands near the Colorado Plateau, located near Flagstaff and surrounding the Hopi Reservation.

Redsteer found that besides growth and new movement in existing dunes, new dunes were increasing in number. The new dunes form downwind from rivers and washes, largely from dry, windblown river sediment. For instance, the dune field outside Flagstaff has grown by 70 percent since 1995, when the most recent drought gripped the Nation.