People and the Environment

Depend, Adapt, Modify

Geographers use five themes to study the world. One of them is human-environment interaction: how people and places affect each other. It has three parts.

• Depend. People rely on nature for water, soil, wood, fish and clean air.
• Adapt. People change how they live to fit a place. They build terraces on hills or thick walls in hot deserts.
• Modify. People change the place itself. They clear forest for farms, dam rivers and pave land for cities.

Modifying a place is not always bad. A dam can supply water and power. The question geographers ask is: who gains, who pays, and what happens over time?

Forests: The Amazon

Deforestation means clearing forest and using the land for something else, such as cattle pasture or crops. The Amazon in South America is the world's largest tropical rainforest. Most of it is in Brazil.

Brazil's space agency, INPE, uses satellites to measure forest clearing in the Legal Amazon every year. Its PRODES system counts each year from August to July.

Clearing was very high in the mid-1990s and early 2000s, at close to 28,000 square kilometers in 2004. It fell sharply by 2012 after Brazil added patrols, protected areas and satellite alerts. It rose again after 2012, peaked around 2021, then dropped. INPE measured about 5,700 square kilometers for 2025, down 12 percent from 2024.

Global Forest Watch tracks forests worldwide. It found that tropical primary forest loss fell 36 percent from 2024 to 2025. But 2024 was a record year with huge fires, and 2025 was still higher than a decade earlier. So the trend is better, but the problem is not solved.

Drylands and the Great Green Wall

Desertification does not mean a desert marching forward like a wave of sand. The UN defines it as land getting worse in dry areas. Soil loses nutrients, plants die back and land blows or washes away. Causes include overgrazing, poor farming, cutting trees and changes in climate.

The UN group that works on this, UNCCD, says up to 40 percent of the world's land is degraded. Estimates range from about 20 to 40 percent, depending on how scientists measure it.

In 2007, African countries launched the Great Green Wall across the Sahel, south of the Sahara. It is not one line of trees. It is a set of projects that restore farms, grazing land and forests from Senegal to Djibouti. The goal for 2030 is to restore 100 million hectares of land and create 10 million jobs.

How far has it come? Reports disagree. A 2020 UN review counted about 4 million hectares inside the wall zone, or about 18 million if wider projects in the same countries are added. A 2026 UNCCD review counted about 1.7 million hectares under restoration, but fewer than 90 of its 389 projects reported usable data. Both are far below the 2030 goal.

Water: The Aral Sea and Lake Mead

The Aral Sea

The Aral Sea, between Kazakhstan and Uzbekistan, was once the fourth-largest lake in the world. In the 1960s, the Soviet Union sent water from its two rivers, the Syr Darya and the Amu Darya, to grow cotton in the desert. With less water flowing in, the lake shrank fast.

Fishing towns lost their jobs. The water left behind grew salty. Wind blew dust off the dry seabed, carrying salt and farm chemicals that hurt people's health. In 2014, NASA satellites showed the eastern part of the South Aral had dried up completely.

There is some good news. In 2005, Kazakhstan finished the Kok-Aral dam to hold water in the North Aral. The North Aral's water rose, and its fisheries recovered.

The Colorado River and Lake Mead

The Colorado River flows about 1,400 miles from the Rocky Mountains toward the Gulf of California. Seven U.S. states and Mexico depend on it. Farms use about 70 percent of its water, and 35 to 40 million people rely on it for some or all of their city water.

Hoover Dam holds back the river to form Lake Mead, a huge reservoir near Las Vegas. Years of drought and heavy use drained it.

In July 2022, Lake Mead fell to about 1,040 feet above sea level, its lowest since it was first filled. When full, it reaches 1,229 feet. Since then, states have agreed to use less water, and the level has gone up and down with each year's snow.

Farming and Terraces

Farming feeds the world, and it uses a lot of water. The UN's Food and Agriculture Organization, FAO, says farming takes about 70 percent of the fresh water people withdraw from rivers, lakes and the ground. Most of that is for irrigation, bringing water to crops.

Farmers have also adapted to hard places for thousands of years. In the mountains of the Philippines, the Ifugao people built rice terraces that are traditionally said to be 2,000 years old, though newer studies suggest many are closer to 400. Terraces are flat steps cut into a slope. They slow running water, hold soil in place and let rice grow on steep hills. UNESCO lists them as a World Heritage site.

Cities Spread Out

As cities grow, they cover farmland, forest and desert with roads and buildings. Geographers call this a city's urban footprint.

Las Vegas, Nevada, is a clear example. Clark County, home to Las Vegas, grew from 463,087 people in 1980 to 2,265,461 in 2020, almost five times as many. NASA's Landsat satellites photographed it from 1984 to 2009. The images show new neighborhoods spreading across the desert year after year. A desert city needs a lot of water, and the Las Vegas area gets about 90 percent of its water from the Colorado River, drawn from Lake Mead. By the early 2000s, the city had begun recycling wastewater and paying residents to replace thirsty grass lawns.

Things That Worked

Some of the strongest evidence in environmental science shows problems getting better when people act together.

• The ozone layer. The ozone layer high in the sky blocks harmful ultraviolet light. In the 1980s, scientists found chemicals in sprays and fridges were thinning it. In 1987, countries signed the Montreal Protocol to phase them out. Every country in the world has joined it. About 99 percent of those chemicals have been phased out, and the ozone layer is projected to recover by about 2040 in most places, 2045 over the Arctic and 2066 over Antarctica (WMO, 2022).
• Costa Rica's forests. By the late 1980s, much of Costa Rica's forest had been cleared for cattle. Starting in 1997, the country paid landowners to protect and replant trees. Forest cover rose to more than half the country, according to the UN Environment Programme.
• Protected areas. National parks and other protected areas cover about 17.6 percent of land and 8.4 percent of the ocean, according to the 2024 Protected Planet Report. In 2022, countries agreed on a goal of protecting 30 percent of land and sea by 2030.

The Amazon also shows that trends can change both ways. Clearing dropped after 2004, rose again after 2012, peaked around 2021 and fell after that.

What Students Can Do

Big changes come from governments, businesses and farmers. Students can still help, and their choices add up.

1. Check the evidence. Ask where a number comes from and how sure scientists are.
2. Save water. Report leaks and turn off taps while brushing teeth.
3. Get outside. Join a tree planting, a stream cleanup or a school garden.
4. Learn your watershed. Find out where your tap water comes from.

Links to Other Units

• Climate and Biomes: rainforests, deserts and the dry Sahel.
• Landforms and Water: rivers, lakes and mountain slopes.
• Cities and Urbanization: why cities grow outward.
• Resources and Trade: how resources are used and traded.

Game: Claim Check

Each round shows a claim. First decide if it is true or false. Then pick the evidence that proves your answer. Every answer comes from this page.

Quiz: People and the Environment

Ten questions. Choose one answer for each, then check your score. You can try as many times as you like.

Credits

Written by Marco for Jugami's World Geography course. The maps, chart and diagrams are original SVG illustrations made for this page. The Great Green Wall map uses public-domain land outlines from Natural Earth. The Aral Sea shapes are simplified drawings based on NASA satellite images, not exact shorelines. The chart uses INPE's yearly figures.