(These parameters apply to the MABIA Method. For the Simplified Coefficient Method, see Simplified Coefficient Method, Climate; for the Soil Moisture Method, see Soil Moisture, Climate; for the Plant Growth Method, see Plant Growth Method, Climate.)
The MABIA Method requires daily climate data for precipitation, reference evapotranspiration (known as ET0 or ETref), wind speed and minimum daily relative humidity.
For ETref, you have two options:
Enter ETref directly (some climate stations provide derived ETref as data), OR
Calculate it using the Penman-Monteith equation. This approach has its own data requirements, with various options. Penman-Monteith requires:
Minimum and maximum daily temperature.
Relative humidity. Depending on the availability of data, different equations are used. The following are the data requirements, in decreasing order of preference.
Minimum and maximum daily relative humidity, OR
Maximum daily relative humidity, OR
Average daily relative humidity, OR
If humidity data is not available, and estimate can be obtained by assuming that the dew point temperature is the same as the daily minimum temperature.
Solar radiation. Depending on the availability of data, different equations are used. The following are the data requirements, in decreasing order of preference.
Enter solar radiation data directly, OR
Hours of sunshine per day, OR
Cloudiness fraction, OR
If neither sunshine hours nor cloudiness fraction are available, solar radiation can be estimated using the Hargreaves formula, based on minimum and maximum daily temperature and an adjustment coefficient (Krs)
Wind speed. (An adjustment can be made if the wind speed measurement height is known.)
Latitude and altitude of the climate measurement station.
Depending on the setting in General: Basic Parameters, the values for precipitation and ETref can either be entered once for each catchment and will apply to all the land use branches within that catchment, or they will be entered separately for each branch within each catchment. This second option might be necessary if there is a large variation in the elevation among different land uses within a catchment. Alternatively, the catchment could be divided into several different catchment nodes according to elevation, so that the climate within each catchment did not vary by land use.
Because the MABIA method calculates on a daily timestep, you will need daily data for most climate parameters (which will typically be read from a text file). However, if you only have monthly data, it can be disaggregated into daily data using several different methods (Interpolate, Repeat, Divide, and Divide with Gaps). See the section titled "Disaggregating Annual Data to Monthly, or Monthly Data to Daily" under the ReadFromFile function for more information.
The daily precipitation time series can either be read in from a file or entered in manually.
Evapotranspiration from the reference surface, the so-called reference crop evapotranspiration or reference evapotranspiration, denoted as ETo. The reference surface is a hypothetical grass reference crop with an assumed crop height of 0.12 m, a fixed surface resistance of 70 s m-1 and an albedo of 0.23. The reference surface closely resembles an extensive surface of green, well-watered grass of uniform height, actively growing and completely shading the ground. The fixed surface resistance of 70 s m-1 implies a moderately dry soil surface resulting from about a weekly irrigation frequency.
Leave blank to calculate ETref using the Penman-Monteith equation (as described above).
Minimum daily temperature
Maximum daily temperature
Latitude of the climate measurement station. Note: The value for Latitude will be filled in automatically if the catchment was created in Catchment Delineation Mode.
Altitude of the climate measurement station.
Minimum daily relative humidity. Used to calculate Kcb. If blank, will default to 45%. Also used if calculating ETref--if blank, will use maximum relative humidity, or average humidity, or Hargreaves formula.
Maximum daily relative humidity. Used if calculating ETref. If blank, will use average humidity, or dew point temperature estimate.
Average daily relative humidity. Used if calculating ETref. Only needed if no data for maximum humidity. If this and other humidity data are blank, an estimate will be made by assuming that the dew point temperature is the same as the daily minimum temperature.
Average daily wind speed. If blank, will default to 2 m/s.
An adjustment can be made if the wind speed measurement height is known.)
For the calculation of evapotranspiration, wind speed measured at 2 m above the surface is required. However, an adjustment can be made if the wind speed measurement height is known.
Daily solar radiation. If blank, WEAP will calculate using Sunshine Hours, Cloudiness Fraction or Hargreaves formula.
Actual number of daytime hours with no clouds. If blank, WEAP will use Cloudiness Fraction. If both Sunshine Hours and Cloudiness Fraction are blank, WEAP will use Hargreaves formula.
Fraction of daytime hours with no clouds (0.0=completely overcast, 1.0=no clouds). If blank, WEAP will use Sunshine Hours. If both Sunshine Hours and Cloudiness Fraction are blank, WEAP will use Hargreaves formula.
Adjustment coefficient for Hargreaves radiation formula. Only needed if neither sunshine hours nor cloudiness fraction are available. Typical range is 0.16 - 0.19.
See also: MABIA Calculation Algorithms
Entered on: Data View, Branch: Catchments, Category: Climate, Tabs: Precipitation, ETref, Min. Temperature, Max. Temperature, Latitude, Min. Humidity, Max. Humidity, Average Humidity, Wind, Wind speed measurement Height, Altitude, Sunshine Hours, Cloudiness Fraction, Solar Radiation, Krs.