Quantity and quality of the Nation's water resources has been and will continue to be critically important to ensure, protection of life and property, economic well-being, and healthy coastal ecosystems. Moreover, in light of the alarming decline in water supplies in certain regions of the U.S. and world-wide, protecting and preserving vital water resources in the future will depend largely on sound management decisions supported by an in-depth, reliable scientific knowledge base. Key to this base is the full understanding of the hydrological cycle, the natural process by which water circulates among air, land, and water. Across NOAA Research, scientists are using hydrology, a scientific assessment of the volume, location and movement of water to build complex mathematical models to understand the intricacies of this vital cycle