Evaporation from a Desert Playa Following Rainfall

Of all the landscapes found across the earth surface, desert playas (dry lakes) can a priori be thought as not very challenging to study. Indeed, they are flat, smooth, devoid of vegetation and from a distance, appear very homogeneous. Yet, they present their own set of specificities – soil textures can vary tremendously over short distances, the soil has a high thermal inertia owing to the high water table, salt crusts can form on the surface – each with a significant impact on its interactions with the overlying atmosphere. This study presents an analysis of evaporation following occasional rain events over a desert playa in western Utah, USA, as part of the Mountain Terrain Atmospheric Modeling and Observations (MATERHORN) program. The results show that decreasing surface albedo, decreasing Bowen ratio and increasing net radiation sustained a powerful positive feedback mechanism supporting fast evaporation immediately following rain events. Furthermore, owing to a clay rich soil with low permeability and high water capacity, water was kept close to the surface after rain events, thus promoting large evaporation rates. Finally, strong spatial heterogeneities in evaporation rates following rainfall were found. The cumulative evaporation from the different sampling sites (a 240 m x 160 m grid) over a five-day period varied from 0.1 mm to 6.6 mm. We hypothesize that these differences are due to great spatial variability in soil textures.