Module 2: The Climatology of Water
In this module, we investigate the underlying causes of variations in precipitation on Earth, with a specific focus on large-scale climate belts and the role of mountain ranges in affecting the distribution of rainfall (and snow). The goals of the module are to develop a quantitative understanding of the physical processes that control the distribution of precipitation, and which ultimately govern regions where water is abundant and where it is scarce, both across the United States and globally.
The goal of Module 2, The Climatology of Water, is to enable students to understand basic atmospheric circulation, interactions of air masses with topography, and the local and global distributions of rainfall. After completing the module, students will be able to:
- identify the unique physical properties of water that contribute to its fundamental role in driving Earth systems;
- identify US and global precipitation patterns by reading precipitation maps;
- quantitatively compare fluxes of water in the hydrologic cycle;
- calculate relative humidity, and use it to quantitatively explain Earth's first-order patterns of precipitation;
- assess the relationship between precipitation, topography, and location on the globe.
Context for Use
Overall, this one-week module is intended for use as a stand-alone lesson or as part of an online or blended general education or introductory-level course that would satisfy a science distribution requirement. The module would be appropriate for non-majors and undeclared students looking for a major. There are two formats: (1) blended, where the students meet at least once to perform the activities in teams; and (2) 100% online. As a general guideline, the delivery of content and assessment of learning goals/objectives have been designed to accommodate the logistics of large class sizes where students are expected to work approximately three hours per week covering lecture content with an additional six hours per week of additional reading and work on assessments. Note that some students will require more or less time to meet the goals and objectives of the module.
Description and Teaching Materials
In this module, students will:
- interact with online teaching materials pertaining to the distribution of water on Earth;
- analyze the inputs and outputs in the global water cycle to gain insight into systems thinking;
- determine relative humidity and dew point by reading a graph;
- interpret the orographic effect after watching an animation;
- track the movement of water by atmospheric circulation in a Hadley cell;
- analyze precipitation data to demonstrate the reality of the orographic effect in the United States.
All materials for students are available online using the Student Materials link below. These can be implemented entirely in the context of distance learning, with students completing any discussion questions in the form of a blog or discussion group. In a traditional or blended classroom setting, students can complete the online unit as homework, using class time to address the discussion questions and the Summative Assessment.
Teachers can find documentation of the activities as well as rubrics for students at this location. Rubrics for teachers are compiled under Assessment on this site. Suggestions for teaching and a list of the assessments are found below.
Teaching Notes and Tips
What works best for the module?
This module introduces the most relevant aspects of Earth's climate system driven by differences in receipt of solar energy at the Earth's surface—primarily principles of relative humidity, dew point, orographic effect, and the Hadley circulation—that determine the distribution of precipitation and runoff. This is fairly complex material that is best illustrated in animations. We compiled a variety of videos to illustrate some of the intriguing physical characteristics. While all students should have been exposed to these concepts in high school, this provides a good recap and is especially useful when tied to the large-scale processes that govern our climate system. We do not fully explain the role of the Coriolis effect in wind and ocean current patterns because it is not so critical to our objective of promoting student understanding of the basic processes driving precipitation and water resource distribution. Students struggled somewhat with each of the Formative Assessments (see below), but found the Summative Assessment useful and straightforward after a brief initial summary lecture on processes, and after their having already attempted Formative Assessments 3 and 4. Again, the Summative Assessment emphasizes plotting and interpreting x-y graphs and reinforces this skill.
What students found difficult
Formative Assessments 1 and 2 were relatively straightforward, but some students failed to properly convert units in Formative Assessment 1 or to correctly calculate relative humidity in Formative Assessment 2. Most students did these correctly. A few students had problems understanding that the water fluxes to and from the ocean had to balance and asserted that there was an imbalance even with the numerical support for overall balanced fluxes; one strategy for gaining understanding would be to point out the consequences of a long-term imbalance for such a system (like the bathtub example). The instructor could set up a simple model system with inputs and outputs and demonstrate quantitatively how a change in one output would produce a cascade of changes in other inputs/outputs. The concept of "dry land farming" was not familiar to some students and should be defined in class. Several students were confused by the term and did not see how it could apply to the northeastern United States, for example, where there was ample rainfall. Formative Assessments 3 and 4 were challenging to a greater proportion of students (but varied by pilot group). The biggest issue was interpreting the graph of water content of an air mass vs. temperature, even though a concise tutorial is illustrated in the module. It was worthwhile, however, having the students struggle with these problems prior to doing the Summative Assessment. As a result of having attempted the Formative Assessments they realized what they did not understand, and, after 10 minutes of question and answer in class (with students coming to the plot exhibited on a white board and plotting points, then doing calculations of relative humidity), they launched easily into the Summative Assessment. When teaching this class fully online, it is recommended to have the students complete Formative Assessments 2, 3, and 4 before proceeding to the Summative Assessment, unlike many other modules in which it is possible to pick and choose assessments or skip straight to the Summative Assessment. It may be advisable to set aside some question and answer time using Skype, Google Hangouts, or your Learning Management System to help online students through the Formative Assessments.
Module 2 only includes a simplified discussion of the climate system that is relevant to understanding the patterns of precipitation shown in various maps. The module does not discuss climate variability or deal with mechanisms of or changes in solar or greenhouse gas forcing of climate change. The emphasis is placed on evaporation-precipitation patterns and atmospheric transport of water vapor as a lead in to Module 3, which considers consequences for watersheds and river systems. Variability in precipitation and runoff is covered in Module 4, and implications of climate change for future water resources is covered in Module 8.2, so it is essential that students master the material in Module 2.
- Formative Assessment 1: The Water Cycle
- Formative Assessment 2: Relative Humidity and Dew Point
- Formative Assessment 3: Orographic Effect
- Formative Assessment 4: Hadley Circulation
- The Summative Assessment for this module is Hadley Cells and the Orographic Effect.
References and Resources
- Readings from Student Materials – Module 2: Climatology of Water
- The Big Thirst: The Secret Life and Turbulent Future of Water by Charles Fishman: Chapter 3