Question

Describe the movement of water through the hydrologic cycle. Explain briefly how energy is also cycled by the same processes.

Short answer

The hydrologic cycle describes water moving through evaporation, condensation, precipitation, runoff, infiltration, and transpiration. Energy is cycled via solar heat driving evaporation and transpiration, and is released in the atmosphere during condensation.

Step-by-step solution

Evaporation

The hydrologic cycle begins with the evaporation of water from the Earth's surface, primarily from oceans, rivers, and lakes. The sun's energy heats the water, causing it to change from a liquid to a gas and rise into the atmosphere.

Condensation

As the water vapor rises, it cools and condenses into tiny droplets, forming clouds. This step releases heat energy into the atmosphere since condensation is an exothermic process, impacting energy dynamics and temperature profiles.

Precipitation

When the cloud droplets combine to form larger droplets, they become too heavy to remain suspended and fall back to the Earth's surface as precipitation, such as rain, snow, or sleet.

Runoff and Infiltration

Once on the ground, water can either flow over the surface as runoff, moving towards rivers, lakes, and eventually returning to the oceans, or it can infiltrate into the soil, replenishing groundwater supplies.

Transpiration

Plants absorb groundwater through their roots and release water vapor into the atmosphere through a process known as transpiration. This step also involves energy transfer, as water is absorbed and expelled by plants using solar energy.

Energy Cycling

Throughout the hydrologic cycle, energy is transferred and transformed. Solar energy drives evaporation and transpiration, while heat energy is released during condensation, contributing to atmospheric heat transport.

Key concepts

Evaporation

Evaporation is the initial step in the hydrologic cycle where water changes its state from liquid to gas. This transformation happens when the sun warms water bodies like oceans, lakes, and rivers. The energy from the sun causes the water molecules to increase in energy, breaking their bonds and escaping into the air as vapor.

• Water absorbs heat from the sun.
• Molecule activity increases.
• Liquid water becomes water vapor.

The process of evaporation is crucial as it helps transport heat from the earth's surface into the atmosphere, playing an essential role in weather patterns and climate regulation.

Condensation

Condensation occurs when the water vapor rises into the atmosphere and cools down. As it cools, the vapor loses energy and changes back into liquid form, creating tiny water droplets. These droplets collect to form clouds.

Condensation plays a key role in releasing energy back into the atmosphere. It is an exothermic process, meaning it releases energy. This released heat impacts the energy dynamics of the surrounding environment, contributing to weather phenomena as it affects air temperature and pressure.

• Water vapor cools in the atmosphere.
• Energy is released during droplet formation.
• Clouds are formed from condensed water droplets.

Precipitation

Precipitation is the process of water droplets in clouds combining and becoming heavy enough to fall back to the earth's surface. This can happen as rain, snow, sleet, or hail, depending on the atmospheric conditions.

The type of precipitation depends on the temperature and atmospheric conditions at different heights in the atmosphere. Precipitation is vital for replenishing fresh water in ecosystems, sustaining plant and animal life, and maintaining groundwater levels.

• Water droplets merge into larger drops.
• Larger drops fall to the earth's surface.
• Forms of precipitation vary with conditions.
  

Energy Transfer

Energy transfer is inherent in the hydrologic cycle's processes. Solar energy is the primary driver, initiating evaporation and transpiration. During evaporation, energy is absorbed by water, which transforms into vapor, indicating energy gain.

In contrast, during condensation, the water releases energy into the atmosphere. This heating and cooling process facilitates energy movement, impacting thermal conditions and the movement of air masses in atmospheric circulations.

• Solar energy powers evaporation.
• Energy released during condensation.
• Drives atmospheric processes.

Transpiration

Transpiration is the process where plants absorb water through their roots and release it as vapor into the atmosphere from their leaves. This transfer of water is driven by solar energy, and it plays a similar role to evaporation in the hydrologic cycle.

Transpiration accounts for a significant amount of atmospheric humidity and is crucial for plant vitality and the regulation of temperature. It helps in nutrient transport within the plant and cooling the plant efficiently by releasing heat through the vapor release.

• Plants draw water from the soil.
• Water vapor released from leaves.
• Helps cool plants and supports humidity.