A modeling-GIS approach for assessing irrigation effects on soil salinisation under global warming conditions

Soil salinisation is very often due to excessive irrigation. However, irrigation is absolutely essential for obtaining reliable crop yields, particularly under predicted global warming conditions. A simple methodology for assessing the salinisation risk for any water management situation and under predicted global warming conditions is presented. The methodology is illustrated by the assessment of irrigation effects on soil salinity at San Antonio del Sur Valley, in the southeast of Cuba. Irrigation from a new dam will support agriculture in the Valley, but at the same time soil salinity is expected to increase. Soil electrical conductivity at several depths and topographical altitudes were used to create raster layers in a Geographic Information System (GIS), thus, determining the border of the saline-affected zones by a GIS analysis. Water-table depth at the border of the saline zones was assumed to be 2 m. The physically based SWAP model was used to predict future water-table depths after irrigation begins and under global warming conditions. Future temperature and precipitation daily values were calculated from a linear increase/decrease of the daily values corresponding to a typical year, according to a global-change forecast for the zone. Soil hydraulic properties were estimated from pedotransfer function and published soil data. Simulated results predict a fast water-table raise of 1 m, due to the increase of irrigation water. Borders of the new saline zones under these conditions (i.e. the places where the water-table is at a 2 m depth) were calculated using a digital terrain model, assuming that the water-table rose 1 m over the whole valley. According to the simulation results, the original saline zones of the valley will be enlarged from 31.4 to 96.8 ha 15 years after the scheduled start of irrigation. The methodology could be used by farmers and decision-makers to select the most suitable water management solution considering both economical and environmental criteria.