IDENTIFICATION OF THERMAL ANOMALIES IN NORTH SINAI, EGYPT: IMPLICATION TO RENEWABLE GROUNDWATER ACCUMULATION

Sinai is a profoundly strategic asset to Egypt. Yet efforts to understand and locate renewable groundwater accumulations in this dry land are often hampered by scarcity of flow data and lack of appropriate runoff monitoring systems. Although rainfall events in northern Sinai are occasional, monitoring thermal variation in bare sandy surface following a rainfall event could provide indirect indications to groundwater accumulations. This work aims at detecting thermal anomalies in El-Arish watershed to understand the recurrence causes of this phenomenon in only specific locations, using thermal remote sensing data and field investigations. It is here attempted to reveal possible connections between these anomalies and the surrounding factors, such as basin hydrologic behavior, structure, topography, paleoriver courses and the groundwater quality of the area. Systematic analysis for thermal inferred (TIR) data of daily MODIS LST, ASTER and ETM+ satellite images are correlated with major rainfall events from TRMM data to reveal cool patches within the watershed. Results of thermal analysis show several patches of dark signals that indicate a cooler surfaces of approximately 10 °C lower than the surroundings with a lifespan of more than a week. The most frequent anomaly is located in El-Sirr and El-Guwarir depression. According to our previous research in the study area, this location contains the ancestral paleoriver course of Wadi El-Arish, which is filled by paleofluvial deposits, and may serve as an unconfined aquifer. High-density fracture zones structurally control the paleodrainage course. These fractures, therefore, may have channeled the runoff to accumulate beneath the paleo-channel courses. In addition, the hydrologic behavior analysis indicates that thermal anomalies appear in a sub-basin of high groundwater potential with wide flat pick flow hydrograph. Furthermore, field investigations of water wells prove that salinity values decrease toward the thermal anomaly west of Gebel Halal and increase in an easterly direction. From these findings it is concluded that structure, topography and paleodriange are the key elements, which control the appearance of thermal anomalies in arid lands, and could contribute to groundwater exploration.