Ground temperature measurements to verify thermal anomaly observed on satellite image of arid ecosystem across the Israel-Egypt border

Abstract

A unique arid environmental ecosystem exists in the Israel-Egypt border region. Remote sensing images shows that the Israeli side with much more vegetation cover has notably higher land surface temperature (LST) during daytime than the Egyptian side where bare sand prevails. In this paper, we present our results of ground temperature measurements to verify the observed thermal anomaly. The region is mainly composed of four basic surface patterns: biogenic crust, bare sand, vegetation and playa (physical crust). Results from our ground temperature measurements during 1997-1998 validate the hypothesis of a significant LST difference existing among the main surface patterns. In dry summer at about noon biogenic crust covering ~72% on the Israeli side and only about 12% on the Egyptian side has an average kinetic surface temperature (KST) of above 3degC higher than bare sand covering above 80% of ground surface on the Egyptian side. In early and late dry seasons the difference is still above 2.5degC at about noon. The difference reverses only in a few days alter heavy rain when the biogenic crust is very wet or at higher water content while the bare sand surface is relatively drier. Under this extreme condition bare sand has an average KST of ~1degC higher than biogenic crust. However, the reverse KST difference between the two main surfaces becomes very weak after about two weeks of strong rain. Shrub canopy has the lowest canopy temperature in all seasons with a difference of 15degC from biogenic crust KST in summer at noon. The obvious lower canopy temperature than surrounding environment demonstrates that evapotranspiration still functions to cool down desert plants though the plants may remain in a status of semi-dormancy to minimize the evapotranspiration