| Description |
Specifying surface albedo accurately as a function of land surface type is critical for simulating boundary layer processes in weather and climate models. Desert playas, such as those in northern Utah, form a landscape often in stark contrast to surrounding mountain ranges due to their minimal topographic relief, lack of vegetation, and saline soils. Dry highly-reflective halite surfaces are generally characterized by surface albedo over 40 %. However, the surface albedo of desert playas can be reduced abruptly to less than 25 % by flooding due to rainfall, runoff from surrounding higher terrain, or surface winds advecting shallow water across the playas. A weather station installed during September 2016 to support a comprehensive geomorphologic study of the Bonneville Salt Flats (BSF) in northern Utah provides estimates of albedo that can be related to cycles of flooding and desiccation of the halite surface. Another weather station located on the playa margin of the Great Salt Lake's Farmington Bay, which is composed primarily of sand and clay, provides contrasting estimates of albedo. Discriminating high albedo playa surfaces from clouds is difficult from current satellite retrieval algorithms. The Moderate Resolution Imaging Spectroradiometer (MODIS) MCD43A3 surface albedo product is unable to provide high-quality albedo data for playa pixels in northern Utah. However, the MODIS MOD09A1 land surface reflectance product can be used to estimate the fractional coverage of water over the playas based on a normalized difference water index (NDWI). NDWI values computed iv over 8-day periods from 2000-2018 highlight year-to-year and seasonal variations in playa flooding events over the Bonneville Salt Flats and Farmington Bay of the Great Salt Lake. Shorter term fluctuations in water level are estimated from a water depth sensor on the Bonneville Salt Flats since September 2016. Periods of playa flooding were observed with both ground-based observations as well as NDWI with sharp reductions in albedo when the surface is flooded. |
