Climate model

The Climate model accepts a number of commonly available climate inputs and converts them into precipitation and the input required by the reference ET model, according to the selected Climate model.

Two Climate model types are currently available:

·         Rainfall only. This is the simplest climate model, only requiring a Rain­fall time series and a reference ET time series as input.

·         FAO 56. The FAO 56 model requires the specification of Climate time series as input for the calculation of the FAO 56 reference evapotranspi­ration.

The required inputs are:

·         Rainfall time series. A rainfall data time series is required for both the Rainfall only and the FAO 56 models.

·         Climate time series. Climatic data are required input when the FAO 56 model is selected. The climate time series must include Relative humid­ity, Air temperature (min and max), Wind speed and Sunshine hours.

·         Coordinates. When the FAO 56 Climate model type is selected, the Lat­itude and Altitude of the location of the irrigation water user are required. These coordinates will be set automatically if a coordinate system is defined for the features (cf. 5.1 Coordinate System (p. 55))

·         Disaggregate rainfall. If rainfall is provided on a low temporal resolution (e.g. monthly data), functionality to disaggregate the data into a higher temporal resolution is provided. Checking the ‘Disaggregate rainfall’ checkbox enables the field where the new aggregation period can be specified. Setting the time span to 10 days, for example, results in a rain event every 10 days, of a magnitude that corresponds to:

–         Rain depth = (Aggregation period) / (Input time step) * (Rainfall depth for input time step)

–         Disaggregation of rainfall is possible for both the Rainfall only and the FAO 56 climate model.

·         Reference ET time series. When the climate model type is Rainfall only, the time series of reference evapotranspiration must be entered. If the FAO 56 model is selected, the reference ET is calculated according to the FAO 56 method (see Appendix A.3 for additional details).