What Factors Determine Climate?
The map on the next page shows a hypothetical continent on Earth. Assume that biomes and climates on this continent are produced by the same factors that produce biomes and climates on Earth’s real continents. Use this map to answer the questions in this activity. Where needed, draw the required features directly on the map.
1. On the map of the hypothetical continent, indicate the location(s) of these types of biomes:
Use the information in Figures 50.10, 50.18, and 50.19 of Biology, 7th edition, to answer these questions.
a. Tropical rainforest(s)
In general, tropical rainforests lie between the equator and about 25° north and south latitudes, where the annual mean precipitation exceeds 150 cm and the annual mean temperature exceeds about 23°C.
b. Temperate coastal desert(s)
Temperate coastal deserts tend to lie between 25° and 45° north and south latitudes, where the general direction of the trade winds is away from the coast and the annual mean precipitation is less than 40 cm.
c. Temperate deciduous forest(s)
Temperate deciduous forests tend to lie between 30° and 60° north and south latitudes, where the annual mean precipitation exceeds 102 cm and the annual mean temperature exceeds about 11°C.
To do this, draw approximate boundary lines to delimit each biome type, and then label each delimited area with the type of biome it contains.
2. Atmospheric circulation is driven primarily by differential heating of Earth’s surface. More heat is delivered near the equator than near the poles. This seems to explain the northward and southward flows of air. What introduces the eastward and westward components into air movement? (Hint: Review Figure 50.10, Global Air Circulation and Precipitation Patterns and Global Wind Patterns, and its associated text in Biology, 7th edition.)
As indicated in Figure 50.10, “as Earth rotates on its axis, land near the equator moves faster than that at the poles, deflecting the winds from the vertical paths” introduced by differential heating. This deflection creates more easterly flow patterns between the equator and 30° north and south latitudes and more westerly flow patterns between 30° and 60° north and south latitudes.
A hypothetical continent
3. Use your understanding of global air circulation and wind patterns to draw arrows on the map of the hypothetical continent indicating:
a. The direction of prevailing winds at points W1, W2, and W3
b. The direction of flow of surface currents in the ocean at points O1, O2, and O3
(Hint: Note on the map in Figure 50.10 that surface currents in the ocean follow the major wind systems at the surface.)
4. Are the surface winds at the given points warming or cooling as they move? Explain.
Point on the map / Are the winds warming or cooling as they move? / Explanationa. X1 / The winds are warming. / The general wind pattern in this area is from the south west (westerlies). These winds tend to pick up moisture as they move from 30° to 60° N latitude.
b. X2 / The winds in this region tend to be cooling. / This region tends to be under the influence of the cooling easterly winds. These winds tend to pick up moisture as they flow from 30° to 0° N latitude.
c. X3 / The winds are warming. / The general wind pattern in this region is westerly. These winds tend to pick up moisture as they flow from 30° to 60° S latitude.
5. What biomes or vegetation types would most likely be found at the given points? (Assume all are at sea level or low altitudes.)
Point on the map / Most likely type of biome or vegetationA / This region would most likely contain coniferous forest
B / This region would most likely be a temperate grassland which will graduate into temperate deciduous forest as it moves east.
C / This could be a region of chapparal which would graduate into tropical forest as one moves south
D / This is most likely a region of tropical rainforest.
6. Would the climate at point E be relatively wet or dry? Explain.
This region would be relatively wet. It lies in the rainshadow of the mountains. In addition it lies at about 30° N latitude, a region of very drying winds.
7. What would the direction of the prevailing winds be at Earth’s surface at point X3?
The prevailing winds at this point should be westerly.
8. In the United States, deciduous forest extends from the east coast westward for about 1,200 miles (to the Mississippi River Valley). From there, the forest begins to thin out toward the west into oak savannas (or temperate woodland), and it finally gives way to open grassland (Great Plains). The grasslands extend 1,000 miles westward to the foothills of the Rocky Mountains.
a. Why does grassland replace forest west of the Mississippi River?
This area is under the influence of the westerlies (wind flow pattern), which carry moist air from the Pacific Ocean onto the North American continent. When these winds reach the Rocky Mountains, they rise and cool. This causes the moisture in the air to condense and fall as rain on the western slopes of the Rockies. The wind that reaches the eastern slopes is dry, so much of the land in this “rain shadow area” is desert. As the winds continue overland, they pick up some water; however, the area west of the Mississippi receives less rainfall than areas farther east. Grasslands are found in such regions where the mean annual precipitation is between about 30 and 80 cm.
b. What is the rain shadow effect?
As noted in part a, the rain shadow effect occurs on the leeward side of mountain ranges. When the air currents encounter the mountains, they rise. As air rises, it cools and the moisture in it condenses and falls as rain. As a result, the air that reaches the other side of the mountain is dry, so the leeward side of the mountain is dry.
c. Draw a rain shadow somewhere in the southern hemisphere of the map.
The rain shadow is always on the leeward side of the mountain. Therefore, in the southern hemisphere, the rain shadow should be on the western side of the mountains if the site is between 0° and 30° south latitude but on the eastern side if the site is between 30° and 60° south latitude.
9. What kind of vegetation (or biome) would be found on the western slope of the mountains at point F at intermediate levels—say, 2,000 meters or approximately
6,000 feet? Explain.
The western slope of the mountain at this point should be temperate rainforest.
For every 1,000 meter rise in altitude there is an approximate 6 degree C decrease in temperature. As a result, at about 2,000 meters elevation (about 6,000 feet) the vegetation should appear more temperate. In other words, the biome at this elevation would appear more similar to temperate forest.
10. How are the general characteristics of plants (for example, morphology) influenced by climate? In other words, explain what effects climate has on the types of plants that grow in an area.
As indicated in Figure 50.18, the type of biome is strongly influenced by both the annual mean temperature of the region and the annual mean precipitation. When both are relatively high you find temperate rain forests. Plants in these regions do not experience extremes in temperature or water over the year. When mean annual temperature is high and mean annual precipitation is low, deserts are formed and the plants are those that can survive in this type of climate. Refer to Figure 50.20 for examples of the types of plants that would be found in the various types of biomes.
11. Refer to Figure 50.18 in Biology, 7th edition. In general, how is the distribution of major ecosystems or biomes related to climate? If you know the mean annual precipitation and the mean annual temperature of an area, would you be able to accurately predict the type of biome that could exist there? Explain.
As noted above, the type of biome or ecosystem is determined by the mean annual temperature and the mean annual precipitation in an area. However, how the precipitation and temperature are distributed over the year also has a significant impact on the type of biome. For example, is the temperature relatively constant over the course of the year or does it range between high summer temperatures and very low winter temperatures? Other factors—for example, type of soil—can also affect the type of biome.
12. Why isn’t Earth’s climate uniform? To answer this, summarize the major factors that can produce differences in climate from place to place.
The primary factors affecting the type of climate are the annual amount of solar energy received and the annual amount of water received. The amount of solar energy received per year in a given area is directly related to its location on the globe and the fact that the earth is tilted 23 degrees on its axis. As a result, the equator receives approximately the same amount of solar energy throughout the year. On the other hand, more northern areas in the United States will experience different seasons over the course of the year. The major wind patterns are set up by differential heating at the equator. The major precipitation patterns are a function of these wind patterns.