The modified Penman (Penman/Monteith) Formula

As input, the Penman formula uses both time-related climatic data and time-independent data which have usually a geographic reference.

Calculation-wise, the evapotranspiration is calculated by a sequence of queries.

The first query, Q_Station_data, calculates certain parameters out of the time-independent station data.

The second query, Q_Penman is used to process the time-related (monthly) meteorological records.

E_comb is the final monthly Penman Evapotranspiration mETP.