Abstract
Playas are common in arid environments and can be major sources of mineral dust that can influence global climate. These landforms typically form crusts that limit evaporation and dust emission, modify surface erosivity and erodibility, and can lead to over prediction or underprediction of (1) dust-emission potential and (2) water and heat fluxes in energybalance modeling. Through terrestrial laser scanning measurements of part of the Makgadikgadi Pans of Botswana (a Southern Hemisphere playa that emits significant amounts of dust), we show that over weeks, months, and a year, the shapes of these surfaces change considerably (ridge thrusting of >30 mm/week) and can switch among continuous, ridged, and degraded patterns. Ridged pattern development changes the measured aerodynamic roughness of the surface (as much as 3 mm/week). The dynamic nature of these crusted surfaces must be accounted for in dust entrainment and moisture balance formulae to improve regional and global climate models.
Highlights
Playas are common landforms in arid regions and are one of the biggest sources of mineral dust emission (Washington et al, 2003; Prospero et al, 2002). They contribute to surface energy balances by modifying moisture and heat fluxes in the atmosphere (Bryant and Rainey, 2002)
(2) The salt chemistry and changes in moisture may result in the formation of weak, low-bulk-density sediment, thereby increasing the supply of potentially emissive material (Reynolds et al, 2007), on sulfate-rich playas (Buck et al, 2011)
We first introduce the surface variability, and use Fourier transforms to assess how surface patterns develop over time, linking surface change to atmospheric and subsurface controls through a conceptual model that identifies trajectories in crust patterning
Summary
Playas are common landforms in arid regions and are one of the biggest sources of mineral dust emission (Washington et al, 2003; Prospero et al, 2002). This paper assesses surface moisture, aerodynamic roughness, and crust pattern change on a large playa (Sua Pan) in Botswana over weeks, months, and one year. RIDGED PATTERN DEVELOPMENT The combination of a high water table and flooding in 2011 reset the surface and enabled a flat, continuous crust to develop on the northeastern section of the playa (L5).
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