Evaporation
Evaporation is the process by which a liquid turns into a gas. In the water cycle, liquid water (found in oceans, lakes, or rivers) evaporates and becomes water vapor. Water vapor surrounds us as an important part of the air we breathe. Water vapor is also an important greenhouse gas. Greenhouse gases, such as water vapor and carbon dioxide, insulate Earth and keep the planet warm enough to sustain life as we know it. The evaporation process of the water cycle is driven by the sun. When the sun interacts with liquid water on the ocean surface, the water turns into an invisible gas (water vapor). Evaporation is also influenced by wind, temperature, and the density of the water mass.
Condensation
Condensation is the process by which a gas turns into a liquid. In the water cycle, water vapor in the atmosphere condenses and becomes liquid. Condensation can occur high in the atmosphere or at ground level. Clouds are formed through the condensation or concentration of water vapor. Water vapor condenses around small particles called cloud condensation nuclei (CCN). CCN can be dust, salt, or pollutants. Clouds at ground level are called fog. Like evaporation, condensation is also influenced by the sun. As water vapor cools, it reaches its saturation point or dew point. Air pressure also has a significant impact on the dew point of an area.
Prec
ipitation Like evaporation and condensation, precipitation is also a process. Precipitation refers to any liquid or solid water that falls to the Earth or ocean as a result of atmospheric condensation. Precipitation includes rain, snow, and hail. Fog is not precipitation because the water in fog is not dense enough to fall or become liquid and fall to the Earth. Fog and suspension are part of the water cycle: liquids suspended in the atmosphere. Precipitation is one of many ways that water is converted from the atmosphere to the Earth or ocean.Other Processes
Evaporation, condensation, and precipitation are important parts of the water cycle. However, they are not the only ones. For example, flow describes the various ways in which liquid water moves on land. Melting snow, glaciers, and icebergs producing important types of flows by creating rivers or pools. Transpiration is another important part of the water cycle. Transpiration is the process by which water vapor is released from plants and soil. Plants release water vapor through microscopic pores called stomata. The opening of the stoma is strongly influenced by light and therefore is usually associated with the sun and evaporation process. Evapotranspiration is a combined component of evaporation and transpiration and is sometimes used to evaluate the movement of water in the atmosphere.
Water Phases
Throughout the water cycle, water constantly circulates in three states: solid, liquid, and gas. Ice is solid water. Most of the Earth's freshwater is locked up in massive glaciers, ice sheets, and ice caps. As ice melts, it becomes liquid. Oceans, lakes, rivers, and groundwater all contain liquid water. Water vapor is an invisible gas. Water vapor is not evenly distributed in the atmosphere. Above the ocean, water vapor is much more abundant, making up four percent of the atmosphere. Above isolated deserts, it can be less than one percent.
The Water Cycle and Climate
The water cycle has a dramatic impact on the climate and ecosystems of the Earth. Climate is all the weather conditions evaluated over a specific time period for a particular region. Two weather conditions that contribute to climate are humidity and temperature. These weather conditions are affected by the water cycle. Humidity is simply the amount of water vapor in the air. Since water vapor is not evenly distributed by the water cycle, some regions experience higher humidity than others. This contributes to radically different climates. Islands or coastal regions where water vapor makes up more of the atmosphere are generally much more humid than inland areas where water vapor is less abundant. A region's temperature is also tied to the water cycle. Heat exchange occurs throughout the water cycle, and temperatures fluctuate. For example, as water evaporates, it absorbs energy and cools the local environment. As water condenses, it releases energy and warms the local environment.
The Water Cycle and Landscapes
The water cycle also affects the physical geography of the Earth. Two ways that water causes glacial melting and erosion help create physical features of the earth. As glaciers slowly expand across a landscape, they can carve out entire valleys and create mountain peaks, leaving boulders as large as rocks behind. Yosemite Valley, which is part of California’s Yosemite National Park, is a glacial valley. The famous Matterhorn, a peak between Switzerland and Italy, was carved out by the collisions of glaciers as they moved and receded over time. Erosion, on the other hand, occurs when water wears away at rocks and soils. Rivers carve canyons over time as they flow through mountains or hillsides. Coastal erosion is a significant issue in many areas where tides and waves slowly erode shorelines. The water cycle also affects the types of plants and animals that are found in different landscapes. Plants need water to survive, and the availability of water has a direct impact on the types of plants that can grow in an area. Animals also depend on water sources for survival, and the water cycle creates habitats that support a wide variety of species.
The Water Cycle and Human Activities
Human activities can have a significant impact on the water cycle. For example, deforestation can affect the amount of water vapor that is released into the atmosphere through transpiration. Urbanization also contributes to changes in the water cycle. Paved surfaces prevent rainwater from being absorbed into the ground, meaning it runs off into streams and rivers, increasing the risk of flooding. Large-scale agriculture can also contribute to changes in the water cycle by altering the landscape and changing the natural balance of water distribution. Climate change is also having a profound impact on the water cycle. Changing temperatures and weather patterns are affecting evaporation rates, precipitation amounts, and the timing of seasonal changes.