---
title: "Evapotranspiration — AP Enviro Definition & Exam Guide"
description: "Evapotranspiration is evaporation plus plant transpiration moving water back to the atmosphere, a key step in the hydrologic cycle tested in AP Enviro Unit 1.7."
canonical: "https://fiveable.me/ap-enviro/key-terms/evapotranspiration"
type: "key-term"
subject: "AP Environmental Science"
unit: "Unit 1"
---

# Evapotranspiration — AP Enviro Definition & Exam Guide

## Definition

Evapotranspiration is the combined movement of water to the atmosphere through evaporation from soil and water bodies plus transpiration from plants, a sun-powered step in the hydrologic cycle (CED 1.7).

## What It Is

Evapotranspiration is two water-moving processes bundled into one word. **[Evaporation](/ap-enviro/key-terms/evaporation "fv-autolink")** is liquid [water](/ap-enviro/unit-6/hydrogen-fuel-cell/study-guide/VBHYpOxkIwXQuPkI6px8 "fv-autolink") turning to vapor from oceans, lakes, soil, and puddles. **Transpiration** is water that plants pull up through their roots and release as vapor through their leaves. Add them together and you get the total amount of water leaving Earth's surface and heading back up into the atmosphere as gas.

This matters because it's a major arrow in the hydrologic cycle, the sun-powered movement of water between its solid, liquid, and gaseous phases (EK ERT-1.G.1). The sun supplies the energy that flips liquid water into vapor. When water evaporates it absorbs heat (latent heat), so evapotranspiration also cools the surface, which is why a forest feels cooler than a parking lot. The oceans are the planet's biggest water [reservoir](/ap-enviro/key-terms/reservoir "fv-autolink") (EK ERT-1.G.2), and ocean evaporation is the single largest transfer of water from the surface to the sky.

## Why It Matters

Evapotranspiration lives in [Unit 1](/ap-enviro/unit-1 "fv-autolink") (The Living World: Ecosystems), specifically topic 1.7, and it supports learning objective [AP Enviro](/ap-enviro "fv-autolink") 1.7.A: explain the steps and reservoir interactions in the hydrologic cycle. You're expected to know where water moves and what powers each step. Evapotranspiration is the 'up' arrow that returns surface water to the atmosphere, balancing precipitation falling back down. It also connects to the bigger AP theme of energy transfer in systems, since the sun drives the whole cycle and latent heat moves energy along with the water vapor.

## Connections

### [Transpiration (Unit 1)](/ap-enviro/key-terms/transpiration)

[Transpiration](/ap-enviro/key-terms/transpiration "fv-autolink") is the plant half of evapotranspiration. Vegetation pulls groundwater up through roots and releases it as vapor through leaves, so a dense rainforest sends far more water back to the atmosphere than bare soil does.

### Groundwater and groundwater depletion (Units 1, 5)

Plants tap [groundwater](/ap-enviro/key-terms/groundwater "fv-autolink") to transpire, so evapotranspiration is one way water leaves the underground reservoir. Replacing forests or vegetation with impervious surfaces cuts evapotranspiration and shifts that water into runoff instead, which can drop water tables.

### [Reservoir (Unit 1)](/ap-enviro/key-terms/reservoir)

Evapotranspiration is a flux, the rate water moves out of surface reservoirs like [oceans](/ap-enviro/unit-1/hydrologic-cycle/study-guide/Mnp6Jfh7MANP2YtOhxCb "fv-autolink"), lakes, and soil. Understanding it means tracking which reservoir loses water and which one (the atmosphere) gains it.

## On the AP Exam

On the multiple-choice section, expect stems asking which process is the largest transfer of water from Earth's surface to the atmosphere (the answer points to evaporation from the oceans). You'll also see scenario questions where land use changes the balance: dense tropical vegetation pushes more precipitation back to the sky through evapotranspiration, while a 40% rise in impervious surfaces slashes it and spikes runoff, peak stream flows, and erosion. The skill is reading those numbers and explaining cause and effect in the cycle. No released FRQ has used the word verbatim, but it underpins free-response prompts about how deforestation or urbanization disrupts water reservoirs and flow.

## evapotranspiration vs Transpiration

Transpiration is only the water plants release through their leaves. Evapotranspiration is the total of transpiration PLUS evaporation from soil, lakes, and oceans. If the question is just about plants, it's transpiration; if it lumps together every way water leaves the surface as vapor, it's evapotranspiration.

## Key Takeaways

- Evapotranspiration is evaporation from surfaces plus transpiration from plants, the combined return of water to the atmosphere.
- It's powered by the sun, and it cools the surface because evaporating water absorbs latent heat.
- Ocean evaporation is the single largest transfer of water from Earth's surface to the atmosphere (EK ERT-1.G.2).
- More vegetation means more evapotranspiration and more water recycled back to the sky; paving land over cuts it and boosts runoff.
- It supports learning objective AP Enviro 1.7.A on the steps and reservoir interactions of the hydrologic cycle.

## FAQs

### What is evapotranspiration in AP Environmental Science?

It's the combined process of water evaporating from soil, lakes, and oceans plus water transpiring from plant leaves, all moving water back to the atmosphere. It's a key step in the hydrologic cycle covered in topic 1.7.

### Is evapotranspiration the same as transpiration?

No. Transpiration is just the water plants release through their leaves. Evapotranspiration adds evaporation from soil and water bodies on top of that, so it's the total upward water flux from the surface.

### What powers evapotranspiration?

The sun. Solar energy provides the heat needed to turn liquid water into vapor, which is why the whole hydrologic cycle is described as sun-powered (EK ERT-1.G.1).

### How does deforestation or urbanization affect evapotranspiration?

Both reduce it. Fewer plants means less transpiration, and replacing land with impervious surfaces means water runs off instead of evaporating, which raises peak stream flows and erosion while lowering groundwater.

### Is evapotranspiration on the AP Enviro exam?

Yes. It shows up in Unit 1 under the hydrologic cycle, especially in multiple-choice questions asking which process moves the most water to the atmosphere and how vegetation or land use shifts the balance between evapotranspiration and runoff.

## Related Study Guides

- [1.7 The Hydrologic Cycle](/ap-enviro/unit-1/hydrologic-cycle/study-guide/Mnp6Jfh7MANP2YtOhxCb)

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