Effects of prolonged drought on the vegetation cover of sand dunes in the NW Negev Desert: Field survey, remote sensing and conceptual modeling

Luminescence dating of stable sand dunes in the large deserts of the world has shown several episodes of mobility during the last 30 k years. The logical explanation for the mobility of fixed dunes is severe drought. Though drought length can be estimated, the level of precipitation drop is unknown. The stabilized sand dunes of the northwestern Negev Desert, Israel have been under an unprecedented prolonged drought since 1995. This has resulted in a vast decrease of shrubs cover on the fixed sand dunes, which changes along the rainfall gradient. In the north, an average of 27% of the shrubs had wilted by 2009, and in the drier southern area, 68% of the shrubs had withered. This loss of shrubbery is not expected to induce dune remobilization because the existing bio-crust cover is not negatively affected by the drought. Eleven aerial photographs taken over the drier southern area from 1956 to 2005 show the change in shrub cover due to human impact and the recent severe drought.

► A curve of change in vegetation cover on sand dunes vs. rainfall is presented.
► As rainfall increases the productivity approaches a stage of no/negligible change.
► The minimal precipitation for negligible vegetation in desert dunes is 50–60 mm.
► During mega-droughts shrubs are wilted while bio-crusts survive.