The term "hydrological year type" refers to the conditions of rainfall and evapotranspiration. These conditions are specific for each of the 12 agro-climatic zones in Jordan. The frequencies are empirical frequencies interpolated from observed values.
The hydrological conditions are affecting the NIR (net irrigation requirements) for each crop and each agro-climatic zone. The basic data, particularly those for evapotranspiration, use data from the Meteorological Department of Jordan which are not contained in the database of the Ministry of Water and Irrigation.
The NIR values for the 3 different year types have been calculated in the NIR_calc module and are stored in table YEAR_TYPE_NIR.
Dry / medium / wet years for historical years
The poor data situation relating to climatic data (as required for the calculation of Penman evapotranspiration) does not permit the calculation of evapotranspiration for all 12 agroclimatic zones for any historical year. Therefore, the summary of water demands (as shown in Form "Historic Areas and Demands") is calculated for all 3 year types. It must than individually decided, which hydrological conditions prevailed in that year and region (a median year in the north might had been a wet year in the south and vice versa). The saving of demands to the STP tables is only for the single year type selected.
Dry / medium / wet years for projected years (scenarios)
In the formulation of future scenarios, irrigated areas for main crop groups / individual crops, the applied irrigation methods, efficiencies and salinities are modified. Independent for these features that are subject to planning, any hydrological year type may occur. Therefore, for future scenarios, the demands for all 3 hydrological year types are saved to the STP tables.