The CUAHSI Hydrologic Information System

Defining the nature of a Hydrologic Information System is a challenge. The HIS team is trying to create something that has never existed before, and is operating at the outer limits of current technology. By definition, a system is an array of connected components, and in this instance the components can be defined as software applications that store, access and index hydrologic information. The connection among them is established by web services which are automated functions that enable one computer to make appropriate requests of another computer and receive responses through the internet. In this sense, the HIS team and its partners are creating a services-oriented architecture for water information. Josuttis (2007) defines a services-oriented architecture as “a concept that applies to large, distributed information systems that have many owners, are complex and heterogeneous, and have considerable legacies from the way their various components have developed in the past.” This definition certainly applies to the water resources field which has thousands of agencies and individuals who collect and archive water information in their own way. It also applies to other fields such as insurance, banking, health care and public safety, that also have many institutions and individuals who store and exchange information.

Another way of thinking about a Hydrologic Information System is by analogy with a Geographic Information System (GIS). Tomlinson (2003) states that “a GIS stores spatial data with logically-linked attribute information in a GIS storage database where analytical functions are controlled interactively by a human operator to generate the needed information products.” This definition implies that all the information has been harvested and stored in a local database and is then available for analysis and interpretation. However, unlike GIS where the data are static and change little through time, a hydrologic information system is representing phenomena that are inherently dynamic and vary greatly through time.

If we combine these two concepts, the services-oriented architecture, and the desktop application which stores and operates on the information on a local desktop computer, we may define a Hydrologic Information System as shown in Figure 1 as comprising three components:

  • HydroServer is a repository of hydrologic time series and spatial data published as WaterML and map web services;
  • HIS Central is a metadata catalog of data accessible through search services;
  • HydroDesktop accesses hydrologic data discovered on HIS Central and acquired from HydroServers.
HIS Triangle Diagram

Figure 1. The three components of a Hydrologic Information System linked by web services.

In developing these definitions it is important to recognize that these three components are not unique to hydrology, and indeed the internet itself is also based on these three elements: information servers that publish text and images in Hypertext Markup Language (HTML), portals such as Google and Yahoo that index published documents and enable searching across them, and applications such as web browsers that access and display the resulting documents and files. Also, it is important to note that, like the internet, there may be multiple instances of each component.

As Figure 1 shows, a HydroServer publishes both data and metadata services. For example, for a stream gage, the data consists of the time series of discharge and stage height values recorded at the gage, while the metadata describes the location of the gage, the variables measured there, the period of record, and the organization that operates the gage. By contrast, HIS Central indexes and catalogs only metadata, but it does so across many HIS Servers which contain hydrologic information for a particular geographic region. This supports a user of HydroDesktop who can search the metadata stored in HIS Central and then acquire the data directly through data services provided by HydroServer. Because data and metadata services are public information sources they can be accessed by any appropriate computer application not just HydroDesktop.

© 2008-2010 CUAHSI-HIS

This material is based upon work supported by the National Science Foundation (NSF) under Grant Nos. 04-12975, 041-3265, and 06-22374.
Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the NSF.