Transpiration is a process in which water is lost from the aerial parts of a plant and usually through the stomata. It is described as the loss or evaporation of water occurring at the leaves. Transpiration is a vital process that occurs in all plants. Its rate is controlled by external factors such as wind, humidity, light intensity and temperature. A rise in air temperature increases the kinetic energy of water molecules, thus speeding up their evaporation. This also increases the concentration gradient between the leaf and the surrounding air.
Plants draw water up into their stems and leaves from the ground through roots, then release some of that water back to the atmosphere through a process called transpiration (when combined with evaporation, it’s known as evapotranspiration). This water loss helps regulate the amount of water in the upper soil zone where most plants grow. Transpiration rates vary greatly depending on weather conditions, including temperature, humidity, sunlight availability and intensity, precipitation, soil type and saturation, wind and land slope. Human activities can also alter transpiration rates, including irrigation and drainage practices and diversion of water for agriculture.
Temperature: The higher the temperature, the faster a leaf will release water. This is because warmer air has a higher capacity to hold moisture than cooler air. This allows the stomata on a plant’s leaves to open wider, allowing more surface area for water vapor to escape ( transpiration ).
Humidity: During high temperatures, humidity decreases. This makes it harder for the stomata to close, allowing the rate of transpiration to continue at the same level. During low humidity periods, the stomata may close. As a result, the rate of transpiration drops.
Light Intensity: The light intensity that a plant is exposed to directly affects its rate of transpiration. When a plant is in direct sunlight, it’s stomata will open wide, allowing more surface area for water to be released into the air. If the plant is shaded, however, it will not be able to access as much sunlight, which can cause its stomata to close and limit its ability to release water.
The Number and Size of Stomata: A plant’s stomata are small holes in the surface of its leaves that allow for gas exchange. The larger a plant’s leaves, the more surface area there is for its stomata to open. The number and size of stomata varies among different species of plants, as well as the environment in which they live.
The xylem is the tissue that transports water and some nutrients throughout a plant. The stomata are connected to the xylem via small pores known as lenticel. The lenticel pores are small and can be found on the underside of the leaves, as well as in the barks of some plants. Number and size of stomata plays a key role in transpiration.
Humidity: Humidity is a measure of how much water vapor is in the air. It depends on many factors including availability of surface water, ground moisture saturation levels, air saturation level, wind, ground cover (plants), and time of year. It is possible to have a large variation in humidity over a wide area and over long periods of time. The amount of humidity also changes with temperature. This is because when a mass of moist air is heated, the water vapor in the air will expand and the humidity decreases.
Humidity is also an important factor affecting the transmission of oxygen during transpiration. Most plants require the transfer of oxygen to their leaves during stomata opening in order to perform photosynthesis. However, the rate at which the stomata open is dependent on many different factors and can vary significantly between plants. One of these factors is the ambient air moisture and humidity.
High levels of humidity will slow the rates at which stomata open. This is because the water molecules in the surrounding air have a higher concentration than those inside the leaf. As a result, the water molecules have more kinetic energy and therefore evaporate faster into water vapor than they would if the ambient air were dry.
Conversely, when the ambient air is humid, the stomata will open more easily thereby aiding transpiration. This is because the concentration of water molecules in the surrounding air is lower than those in the leaf, allowing for faster evaporation.
The air movement caused by wind also influences transpiration. When there is no wind, the air around a plant will remain still and become saturated with water vapor from transpiration. This will reduce the difference in water potential between the intercellular air spaces of the leaf and the atmosphere and thus slow transpiration. On the other hand, when there is wind, the saturated air is carried away from the leaf and replaced with drier air.
As a general rule, wind speeds between 10 and 30 mph increase the rate at which stomata open. However, there are many other factors that can influence the stomatal opening, including the temperature of the surrounding environment and CO2 concentration. In addition, the stomatal opening of some dicotyledon plants such as soybean (Glycine max), sunflower (Helianthus annuus) and jojoba (Simmondsia chinensis) is negatively impacted by elevated temperatures, whereas monocotyledon plants such as wheat (Triticum aestivum L.), barley (Hordeum vulgare L.) and saltbush (Atriplex halimus L.) are more sensitive to increased temperature.
Wind: Wind is the great equalizer, transporting heat, moisture, pollutants, and dust long distances around the globe. It’s role in transpiration cannot be overemphasized. It dries clothes in summer and chills them in winter, lifts sailing ships across oceans, and rips huge trees from the ground. It is also the force that drives ocean surface currents, such as the Antarctic Circumpolar Current carrying cold, nutrient-rich water around Antarctica and the Gulf Stream transporting warm Atlantic water up the East Coast of North America and across the Atlantic to Northern Europe.
The movement of air, which we know as wind, is driven by the uneven heating of the Earth’s surface by the sun. The pressure gradient force, which is generated by changes in air pressure over a horizontal area, pushes the air molecules away from a region of high air pressure and toward a region of low air pressure. This creates the prevailing wind that we experience.
Local variations in the speed and direction of the prevailing wind are due to the topography of the land, especially hills, mountains and bodies of water. For example, hilly terrain will cause strong up and down drafts to develop as the air flows up over the land surface or down into valleys. Similarly, the flow of air over mountains and other large geographic features will be disrupted, creating strong eddies and winds that can change their direction quickly.
Other natural phenomena also influence the prevailing wind and it’s consequent effect on transpiration. The monsoon, a seasonal shift in the direction of the prevailing winds of a region, brings rain to some areas while bringing drought to others. Winds are also affected by the tilt of the Earth’s rotational axis, which is known as the Coriolis effect.
The influence of the prevailing wind on the transmission of oxygen in water is an important consideration for designing aeration systems for treatment lagoons and other large bodies of water. The oxygen transfer coefficient is a function of Schmidt number, wind speed and temperature. It is predicted that the oxygen transfer coefficient will increase with increasing temperature, because molecular diffusivity increases with temperature.
Water Supply (WSS): Water Supply refers to the availability of clean drinking water. It focuses on both quantity and quality. In terms of quantity, it is a question of whether sufficient quantities of water are available in the region where it is needed and can be delivered to people reliably. Water quality is a question of whether the water is free from harmful pathogens. It is also a question of whether it meets acceptable aesthetic standards in terms of its color, taste and odor.
Water can be extracted from a variety of sources, including groundwater (aquifers), surface water (lakes and rivers) or seawater via desalination. It is then treated, usually by chlorination and possibly fluoridation. It is then stored in reservoirs or other containers that can be pumped to households, businesses and industries as required (for indicators related to the efficiency of drinking water distribution see non-revenue water).
The WSS is often the responsibility of a department within the administration of a city, town or municipality. In many cases, this is problematic because it leads to a risk that tariff revenues are diverted for other purposes and that staff members are appointed on political rather than professional grounds. Moreover, the management of the WSS is challenging, because it requires a large amount of capital investment and good governance.
There are a number of problems that are threatening the sustainability of the water supply sector. They include the fact that the world population is increasing at a rapid pace and the available freshwater resources are limited. They are also threatened by climate change, high levels of pollution and continuing economic crises. In addition, the WSS must meet a wide range of technical, social and environmental requirements. As a result, the system is vulnerable to dynamic and uncertain processes and needs a strong adaptive capacity. This capacity has to be defined, measured and demonstrated. This can be done using a variety of indicators and a comprehensive approach, which is based on an understanding of the multidimensional nature of sustainable development.