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Introduction
The CRONOS H2O database provides access to observations from automated "water" sites in North Carolina and the surrounding states. These water sites include streamflow, groundwater, and reservoir gages maintained by various agencies, including U.S. Geological Survey, NC DENR Division of Water Resources, U.S. Army Corps of Engineers, Tennessee Valley Authority, and Duke Energy. Sites with an extended period of record have calculated percentiles available. More will be explained later regarding these percentiles.
System Requirements
Web Browser
The CRONOS H2O database requires a web browser. Recommended browsers are Microsoft Internet Explorer version 6 or later, Netscape version 7 or later, or Mozilla version 1.4 or later. Other browsers, such as Mac OSX’s Safari or Opera, have been tested but do not provide all the same functionalities.
Internet Access
Access to the CRONOS H2O database is via the Internet and a web server located in the State Climate Office at North Carolina State University. While high speed Internet improves access to CRONOS H2O features, it is not required.
Getting Started
Point your web browser to http://www.nc-climate.ncsu.edu/cronosh2o [1]
Your screen should look like the one below.
There are three ways to begin retrieving data for water sites within the CRONOS H2O database. These options are as follows:
Search Box – Type in a site name, ID, county location, HUC region, or parameter to retrieve a list of sites that meet your search criteria. Each site is color-coded based upon data type, which will be explained in more detail below.
Inventory of Sites – Choose a site from a list of all sites available in the database, which are also color-coded by data type.
Interactive Map of Sites – Display sites on a map and choose the site of interest.
Using the Search Box
By typing in a site's name, ID, county location, HUC region, or parameter into the search box, you will see a list of all sites in the CRONOS H2O database that match your search criteria. As previously mentioned, each result row is color-coded based upon the types of data that particular site measures.
A table explaining these color codes, as well as the parameter and time interval codes in the last two columns is located towards the top of the search page (see image below). You can select a site by clicking on the links associated with the site ID, or with the time interval type.
Using the Site Inventory
Towards the bottom of the search page, you will see a link that will take you to a table of all sites with archived data in CRONOS H2O. This table can be sorted by site name, ID, or HUC region by clicking on the column headers. Similar to the results using the site search method, each row is color-coded based upon available data types for that particular site (refer to table above). In addition, you can use the menus towards the top of the page to view all sites within a particular HUC region, or that measure a specific parameter.
Using the Interactive Map of Sites
By clicking on the map image or on the link entitled "Interactive Map of Sites" (on main CRONOS H2O page), you will see a map of North Carolina and the surrounding states. To the left of the map is a menu listing layers that can be turned on or off for the map display. Such layers include county boundaries, HUC regions, rivers and streams, as well as the various sites within the CRONOS H2O database. A legend that depicts the currently displayed layers is located to the right of the map.
The menu to select layers is divided into four sections:
Water Data Networks – Select streamflow, groundwater, reservoir, and/or precipitation sites in the database
Geographic – Display counties, rivers/streams, HUC regions, etc.
Percentiles – View color-coded percentiles for streamflow, precipitation, and groundwater over various daily and monthly ranges
Transportation – Overlay interstates, as well as primary and secondary roads
Located above the map are icons that allow you to manipulate what you view. After selecting or de-selecting any layers, you can refresh the map with your new choices by clicking on the "Redraw Map" icon. The "Information" icon displays metadata for the closest site to the point you click on the map. This information will appear above the interactive map. You can also view a list of the next 5 closest sites by clicking on the "show/hide list of nearby stations" link within the metadata information. To begin retrieving data from the chosen site, select the "Get More Data for . . ." link.
A more detailed tutorial of the map interface can be found here [2].
Retrieving Data
After selecting a site of interest through the search box, site list, or map interface, you will be taken to the data retrieval page. At the top of the retrieval page is a metadata table similar to that on the map interface. Below this table are links showing data availability for the given site with respect to the time interval over which it is measured (realtime, daily, and/or peak). Clicking on one of links will display the available parameters for the chosen time interval.
To begin retrieving records, you must first choose a period over which to get data. The general public is restricted to certain time periods, while internal users are allowed access to all records for any site. Next you can choose the desired parameters by checking the box located to the left of each choice. Descriptions of each parameter can be obtained by clicking on the question mark icons.
Drop-down menus for choosing percentiles only appear on the page if they have been calculated for the respective parameter. Percentiles represent the rank of a particular value on a percentage scale from 1 to 99, where the 1st percentile represents the lowest value (minimum), and the 99th percentile represents the highest value (maximum). To calculate "worthwhile" percentiles, a decent sample size is needed. For streamflow and precipitation sites, at least 20 years of data is preferable before percentiles will be generated. Streamflow and precipitation percentiles are calculated based on the day of the year (1-365), giving a sample size of 20 or more for each day. Groundwater percentiles are broken down by month, so fewer years of data are needed before percentiles are generated.
After choosing all the parameters of interest, you can choose the output format for which you want the data to be in, and click the "Retrieve Data" button. If you are only interested in graphing the data, you can click on the "Graph Data" button to see the graphs displayed to the web.
The web page output shows the observations selected, along with summaries of the data included at the bottom of the table.
In the header of each column, users can click on the graph icon to view a graph of those observations over time. This is an especially useful feature for looking at general trends in the data.
In addition, you may have noticed a "Graph Data" button on the data retrieval page. This feature allows the user to view only the graphs of the selected parameters, without retrieving the actual data in some sort of tabular format. It must be noted, however, that these graphs are available through the web only.
In addition to the web, other output formats include a tab delimited text file, a comma delimited text file, and an Excel spreadsheet. These options can be found in the "Output Format" menu on the data retrieval page.
(Tab Delimited Format) (Excel Format)
Examples of graph outputs can be found below. Some graphs, such as that of streamflow data, display shaded percentiles in the background. This gives the user a good idea of how the chosen observations compare historically over the same time period during the year.
