Earth Science: Desertification and Land Degradation
Causes, impacts, and solutions for dryland ecosystems
Earth Science: Desertification and Land Degradation
Causes, impacts, and solutions for dryland ecosystems
Earth Science - Grade 9-12
- 1
Define desertification in your own words. Include one natural factor and one human activity that can contribute to it.
Focus on changes in soil, vegetation, and water availability.
Desertification is the process in which productive land in dry or semi-dry regions becomes less fertile and more desert-like. A natural factor that can contribute to it is long-term drought, and a human activity that can contribute to it is overgrazing by livestock. - 2
A semi-arid region receives below-average rainfall for five years in a row. Farmers continue planting the same water-demanding crop and pumping groundwater for irrigation. Explain how these conditions could lead to land degradation.
The long drought reduces natural soil moisture and plant growth, which makes the land more vulnerable to erosion. Continued irrigation with groundwater can lower the water table and may increase salt buildup in the soil. Together, these factors reduce soil fertility and make the land less productive. - 3
Study the described land surface: Area A has native grasses covering most of the soil, while Area B has bare soil with scattered shrubs after heavy grazing. Predict which area is more likely to experience wind erosion and explain why.
Think about the role of vegetation as a soil cover and anchor.
Area B is more likely to experience wind erosion because bare soil is not protected by roots or plant cover. In Area A, grasses slow the wind at the surface and roots help hold soil particles in place. - 4
A soil sample from an irrigated field shows a white crust on the surface after water evaporates. Identify the likely soil problem and explain how it affects plant growth.
The likely problem is soil salinization, which means salts have accumulated in the upper soil layers. High salt levels make it harder for plant roots to take up water and can damage plant tissues, reducing crop growth. - 5
Explain how deforestation on the edge of a dryland region can increase the risk of desertification.
Include both soil protection and water cycle effects in your answer.
Deforestation removes trees and other vegetation that protect the soil from wind and water erosion. Without roots to stabilize the soil and leaves to reduce evaporation, the land can become drier, less fertile, and more vulnerable to desertification. - 6
A ranch can sustainably support 200 cattle during a normal rainfall year. During a drought, plant growth drops by 40 percent. Estimate how many cattle the land can support during the drought if the rancher wants to keep grazing pressure sustainable. Show your work.
Find 60 percent of 200 because 100 percent minus 40 percent equals 60 percent.
A 40 percent drop in plant growth means the land can support about 60 percent of the usual number of cattle. Since 60 percent of 200 is 120, the ranch can sustainably support about 120 cattle during the drought. - 7
Compare physical weathering and erosion in the process of land degradation. How are they different, and how can both reduce soil quality?
Physical weathering breaks rock or soil particles into smaller pieces without moving them far away. Erosion transports soil particles by wind, water, ice, or gravity. Both can reduce soil quality because they can break down soil structure and remove nutrient-rich topsoil. - 8
The table shows annual rainfall for a dryland area: Year 1: 410 mm, Year 2: 390 mm, Year 3: 250 mm, Year 4: 220 mm, Year 5: 260 mm. The long-term average is 400 mm. Describe the rainfall trend and explain one possible effect on the ecosystem.
Compare each year to the long-term average of 400 mm.
The first two years are close to the long-term average, but Years 3 through 5 are much drier. This trend suggests a multi-year drought, which could reduce plant cover, lower soil moisture, increase erosion, and stress wildlife and livestock. - 9
Explain why land degradation is not only an environmental problem but also a social and economic problem.
Land degradation is an environmental problem because it reduces soil fertility, vegetation, biodiversity, and water quality. It is also a social and economic problem because it can lower crop yields, reduce income, increase food insecurity, force migration, and create conflict over limited resources. - 10
A community wants to restore degraded farmland on a slope. Choose two restoration practices from the list and explain how each one helps: terracing, cover crops, rotational grazing, drip irrigation, reforestation.
Select practices that directly reduce erosion, conserve water, or rebuild soil.
One useful practice is terracing because it slows runoff on slopes and reduces soil erosion. Another useful practice is cover cropping because plant roots hold soil in place and add organic matter, which improves soil fertility and water retention. - 11
Some people describe desertification as the movement of existing deserts into nearby regions. Explain why this description is incomplete.
This description is incomplete because desertification does not only mean that sand dunes or deserts spread outward. It is a process in which dryland ecosystems lose productivity because of factors such as drought, poor land management, soil erosion, salinization, and vegetation loss. - 12
Design a simple monitoring plan for detecting early signs of desertification in a semi-arid region. Include at least three indicators scientists or land managers should measure.
Good indicators can be measured repeatedly and compared over months or years.
A monitoring plan should measure vegetation cover, soil moisture, erosion rates, and soil salinity over time. Scientists or land managers could also track rainfall, groundwater levels, crop yields, and satellite images of plant health. Changes in these indicators can reveal whether the land is becoming less stable and less productive.