Introduction to Hydrology

Introduction to Hydrology

Introduction to Hydrology

 Introduction to Hydrology

Lab #1


Please read lab carefully. Step-by-step instructions are presented. Questions (in bold) should be answered in your lab report, which can be submitted in the form of a word document to Blackboard.


Part 1: Download & Graph Precipitation Data from the NCDC


1) Navigate to the National Climatic Data Center website (

2) Click on Data Access in the top menu bar, take a few minutes to read through the page to see what types of data are available.


Question 1: Briefly describe three(3) different types of climate/weather data available from the NCDC website. Please use your own words, DO NOT copy and paste.

1WeatherBalloonClimate information from the environment, starting at three meters over the Earth's surface. These information are acquired from radiosondes, which are instrument bundles fastened to inflatables that transmit information back to the getting station.

2ModelAccess to close continuous, high-volume numerical climate forecast and worldwide atmosphere models and information. Investigating the past, present, and future to help with the examination of multidisciplinary datasets and advance interoperable information examination.

3 RadarAn acronym for Radio Detection and Ranging, a radar is a question recognition framework that utilizations radio waves to decide the range, height, bearing of development, and speed of articles delivering crude information and also creating investigation items.


3) Click on Quick Linksà U.S. Local Climatological Data à Quality Controlled Local Climatological Data. On this page you will find documentation and samples of data in html or ASCII (comma-delimited text file) format. On the right you can search for weather stations by map or from a list of states.


4) Select a station of your choice to access daily &hourly precipitation data for the month of December 2016. NOTE: Daily data is not available from all stations. Please choose a station for which daily data is available. How do you know which stations have daily data available?


5) After selecting the month of interest, you will be given the choice to select a particular day or the entire month. You should select the entire month.


6) You can access the data in either html or csv format. However, the entire dataset is most easily viewed in html format. Choose daily data and submit.


Question 2: What are the units for precipitation? What do M and T mean?


Question 3: How can you tell the form of precipitation?


Question 4: What does 2400 LST mean?


Note: If you don’t know the answer to the above questions, you may want to refer to the documentation files.


6) The data column you will be plotting is precipitation (water equivalent). You want to get this data into an Excel spreadsheet. This can be down by copying and pasting from the html table or by importing the entire dataset as a saved csv file.

If you choose ACSII (CSV) the web browser will display a comma-delimited text file. You can right-click and save page as a text file. This text file can then be imported into Excel using the File à Open command. By default Excel will only display excel file extensions, so make sure you select all file types in the Open File dialog box.


Note: If your station has no significant precipitation events for the month of December, try a different station or a different month.


7) Now that you have the data in Excel, you need to clean it up for easy plotting. Replace any missing data with zeros. Replace any trace precipitation with a non-zero, non-negative value less than one hundredth of an inch (for example 0.005). The replace function can be found in the Home Tab under Find & Select.


8) Plot the data as a column graph. Your graph is not complete without properly labeled axes, a title, and a caption. Be sure to include the following information: Units, Month/Year, Station Name and #, Station Location, Latitude, Longitude, & Elevation.

Note: A caption can be added directly to the graph using Insert à Text Box or you may add the caption after copying your graph into Word.


Question 5: Identify any significant precipitation events in your data. On what day did they occur and what type of precipitation (rain, snow)? Include your daily precipitation total graph here.


9) Looking at your spreadsheet or graph, select one day with significant precipitation and retrieve the hourly precipitation data corresponding to that day. Plot this data as you did for the daily data.


Question 6: What was the total duration of this precipitation event? What time(s) of day featured the most intense precipitation? Include your hourly precipitation total graph here.


Part 2: Estimating effective depth of precipitation, Mono Lake, California


In water budget studies, it is necessary to quantify inputs and outputs of water. One of the inputs is precipitation. How do we estimate the total volume of precipitation for a given drainage basin? We measure precipitation at fixed locations using rain gauges. This provides a value for linear depth of precipitation at one point. How can we extrapolate that across the entire area of interest? In this section of the lab you will use two methods to estimate the effective depth of precipitation over a given area.


Arithmetic Average Method: If the rain gauge network is of uniform density, then a simple arithmetic average of the point-rainfall data for each station may be sufficient to determine the effective uniform depth (EUD) of precipitation. This value can then be multiplied by the total area of the drainage basin to arrive at an estimate of precipitation volume for a specified time period (e.g., storm event, month, or year). Using thearithmetic average method, all data points were equally weighted.


Distance Weighting Method: This method is based on estimating rainfall at uniformly distributed grid points and then applying the arithmetic average method to those grid point estimates. How are grid point estimates made? Each observed point value (station) is given a unique weight for each grid point based on its distance to the grid point in question. The grid point precipitation estimate is calculated based on the sum of the individual station weights multiplied by observed station value. Weights are calculated as a fraction of the sum of the inverse of squared distances (more details follow).


You will use data from the Mono Lake Basin in the following exerciseto calculateannual volume of precipitation. Mono Basin is an intermontane, closed drainage basin in central Mono County, California and Mineral County, Nevada. The basin is about 300 km east of San Francisco and forms part of the eastern boundary of Yosemite National Park. The area of Mono Lake drainage basin is 1748 km2 and the area of Mono Lake is 215 km2.


Table 1: Precipitation data for Mono Basin and nearby stations.

StationStation CodeLong (°W)Lat (°N)Elevation (ft)Elevation (m)Average Annual Precip. (in)Average Annual Precip. (cm)Period of Record
BodieBDE119.01738.2178370 9.7 1997-2013
BentonBTN118.47837.8435450 7.6 1965-1968
Ellery LakeERY119.23337.9339645 24.4 1925-2005, 2009-2013
Gem LakeGLK119.14037.7529054 20.8 1925-2002, 2009-2013
Mono LakeMNL119.14938.0106450 13.2 1951-1980, 1983-1987
Mark Twain Campn/an/an/a7230 6.8 1950-1955
Cain Ranchn/an/an/a6880 11.1 1921-1964


1) Fill in table by converting units from feet to meters and inches to centimeters. Conversion ratios: 1 foot is equal to 0.3048 m; 1 inch is equal to 2.54 cm.



Question 7: Arithmetic Average Method. Determine the average annual precipitation (in cubic meters, m3) by averaging the precipitation data for stations within the Mono Lake Basin (for this method use stations within the basin ONLY). Calculate annual precipitation volume in the Mono Basin and separately, on Mono Lake.


Be careful with your units! Everything should first be converted to meters before multiplying the average precipitation value by the total area of the basin and (separately) of the lake. You should have two values in cubic meters when you are finished.

2) For the inverse distance method, you will only estimate effective depth of precipitation for a single grid point. Using the full page basin map provided, place this grid point as close to the center of the basin as possible. Next, measure the distance between the rain gauges and the grid point.



3) To calculate the weight, first compute the inverse of the squared distance (A) for each station. Sum these values (B). To calculate the weight, find the fraction of the total for each station (C). Multiply the weight by the observed precipitation value for the associated station (D). Sum the weighted precipitation values for an estimate of the effective depth of precipitation (E).




4) Use the effective depth of precipitation estimate for the central grid point to calculate the annual volume of precipitation falling over Mono Basin.


Question 8: What is the average annual precipitation in m3 for the Mono Lake Drainage Basin based on the weighted distance method applied to a grid point located at the center of Mono Basin?





Question 9: Compare the results of both methods. How much do they differ from one another (in percentage terms)? Which estimate do you trust the most?





*You can place all of your answers (including your precipitation graphs) in a single word document and submit it through Blackboard. A digital version of this lab is present on the Blackboard site for the course.


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