GIS—based application of Benfratello's method to estimate the irrigation deficit and its uncertainty under different climate change scenarios

Benfratello's Contribution to the study of the water balance of an agricultural soil (Contributo allo studio del bilancio idrologico del terreno agrario) was firstly published in 1961. The paper provides a practical conceptual and lumped method to determine the irrigation deficit in agricultural districts, and it generalizes previous Thornthwaite (1948) and Thornthwaite and Mather (1955) water balances thanks to the application of the dimensionless approach introduced by De Varennes e Mendonça (1958). Since then, it has been used in many areas in Southern Italy. It is our opinion that, due to its simplicity and to the small number of required parameters, Benfratello's method could be regarded to as an effective tool to assess the effects of climatic, landuse and anthropogenic changes on the soil water balance and on the irrigation deficit.

In previous contributions we presented (i) a GIS—based application of Benfratello's method to the case study of the semiarid Capitanata plane (4550 km²), one of the most important agricultural districts in Italy, and (ii) a theoretical development of the method that allows to simply estimate in closed form the uncertainity of the calculated irrigation deficit, once known the interannual variability of the required climatic variables (air temperature and precipitation). In this contribution we present the results obtained by applying the GIS—based Benfratello framework to estimate the irrigation deficit and its uncertainty of the Capitanata plane case study under different climate change scenarios.

The scenarios were generated with the following procedure: (i) combination of different GCMs (CNRM-CM5, CMCC-CM and IPSL-CM5A-MR) with the IPCC RCP4.5 and RCP8.5 scenarios as well as with historical data, (ii) statistical downscaling of the obtained models to estimate future time series of air temperature and precipitation for the meteorological stations of interest in the considered case study and (iii) spatial interpolation with ordinary kriging. The obtained maps were then used as input data for the already developed GIS—based application of Benfratello's method.