A numerical modeling study on desert oasis self-supporting mechanisms

Oasis self-supporting mechanisms due to oasis breeze circulation (OBC) are proposed and simulated numerically in this study using a coupled mesoscale and land-surface model. Excessive evaporation from the oasis makes the oasis surface colder than the surrounding desert surface. The sensible heat-flux gradient from oasis to surrounding desert drives the OBC with downdraft over the oasis and updraft over the desert. The horizontal length-scale of the OBC is around four times as large as the oasis scale. This secondary circulation creates two mechanisms to reduce heat and moisture exchange between the oasis and the surrounding desert: (1) the updraft over the desert reduces low-level hot, dry air flowing from the desert into the oasis; and (2) the downdraft increases the atmospheric static stability that reduces the oasis evaporation. Reduction of the oasis scale weakens the oasis self-supporting mechanisms through the decrease of the OBC associated with the increase of the oasis surface evaporation and decrease of the atmospheric stability over the oasis.