GEOL1111_when precip changes
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Jan 9, 2024
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GEOL1111 – When precipitation patterns change – Water Resources; lab is worth 30 points!
Part A: What is Drought?
In this two-week lab, you will work through data associated with precipitation, climate and rivers. This handout is based on lab 4 in the Science Education Resource Center (SERC) Earth Lab module on droughts (https://serc.carleton.edu/eslabs/drought/4.html). I encourage you to follow along on the webpages to get more information and hints on how to proceed. There are a series of show-me links on the webpages that will help you navigate this exercise. Note this is a LONG exercise, so please start it sooner rather than
later. I will also post a recording on how to go about completing this work. You will need access to Google Earth. If you do not have access please let me know so I can help you sooner rather than later. The questions (provided on a separate handout) will be due Tuesday, November 2, 11:59PM via the electronic submission folder. Have fun exploring -
Image from the SERC webpage. Click on the image for a larger view:
Climographs can be used is to plot current conditions over a background of the average conditions
—
this provides a graphic way to see how the current year compares to the long term average. These dynamic graphs indicate if current conditions are abnormally hot, cold, wet, or dry.
1.
Click the thumbnail image at right to see a larger view of a climograph for San Antonio, Texas. The graph shows conditions for January through mid-July
of 2008.
2.
Examine the graph to interpret the conditions in San Antonio. The background colors (pale red for temperatures and light green for accumulated precipitation) show the average conditions compiled from many years of data. The brighter red and green lines show daily temperatures and accumulated rainfall through July of 2008.
Checking In
o
What does the graph indicate about San Antonio's temperature?
The temperature was above average during January but has been in the normal range since then.
o
What does the cumulative rainfall graph indicate?
Rainfall has been below normal all year. The cumulative total for 2008 is roughly one third of the normal total for the end of July.
3.
NOTE – this instruction is different from what is on the SERC webpage. To look at other long-term climate related data and weather patterns, go to https://www.ncdc.noaa.gov/cag/
. Here you can select different states, cities and timescales. Locations are selected from the dropdown menus. See zoom recording for more information on how to access data. After you have explored different areas of interest to you, answer the question in the stop and think box. This question is also on the separate word document to be submitted in the Electronic Submission folder.
Stop and Think
1.
List 5 cities or locations for which you examined dynamic climographs (climate data) or accumulated precipitation maps. Include the date range that you observed. Tell whether each location is wetter than normal, about normal, or drier than normal. Explain your reasoning.
Defining drought
The word "drought" means different things to different people. What visions does the term bring to your mind?
Parched land, dried crops, dust storms, and starving livestock are some of the scenes that people associate with the term drought. Unlike most hazardous weather conditions,
drought is not always obvious. Drought can be years in the making, as moisture in the soil evaporates and surface water sources disappear due to the lack of rain.
1.
Read the information at What is drought?
to come up with your own meaningful definition of drought. Discuss your definition with a lab partner to see if it can be improved.
Stop and Think
2.
Write a definition for drought, in your own words.
2.
Learn all about drought at the UNL Drought for Kids
page.
3.
Find out what the how drought is studied by reading the links on the, How Do People Study Drought?
page.
4.
Learn about the physical processes that cause or contribute to drought in Earth Observatory's North American Drought Article
. Read the information
about each contributing factor and view the animations about soil moisture
(on the second page of the article). The animations will help you to visualize the feedback loop that exists among rainfall, soil moisture, and temperature.
Is it a drought today?
Based on the signs and symptoms of a drought, scientists classify drought as in one of three stages. Listed in increasing in severity, the three stages are: meteorological drought, agricultural drought, and hydrological drought.
1.
Examine the diagram above to see the signs of meteorological, agricultural, and hydrological droughts.
2.
Interpret the chart to answer the following questions.
o
What are the causes of soil water deficiency?
o
If an area is experiencing reduced streamflow, which stage of drought is occurring?
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Part B. Visualizing Drought Indicators
Three of the most obvious indicators of drought are below-normal soil moisture, lack of precipitation, and decreased streamflows. You'll explore each of these parameters briefly to develop a sense for what happens to land that is experiencing drought.
Reduced soil moisture: hands-on activity
Photo of drought activity. Courtesy of Betsy Youngman
1.
Acquire two matching clear containers (use 400 ml beakers or the bottom half of 1-liter soda bottles).
2.
Label one container as "wet" and the other as "dry."
3.
Place equal amounts of dry potting soil (about 250 ml) into each container.
4.
Add 50 ml of water to the "wet" container and cover both containers with clear, colorless plastic wrap.
5.
Place the containers in direct sunlight or under a bright lamp.
6.
After 5 minutes and again at 15 minutes, observe the plastic wrap covering.
Stop and Think
3.
Compare your model to the real world: describe the situation represented by each container. 4.
On average, the Western U.S. experiences fewer cloudy days per year than the Eastern U.S. Based on this fact, which area is more likely to have drier soil and therefore, be more prone to drought?
Decreased precipitation
The National Weather Service keeps records of the amount of precipitation across the contiguous United States. You'll explore some of these images in Google Earth, such as
the one pictured right, and interpret them to predict which areas might be developing or
experiencing drought.
1.
Launch Google Earth. 2.
Use the information in the two sections below to walk you through interpreting the two different types of images in the file. NOTE: The file you downloaded shows data images for the Spring of 2008. To view web-based images of current data, go to the Advanced Hydrologic Prediction Service: Precipitation
.
Interpreting Precipitation Images
Turn on the January 2008 Precipitation layer. Use the color scale on the right to interpret
the map colors.
On the map, look at the area where you live to see what color it is. Check where that color is on the scale.
Find an area on the map that is a different color. Check that color on the scale to see if the second location received more or less rain than your area.
Check carefully to find areas on the map that had the most and least precipitation.
After you've worked on understanding the patterns, check your interpretation by revealing the example interpretation below.
Un-check the box to the left of the name of the January Precipitation layer.
Interpreting Departure from Normal Precipitation Images
The National Weather Service also produces Departure from Normal Precipitation images. These show if areas had more or less precipitation than normal for the month.
Turn on the January 2008 Departure from Normal Precipitation layer. Use the color scale on the right to interpret the map colors.
Check carefully to find areas on the map that had more and less than normal precipitation.
After you've worked on understanding the patterns, check your interpretation by revealing the example interpretation below.
Stop and Think
5.
Which areas in the continental U.S. consistently received less precipitation than normal during January 2008?
6.
Based on your explorations, describe the locations that you think were developing or experiencing drought by June of 2008.
1.
Once you're confident that you can make meaning of the colorful images, one of the image sublayers at a time. Check the precipitation amount and departure from normal for your own location and look for areas that received
less precipitation than normal.
2.
Return to the Advanced Hydrologic Prediction Service: Precipitation
page. Turn on the Map Overlay for River Forecast Center boundaries.
3.
Explore the data across the contiguous United States, and within a region of interest. Choose for example, an area near your home, or in an area of known drought.
4.
Look at the 7-day, 30-day, and year-to-date maps. Switch between the Observed, Normal, and Departure from Normal maps. Look for areas that may be currently experiencing meteorological drought conditions.
Reduced streamflow
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The United States Geologic Survey (USGS) provides streamflow data from gauging stations across the country. At each station, instruments estimate the downstream flow of water and use wireless communication devices to submit the information to central locations. Flow rates are classified according to historical records so you can tell at a glance of a stream is above, at, or below normal levels.
1.
Go to USGS Waterwatch Google Earth Streamflow
On the page that opens, choose Streamgages, colored by streamflow condition
(390K)
. It is the first link in the list.
Choose the KMZ file, real_us.kmz, that is re-created every hour.
If necessary, open the real_us.kmz file in Google Earth. Turn the layer on by clicking in
the checkbox to the left of its name. Click the arrow to the left of the check box to reveal
the various layers of the streamflow data.
Checking In
From the legend, which colors indicate gauging stations that are reporting low streamflows?
Which regions of the United States show below normal (or dry) streamflows?
Use the check boxes in the legend to turn off the streams that are normal or higher or
not ranked. You will have 3 sets of gauges remaining on your map. They represent rivers
and streams where the flow is below the 25
th
percentile of normal flow for that day of the year.
Stop and Think
7.
If an area shows just one stream gage location with lower-than-normal streamflow, can you assume that the area is in drought? Why or why not? Describe one or more conditions besides drought that could account for low streamflow.
8.
Based on patterns in the streamflow data, predict which areas of the country are experiencing drought.
Compare your predictions to the Drought Monitor
1.
Go to the Drought Monitor Data Download page
to retrieve the KMZ data layer that shows current drought conditions.
Use this legend to interpret the Drought Monitor map.
2.
In Google Earth, choose File >Open
, and browse to the location where you stored the file. Turn the layer on and click the toggle (arrow) to reveal the sub-layers of data.
3.
You can find detailed information about the drought categories in the map from the National Drought Monitor Center
where the maps are produced.
4.
To focus in on the areas where drought is severe, extreme, or exceptional, turn off the drought index layers that are less than D2.
5.
Compare the areas of drought with the predictions you made based on precipitation and streamflow.
Stop and Think
9. How well did your predictions match the drought monitor map? Describe areas where your predictions were correct and areas where they did not match.
10. Of the two main types of data you examined
—
precipitation and the streamflow
—
which of the two seems to be a better predictor of drought conditions identified by the Drought Monitor layer?
Part C. How is Drought Measured?
1.
Go to the Current Conditions
webpage (links will open in a new window)
. Scroll down through the list and explore some of links to get a sense of all the maps and data products that are available for tracking drought.
2.
Read the about Drought Classification and Indicators at the About the Data
page from the US Drought Monitor.
3.
Several different Drought Indices have been developed, and each has its own strengths. We'll look at an index that has been widely used in agricultural regions of the U.S. Go to the National Weather Service's page on
the Palmer Drought Severity Index (PDSI)
to learn more about this index.
Checking In
o
What is the main parameter on which the PDSI is calculated?
o
Describe the range of values for the PDSI. Do positive values represent wet or dry conditions?
Palmer Drought Severity Image for the month of May 2016.
4.
Look at the PDSI map on the right (click the image for a larger view)
. It shows conditions for the month of May 2016. Use the color legend to interpret the conditions that existed across the contiguous U.S. at that time. Based on your interpretation, predict what might have been occurring at that time?
Stop and Think
11.
Access and interpret the current PDSI map image
. Write a description of current drought status for areas across the U.S.
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