Groundwater Recharge Analyzed Using NASA GLDAS Data Products and Environmental Isotopes in Jordan

The water balance of an underground storage reservoir is determined by evaluating precipitation, surface runoff, evaporation and transpiration, changes in soil moisture and anthropogenic abstractions.  These hydrological components can be directly or indirectly derived from remote sensing data products via the National Aeronautics and Space Administration (NASA) Global Land Data Assimilation System (GLDAS).  The GLDAS is a global archive of modeled and observed surface meteorological data, parameter maps and hydrological model outputs.  The archive includes 1-degree and 0.25-degree resolution, 1979-present and 1948-present simulations of various land surface hydrology models.  The temporal resolution for GLDAS products is 3-hourly making it suitable for tracking fast moving extreme hydrologic events that are important in arid and semi-arid climates.  Daily, monthly and annual products can be generated by temporal averaging of the 3-hourly products.  NASA GLDAS products have been used to calculate average annual groundwater recharge rates throughout the country of Jordan.  The GLDAS-derived rates of groundwater recharge for the Eastern Jordan desert appear to be higher than have been previously recognized.  GLDAS derived recharge rates are compared to surface and subsurface geological features, groundwater elevation maps, environmental isotopes, current abstractions and groundwater discharge features to better understand the implications of these results.  Comparisons of environmental isotopes in the precipitation and groundwater indicate that the origin of the groundwater recharge can be construed as generally consistent with the area of increased recharge although recharge from the Syrian steppe cannot entirely be ruled out.  Groundwater flow directions in the area are defined by a local groundwater high and consisting of several groundwater divides and also appear to be consistent with the area of higher recharge.  These analyses provide important tools for exploring possible relationships between groundwater recharge and groundwater discharge and improving the state of knowledge for the management of water resources.