c_ETP — Function to generate potential evapotranspiraton time series
[ETP] = c_ETP(NbVal,TimeSteps,Latitude,DATA_M,TYPE,DateStart)
Number of value in the returne time serie (ex. NbVal = 100 > return 100 ETP values).
Length of the time step expressed in hour. TimeSteps must vary within [1/1440 (1 minute) .. 24]. There must be an integer number of timestep in 24 hours (ex. TimeSteps=5 is not allowed). Ex : for a 6 hourly time-series, TimeSteps = 6.
Latitude (in radians) of the point to which the potential evapotranspiration values are assigned.
Mean monthly temperatures or potential evapotranspiration (matrix [12x1]).
Date of the first value generated (format YYYYMMDDhhmm, ex: DateStart = 199001010000, the ETP time series will start on the first of January 1990).
Type of data in DATA_M. 1=Temperature data / 2=potential evapotranspiration data (no transformation in this case)
Potential evapotranspiration generated (matrix [NbValx1]).
CAUTION : The evapotranspiration values are inter-annual values. The time series is identical every year.
WARNING : This function is written in C language and interfaced with SCILAB (HYDROGR.dll).
The function adjusts a Fourrier transform on the monthly temperature values and apply the formula proposed by Morton (see bibliography) based on temperature and latitude).
// Mean monthly temperature T = [0.687;0.498;2.774;6.086;10.565;13.702;16.159;15.585;12.619;8.486;3.300;0.778]; // Generation of ETP daily time series (2000 days), latitude = 45deg, start = 1/1/1980 E = c_ETP(2000,24,%pi/4,T,198001010000,1); // Graph plot(c_CONVDATE(0,198001010000)+(0:1999),E,style=-1); // Date on the x axis GRAPH_DATE('6.m'); xgrid(2);xtitle('PE with the Oudin formula','date','PE (mm)')
CEMAGREF Antony, HBAN Unit, julien.lerat@cemagref.fr
Oudin, L., C. Michel, et al. (2005). "Which potential evapotranspiration input for a lumped rainfall-runoff model?: Part 1--Can rainfall-runoff models effectively handle detailed potential evapotranspiration inputs?" Journal of Hydrology 303(1-4): 275-289