Irrigation Sustainability in the Land Use/Soil System in South Italy: Results from a GIS Simplified Approach and Future Methodological Developments - Water and Agriculture: Sustainability, Markets and Policies - page 245

Figure 4. Consortia CWR data

Crop evapotranspiration (ETc) calculation is based on the following FAO two step
approach:

1. Reference evapotranspiration (ETo) computing;

2. Crop coefficient (Kc) application, that takes into account the differences in the crop

canopy and aerodynamic resistance relative to the hypothetical reference crop.

ET ETo K

c c

ET 0 computing is based on the following Hargreaves-Samani equation (Penman-
Monteith equation is not applicable, because of the lack of solar radiation, relative
humidity and wind speed data):

where:

R

A

ET C T T 17 .

0

ET 0 = evapotranspirative flux [mm d -1 ] C = empiric constant, normally fixed at 0.0023 value

R a = extraterrestrial radiation [MJ m -2 d -1 ]

￿ = thermal monthly range [°C]

￿ ￿ ￿ ￿ ￿ ation [MJ kg -1 ] T = monthly average temperature [°C]

The R CWR is based on the calculation of effective water volumes, utilising a SWAP
implemented application that has been validated on five consortia test sites. The final
value refers to each land use polygon and, taking dynamically into account the irrigation
techniques, the land use changes, the soil and the metrological variability, represents the
optimal water volumes to use for each soil/crop/technique system (Table 3).