Evaporation driven by Atmospheric Boundary Layer Processes over a Shallow Salt-Water Lagoon in the Altiplano

Abstract

Observations over a salt-water lagoon in the Altiplano show that evaporation (E) is triggered at noon, concurrent to the transition of a shallow, stable atmospheric boundary layer (ABL) into a deep mixed layer. We investigate the coupling between the ABL and E drivers using a land-atmosphere conceptual model, observations and a regional model. Additionally, we analyze the ABL interaction with the aerodynamic and radiative components of evaporation using the Penman equation adapted to salt-water. Our results demonstrate that non-local processes are dominant in driving E. In the morning the ABL is controlled by the local advection of warm air (∼5 Kh−1), which results in a shallow (<350 m), stable ABL, with virtually no mixing and no E (<50 Wm−2). The warm-air advection ultimately connects the ABL with the residual layer above, increasing the ABL height (h) by ∼1-km. At midday a thermally-driven regional flow arrives to the lagoon, which first advects a deeper ABL from the surrounding desert (∼1500 mh−1) that leads to an extra ∼700-m h increase. The regional flow also causes an increase in wind (∼12 ms−1) and an ABL collapse due to the entrance of cold air (∼−2 Kh−1) with a shallower ABL (∼−350 mh−1). The turbulence produced by the wind decreases the aerodynamic resistance and mixes the water body releasing the energy previously stored in the lake. The ABL feedback on E through vapor pressure enables high evaporation values (∼450 Wm−2 at 1430 LT). These results contribute to the understanding of E of water bodies in semi-arid conditions and emphasize the importance of understanding ABL processes when describing evaporation drivers.