Regional scale irrigation scheduling using a mathematical model and GIS

A user-friendly software that contributes to the regional scale irrigation scheduling is presented. The software is based on the numerical solution of Richards equation which is integrated into the ArcGIS environment. Irrigation water needs are visualised by the production of coloured maps of the cultivated area. The software is aimed to the managers of the collective irrigation networks to assist them in the efficient distribution of water. In addition to that the software calculates the proper amount of water that must be applied to meet the crop needs. Therefore it offers the ability to the managers to provide specific irrigation advice to the farmers. A requirement of the software is that the study region must be densely sampled in order to be divided into homogeneous crop and soil texture sub-regions. Spatial variability of the soil hydraulic parameters is handled by applying the scaling method to the set of point measurements contained within each sub-region. This paper describes the main theoretical considerations behind this software and compares two irrigation cases: one with real and one with hypothetical data.

An open-source GIS integrated software that contributes to regional irrigation scheduling has been presented herein. To achieve its goal, the initial region was divided into homogeneous subregions. The mean hydraulic properties of each sub-region were calculated using the scaling method. Soil water contents over time and depth are presented via graphs or coloured maps from inside ArcGIS 9.x environment. The software was applied in a 6302 hectare area of the Thessaloniki plain. Two cases were investigated. In the first one the 2004 weather and crop data were used. In the second case an 80% decrease in rainfall with a concurrent 10% increase in the mean daily temperature of the 2004 data was assumed. The regional irrigation schedule suggests an increase of up to 58% in applied irrigation water, if the scenario weather data prevail in the region. Essential requirements for using this type of software are: (1) an adequate number of sampling points for the determination of the mechanical composition and the hydraulic properties of the soils in order to delineate uniform soil subregions in the most representative way, (2) a sound and easy to implement method that describes the spatial variability of the θ(h) and K(h) functions and provides the user with their mean values, (3) weather data that fully represent the microclimate of the study region. Future improvements needed to optimise the regional irrigation scheduling using this type of software are: (1) the integration of plant-water relation in order to fine-tune the irrigation scheduling under conditions of reduced irrigation water availability and (2) programming of a variable in time maximum allowable depletion limit.