Spring 2011


John Pitlick

OFFICE: Guggenheim 315



Naomi Arcand

Anya Byers

Preston Cumming

Accessing Streamflow Data via the Worldwide Web

OBJECTIVES: (a) to use the worldwide web to access hydrologic data;

(b) to compare precipitation/runoff characteristics in different regions.

BACKGROUND: The National Weather Service (NWS), the US Geological Survey (USGS), and various other federal and state agencies in the US share the responsibility of collecting, reporting and maintaining hydrologic data. There are literally thousands of precipitation and streamflow measurement stations across the country. Some of these stations have been in operation for over 100 years and they provide key information on long-term changes in climate and surface-water hydrology. 

DATA: Web sites maintained by the USGS and the NWS provide information on current conditions of precipitation and streamflow throughout the country. Through these sites you can also access historical records of precipitation and streamflow, and recently published reports.


We suggest you open a WORD document, and use the copy/paste commands to place your graphs and results within that document.  Clearly identifying the question number, e.g. 1a) 1b) ..... 6a) 6b) and so on.

Be sure to include: SUGGESTION: Open TWO WINDOWS in the web browser of your choice.  Keep the assignment on one page and use the other page as a base to access links. This will allow you to have the questions available as you look at the reference sites.

1. Open the USGS water resources web site

a) Select the small map of the US labeled WaterWatch

b) List two general regions of the country where streamflows are presently above / below average:

above average:

below average:

c) Click on one of the states in a region with above average flow, and you should see a more detailed map showing the locations of individual gaging stations.  Click on one of the black dots.

You should see a menu similar to the one shown below on the left panel.  Click on the tab labeled 'hydrograph' and you will see recent changes in discharge, as shown in the middle panel.  Click on the tab labeled 'peak' and you will see peak discharges for each year in the period of record. 

The data presented in these graphs can be retrieved by selecting different options, and if you are interested in doing further data analysis, such as flood frequency analysis, you can download individual data sets in different formats.

2. In addition to streamflow and water quality data, the USGS provides information on drainage basin characteristics for many streams and rivers (e.g. drainage area, average elevation, channel gradient, mean annual precipitation, percent forest cover, and so on). These data can be used to develop relations for streamflow and floods in drainage basins where there are no gaging stations. To illustrate this approach we will use data from 20 streams in the Colorado Front Range, and try to correlate the mean annual flood (MAF) with relevant variables such as drainage area (DA), mean annual precipitation (MAP), and average basin slope (SLOPE).

a) Open Microsoft EXCEL.  Then, click on the link below. You should see a table listing data for the individual drainage basins.

Table 1.  Values of drainage area (DA), mean annual precipitation (MAP) and average basin slope (SLOPE) and mean annual flood (MAF), for 20 streams in the Colorado Front Range.

b) Highlight the values listed in the table, and use the Copy and Paste commands to paste the values into the EXCEL spreadsheet.

c) Using the chart options within EXCEL, construct three X-Y scatter plots showing relations between (i) MAF and DA; (ii) MAF and MAP; and MAF and SLOPE.  The procedures for making X-Y scatter plots are as follows:

d) Add axis labels to your chart.  In new versions of EXCEL, the tab for axis titles can be found under the layout menu.  In old versions of EXCEL, select Chart Options under the Chart menu.

e) Add linear trendlines to each of the plots. 

f) Repeat steps c) - e) to construct the two additional plots, MAF vs. MAP, and MAF vs. SLOPE.

g) Select each of the plots individually, copy them, and paste them into your WORD document.  Perhaps re-size them so they fit on one page.

h) Answer the following question: Which of the three variables- DA, MAP, or SLOPE- is better for predicting the MAF?  Explain.


3. Climate observations and data characterizing trends in precipitation, temperature, snow accumulation, etc. are available through various federal and state agencies, including the National Weather Service, the Natural Resources Conservation Service, the US Forest Service and state climatology offices.  For this next exercise, we will use NWS data to evaluate the significance of long-term trends in precipitation at two locations in the USA, Burlington, VT, and Boulder, CO.

a) Using your web browser, go to the NWS web site for Burlington, VT:

b) Select the tab Local Data/Records, and click on the link to Monthly Temperature/Precipitation/Snowfall Averages & Totals.  Click on the link to Precipitation.  You should see a table of monthly and annual precipitation, starting in 1884.

c) Open a new spreadsheet in Microsoft EXCEL.  Highlight all the data from 1884-2008, and use the Copy and Paste commands to paste the values into the EXCEL spreadsheet.

d) If the data fall nicely into 14 columns, go to the next step; otherwise, go to the Data menu at the top of the page and select Text to Columns.   Select Fixed Width, then Finish.

e) Delete the columns corresponding monthly precipitation (JAN-DEC).  To do this, highlight columns B-M and select delete from the edit menu.  You should now have just two columns corresponding to the year and the annual precipitation, in inches.

f) Using the chart options within EXCEL construct a scatter plot of annual precip vs. year.  Label the axes accordingly and fit a linear trendline to the data.

g) What would you say just looking at the data... is the trend significant?  Sometimes it's hard to tell.  We can, however, conduct a statistical test of the slope of the trendline, m, to determine whether it is (or is not) significantly different from zero. The procedure is as follows:

slope of the regression line, m 
  intercept, b
standard error of m, SEm
  standard error of b
coefficient of determination
  standard error of y
F statistic
  degrees of freedom
regression sum of squares
  residual sum of squares
Ho : m = 0
H1: m ≠ 0
h) Copy and paste the plot of PRECIP vs. YEAR into your Word document.  Also copy the table of parameter values and results of the t test.  What do you conclude about trends in annual preciptation in Burlington, VT?

i) Conduct a similar test of trends in annual precipitation in Boulder, CO for the period 1894-2008.  To access these data, click on the link to Table 2.