Description:
Infrequent extreme rain events in extraordinarily dry environments can dramatically shape the landscape. Here, Landsat 8 OLI images are used to study the spatial variability of land surface modification due to two extreme rain events which impacted the Atacama Desert, one of Earth’s driest places. Images for 4 dates, in 3 date-pairs, are analyzed using a Change Vector Analysis (CVA) technique which delivers two outputs at each pixel: the intensity of change (Intensity-CVA) and the direction of change (Direction-CVA). A 2015 extreme rain event affected the southern Atacama and one in 2019 affected the northern Atacama. In this work, we test with the 2015 event the efficacy of CVA by comparing it to published Interferometric Synthetic Aperture Radar (InSAR) coherence results. This comparison showed that Intensity-CVA tends to agree with the InSAR permanent coherence loss for areas located in nearly flat terrains, suggesting that Intensity-CVA can identify areas of mass transference. The efficacy of Intensity-CVA was also demonstrated for the 2019 rain event, where it identified mass transference and mineral transformations. In contrast, the Direction-CVA does not result in reliable identification of the major type of change. To clarify the physical processes behind the Intensity-CVA response, we divided parts of both study areas into sectors containing uniform surface materials and applied Principal Component Analysis (PCA) on quadratic difference of Surface Reflection (SR) values of Landsat 8 scenes for multiple dates. In addition, we analyzed the Intensity-CVA trends of the Landsat 8 OLI data within each of these sectors compared to the main composition of each surface material. These two analyses reveal that, among locations with strong Intensity-CVA change, remotely identified changes are dominated by soil moisture variations associated with a playa lake and evaporitic units verified by PCA. Secondarily detected are salt crystals grown in the months after the rain