Grand Canyon Microclimate (Synthesis Essay)

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Lab Title Microclimates and their link to vegetation in the Grand Canyon

Courtesy of the National Park Service (NPS), a helicopter view of mixed Ponderosa Pine – Oak forest on the rim transitioning toward desert scrub vegetation near the bottom of the Grand Canyon.

What is this lab all about?

Arizona is the “Grand Canyon State.” From the perspective of climate and its associated biota, this is especially true. The full range of Arizona’s climates and ecoregions is on display. The highest elevations on the Kaibab Plateau’s north rim host spruce-fir-aspen forest, while Mojave and Sonoran desert plants pepper its lowest elevations. This lab tasks you with analyzing how the Grand Canyon’s topography influences its climate and vegetation patterns. The goal is for you to better understand basic concepts of physical geography science by interrogating the sorts of data used in scientific research – but all in a 100-level class (no prerequisites).

Lab Worth The points you accumulate for correct answers count towards your grade. Incorrect answers do not hurt your grade.

Computer program used in this lab

You will be given instructions in a canvas module page on how to download virtual world of Grand Canyon microclimatology and vegetation. In this program, you are a virtual character able to wander around the Grand Canyon’s landscape, summer temperatures, winter temperatures, and vegetation. WARNING: There are two different Grand Canyon geovisualizations – this one and one focusing on the topography and its connection to rock types. They are different video games with different data. You must use the microclimate game to complete this lab.

Interesting maps to download – not necessary to do the labs, but helpful to some students

National Park Service map of Grand Canyon National Park: https://www.nps.gov/carto/hfc/carto/media/GRCAmap1.jpg NPS 3D map of the Grand Canyon https://www.nps.gov/carto/hfc/carto/media/GRCA3DMap.jpg Shaded relief map of the Grand Canyon area: https://legacy.lib.utexas.edu/maps/national_parks/grand_canyon_map.jpg Vegetation Map of the Grand Canyon (23.4 MB) https://irma.nps.gov/DataStore/Reference/Profile/2221240

SQ general studies criteria

Students analyze geographical data using the scientific method, keeping in mind scientific uncertainty. Students also use mathematics in analyzing physical geography processes and patterns.

TABLE OF CONTENTS OF THIS DOCUMENT 1. Preface: How do you begin to understand the complexity of microclimate and its role on vegetation?

Page 3

2. Overview of lab activities Page 5 Stage A: Lecture Basics on Grand Canyon ecoregions and microclimate

Page 7

Stage B: Exploration: Making observations related to climate and biogeography of the Grand Canyon

Page 14

Stage C: More detailed investigation of microclimate and vegetation

Page 24

Stage D: Synthesis

Page 37

1. Preface: How do you begin to understand the complexity of microclimate and its role on vegetation? The Grand Canyon is famous for many reasons, primarily its stunning landscape. Part of that landscape involves diverse ecoregions. The diagram below is famous for portraying this diversity, and it was redrawn by the National Park Service (with the elevations higher than the dashed-line Grand Canyon found in the nearby San Francisco Peaks). The idea conveyed so cleanly and so neatly in this diagram is that higher locations are cooler and wetter, with north-facing slopes being protected from solar radiation more than south- facing slopes. This one diagram does a nice of idea of communicating the basic idea of microclimate influencing these ecoregions (sometimes called life zones).

When the National Park Service tried to create a more realistic mapping of plant types in the Grand Canyon, a very complicated map was produced: Vegetation Map of the Grand Canyon (23.4 MB) https://irma.nps.gov/DataStore/Reference/Profile/2221240 . In this map below, you can see a bewildering complexity of plant associations displayed by different colors. In all, there are over 30 groups presented. This map is a generalization of reality found in the field. It is a product of a mixture of a lot of fieldwork and study of remotely sensed imagery.

These plant associations are intimately connected with climate, and the climograph below summarizes the sort of decadal conditions that promote a Ponderosa Pine forest (tan color in the above map) on the rims of the Grand Canyon: cool winters, and both winter (snow) and summer (thunderstorm) peaks in precipitation. Even in the same sort of Ponderosa Pine forest, there are differences. On the North Rim of the Grand Canyon the Ponderosa Pine is mixed with some fir and other sorts of cool-loving plants that require more precipitation. On the South Rim, the Ponderosa Pine tends to be mixed with oak and needs less precipitation and can tolerate warmer temperatures.

These sorts of plots are also called climographs, and they portray both temperature and

precipitation information throughout the year. Note the warmer summer highs on the South Rim and the higher January-March precipitation (as snow) bars on the North Rim.

Before this lab, flat maps and climographs formed the basis of student learning of this material. Everything was generalized for the student. The vegetation maps and diagrams are either extremely complicated or too general, and both are frustrating for introductory students. That is why we turned to video game technology and geovisualization of climate and plants in and around the Grand Canyon. You can explore these relationships, and our job as laboratory builders is to try to do justice to the change in educational technology. I hope you think we did an okay job with this lab. 2. Overview of Laboratory Activities

You are undoubtedly familiar with the key scientific concepts that this lab covers, based on your life experiences (see the left column). The different stages of this laboratory delve deeper into these experiences by linking them to core aspects of physical geography.

Life Experience of Students

Stage A – Videogame exploration

Stage B- presentation of academic concepts (lecture, reading, or both) that are a review of GPH 111

• the sun rises in the east, reaching its highest point at noon, and sets in the west

Surface temperatures are acquired at 10am and can be interpreted from life experience.

Understanding diurnal temperature variations are a core concept in physical geography

• in the coterminous USA, the sun is always in the south part of the sky

North-facing slopes receive less solar radiation and tend to be cooler than south-facing slopes

Seasonal temperature fluctuations and seasonal radiation balances are greatly influenced by the location of the sun and how it varies annually.

• wintertime sun angles are much lower than summertime sun angles

The steepest slopes facing north might not receive any (or very little) winter insolation

Noon sun angle calculations help explain local radiation balances

• precipitation (both rain and snow) increases with higher elevations

More precipitation helps increase biomass (more plant material) and influences type of plants

The bimodal precipitation of winter high elevation snows and summer thunderstorms is vital to explaining Grand Canyon biogeography

• temperature decreases with higher elevations

Hotter temperatures help decrease biomass and promote more xeric (dry- loving) plants

Lower temperatures reduce evapotranspiration stresses on plants, while higher temperatures limit plants severely

Different life zones exist, such as deserts, rainforests, conifer forests, and others.

Ecoregions consist of different assemblages of plants that combine together to produce a biomass signal recorded by satellites.

By taking ratios of different parts of the electromagnetic spectrum, its possible to calculate a NDVI (normalized difference vegetation index) that can be used to interpret plant types

The “rules” governing SQ laboratory science courses indicate that students practice the scientific process of gathering and interpreting data, given the prior understanding of a field of study (Stage B). The lecture in Stage B (or reading material; they are the same) reinforces and elaborates on basic concepts from GPH 111, but in the context of the Grand Canyon:

• Diurnal (temperature) variation is driven by solar radiation that peaks at noon, but there is a lag when the warmest temperatures are felt (mid-afternoon). Thus, there is a radiation balance of incoming solar radiation and outgoing terrestrial radiation with a diurnal cycle • There are also annual changes in the radiation balance, driven mostly by seasonal changes in the amount of solar radiation. This is heavily influenced by the angle of the sun. • Lapse rates are another way of saying how temperature changes with elevation (both on the ground, and up into the atmosphere). • Precipitation varies seasonally, and in the case of the Grand Canyon, there exists a winter-time peak with snow at higher elevations and a summer-time peak with thunderstorms during Arizona’s monsoon season. • All of the above creates a complex fabric of daily, seasonal, and annual changes in temperature and precipitation that influences the amount of biomass (all plant and animal material) and the type of plants/animals living at different locations. The hope is that by gathering and interpreting these sorts of data in Stage C, the science becomes more powerful and enjoyable for you. Then, you are challenged (without any grade penalty) to synthesize ideas for yourself (and also earn additional points) by writing a 4 paragraph essay in Stage D.

STAGE A: Lecture (or read the same content below) about microclimates and vegetation.

Link to video lecture: https://www.youtube.com/watch?v=gT-OQpWSvWc

The idea of this section is to provide you basic background information about the

interrelationships between microclimate the weather. The content in this PDF file is the same as the content in the lecture that is linked through the Canvas page for the Stage A part of this lab. There is a quiz on the information that you are welcome to take that is administered in canvas. Points from this quiz will be added to your GPH 112 point total. However, there’s no penalty for incorrect answers or not taking the quiz

Introduction Several different climates exist around and within the canyon, a result of a vertical mile of elevation change from rim to river. Temperatures at the bottom of the canyon soar regularly over 100F while the North Rim sometimes sees temperatures below 0F. Over 11 feet of snow closes the North Rim every winter while the bottom of the canyon sees only 8 inches of rain annually. Locations around the Grand Canyon also have localized microclimate variations. Small changes in solar radiation, cast by shadows from the canyon walls, can have a noticeable influence on temperature within the small regions of the canyon. In this lab, we’ll look closer at what influences the microclimates of the Grand Canyon and how that impacts plants and animals within its walls. Atmosphere and Lapse Rates If you’ve ever been on top of a large mountain or at a significant elevation and felt that it was harder to breath, you’ve noticed that higher altitudes have lower air pressure, and as a result lower oxygen for you to breath. This is because the further away from the center of the earth you are, the less gravity pulls on you and as a result, pulls on the air molecules. This leads to the atmosphere being thinner, with most of the air down closer to the surface. As a result, the air pressure is at higher altitudes. Lower air pressure means temperature also decreases. Generally, in the free atmosphere, for every kilometer ascended into the atmosphere it is 6.5C cooler (3.5F/1000feet). This is called the normal, or environmental lapse rate. However, because of the complex topography and surface heating within the Grand Canyon, this air temperature lapse rate is generally greater than the environmental lapse rate, particularly in the summer where the lapse rate can approach 7.5C per kilometer. (5.5oF per 1000 feet). We will call this lapse rate the near-surface lapse rate because of the influence surface variables (reflectivity, moisture, heat release/absorption, etc). This lapse rate changes seasonally; in the winter, the surface lapse rate can drop below 3C/km. This winter change is a result of multiple factors. Since cool air is denser, it sinks off the top of the rim into the canyon below, called cold air pooling. Combined with the fact that the canyon bottom gets less sunlight in the winter, resulting in less surface heating, it can remain cooler than expected at the canyon floor. On occasion, the temperature in the canyon can be lower than the temperature on the rim. This happens in the winter, especially in the morning while the sun heats up the canyon rim above. Cool, dense air has sunk into the canyon and being trapped below warmer air above. When this happens, it’s called an inversion. On occasion, when the air in the canyon has reached saturation (a temperature which clouds form), a sea of clouds can form inside the canyon walls.

Grand Canyon Clouds Inversion: https://www.youtube.com/watch?v=dBm7jgNX3hQ Radiation Balance So why does winter see a change in this lapse rate and the presence of inversions in the Grand Canyon? That has to do with the amount of insolation, or incoming solar radiation, sunlight, received. As sunlight enters the Earth’s atmosphere, some of it gets absorbed or reflected by the atmosphere, and the rest is absorbed or reflected by the surface. The earth’s surface warms up and reemits this energy as longwave radiation, which helps warm the air above. However, the amount of insolation and longwave radiation changes throughout the course of the year, as the Earth rotates on its axis around the sun. During the summer, the northern hemisphere is pointed towards the sun, causing more direct sunlight. During the winter, the opposite occurs, with the northern hemisphere pointed away. This results in the sun being lower in the sky, and insolation more spread out across Earth’s surface, and an overall lower amount of insolation received. This leads to less energy being absorbed by the surface, and less warming of the air, leading to cooler temperatures. In the bottom of the canyon, this is especially true, as many deep, shadowed sections of the canyon may see little to no sunlight during the day in the winter, as high walls block the already low, shallow sunlight. Watch the shadows in this rafting video: https://www.youtube.com/watch?v=NIicjzP8CwM Precipitation / North American Monsoon The Grand Canyon, along with much of the southwest United States, sees a seasonal pulse of precipitation in the winter and summer, separated by drier periods in the spring and fall. In the winter, large low-pressure storms from the Pacific sweep across the region, pulling moisture from the Pacific and bringing soaking rains and snow. The higher and colder North Rim sees the heaviest snowfall, averaging 142 inches of snow (nearly 12 feet) every winter while the South Rim sees 58 inches of snow (or a little over 6 feet). The inner canyon rarely sees snow, as any snow falling overhead melts into rain by the time it reaches the bottom. This disparity in winter precipitation is largely a product of orographic uplift, with higher regions of the park pushing air up to elevations which clouds begin to form, leading to precipitation. The summer precipitation pattern for the Grand Canyon is characterized by the North American Monsoon. A monsoon is a pronounced seasonal reversal in wind direction (N to S, E to W). The seasonal reversal of wind direction is associated with large continents. In winter, the wind blows from land to sea; in summer, it blows from sea to land as the surface pressure changes over land.

The North American monsoon is a wind pattern that produces a dry spring with a relatively wet summer across the southwestern US and northwestern Mexico. In June, a high-pressure ridge in the upper atmosphere blocks moisture from moving into the Southwest. Winds during this time generally flow from the west, bringing dry continental air. As the summer progresses, the high pressure progresses north. This causes a change in winds over the Southwest. The dry conditions combined with intense direct sunlight produce extremely hot conditions over Arizona and California. This hot air lowers the pressure over the southwestern US, creating a thermal low at the surface. By July, this thermal low, along with the high pressure aloft then begins to draw air from the south, bringing warm, moist air from the Gulf of California and even the Gulf of Mexico toward Arizona. The increase in moisture, combined with the hot conditions leads to an increase in precipitation over the southwestern US and northwestern Mexico around July and August. Days often begin clear, but strong surface heating, results in powerful updrafts into the humid air, particularly along the rims. This is because the higher elevation North/South Rim act as focusing mechanisms for updrafts, with air over the rims exhibiting higher temperatures than air at the same elevation over the canyon. This imbalance in temperature results in air being more buoyant over the rims, causing rising updrafts and resulting in powerful thunderstorms, lightning, heavy localized precipitation, and flash flooding. Storms that move off the rim can dissipate because of the dramatic drop in precipitation and lack of rising air, and rain that does fall over the canyon floor can evaporate on its way down, called virga, leading to generally lower precipitation values over the course of the summer between rims and canyon floor. Watch this video on canyon rain: https://www.youtube.com/watch?v=10lI2fwA4pY

Satellite view of WINTER SNOW

Satellite view of SUMMER CLOUDS

Life Zones (basic term used by rangers in the park) or Ecoregions (term more commonly used in science) Precipitation, and temperature, are the most relevant variables for determining the ecoregions within the Grand Canyon. Multiple ecoregions exist within certain temperature or precipitation regimes (an annual average temperature of 10C, or roughly 50F, has four different habitats that are possible, depending on the amount of annual precipitation). While the general trend for precipitation is an increase with height in the Grand Canyon, the annual temperature and other important factors influencing microclimate temperatures (such as slope or orientation) are going to determine ecoregions within the Grand Canyon. Due to the great range in temperatures and precipitation over a relatively small area, the Grand Canyon sees an incredible diversity of plant and animal life. Five distinct biotic communities exist in the Grand Canyon’s ecosystem: boreal forest, ponderosa pine forest, pinyon-juniper woodland, desert scrub, and riparian. Above 2400 meters (8000 feet), the Boreal Forest is only found on the North Rim. This community is the coolest and wettest in the park. Life here adapts to an extreme winter climate and short, frenzied growing seasons. Here, dense dark spruce and fir forests are mixed with quaking aspen, which drop their golden leaves as winter approaches. These forests are broken by bright, open meadows filled with wildflowers and birds in the summer. Some species avoid the harsh winters through hibernation or migration, or through adaption like the evergreen trees and their tough, narrow needles that resist freezing.

Between 2100 and 2400 meters (6800-8000 feet), the Ponderosa Pine Forest thrives on both the North and South Rim, and act as a transition zone between the mixed conifer above, and pinyon- juniper woodlands below. Air temperatures increase and precipitation decreases slightly here. Like the mixed conifer forest, this ecosystem is specialized for fire, brought on by lightning during monsoon season. Tall ponderosa pine trees, with the thick fire-resistant bark stand tall among thickets of Gambel’s oak. Naturally occurring, low intensity fires clear the forest and add crucial nutrients to the soil here. These fires reduce competition, allowing trees to grow tall and healthy. However, in the past, humans suppressed these natural wildfires, resulting in the buildup of dense debris and thick underbrush in the naturally open forests. Faster, hotter fires tore through the forests, consuming even the large trees. Thankfully, we now better understand the role of fire in these forests and fire managers work to safely restore the forests using prescribed burns and forest thinning.

Watch this video on the history of fire in the canyon: https://www.youtube.com/watch?v=hDnP5TVOvjY Below the canyon edge, between 1500 – 2100 meters (5200-6800 feet), hot dry breezes rise from inside the canyon in the Pinyon-Juniper Woodland. Thin soils here hold little water, and with less precipitation (between 10 and 15 inches annually) and warmer temperatures than along the canyon rim, the pinyon and juniper trees here grow short and gnarled. To conserve water, these trees have developed waxy coatings on their needles and leaves. Around five feet of snow still falls in this ecosystem in the winter while summers are very warm.

The hottest and driest community, the Desert Scrub, is found between 700 and 1500 meters (2000 and 5200 feet). Life here adapts to extreme heat and a very dry climate. Limited precipitation, less than 10 inches annually, comes in the form of cool, gentle winter rains and violent, localized summer monsoon thunderstorms. Drought tolerant desert plants thrive down here, like yucca, creosote, and ocotillo. Nocturnal animals like bats, ringtails, and owls avoid the heat of the day.

Generally sharing the same dry and hot climatic conditions as the desert scrub community, the riparian habitat is found along the Colorado River at the bottom of the canyon, around 700 to 800 meters (2000-2500 feet). This ecosystem can also be found higher in the canyon wherever water can be found, in hanging springs or creeks located among canyon walls. This habitat is the smallest in the Grand Canyon but supports the greatest biodiversity. Cottonwood trees, ferns, willows, frogs, and other unique plants and animals found nowhere else thrive in these small corridors where water is in constant supply. The following PDF from the National Park Service gives some more information and background on these ecoregions in the Grand Canyon if you are interested: https://www.nps.gov/grca/planyourvisit/upload/grca_ecology.pdf

It’s a bit more complicated than that though. These habitat zones cover a wide elevation gradient, a result of the north/south facing slopes of the canyon walls. Locations on the south facing walls receive more direct sunlight and encounter higher temperatures and greater evaporation than north facing locations. This allows for cooler habitat zones to exist lower in elevation on north facing walls of the canyon, while habitat zones on the south face exist at a higher elevation. For example, on the south facing side of the canyon, the pinyon-juniper woodland’s range is between roughly 1800 – 2100 meters (6800-6000 feet), while on the north face, this habitat zone extends from roughly 1500 – 1900 meters (6200-5000 feet). Remote Sensing and NDVI Remote sensing is a way of observing the Earth without making physical contact with it. In the case of this lab, remote sensing will be using imagery created by satellites. These satellites generally rely on energy coming off the Earth’s surface, such as heat (infrared wavelengths) and color (visible wavelengths).

The NDVI layer in the geovisualization represents the Normalized Difference Vegetation Index (NDVI) layer. It is a measure of the greenness and health of vegetation. The index is calculated based on how much red and near-infrared light is reflected by plant leaves. The index values range from 0 to 1 where higher values (0.3 to 1) indicate areas covered by green, leafy vegetation and lower values (0 to 0.3) indicate areas where there is little or no vegetation. Areas with a lot of green leaf growth, indicates the presence of chlorophyll which reflects more infrared light and less visible light, are depicted in dark green colors, areas with some green leaf growth are in light greens, and areas with little to no vegetation growth are depicted in tan colors.

Within the Grand Canyon, these are going to generally be related to the life zones found within the park. Boreal forests represent dark green, and light green represents Pinyon-Juniper, with Ponderosa Pine forests in between. Low-hot deserts are light brown/gray colored.

STAGE B: EXPLORING THE GRAND CANYON MICROCLIMATE AND

VEGETATION GEOVISUALIZATION The idea of this stage is for you to explore some of patterns observed in physical

geography data on climate and its connection to vegetation. Use these questions to decide if the information is of enough interest to warrant a deeper investigation in Stage C.

This section explains each type of question and gives you an example. Then, when you

take the quiz on Stage A in canvas, you will see questions very similar to the examples presented here; however, the questions will not be identical. In fact, different students will be presented slightly different questions.

B1. QUESTION ON INTERPRETING SURFACE TEMPERATURES Background for B1: Diurnal temperature cycle and movement of the sun In the area of the Grand Canyon, this diagram shows the path of the sun throughout the day at winter solstice and summer solstice. The sun rises in the east, reaches its highest point at noon, and sets in the west. The amount of solar radiation received at Earth’s surface is greatest when the sun is highest in the sky.

Temperature is of major importance in the Grand Canyon. For animals and plants, as well as human hikers, the changing temperatures throughout the day and throughout the canyon fluctuate wildly.

As the sun rises in the east, reaches its highest point at noon, and sets in the west, the amount of solar radiation (sunlight) a surface receives changes throughout the day. This is especially true in a place with complex topography such as the Grand Canyon.

Air and surface temperatures lag behind the time of maximum solar radiation (sometimes called insolation for incoming solar radiation). The reason for the lag in air temperature is that the air is being heated by both reflected solar radiation and also the infrared radiation that is coming from the Earth (as it heats up).

B1 EXAMPLE QUESTION: Fast Travel to the South Rim meteorological station (36.0443° -112.0586°). Then, display the summer surface temperatures. Look around the area just off the rim, into the Grand Canyon. These are the steep slopes that have different temperatures. One slope beneath this station faces towards the east. The other slope faces towards the northwest.

Question: What is the best explanation for what you see? Hint: The surface temperature data were acquired about 10am in the morning, and think about the diurnal temperature cycle and how the sun travels through the sky during the day. Keep in mind that these surface temperatures were taken from remote sensing satellite imagery, collected at 10 am. This will influence the temperature greatly for your observation. You should notice a difference in surface heating, as one surface is warming up through the entire morning, while the other is cast in shadows until the afternoon. Once you answer this question, think about what the surface heating would look like through the whole day. The surface temperatures shown can only be a snapshot when the sensor is collecting data. If the sensor acquired data in the afternoon, the images would look quite different.

B2. QUESTION ON NORTH VS. SOUTH EXPOSURES IN DIFFERENT SEASONS Background for A2: How noon sun angle changes throughout the year Look at the diagram of the “Apparent Path of the Sun Across the Sky” in the background for B1 on a previous page. Notice that at the latitude of the Grand Canyon, the angle of the sun at noon is much lower at winter solstice than summer solstice.

The reason is that Earth is tilted 23.5o on its axis. As a result, as it orbits around the sun throughout the year, the northern and southern hemispheres are either tilted towards the sun (summer) or away (winter). This results in the sun appearing lower or higher in the sky depending on the season. The angle the sun makes from directly overhead to its location is called the zenith angle, while from the horizon is called the solar angle.

We can calculate the zenith angle if we know the latitude of the location we’re interested in and latitude of the subsolar point, or where the sun is directly overhead on a given day. For this section, we’ll use the summer and winter solstices for the northern hemisphere, around June 21 and December 21, respectively. Summer Solstice: subsolar point is at the Tropic of Cancer (23.5o) Winter Solstice: subsolar point is at the Tropic of Capricorn (-23.5o) Noon solar angle = 90 – [Number of degrees of latitude between your site and the location of the

subsolar point] Summer solstice noon solar angle = 90 - (36 - 23.5) = 90 - 12.5 = 77.5° above the horizon. Winter solstice noon solar angle = 90 - (36 - -23.5) = 90 - 59.5 = 30.5° above the horizon. The reason you subtract a negative value for the winter solstice is because the subsolar point is in the opposite hemisphere as our Grand Canyon location, across the equator.

B2 EXAMPLE QUESTION: Fast Travel to the South Rim meteorological station (36.0443° -112.0586°). Then, display the winter surface temperatures. Look around the area just off the rim, into the Grand Canyon. Compare the slope that faces north (and a little west) to the slope that faces to the east.

Question: What is the best explanation for what you see? Hint: Think about the angle of the sun and how it changes throughout the day and also how it changes throughout the year. Think about how much sun a south-facing slope would receive vs. a north-facing slope in winter. North-facing slopes would receive little to no sunlight at winter solstice, and only the steepest north-facing slopes would be shaded (slopes greater than 77.5˚ or almost vertical.

B3. QUESTION ON TEMPERATURE CONTROLS ON PLANTS Background for B3: Factors that influence plant distribution, focusing on temperature and key plants in and near the Grand Canyon Many factors influence the biogeography of plants. Plants have ecological niches (the combination of conditions required for reproduction). They need energy and nutrients. The need to be able to disperse and colonize new locations, and disturbances like fire influence their distribution. In particular, this lab focuses on temperature influences at the low (winter) end and also the high (summer end). Typical temperature limitations are shown in this graph by Professor Karen Lemke.

At the higher elevations of the geovisualizations on the North Rim’s Kaibab Plateau, spruce is found with its ability to tolerate extreme low temperatures (e.g. -40˚ F) and its preference for lower summer temperatures (e.g. 60-76˚ F). At the lower elevations where trees are found (typically Juniper trees, such as Utah Juniper). These junipers often live to be hundreds of years old, and they are in mean annual temperatures that range from below freezing to 104˚ F. However, if it is much hotter for a prolonged period of time, they are not usually found. Keep in mind that the temperature chart above is for air temperature. Air temperature has to be measured at meteorological stations, but surface temperature can be imaged from space. Thus, the game displays surface temperatures with the following scale:

Areas with a lot of green leaf growth, indicates the presence of chlorophyll which reflects more infrared light and less visible light, are depicted in dark green colors, areas with some green leaf growth are in light greens, and areas with little to no vegetation growth are depicted in tan colors. Within the Grand Canyon, these are going to generally be related to the life zones found within the park. Boreal forests represent dark green, and light green represents Pinyon-Juniper, with Ponderosa Pine forests in between. Low-hot deserts are light brown/gray colored.

B3 EXAMPLE QUESTION: Fast Travel to a high point on the Kaibab Plateau, where the edge of the plateau faces northeast (36.3186° -112.0065°). The avatar is just off the edge of the plateau. If you change the camera angle (pull it back and high above), you can see the edge of the East Rim of the Kaibab Plateau as shown here:

Compare the dark green color with the NDVI scale above. You can see that this area is boreal forest with a lot of spruce (genus Picea) trees and some fir (genus Abies) trees. In particular, the most common trees here are Picea engelmannii and Abies lasiocarpa. However, you do not need to know the Latin names for plants in this lab. We present just the common names as they are used in the Grand Canyon National Park. Question: Using the temperature scale in the geovisualization (presented above for your convenient), what are the 10 am typical summer surface temperatures in this

area and the typical winter surface temperatures. Select the best answer. Hint: Do not fret much about precision. The answer will have a range of temperatures, and the different answers will vary enough so that there should not be a worry about mis- interpreting the scale. Correct Answer: In winter, temperatures range from 20-35˚F, while in summer they are in the 80-95˚ F range Explanation: If you examine the screenshots of this location for summer and winter, you can match the colors and estimate the range of temperatures where there’s the darkest green spruce. Keep in mind that these are 10 am surface temperatures, and the air temperatures at that time will be slightly cooler at 10a,. Also, keep in mind that northeast-facing exposures like this do not get nearly as hot as west-facing exposures that really heat up in the afternoon. It is the reason why boreal plants like spruce and fir can grow here.

B4. QUESTION ON ELEVATION’S INFLUENCE ON TEMPERATURE Temperature gradient is a term to describe how temperature changes with altitude. You have likely encountered or will encounter this concept in this course.

This question will focus on the concept of temperature gradients with respect to the ground surface temperature, and how these temperatures change seasonally. The temperature of the ground is a decent proxy for actual air temperature, although the air temperature is going to alternate due to circulations inside the canyon and ground surface temperatures are influenced by surface cover (water, vegetation, etc.) and generally more extreme than air temperatures.

You should be familiar with the idea that complex topography is an important factor on determining the amount of sunlight that can reach the surface of the canyon. Sunlight that makes it to the surface heats the ground up, and warms the overlying air. However, seasonal changes in solar angles and surface heating will alter the temperature gradients between the bottom of the canyon and rim. For example, the near-surface temperature gradient (air temperature we experience hiking) between rim and river can be as high as 8.2˚C per 1000 meters (5.5˚ per 1000 feet) in summer, but in winter, the temperature gradient lowers to around 5-6˚ C per 1000 meters. These values are just generalizations. The real near-surface lapse rate depends a lot on the complex topography.

So keep in mind that so much more influences the temperature you experience when you hike in the Grand Canyon or stroll around the rim. The list of factors includes: cloud cover, surface heating that occurs, reflectivity of the surface, the moisture in the ground, how the surrounding topography and plants release or absorb heat, pooling of cold air in low spots, movement of air up and down the canyon, and movement of air upslope and downslope. These and other factors make the microclimatology of the Grand Canyon complex.

B4 Example Question: How does the surface temperature gradient change between the North Rim and Colorado River locations between summer and winter? Fast Travel to the meteorological station at the bottom of the Grand Canyon, the Colorado River (36.0976° -112.0969°). For this example, we'll jump up just above the river to make our observations, because the we want to look at the surface temperature of the ground, not the river. First, make a note of its elevation. Then, in the geovisualization, click on the summer and winter surface temperatures and measure the surface temperature where the avatar is standing using the temperature key. You will be using the elevation and seasonal surface temperature for to estimate the lapse rate between the bottom of the Grand Canyon and the North Rim. Thus, you need to repeat these steps for the meteorological station on the North Rim, that you can get there via fast travel (36.2274° - 112.0296°).

NOTE: When determining the temperature value, use the color that the character most stands upon - use your best judgement, just know you won't be tricked in the Canvas questions. You can use this table, if you wish, to help you organize the observations and calculations

Elevation (meters) Summer Surface Temperature Winter Surface Temperature

Location 1 ˚F ˚C ˚F ˚C

Location 2 ˚F ˚C ˚F ˚C

Change from bottom to top of Grand Canyon Change in ˚C: Change in ˚C:

Surface temperature gradient ˚C per 1000 m ---

Elevation (meters) Summer Surface Temperature Winter Surface Temperature

Colorado River 721 125˚F 51.6˚C 50˚F 10˚C

North Rim 2611 95˚F 35˚C 35˚F 1.7˚C

Change from bottom to top of Grand Canyon 1890 Change in ˚C: 16.6 Change in ˚C: 8.3

Surface temperature gradient ˚C per 1000 m --- 8.8C / 1000m 4.4C / 1000m

ANSWER: The summer surface temperature gradient from the Colorado River to the North Rim is about 8.8˚C/1000 m, while the winter surface temperature gradient is lower, at about 4.4˚C/1000 m. An incorrect answer would likely stem from dividing the temperature difference by 1890 instead of 1.89. This is a calculation for the temperature change per kilometer (1000m). So what you should see is the change in temperature between the top and bottom of the canyon is greater during the summer than during the winter. Try to see if this is the case for your question, and think of the explanation for why this might be. For this example, it’s a bit more complicated. The location of the Colorado River is also influenced by the temperature and evaporation of the Colorado River itself, so the summer temperature especially is cooled by a several degrees. Hopefully by now, you’ve started to connect the influences of how seasonality and complex topography impact climate within the Grand Canyon. Keep thinking about this, as you’ll look more in-depth at this concept in later sections.

STAGE C: More detailed investigation of the geovisualization of the Grand Canyon’s microclimate and vegetation

The idea of this stage is for you to explore some patterns observed in physical geography

data on climate and its connection to vegetation. However, you are the one who decides if the topic is of enough interest to warrant a deeper investigation in Stage B.

This section goes over each type of question administered by canvas and gives you an

example. Then, when you take the quiz on Stage C in canvas, you will see questions very similar to the examples presented here; however, the questions will not be identical. In fact, different students will be presented slightly different questions.

The detailed investigation is broken into several sorts of tasks:

1st Task: Using meteorological stations data and the geovisualization, investigate the connections between precipitation, elevation in the canyon, and the types of plants that are growing. 2nd Task: Investigate precipitation trends across the Grand Canyon, looking at seasonality and elevation. 3rd Task: Investigate microclimates within the canyon caused by elevation, slope, orientation, surface cover, and other factors. 4th Task: Investigate the elevation of treelines in the Grand Canyon (where juniper trees no longer grow) on different exposures (north-facing and south-facing)

1st Task: Using meteorological stations data and the geovisualization, investigate the connections between precipitation, elevation in the canyon, and the types of plants that are growing. Question Overview For 1st Task There are meteorological stations in and just above the Grand Canyon used in this lab. You will be supplied randomly generated questions that task you with analyzing the information from different stations. Some of the information will come from the geovisualization (bold font in table below). Some will come from information supplied to you in a question. You may find this table useful in compiling your observations of a forested station site (C1.1) and a non-forested station site (C1.2).

Station Name: Geographic Coordinates: Elevation:

Annual Precipitation: % Precip During Summer Monsoon (Jul-Sep):

June-Aug Summer Max Temps

Summer Ground Temp Winter Ground Temp Months Min Temp Freezing:

NDVI Estimate Using This Scale

You will be asked three questions in canvas related to this task. One question will ask for an analysis of a station with trees nearby. Another question will ask for an analysis of a station without trees. The third question will ask a comparison question.

Example Material for Questions 1.1 and 1.2 for Task 1: Cedar Ridge What is the basic climate-vegetation relationships that you can observe at the Cedar Ridge station from the geovisualization and information supplied in the question? Select answer that best matches the available information. Location: 36.0646° -112.0738° Photograph of the area

Elevation as determined in the geovisualization: 1620m

Cedar Ridge Climate Variables Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Temperature Max 46.8 50.4 57.8 65.9 76.4 86.9 90.3 86.8 80.0 68.0 55.6 46.2 Temperature Min 26.0 28.3 33.2 39.4 47.3 54.9 60.6 58.7 52.3 42.5 32.9 26.0

Precipitation 1.3 1.3 1.5 0.9 0.5 0.3 1.5 2.1 1.3 1.2 1.0 1.1 This graphic from Professor Karen Lemke indicates that the freezing temperatures experienced in December through February can limit many plants, but that the maximum temperatures typically do not exceed damaging temperatures.

NDVI INTERPRETATION: The biomass scale (NDVI) in the game screenshot below matches the vegetation survey information. The color is not a dark green of a dense forest. Neither is it a brown of no trees. The site is near the lower elevation where you would find trees on the south rim.

THIS WOULD BE AN EXAMPLE OF A CORRECT ANSWER: At an elevation of 1620 m, precipitation averages 14 inches at the station. About a third of the precipitation falls during the monsoon summer thunderstorm season (July-September) with the remaining coming during the cooler months of October through April. May and June are the driest months. Maximum temperatures range from the upper 40s ˚F around winter solstice to the upper 80s-low 90s ˚F around summer solstice. However, these are air temperatures. The ground temperatures experienced even in the late morning about 10 am in summer can be considerably hotter than the air temperature. Minimum temperatures do typically fall below freezing, both recorded at the meteorological station and seen areas shaded from the sun. These conditions have led to the growth of small trees (e.g. oak, ash, juniper) and shrubs (e.g. mountain mahogany). THE INCORRECT CHOICES would have false information mixed in. They may have the elevation wrong. They may have a temperature range wrong. They may have the wrong mix of summer and winter presentation. The intent is not to trick you, but to promote careful observations on your part. The hope is that you gather in a file on your computer the sorts of information you see here.

The third question (C1.3) for Task 1 asks you to compare your observations for the forest site (question 1) and a desert site (question 2). The questions in the pool will have slightly different wording, but this is a typical one. QUESTION: Match the microclimate information to the impact on vegetation at forested and desert sites in and around the Grand Canyon. Select the best matches. QUESTION SETTING: You analyzed microclimatology and vegetation information from a site in and around the Grand Canyon with trees (mostly forested) and without trees (desert). You compiled the annual precipitation values and the seasonality of this precipitation. You observed the extremes of ground surface temperatures found in winter at 10am and in summer at 10am. You analyzed air temperatures extremes of the coldest minimums and the hottest maximums, and you tabulated precipitation totals and seasonality, and thought about the issue in terms of the impact of these temperatures on plants contextualized by this diagram:

2nd Task (C2.1): How does elevation impact precipitation?

Even though the Grand Canyon is roughly 10 miles wide, the change in elevation causes dramatic fluctuations in precipitation. First, we’ll look at the basic relationship between precipitation and elevation in the Grand Canyon. Using the images below, calculate the annual precipitation gradient per kilometer between Cedar Ridge and the South Rim weather station. [There will be another question in canvas about calculating between the location and the Rim weather station]. EXAMPLE: What is the precipitation gradient per kilometer between the Cedar Ridge climate station (36.0646°, -112.0738°) and the South Rim Station (36.0442, -112.0586) annually? First, calculate the annual precipitation for both locations. Cedar Ridge has an annual precipitation of 14 inches, while the South Rim has an annual precipitation of 15.9 inches. To find the kilometer rate of change, you would find the change in elevation between two locations (South Rim: 2191m , Cedar Ridge: 1620m) and divide that by 1000 (.571). The precipitation gradient will be the difference in annual precipitation divided by the 100 m change GRADIENT = (15.9 – 14in) / (.571km) = 3.4 inches per kilometer. Your calculations will look at gradients over larger distances into the canyon, and you’ll compare the North Rim gradient to the South Rim gradient.

2ND TASK QUESTION (C2.2): Analyze the Lapse Rate in the Winter You should have observed a strong gradient between canyon bottom and rims, as well as a change in gradients between South/North rim. The next task will be to understand why this gradient exists as well as why there is a difference in precipitation between North and South Rims. In the summer, precipitation is generally higher on the rims compared to the canyon floor due multiple factors. Higher elevation locations are typically the starting locations for monsoon season thunderstorms. Storms that move over the canyon often dissipate as well, and any rain that falls over the canyon has a chance of evaporating before the rain hits the canyon floor. Lastly, the high elevation of the North/South Rims can influence orographic lifting, which is particularly prevalent in winter precipitation, which we’ll look at next. HOW TO THINK ABOUT THIS QUESTION: When air lifts up above the surface, it cools at what is called the dry adiabatic lapse rate, or roughly 10C per 1000m (1C per 100m). This cooling will eventually lead to the air reaching its dew point temperature. Then, when an air parcel reaches dew point, clouds begin to form, and with enough uplift, precipitation can occur. If the air continues to rise, it will cool off at the wet adiabatic lapse rate. The exact wet adiabatic lapse rate will vary depending on how much water vapor is in the atmosphere. For this lab, you will use the rate of 6C per 1000m (.6C per 100m). This is because as water vapor (a gas) condenses into a cloud (liquid), it gives off a bit of heat during the change between gas and liquid. This heat slightly warms the air parcel, which is still cooling as it rises, leading it to cool at a slower rate (10 vs 6) compared to the dry adiabatic lapse rate. Please use the elevations found in the earlier sections of the lab and round them to the closest 100m value. The North Rim has an elevation of roughly 2600 meters, and the Colorado River has an elevation of roughly 700 meters, while the South Rim has an elevation of 2200 meters Locations in the Grand Canyon experience significant winter precipitation brought by strong mid- latitude cyclones pulling moisture from the Pacific Ocean. The dramatic changes in elevation mean different types of precipitation fall at different locations within the park. Even if there is no precipitation at the South Rim, there still might be precipitation at the North Rim, simply because it’s pushing the air mass moving over the Grand Canyon up higher into the atmosphere. Think about an air mass south of the Grand Canyon, at an elevation of 1500 meters and it is pushed up by the motion of the atmosphere onto the South Rim, at 2200 meters in elevation. You have the knowledge now to estimate if there would be clouds/precipitation if you just knew the air temperature/dew point of that air mass when it started..

EXAMPLE: Consider an air mass with a temperature of 7˚ C and a dew point of 3˚ C to start with. The air miss is then lifted from 1500m up to the South Rim at 2200m. It will first cool off at 10˚ C/km (1C/100m). When it reaches dew point at 1900m, clouds begin to form, and precipitation can begin occurring if the cloud is lifted further. Since clouds have started to form, = it has reached dew point. The parcel is saturated, so you now use the wet adiabatic lapse rate (6˚ C/km or 0.6˚/100m). Continuing at this rate, the temperature of the air parcel at the South Rim is 1.2C and if the parcel is lifted even more the height of the North Rim, the temperature drops to -1.2˚C. This means that if precipitation is falling, the South Rim will have rain, while the North Rim will have snow (since -1.2˚ C is below freezing).

ELEVATION TEMPERATURE CONDITION

2600 (North Rim)

-1.2 SNOW

2500 -0.6 SNOW

2400

0.0 SNOW

2300 0.6 RAIN

2200 (South Rim)

1.2 RAIN

2100

1.8 RAIN

2000

2.4 RAIN

1900 3.0 DEWPOINT – clouds form

1800 4.0 Not saturated

1700 5.0 Not saturated

1600 6.0 Not saturated

1500 (Start)

7.0 Not saturated

3rd Task: Investigate Temperature Stresses for plants in and around the Grand Brief Review of the Importance of Temperatures on Plants

In the exploratory Stage B of this lab, the third question examines the role of temperatures on trees. The highest elevations around the Grand Canyon have spruce trees that are not very sensitive to very cold temperatures. They have the ability to survive at temperatures of - 22˚ F (-30˚C) where other plants cannot.

Juniper trees (e.g. Utah Juniper), in contrast, cannot survive super cold temperatures. They also cannot survive super hot temperatures for very long. Still, they very hardy. They can tolerate freezing and 100˚ F temperatures- just not the extremes found around the Grand Canyon.

This graphic made by Professor Lemke gives a snapshot of some of the temperature issues associated with different types of plants.

While the graphic above was made for air temperature measurements (e.g. meteorological stations), the ground temperature information in the geovisualization still applies. Extreme cold and extreme heat can influence whether a particular type of plant can survive. For your reference, this is the key for ground temperatures seen in the geovisualization.

3rd Task questions related to temperature differences in and around the Grand Canyon There are dozens of ways that microclimates can develop and influence plants. The ways vary at different spatial scales. For example, on the scale of tens of centimeters, the orientation of a boulder can influence whether precipitation is channeled to a spot where a tree might or might not germinate.

The temperature data in the geovisualization is at the highest resolution available at the present time – at least for the coverage of the entire Grand Canyon. Thus, this investigation is limited to the resolution of about a 30 m pixel. Those are the squares seen in the geovisualization for winter and summer ground temperatures. At this scale, you can investigate/analyze six connections between topography and temperature that are presented below.

QUESTION: Match the locations with the primary factor influencing temperature . Each location also has the season (winter or summer) that you should investigate. Try to bring the game camera angle up higher, so that you can get an overview of the location and you can spin the view. Make the best matches between the temperatures you see for each location/season with the effect of topography on temperature. You will be given different locations in the geovisualization to “Fast Travel” to and study. Then, you will match those locations with the effect of the topography. The six connections that you will try to identify your location as are presented below:

ALREADY STUDIED IN THIS LAB: Diurnal effect of the 10am time of data acquisition – explaining why east-facing slopes are often warmer than west-facing slopes The satellite gathering the temperature data images at about 10am in the morning. Thus, the east-facing slopes have accumulated more insolation than the west-facing slopes. This image of the South Rim of the Grand Canyon was presented earlier in the PDF file.

ALREADY STUDIED IN THIS LAB: Around the time of winter solstice, North- facing slopes that are steeper than the angle of the sun at noon receive no solar radiation. This slope has an angle of 35˚, and the rabbit is facing south, so the slope is facing north. Because the noon sun angle at winter solstice is only 30.5˚, no sunlight hits this slope. The effect on plants is greatest in winter at high elevations, because the result can be severe cold temperatures.

Cold Air Drainage, especially in winter. The game screen on the right shows a small drainage on the Kaibab Plateau where cold air has collected

Evaporative cooling – In the summer temperature image, the Colorado River is able to exert a cooling effect on the 30 m pixels. This effect is often several pixels wide. The effect of water evaporative cooling is not seen in the winter imagery around the Colorado River. The reason is that the surface temperatures around the river are sometimes colder or similar to the river itself.

Flat treeless surfaces as heat accumulators – Stage B has a section called “Radiation Balance”, which is a significant topic in GPH 111. Flat surfaces can accumulate a lot of energy in summer, when sun angles are high. Solar radiation starts the process. However, treeless surfaces with lots of exposed rock play a big role in absorbing lots of the solar radiation. The result is that these are some of the hottest surfaces in and around the Grand Canyon.

Summertime north-south exposure contrasts. Wintertime temperatures in the lower desert portions of the Grand Canyon are not severe. Freezing rarely occurs, and only for a few hours in the morning. Maximum temperatures are not extreme. In contrast, summer temperatures can cause great stress for plants, especially when air temperatures exceed 104˚ F and ground temperatures exceed 120˚ F. Even though sun angles are much higher in summer, the contrast of south (warmer)-facing and north (cooler)-facing slopes can influence plants. The rabbit is standing on the side of a river canyon that has facing north, where the sun’s rays are not as direct. The hotter surface temperatures on the other side of the canyon are because those surfaces are facing south, and they are getting more direct sunlight.

The questions for Task 3 will be matching. You will be given different locations in the geovisualization to “Fast Travel” to and study. Then, you will match those locations with the effect of the topography.

SUGGESTION ON WHAT YOU MIGHT DO IN TAKING THE QUIZ: You can speed up the answering of these questions by taking full screenshots of the different locations. Try setting the default location for the screenshots to your desktop. Then, they toggled the game to your ‘task bar’ when you are done traveling and taking screenshots. This will allow you to see the latitude/longitude coordinates and also the compass rose for reference in answering the matching question of the sort exemplified below.

4th Task: What influences lower treeline in the Grand Canyon? Exposure of a slope can have a dramatic impact on vegetation due to differences in surface heating and the resulting evaporation. What you’ll be looking at next is how treeline varies between north versus south facing slopes on walls in the Grand Canyon. This portion of the lab will task you with finding the lowest elevation for the treeline on either north facing or south facing slopes, comparing 3 different locations. You will have two questions like this: 2 questions like this. One is for north-facing slopes. The other is for south facing slopes. QUESTION: Fast travel to the three coordinate locations in the geovisualization. What is the slope orientation (north facing, south facing) and mean (average) height of the transition zone between desert (brown, no trees) and pinyon-juniper woodland (green, leafy trees) for these locations? Part of the task has you understand the compass in the geovisualzation. What direction is the slope you are sent to facing. Then, the other part is taking the elevations and averaging them. Two examples are given below, but you’ll have three spots in the question. Look only at the cliff you begin at; you may see spots of vegetation down below your fast travel location, but those are not related to answering this question – they could be related to a natural spring and associated riparian habitat. Just focus on the treeline present on the cliff the coordinates take you to.

For this simple example, Treeline elevation = (1051 + 1201) / 2 = 1126 meters. WARNING: the answer choice in canvas will probably not be EXACTLY what you calculated. The reason is that where you locate your avatar will be slightly different from where we put our avatar. These slight differences will mean that you should pick THE CLOSEST ANSWER. The incorrect choices will be either be far off or facing the wrong direction.

The lab does not end with this question. Hopefully, you feel empowered to try to synthesize everything you’ve learned in writing the essay. But there’s no penalty for deciding not to participate in the next section.

Stage D: Synthesis As with all assignments in GPH 112, there is no grade penalty for skipping this assignment. At the same time, many students have a lot of interesting thoughts about the lab that they just completed, and this essay is a great chance for you to bring these thoughts together. The assignment is to write four paragraphs. Each paragraph is worth a maximum of 0.5 points. We are not English teachers, but proper grammar and well-composed sentences make it a lot easier for us to read your ideas. Still, our focus rests in the details that you use to support your thinking. Paragraph 1: What is the connection between altitude, microclimate, and vegetation in and around the Grand Canyon? Please give examples from the lab, and you can also include your own observations. Paragraph 2: What is the connection between the direction a slope faces (aspect), microclimate, and vegetation in and around the Grand Canyon? Please give examples from the lab, and you can also include your own observations. Paragraph 3: Was there anything in particular that struck you as particularly interesting about the connection between topography, microclimates, and vegetation? Please do not simply write down a sentence. Explain your idea, and elaborate with at least a few sentences. Paragraph 4: Please provide you thoughts on this geovisualization as a tool to investigate connections between microclimate and the biomass (abundance) of vegetation. Please do not simply write down a sentence. Explain your idea, and elaborate with at least a few sentences.