Unit 5.2 - Water Balance Impacts
Concepts and content
- Many measurements are taken at a single point. We use tested methodologies to efficiently scale them up to the spatial extent of interest.
- Both Critical Zone processes and land management decisions impact the water balance. The process of decision-making for water resources requires deep understanding of the water cycle and quantitative data to best balance both societal and environmental water needs.
- Critical thinking, distinguishing differences of scale, relating sets of measurements at different scales, and explaining the assumptions.
- Decision making, synthesis for model justification.
Context for Use
This module covers two 75-minute periods. Calculators and computers are optional in Part 1 and required for Part 2. If you have a longer or less-frequent class time, adjustments can be made to the suggested activities as needed.
Unit 5.2 - Day 1 Classroom-based discussion is best suited for groups of students. The discussion is structured around a pre-class reading that is integral to participation. The Interpolation Introduction and Exercise activity is most beneficial for students to complete independently in conjunction with the second presentation by the instructor.
Unit 5.2 - Day 2 Interactive exercise for students in groups or alone. The activity applies knowledge and skills acquired throughout the unit. Could be completed outside of class, but conducting the exercise in class facilitates discussion and allows questions to be answered promptly.
Description and Teaching Materials
- Goulden, M.L., Bales, R.C. (2014): Mountain runoff vulnerability to increased evapotranspiration with vegetation expansion. Proceedings of the National Academy of Sciences. 111 (39). DOI: 10.1073/pnas.1319316111.
Unit 5.2 - Part 1 (75 minutes total)
- Time: A 75 minute class period (20 minutes for scaling lecture presentation and in-class discussion; 20 minutes for activity interpolation introduction; 25 minutes to complete in-class interpolation exercise; 10 minutes to reconvene and discuss).
- Setting: Prior to class, the students should have read the Goulden and Bales paper. There is a lecture on scaling and much of the preliminary discussion should be centered around assumptions as we scale from point measurements to basin measurements. There is a second presentation that includes an in-class interpolation activity where students work with the instructor to interpolate from multiple point measurements to an areal average.
- Materials: One interpolation worksheet and map per person, plus extra map copies (see description and teaching materials for files); rulers (optional for measuring areas in interpolation activity)
- Lecture 5.2.1: Scaling up - an introduction to moving from point measurements to a basin-scale average
- Spatial Scales Lecture Presentation (PowerPoint 2007 (.pptx) 7.7MB May30 17)
- Include discussion of pre-unit reading assignment by Goulden and Bales
- Recommended in-class discussion questions:
- We just calculated a water balance for a tree using precipitation, evapotranspiration, and change in soil moisture. Can we use the same process to estimate water fluxes across a catchment?
- Does this approach breakdown for short timescales? Why or why not?
- Can the fluxes calculated be scaled up? What are some of the limitations on scaling?
- Could this same approach work to compare the fluxes for wetter or drier years?
- Would more instruments improve the water balance estimation? What kinds and how many? What are some of the limitations to adding more instruments?
Activity 5.2.1: Interpolation introduction and exercise, followed byclass discussion on scaling water balance calculations
This is a skill building exercise to show an approach of how multiple point measurements can be used to develop a spatial average. This activity also provides the structure for a classroom discussion on scaling. Encourage students to consider the assumptions and approximations they are making as they do this exercise. Through the exercise and discussion, students should be able to list challenges to scaling water balance components, discuss how to overcome or work around those challenges to produce usable estimates, and create a theoretical plan for scaling water balance estimates between point-scale and a catchment or regional scale.
- The Spatial Analysis and Interpolation Activity Presentation (PowerPoint 2007 (.pptx) 1.3MB Apr17 17) contains 1) an introduction to spatial analysis and interpolation, and 2) step-by-step instructions and answers for an in-class activity that students will complete to practice Thiessen polygon interpolation.
- Students use the Gridded Map of Norris Basin (Acrobat (PDF) 84kB Oct12 16), along with precipitation information in the above presentation, during the in-class activity.
- 5.2.1 Homework - Interpolation Worksheet (Microsoft Word 2007 (.docx) 284kB Dec23 16)
- Contains instructions, data tables, and questions to answer
- 5.2.1 Homework - Interpolation Map (Acrobat (PDF) 17kB Oct12 16)
- Gridded basin outline with precipitation gauge locations
Unit 5.2 - Part 2 (75 minutes total)
- Time: A 75-minute class period (10 minutes relating previous content and activities to today's activity; 60 minutes for activity Sections 1-3; 5 minutes to wrap up and discuss Section 4 homework). Sections left incomplete at the end of the class period can either be assigned as homework or completed during another class period.
- Setting: This is an in-class activity that can be done individually or in groups. Computer devices compatible with Microsoft Excel are required for Section 3 of the activity.
- One copy per student of SimWater Activity Packet (Acrobat (PDF) 669kB Mar20 17)
- This packet contains all maps and activity questions.
- Map 1 should be used for Sections 1 & 2.
- Map 2 should be used for Question 12.
- Calculators for Sections 1 & 2
- Computer devices with SimWater Allocation Spreadsheet (Excel 2007 (.xlsx) 13kB Mar20 17) loaded for Section 3
- Colored pencils for Section 4
- Activity 5.2.2: SimWater - Simulating Water Supply, Demand, and Management
Mountains to Valley Version
SimWater is an activity that directly connects environmental and societal systems by simulating water management decisions at regional scales to meet environmental standards and societal goals. In Sections 1 and 2, students use their knowledge of spatial scaling and forest water use in the critical zone to extrapolate a surface water budget for the region surrounding the catchments of the Kings River. Students then make data-driven land and water allocation decisions in Section 3, which includes multiple types of water users and two different agricultural economy structures. Finally in Section 4, students reflect on the activity and its broader implications by answering a series of exploratory questions.
Introductory in-class discussion should focus on reviewing the concepts of water inputs and fluxes in the Critical Zone, and conducting hydrologic research across multiple scales. The human component in water budgeting should also be introduced; it is an essential component to consider both in the activity and in the Critical Zone as a whole. If time permits, post-activity discussion topics are provided in Teaching Notes.
For the activity, details for downloadable materials are provided below:
- SimWater Activity Packet (Acrobat (PDF) 669kB Mar20 17)
- Double-sided printing recommended
- Includes activity questions (8 pages) and 2 maps for exercise (2 pages)
- Map 1 contains a satellite image of the region. Students should use this for extrapolating precipitation and forest water use in Sections 1 and 2.
- Map 2 is the same map extent as Map 1 with satellite image removed. This map should be used for Section 4, Question 12, in which students design their land allocations on the map.
- SimWater Allocation Spreadsheet (Excel 2007 (.xlsx) 13kB Mar20 17)
- Required companion Excel spreadsheet for Section 3, Questions 6 and 7. Instructions are included within the spreadsheet.
- Questions 6 and 7 each have their own section in the spreadsheet; cells for Question 7 are below the cells for Question 6. It is essential that students use the correct cells to answer each question.
- Only certain cells should be filled in by students; these cells are listed in the spreadsheet. Many cells in the sheet are automatically calculated and should not be altered.
- See Assessment section for details.
Teaching Notes and Tips
Notes on 5.2 Part 1
Lecture and Discussion
Integrating lecture and in-class discussion together is recommended. One can pause at various points of the lecture presentation and ask class discussion questions. We recommend pair-share or small-group discussion with groups reporting back to the class to share discussion points. Points to be covered in lecture and discussion:
- The paper by Goulden and Bales uses data from the SSCZO elevational transect of flux towers to estimate the evapotranspiration from the whole Kings River Basin and explore the water balance for the Kings River. They use this upscaling to examine the vegetative water demands if temperatures increase and how discharge in the Kings River might decrease in the future. The scaling methodology used is to use point data for evapotranspiration at different elevations and satellite data of the greenness of the vegetation to scale up to the river basin scale. Scaling was also done for other water inputs and outputs (i.e. precipitation and surface water flows).
- Water balance components like soil moisture, precipitation, and runoff can vary greatly across spatial and temporal scales. This makes comprehensive measurements challenging and expensive. In order to understand and model such components accurately and efficiently, field campaigns and experiments should be designed to collect appropriate data types and amounts, and allow scaling across time and space.
If students are struggling to count grid squares/rectangles on the included maps, we recommend that they number rows and columns, or group and number them, to help count. Teachers may also enlarge the maps foe easier viewing by photocopying or printing on 8.5x14-inch or 11x17-inch paper.
Maps of areal extent in this activity do not have scales. While a scale may be interesting to understand the size of the catchment for the activity, it is unnecessary to complete the exercise. When conducting spatial analysis with both Thiessen Polygons and Inverse Distance Weighting, units of area or distance measured in the process cancel mathematically. Consequently, the only unit remaining is the unit of precipitation in millimeters.
- Slides 18 and 19 in the Spatial Analysis presentation pose this topic as a question and discussion point for the class.
- You may also work through this mathematically with units using the Thiessen Polygon example (Slides 14-18) or Inverse Distance Weighting equation (Slide 29). Using the Inverse Distance Weighting equation may be easier to digest because all units are in a single equation.
Notes on 5.2 Part 2
Classroom and Time Management Notes:
- Because the questions are iterative and rely on answers to previous questions, it may be helpful to walk through certain steps together or have students work in groups so they can compare answers with each other as they work.
- Page breaks were inserted between each section of the activity, so the activity can be distributed in parts instead of all at once and completed over multiple class periods.
- We strongly advise that all teachers preview and practice using the Allocation Spreadsheet before instructing students.
- We recommend that teachers unfamiliar with inverse distance weighted extrapolation practice calculating weighted precipitation before instructing students.
Additional Activity Information:
- All quantitative values used in this activity are based on real, publicly available data. Valley zone precipitation values are based on regional historical averages (~1982-2015) obtained via PRISM. Precipitation and evapotranspiration values in the Mountains zone are based on recent (~2010-2015) tower measurements at Southern Sierra Critical Zone Observatory sites, located at four different elevation zones in or near map extent. Annual water usage per user type and provisional rates of housing, job creation, and persons fed were calculated based on publicly available national, state (CA), and regional data.
Additional discussion topics before or after the activity could include:
- Disconnects between water supply and demand, i.e. understanding and appreciating declines in water supplies. Examples from California include:
- Spatial disconnect: In many parts of the western United States, mountains can serve as "water towers". However societal demand for water in the mountains is relatively lower. In California, precipitation falls in mountain ranges and flows via rivers and man-made aqueducts and canals to the areas where higher demand is located. Snowpack also acts as a reservoir, gradually releasing water downstream as it melts.
- Temporal disconnect: Much of California experiences a rainy season in the winter and spring, and a dry season in the summer and early fall. It is naturally driest during the peak of the agricultural growing season, when water demand is greatest. Residential and commercial areas also generally do not adjust their demands to follow the natural supply. To address this, there are large reservoirs to store winter precipitation and snowmelt. These reservoirs and their releases control the downstream flow in streams and rivers.
- Satellite Imagery on Map 1
- Identify and discuss features on the satellite image. For instance, current cities and farmlands in the Central Valley are visible on the map. Are they located along rivers and streams? If not, how do you think water is routed there?
- Groundwater depletion
- When surface water is insufficient in quantity or quality, or too difficult and expensive to access and transport, groundwater is often withdrawn as a solution. Groundwater depletion is the term for a net reduction in groundwater that results from imbalance between subsurface water removal and replenishment.
- Some of the consequences of groundwater depletion are reduced ground- and surface water availability, poorer water quality, expensive well re-installations and deepening, and land subsidence. This is currently a global issue on several continents.
- Background on Western water law
- The history of water law in the Western US is diverse and could be an interesting point of discussion if time allows. For instance, several states independently regulate ground water and surface water management. Many large reservoirs are operated using a rule curve that cannot be changed without federal authority. And several states in the U.S. have gone to court over water; Arizona and California have had "water wars" disputed in court multiple times since the 1930s.
- What water laws does your state government enforce and how? What is the local history of water regulation in your region? How does it compare to other states?
This is a starting template for the discussion. Feel free to add or modify as needed to fit your class and create regional relevance.
Part 1 - Full credit for the discussion will depend on active participation during classroom discussion and performance on interpolation homework. An
Part 2 -
References and Resources
Day 1 Pre-class reading Goulden, M.L., Bales, R.C. (2014): Mountain runoff vulnerability to increased evapotranspiration with vegetation expansion. Proceedings of the National Academy of Sciences. 111 (39). DOI: 10.1073/pnas.1319316111.
Bales, R. C., N. P. Molotch, T. H. Painter, M. D. Dettinger, R. Rice, and J. Dozier (2006), Mountain hydrology of the western United States, Water Resour. Res., 42, W08432, doi:10.1029/2005WR004387.
Hunsaker, Carolyn T., Thomas W. Whitaker, and Roger C. Bales, 2012. Snowmelt runoff and water yield along elevation and temperature gradients in California's southern Sierra Nevada. Journal of the American Water Resources Association (JAWRA) 48(4): 667-678 DOI: 10.1111/j.1752-1688.2012.0064.x
Lui, F., Hunsaker, C.T., Bales, R.B. Controls of streamflow generation in small catchments across the snow-rain transition in the southern Sierra Nevada, California. Hydrological Processes p. 1959, vol. 27, (2013). Published, doi:10.1002/hyp.9304
Tague, C., and H. Peng (2013), The sensitivity of forest water use to the timing of precipitation and snowmelt recharge in the California Sierra: Implications for a warming climate, J. Geophys. Res. Biogeosci., 118, 875–887, doi:10.1002/jgrg.20073.