DROUGHT CONDITIONS ACCELERATE DESTABILIZATION OF SAND DUNES ON THE NAVAJO NATION, SOUTHERN COLORADO PLATEAU

Current drought conditions on the Navajo Nation are producing significant changes in dune mobility. A critical factor controlling dune mobility is the ratio of precipitation to potential evapotranspiration (P/PE), because of its direct link to the amount of stabilizing vegetation. Thresholds in P/PE for changes in dune mobility are based on observations by Muhs and Holiday (1995); where P/PE is < 1.0 there is an overall moisture deficit. Transitions from mostly stable to mostly active sand occur at P/PE=0.315, and from mostly active to fully active sand takes place at P/PE=0.125. Historical meteorological data indicate that P/PE values on the Navajo Nation have consistently fallen below 1.0. However, the range of P/PE values calculated during current severe drought conditions show an accelerated diminution of the already low soil moisture balance. Now, all of the dune fields within the Navajo Nation fall below the threshold of partly active (0.315). An increased number of dune fields also currently fall below the threshold of P/PE for mostly active (0.125). The reactivation of stabilized sand is contributing to myriad problems for the Navajo people, including housing inundated by sand, a loss of rare and endangered native plants, degradation of farming and grazing land, and lower air quality from periodic dust storms.