A novel tool to assess available hydrological information and the occurrence of sub-optimal water allocation decisions in large irrigation districts

Hydrological information on water availability and demand is vital for sound water allocation decisions in irrigation districts, particularly in times of water scarcity. However, water allocation decisions are often taken based on uncertain hydrological information, which may lead to sub-optimal decisions and agricultural production loss. This study aims to assess the availability of hydrological information in large irrigated areas (>250 km2) and evaluate water allocation decisions being taken. An index tool that measures the level of availability of hydrological information in irrigation districts that is used in planning and operation was developed. The index is calculated based on a compound that considers the period of record, temporal and spatial resolution of the data. Contingency tables that compare the observed discharge in water extraction sites, supply in the main canals, and irrigation demand estimates, were generated allowing the rate of occurrence of sub-optimal water allocation decisions to be determined. Through this method, excellent index results were found for an irrigation district in Australia (Murrumbidgee district), while irrigation districts in Colombia (Coello district) and Costa Rica (DRAT district) showed fair to poor information availability, which correspond to a higher rate of occurrence of sub-optimal water allocation decisions. The results imply that the use of additional hydrological information is beneficial in reducing the rate of occurrence of sub-optimal water allocation decisions, ultimately contributing to higher crop yields.