GIS and hydrology

Geographic information systems (GISs) have become a useful and important tool in the field of hydrology to study and manage Earth's water resources. Climate change and greater demands on water resources require a more knowledgeable disposition of arguably one of our most vital resources. Because water in its occurrence varies spatially and temporally throughout the hydrologic cycle, its study using GIS is especially practical. Whereas previous GIS systems were mostly static in their geospatial representation of hydrologic features, GIS platforms are becoming increasingly dynamic, narrowing the gap between historical data and current hydrologic reality. The elementary water cycle has inputs equal to outputs plus or minus change in storage. Hydrologists make use of this hydrologic budget when they study a watershed. The inputs in a hydrologic budget include precipitation, surface flow, and groundwater flow. Outputs consist of evapotranspiration, infiltration, surface runoff, and surface/groundwater flows. All of these quantities can be measured or estimated based on environmental data and their characteristics can be graphically displayed and studies using GIS. In the field of hydrological modeling, analysis generally begins with the sampling and measurement of existing hydrologic areas. In this stage of research, the scale and accuracy of measurements are key issues. Data may either be collected in the field or through online research. The United States Geological Survey ((USGS)) is a publicly available source of remotely sensed hydrological data. Historical and real-time streamflow data are also available via the internet from sources such as the National Weather Service (NWS) and the United States Environmental Protection Agency (EPA). A benefit of using GIS softwares for hydrological modeling is that digital visualizations of data can be linked to real-time data. GIS revolutionized curation, manipulation, and input for complex computational hydrologic models For surface water modeling, digital elevation model are often layered with hydrographic data in order to determine the boundaries of a watershed.