Agricultural water accounting: Complementing a governance monitoring schema with remote sensing calculations at different scales

Water use requires monitoring and quantification at different spatial scales to enhance water security, especially in regions facing water scarcity and threats to food security. Consequently, water metering has been implemented in various countries as part of water governance frameworks. This study aims to evaluate the implementation of a water metering network within the Chilean water governance system, which is based on the commoditisation of water through water rights. Additionally, it assesses the potential of supplementing the water metering network with remote sensing-based estimates of actual evapotranspiration (AET) and discusses the need to integrate these estimates into an appropriate water governance scheme. To conduct this study, publicly available water use reports were obtained from the Water Resources Directorate and subsequently processed to eliminate anomalies in the withdrawal time series. Water withdrawal data was supplemented with information on granted water rights to provide additional insights and contrast water allocations with actual withdrawals. AET estimates from the Mapping EvapoTranspiration at high Resolution with Internalised Calibration (METRIC) model using Landsat scenes were also acquired for the period from 2019 to 2022 to compare withdrawals and water demand in the agricultural sector. It was found that only a small fraction of water rights ( similar to 2%) is currently being metered. Actual reported withdrawals, on average, amount to approximately one fifth to one fourth of the volumes granted through water rights. However, water extractions vary depending on geographical locations and usage categories. Remote sensing-based AET demonstrates a good correlation with withdrawals, suggesting its potential in auditing water withdrawal records provided by water users and calculating water availability and withdrawals at aggregated scales within an adaptive water governance framework. While different applications were explored within the Chilean context, these have a broader application in global water governance, particularly in regions experiencing similar challenges in water resource management.