Paper No. 51-13
Presentation Time: 4:45 PM
TREND ANALYSIS OF SOIL MOISTURE AND ITS IMPLICATION IN UNDERSTANDING GROUNDWATER DYNAMIC IN FOSSIL AQUIFERS: AL-SHARQYA CASE STUDY
In hyper-arid environments with sparse and rare precipitations soil moisture is a key indicator of shallow groundwater dynamic through structural anomalies that can forms vertical conduits for water. Hence mapping variations in surface soil moistures is of primary importance in understanding natural discharges for fossil aquifers such is the case for the Al-Sharqia aquifer in Oman that is the second largest fresh groundwater reserve in the southern Arabian Peninsula. To understand potential natural discharges through vertical groundwater movements, we investigate the relation between variations of soil moisture and shallow subsurface fractures as mapped from ALOS L-band SAR images for the areas surrounding the Wahiba dune field overlaying the in Al-Sharqya aquifer in Oman. Our objective is to quantify the presence of shallow subsurface fractures and their role in varying and accentuating evapotranspiration associated to soil moisture and hence consequently causing a water-table depth variation. Two orbital data sets covering the whole Wahiba dune field and the Al Sharqya basin were incorporated in our analysis; the first is the ALOS L-band Polarimetric scenes providing insights to both textural and dielectric surface and shallow subsurface (<5 m); and the second is the LANDSAT 8 monthly thermal band 11 data acquired from May 2013 to July 2015, providing an insight to surface temperature. First fractures are identified from ALOS scenes assisted by Landsat 8 data, then, soil moisture is estimated, based on surface temperature, from thermal infrared bands of Landsat 8 images. Using the above-mentioned data sets we created time series of surface soil moisture and removed the variability arising from the annual cycle. The result is a time series for specific areas of anomalic variations in soil moisture that are well correlated with the occurrence of subsurface fractures. We applied trend analysis to assess and to map the changes in soil moisture using Theil-Sen median trend and the Mann-Kendall significance procedures. Our results suggest that there is a correlation between the detected fractures and anomalic surface moisture attributed to groundwater vertical movement through these structural conduits.