The oasis effect refers to the creation of a local microclimate that is cooler than the surrounding dry area due to evaporation or evapotranspiration of a water source or plant life and higher albedo of plant life than bare ground. [1] The oasis effect is so-named because it occurs in desert oases. [2] Urban planners can design a city's layout to optimize the oasis effect to combat the urban heat island effect. [3] Since it depends on evaporation, the oasis effect differs by season. [1] [2]
An oasis contains moisture from a water source and/or plants. When that water evaporates or transpirates, heat from the surroundings is used to convert liquid to gas in an endothermic process, which results in cooler local temperatures. [4] Moreover, vegetation has a higher albedo than bare ground, and reflects more sunlight, leading to lower land temperatures, lower air temperatures, and a cooler local microclimate.
The oasis effect occurs most prominently during the summer because warmer temperatures lead to more evaporation. [1] In the winter, the oasis effect operates differently. Instead of making the oasis cooler, the oasis effect makes it warmer at night. This occurs through the fact that trees block heat from leaving the land. Basically, radiation cannot be emitted back into the atmosphere because the trees intercept and absorb it. [2]
The oasis effect plays a role in urban development because plants and bodies of water result in cooler cities. Accordingly, cities with parks will have lower temperatures because plants have higher albedo than bare ground or roads. Areas with higher albedo reflect more light than they absorb, leading to cooler temperatures. [5] Normally, cities are hotter than their suburbs due to dense population, dark buildings and roads, and pollution; this is known as the urban heat island effect. However, by careful placement of trees, parks, and plant life, cities can create their own oasis effect. [6] By maintaining plant life throughout a city, urban planners can produce an oasis effect [7] to counter the urban heat island effect; even a small scattering of trees can significantly reduce local temperatures. However, concerns can arise in arid regions with limited water sources where city planners may not want to leave water sources out in the open to evaporate, and may not want to sacrifice water for upkeep of plants. [5]
Albedo is the fraction of sunlight that is diffusely reflected by a body. It is measured on a scale from 0 to 1. Surface albedo is defined as the ratio of radiosity Je to the irradiance Ee received by a surface. The proportion reflected is not only determined by properties of the surface itself, but also by the spectral and angular distribution of solar radiation reaching the Earth's surface. These factors vary with atmospheric composition, geographic location, and time.
Urban areas usually experience the urban heat island (UHI) effect, that is, they are significantly warmer than surrounding rural areas. The temperature difference is usually larger at night than during the day, and is most apparent when winds are weak, under block conditions, noticeably during the summer and winter. The main cause of the UHI effect is from the modification of land surfaces while waste heat generated by energy usage is a secondary contributor. Urban areas occupy about 0.5% of the Earth's land surface but host more than half of the world's population. As a population center grows, it tends to expand its area and increase its average temperature. The term heat island is also used; the term can be used to refer to any area that is relatively hotter than the surrounding, but generally refers to human-disturbed areas.
A microclimate is a local set of atmospheric conditions that differ from those in the surrounding areas, often slightly but sometimes substantially. The term may refer to areas as small as a few square meters or smaller or as large as many square kilometers. Because climate is statistical, which implies spatial and temporal variation of the mean values of the describing parameters, microclimates are identified as statistically distinct conditions which occur and/or persist within a region. Microclimates can be found in most places but are most pronounced in topographically dynamic zones such as mountainous areas, islands, and coastal areas.
Evapotranspiration (ET) refers to the combined processes which move water from the Earth's surface into the atmosphere. It covers both water evaporation and transpiration. Evapotranspiration is an important part of the local water cycle and climate, and measurement of it plays a key role in agricultural irrigation and water resource management.
An evaporative cooler is a device that cools air through the evaporation of water. Evaporative cooling differs from other air conditioning systems, which use vapor-compression or absorption refrigeration cycles. Evaporative cooling exploits the fact that water will absorb a relatively large amount of heat in order to evaporate. The temperature of dry air can be dropped significantly through the phase transition of liquid water to water vapor (evaporation). This can cool air using much less energy than refrigeration. In extremely dry climates, evaporative cooling of air has the added benefit of conditioning the air with more moisture for the comfort of building occupants.
Desert ecology is the study of interactions between both biotic and abiotic components of desert environments. A desert ecosystem is defined by interactions between organisms, the climate in which they live, and any other non-living influences on the habitat. Deserts are arid regions that are generally associated with warm temperatures; however, cold deserts also exist. Deserts can be found in every continent, with the largest deserts located in Antarctica, the Arctic, Northern Africa, and the Middle East.
A windcatcher, wind tower, or wind scoop is a traditional architectural element, originated in Iran (Persia), used to create cross ventilation and passive cooling in buildings. Windcatchers come in various designs, depending on whether local prevailing winds are unidirectional, bidirectional, or multidirectional, on how they change with altitude, on the daily temperature cycle, on humidity, and on how much dust needs to be removed. Despite the name, windcatchers can also function without wind.
The climate in urban areas differs from that in neighboring rural areas, as a result of urban development. Urbanization greatly changes the form of the landscape, and also produces changes in an area's air. The study of urban climate is urban climatology.
An urban forest is a forest, or a collection of trees, that grow within a city, town or a suburb. In a wider sense, it may include any kind of woody plant vegetation growing in and around human settlements. As opposed to a forest park, whose ecosystems are also inherited from wilderness leftovers, urban forests often lack amenities like public bathrooms, paved paths, or sometimes clear borders which are distinct features of parks. Care and management of urban forests is called urban forestry. Urban forests can be privately and publicly owned. Some municipal forests may be located outside of the town or city to which they belong.
Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility than the original energy source. Sources of waste heat include all manner of human activities, natural systems, and all organisms, for example, incandescent light bulbs get hot, a refrigerator warms the room air, a building gets hot during peak hours, an internal combustion engine generates high-temperature exhaust gases, and electronic components get warm when in operation.
Passive cooling is a building design approach that focuses on heat gain control and heat dissipation in a building in order to improve the indoor thermal comfort with low or no energy consumption. This approach works either by preventing heat from entering the interior or by removing heat from the building.
The Libyan jird is a species of rodent in the family Muridae. It is found in Mauritania, Morocco, Algeria, Tunisia, Libya, Egypt, Jordan, Syria, Saudi Arabia, Iran, Iraq, Afghanistan, Turkmenistan, Uzbekistan, Kazakhstan and Western China. Its natural habitats are subtropical or tropical dry shrubland, intermittent saline lakes, hot deserts, and rural gardens.
A seawater greenhouse is a greenhouse structure that enables the growth of crops and the production of fresh water in arid regions. Arid regions constitute about one third of the Earth's land area. Seawater greenhouse technology aims to mitigate issues such as global water scarcity, peak water and soil becoming salted. The system uses seawater and solar energy, and has a similar structure to the pad-and-fan greenhouse, but with additional evaporators and condensers. The seawater is pumped into the greenhouse to create a cool and humid environment, the optimal conditions for the cultivation of temperate crops. The freshwater is produced in a condensed state created by the solar desalination principle, which removes salt and impurities. Finally, the remaining humidified air is expelled from the greenhouse and used to improve growing conditions for outdoor plants.
Transpiration is the process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. It is a passive process that requires no energy expense by the plant. Transpiration also cools plants, changes osmotic pressure of cells, and enables mass flow of mineral nutrients. When water uptake by the roots is less than the water lost to the atmosphere by evaporation, plants close small pores called stomata to decrease water loss, which slows down nutrient uptake and decreases CO2 absorption from the atmosphere limiting metabolic processes, photosynthesis, and growth.
A desert is a landscape where little precipitation occurs and, consequently, living conditions create unique biomes and ecosystems. The lack of vegetation exposes the unprotected surface of the ground to denudation. About one-third of the land surface of the Earth is arid or semi-arid. This includes much of the polar regions, where little precipitation occurs, and which are sometimes called polar deserts or "cold deserts". Deserts can be classified by the amount of precipitation that falls, by the temperature that prevails, by the causes of desertification or by their geographical location.
Desert greening is the process of afforestation or revegetation of deserts for ecological restoration (biodiversity), sustainable farming and forestry, but also for reclamation of natural water systems and other ecological systems that support life. The term "desert greening" is intended to apply to both cold and hot arid and semi-arid deserts. It does not apply to ice capped or permafrost regions. It pertains to roughly 32 million square kilometres of land. Deserts span all seven continents of the Earth and make up nearly a fifth of the Earth's landmass, areas that recently have been increasing in size.
Climate change in Arizona encompasses the effects of climate change, attributed to man-made increases in atmospheric carbon dioxide, in the U.S. state of Arizona.
Nurse plants are plants that serve the ecological role of helping seedlings establish themselves and protecting young plants from harsh conditions. This effect is particularly well studied among plant communities in xeric environments.
Passive daytime radiative cooling (PDRC) is the use of unpowered, reflective/thermally-emissive surfaces to lower the temperature of a building or other object.
Transpirational cooling is the cooling provided as plants transpire water. Excess heat generated from solar radiation is damaging to plant cells and thermal injury occurs during drought or when there is rapid transpiration which produces wilting. Green vegetation contributes to moderating climate by being cooler than adjacent bare earth or constructed areas. As plant leaves transpire they use energy to evaporate water aggregating up to a huge volume globally every day.