The formula for calculating the rate of evaporation, specifically from a lake, is known as the Penman formula. This formula takes into account several factors that influence evaporation, such as temperature, elevation, latitude, and dew point.
To calculate the evaporation rate using the Penman formula, you can use the following simplified version:
E0 = 700Tm / (100 – A) + 15(T – Td)(80 – T) (mm/day)
Let's break down the different variables in the formula:
1. Tm: This represents the modified temperature, which is calculated by adding 0.006 multiplied by the elevation (h) to the mean temperature (T). The elevation plays a role in determining the evaporation rate, as higher elevations tend to have lower air pressure, which affects the rate of evaporation.
2. T: This refers to the mean temperature of the environment. Temperature is a crucial factor in evaporation, as higher temperatures generally result in faster evaporation rates. Personal experiences can provide examples of the impact of temperature on evaporation. For instance, during hot summer days, you may have noticed that water evaporates quickly from surfaces such as pools or wet ground.
3. A: This represents the latitude, which is measured in degrees. Latitude influences the angle at which sunlight reaches the Earth's surface, affecting the temperature and subsequently the rate of evaporation. For example, areas closer to the equator tend to have higher temperatures and therefore higher evaporation rates compared to regions closer to the poles.
4. Td: This refers to the mean dew point temperature. The dew point is the temperature at which air becomes saturated with water vapor, leading to the formation of dew. Dew point influences evaporation as it reflects the moisture content in the air. Higher dew point temperatures indicate more moisture in the air, which can lower the rate of evaporation.
By plugging in the appropriate values for T, h, A, and Td into the formula, you can calculate the rate of evaporation in millimeters per day (mm/day). This formula provides an estimation of the evaporation rate based on the given variables.
It is important to note that the Penman formula is a simplified version of a more complex equation that takes into account additional factors such as wind speed, humidity, and solar radiation. These factors can further affect the rate of evaporation. Nonetheless, the simplified formula provides a good approximation in many scenarios.
The Penman formula for calculating the rate of evaporation from a lake considers variables such as temperature, elevation, latitude, and dew point. By plugging in the values for these variables, you can estimate the evaporation rate.