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Tutorial: Examining Discharge and Precipitation Data near Lake Tahoe, California

The following tutorial demonstrates how to use HydroClient to search for, download, and visualize time series data from multiple sources and then analyze the data in Excel. This example uses data located near Lake Tahoe, CA during 2012, but the same procedure to download data for other stations is identical and can be followed to get precipitation, discharge, and several other parameters for other locations in the United States and around the world.

Instructions

Open your internet browser and go to the HydroClient URL, http://data.cuahsi.org. The HydroClient uses the Google Maps interface as shown below.

In this exercise we will visit a location of interest, search for, and view a graph of precipitation and streamflow data using HydroClient. First, use the "Enter a location” search box at the top left of the screen to zoom to a geographic area. This example uses Carnelian Bay, CA. Type this or another location in the search box and press enter. You will notice the Map zooms to the location of interest as shown below.

Notice the area of the map is shown at the bottom center of the map with a green thumbs up notifying you the area is small enough to search for data. For this particular example, the search needs to encompass a larger map area. Click on the zoom out option until you can view most of Lake Tahoe - an area of about 10,000 square kilometers. Your map should look similar to the screenshot below.

Now you will define your search criteria in the right side tool bar to find all of the precipitation and discharge data in the area that your map shows from 1/1/2012 to 12/31/2012. Begin by clicking on the blue Select Date Range button and typing in 1/1/2012 to 12/31/2012 in the From and To boxes then click Save. Next, use the Select Keyword(s) button to select Discharge and Precipitation under the “Common” keyword tab as shown below. Click Save to finish selecting your keywords.

Click on the blue Select Data Service(s) to limit the data services being searched. To search data sources with field observations only, click the “Select all non-gridded data services, e.g. NLDAS” checkbox in the right top corner as shown below and click Close.

Click Search Map to begin the search.

After a few seconds several blue markers will pop up on the map as shown above. Each blue marker has a number that indicates how many data series exist for that location. The markers cluster dynamically; if you zoom in you will get more precise locations, while if you zoom out the locations will be more generalized.

To see all of the data series, click Show Search Results on the Search Bar at right as shown below.

A list of all of the data series that are displayed by the blue markers in the map above will appear in a table as shown below.

Narrow your search by typing “SNOTEL 784” in the top right search box. This will filter the table to a specific SNOTEL station that has precipitation data. Highlight the first row of the list as shown below.

Take a minute to understand the data series that you have found. Scrolling from left to right, you will see the following columns amongst others such as Start Date, End Date, and Site Name:

  • Keyword: Precipitation
  • DataType: Incremental
  • ValueType: Field Observation
  • Sample Medium: Precipitation
  • Time Unit: Day
  • Time Support: 1
  • IsRegular: True

 

This information about the data, or metadata, tells us a lot about the particular data set. From this information, you can discern that this is a precipitation time series that is measured in the field and summed on a daily basis. And, according to this metadata, it is measured at a regular frequency.

Once you understand the precipitation data set, continue to locating the discharge data set below.

Leaving this SNOTEL precipitation row highlighted, go back to the search box and type “WARD C AT HWY 89 NR TAHOE PINES CA”, which will filter the table to a USGS monitoring station that has discharge data, and then select the first row that has a Data Type of "MEAN".

Take a minute to review the various metadata for the highlighted Discharge data set. Again, scrolling from left to right, you will see the following fields among others such as Start Date, End Date, and Site Name:

  • DataType: Mean
  • Value Type: Derived Value
  • Sample Medium: Surface Water
  • TimeUnit: Day
  • TimeSupport: 1
  • IsRegular: True

From this information, you can see that this is a daily average of discharge of surface water. The values are derived from other measured observations and computed at a regular frequency.

Once you understand the discharge data, Click Select Action. There are two options: Add 2 Selections to Workspace and Export 2 Selection as shown below.

First, click on Export 2 Selections to save a copy of the data series on your local computer. You will notice a notification appears that says the task has started and "to check the download status, please open the Exports tab."

 

You can access the Exports tab by opening up the Workspace. The Exports tab only provides information on the status of the download. Most downloads complete quickly and checking on the status is not necessary. When a download is complete a pop up will appear as shown below.

After you have saved a local copy of the data to your computer navigate back to the list of data series. The two data series should still be highlight. Go to Select Action again and this time choose Add 2 Selections to Workspace. Click on Workspace located at the top right as shown below.

The Workspace is shown below. The Workspace allows you to save data series for a single browsing session or when logged in as an authenticated Google User, you can save data series for up to 30 days.

Now, you are ready to view the data series. Highlight both data series, click Select Tool and choose Time Series Viewer as shown below.

Once you click Launch Tool: (2), the Data Series Viewer will open up in a new browsing window as shown below.

The Data Series Viewer allows you to view the data and obtain summary statistics. As shown in the graph above, the signal of the precipitation measured in Tahoe City, CA can be seen in the discharge measured in Homewood, CA. Generally, an increase in precipitation is followed by an increase in discharge.

Click on the arrow signs on the data series rows to view additional metadata and a box and whisker plot with summary statistics as shown below.

 Click out of the Data Series Viewer and continue back to your HydroClient page. First refresh our search results by clicking Search Map (do not manipulate the search parameters and do not refresh the webpage).

The location of these monitoring stations are approximated in the screenshot below. The markers may look different and have different numbers, as the HIS Catalog, and thus the data returned in a search, is updated regularly.

If you click on a marker in the map, a table of the data sets at that location is displayed. 

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