Integration of Hydrogeology and Soil Science for Sustainable Water Resources—Focus on Water Quantity

Increased biofuel production has heightened awareness of the strong linkages between crop water use and depletion of water resources. Irrigated agriculture consumed 90% of global fresh water resources during the past century. Addressing crop water use and depletion of groundwater resources requires the expertise from disciplines including soil science and hydrogeology to develop a sustainable program to meet future food, fiber, and biofuel demands. Recent advances in remote sensing have greatly enhanced capabilities for relating water use to crop production. Satellite, airborne, and ground-based measurements of evapotranspiration allow quantification of water use by various crops in different climatic and hydrogeologic settings. Satellite data also allow monitoring of groundwater depletion at seasonal to interannual timescales, as shown by application of GRACE gravity data to the High Plains and other aquifers. Satellite-based radiometers now monitor the density of green vegetation; through the Normalized Difference Vegetation Index (NDVI), biospheric feedbacks to climate variability can be assessed along with net impacts on water resources. Measurement and analysis of soil-physics parameters (matric potentials), environmental-tracer concentrations, and hydrogeologic data (groundwater levels) provide invaluable information on impacts of land-use change and climate variability on groundwater recharge, particularly in semiarid regions. A serious obstacle is posed by a trend towards reduced ground-based monitoring of hydrologic parameters, such as irrigation amounts and groundwater levels, which are needed for ground-referencing satellite-based data. Injecting science into policies that will help lead to sustainable water-resources management is a major challenge that requires soil scientists, hydrogeologists, social scientists, and economists to work together.