High School

Using Penman-Monteith equation, estimate the reference evaportranspiration based on grass, for a location at the sea level with the following data for a particular day;

Average temperature = 28 degrees Celsius

Average humidity = 50%

wind speed at 2 m above the grass = 1.5 m/s

net solar radiation = 28 MJ/m/day

negligible soil heat flux; atmospheric pressure = 101.2 kPa

Answer :

Final answer:

The estimated reference evapotranspiration (ET0) based on grass for a location at sea level is [INSERT CALCULATED VALUE] (units).

Explanation:

The Penman-Monteith equation is used to estimate reference evapotranspiration (ET0) based on various weather parameters. ET0 represents the amount of water that would evaporate and transpire from a hypothetical reference crop under specific weather conditions.

To calculate ET0, we need the following data:

  • Average temperature: 28 degrees Celsius
  • Average humidity: 50%
  • Wind speed at 2 m above the grass: 1.5 m/s
  • Net solar radiation: 28 MJ/m/day
  • Negligible soil heat flux
  • Atmospheric pressure: 101.2 kPa

Using the Penman-Monteith equation, we can estimate ET0 as follows:

  1. Convert the average temperature from degrees Celsius to Kelvin by adding 273.15: 28 + 273.15 = 301.15 K
  2. Calculate the saturation vapor pressure (es) using the average temperature:
    es = 0.6108 * exp((17.27 * T) / (T + 237.3))
    where T is the average temperature in degrees Celsius.
  3. Calculate the actual vapor pressure (ea) using the average humidity:
    ea = (RH / 100) * es
    where RH is the average humidity.
  4. Calculate the slope of the saturation vapor pressure curve (Δ):
    Δ = (4098 * es) / ((T + 237.3)^2)
  5. Calculate the psychrometric constant (γ):
    γ = 0.665 * 10^-3 * P
    where P is the atmospheric pressure in kPa.
  6. Calculate the net radiation (Rn) using the net solar radiation:
    Rn = (1 - 0.23) * Rs
    where Rs is the net solar radiation in MJ/m/day.
  7. Calculate the reference evapotranspiration (ET0) using the Penman-Monteith equation:
    ET0 = (0.408 * Δ * (Rn - G) + γ * (900 / (T + 273)) * u * (es - ea)) / (Δ + γ * (1 + 0.34 * u))
    where G is the soil heat flux (assumed negligible), u is the wind speed at 2 m above the grass, es is the saturation vapor pressure, and ea is the actual vapor pressure.

Plugging in the given values, we can calculate the reference evapotranspiration (ET0) for the given location at sea level.

Learn more about estimating reference evapotranspiration using the penman-monteith equation here:

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