Monitoring the Fluctuations of the Birjand Plain Aquifer Using the GRACE Satellite Images and the GIS Spatial Analyses

Over-exploitation of a limited resource, especially in arid and semi-arid regions such as Iran, entails a strict management of groundwater. In this context, identification of changes and fluctuations in groundwater level can help to make the right decision. The Gravity Recovery and Climate Experiment (GRACE), a joint mission of NASA and the German Aerospace Center, makes detailed measurements of the Earth's gravity field anomalies and fluctuations in groundwater resources at a spatial resolution of a few hundred kilometers. Due to the lack of the in-situ measurements at a regional scale for the quantitative groundwater monitoring, this satellite's unique data are used to monitor the quantitative annual changes in the groundwater resources. Data processing was performed on the Google Earth Engine Web platform using the JPL, GFZ and CSR algorithms. Results were compared using the piezometric data from 2008 to 2018. This comparison was performed by a linear regression between the changes obtained from the GRACE algorithms and the piezometric data, which resulted in a 69% correlation of these two methods. In order to perform spatial and temporal analysis of the water level of the aquifer, the zoning was performed using the ArcGIS software. The results indicated that, the water level in the studied aquifer has been significantly reduced during the 2008 to 2018 period due to a lack of rainfall, thus the net recharge and over-extracting.