Twentieth century dune migration at the Great Sand Dunes National Park and Preserve, Colorado, relation to drought variability

The total net migration of 13 parabolic dunes in 63 years is 0.31 to 0.66 km, whereas 11 barchan dunes moved an average of 0.12 to 0.47 km. Compared to intervening wet year, there is at least a three-fold increase in average parabolic dune migration, during well-documented droughts in the 1930s, 1950s, and 1990s with a concomitant reduction in vegetation cover and surface water resources. The landscape response to the most recent drought in the late twentieth century is documented by an average parabolic dune migration rate of 30 m/year, which is a six-fold acceleration over prior wet years, and similar to dune response during the 1930s. A nonlinear threshold for parabolic dune migration is indicated with lower quartile Palmer Drought Severity Index values of < − 2, which corresponds to at least a 25% reduction in summer and autumn precipitation.