Analysis of the space-based surface temperature distribution in Badain Jaran Desert

The 49,000-km² Badain Jaran Desert lies in the centre of Alxa Plateau in the western Inner Mongolian Region [1;2]. The southern part of this desert is characterised by the unique association of lakes with the tallest megadunes of Earth (general height varying between 150 and 350 m). The mean precipitation rate of this region is below 100 mm yr^-1 and the evapotranspiration one is ~2600 mm yr^-1. Around 140 lakes have been reported, mainly located in the interdunal region and they represent a mean surface of ~23 km². In order to protect the water resource of this desert, scientific research such as the sources of groundwater and groundwater recharge has been carried out. One of the most interesting resulting hypotheses is the existence of a convective circulation of the groundwater [3;4;1;5]. Indeed, the ascending current of groundwater can 1) supply the lakes and 2) may play role in the cementation of the megadunes, process that is considered as the starting point for their development. Interestingly, at the surface of the megadunes, a dry layer is present and its depth varies between 20 and 50 cm. But below this dry layer, the sand is moistened [6].

Space-based thermal images from MODIS of this region display at first approximation a correlation between the topography and the surface temperature evolution. In order to understand the relationship between the surface temperature, topography and soil moisture, a fully coupled hydro-thermal method was adopted to simulate the interaction between the atmosphere and the first metre below the surface. The analysis process includes the determination of material parameters, initial and boundary conditions, the calculations of net solar radiation, actual evaporation and sensible heat. Our methodology relies on the measured temperature distribution by MODIS and the calculation shows the temperature evolution along with the elevation. The factors including sunshine direction (i.e. sunny or shadowed slope) and evaporation on the surface temperature distribution at Badain Jaran will be discussed.

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