Click image to open full size
How Drought Affects Ecosystems
Soil moisture collapses, then everything else
Related Tools
Related Labs
Related Worksheets
Drought is a long period with much less precipitation than usual, and it can change an entire ecosystem. When soil, streams, lakes, and plants lose water, organisms must spend more energy finding the resources they need to survive. Plants often respond first by closing leaf pores, slowing growth, or wilting, which reduces the food and shelter available to animals. Because every part of an ecosystem is connected, drought can cause effects that spread through many species and habitats.
The main driver of drought stress is water shortage in soil and surface water. Low soil moisture reduces photosynthesis and primary production, so less energy enters the food web. As rivers and ponds shrink, water warms, oxygen levels can fall, and fish and amphibians become stressed. Dry vegetation also becomes easier to ignite, which increases wildfire risk and can rapidly transform habitats.
Key Facts
- Drought occurs when precipitation is far below normal for weeks, months, or years.
- Low soil moisture limits plant growth and reduces primary production.
- Photosynthesis equation: 6CO2 + 6H2O + light energy = C6H12O6 + 6O2.
- Transpiration is water vapor loss from plant leaves, and it often decreases during drought as stomata close.
- Water level drop in streams and lakes can reduce habitat space and lower dissolved oxygen for aquatic life.
- Dry fuel plus heat plus oxygen increases wildfire risk: fuel + oxygen + heat = fire.
Vocabulary
- Drought
- A drought is an extended period of unusually low water availability caused by below-normal precipitation and other drying conditions.
- Soil moisture
- Soil moisture is the water held in soil that plants can absorb through their roots.
- Primary production
- Primary production is the creation of plant biomass through photosynthesis, forming the energy base of most food webs.
- Transpiration
- Transpiration is the movement of water from plant roots to leaves and then into the air as water vapor.
- Food web
- A food web is a network of feeding relationships that shows how energy and matter move through an ecosystem.
Common Mistakes to Avoid
- Thinking drought only affects deserts. This is wrong because forests, grasslands, wetlands, farms, rivers, and lakes can all experience drought stress.
- Assuming plants die only because they are hot. Heat can make drought worse, but plants are mainly stressed because they cannot take up enough water for photosynthesis, cooling, and cell support.
- Ignoring water quality when water levels drop. Lower water levels can make water warmer and more polluted, which can reduce dissolved oxygen and harm aquatic organisms.
- Treating wildfire as separate from drought. Drought dries grasses, leaves, and branches, creating fuel that can burn more easily when an ignition source is present.
Practice Questions
- 1 A lake is normally 4.0 meters deep in summer, but during drought it drops to 2.8 meters. By how many meters did the lake level decrease, and what percent of the normal depth was lost?
- 2 A grassland usually produces 900 grams of plant biomass per square meter in a growing season. During drought, primary production falls by 35%. How many grams per square meter are produced during the drought?
- 3 Explain how a decrease in soil moisture can lead to fewer predators in an ecosystem, even if the predators do not eat plants directly.