A probabilistic framework for water budget estimation in low runoff regions: A case study of the central Basin of Iran

Utilizing ground-based measurements to obtain water budget components, especially in large scale basins, is challenging due to the limitation in the spatiotemporal availability of in-situ data. In this paper, we propose a probabilistic framework for estimating water budgets in low runoff regions using remote sensing products. By studying water budgets in the Central Basin of Iran (CBI) over 8 years period (2009–2016), we investigate the locations and time scales at which the water budget calculated from satellite products provides most closure. To this end, we use precipitation from the Tropical Rainfall Measuring Mission (TRMM), evapotranspiration from the Water Productivity Open Access Portal (WaPOR) and terrestrial water storage change from the Gravity Recovery and Climate Experiment (GRACE). The results show better closure and consistency of water budget in the center and South East of the basin at seasonal and annual time scales. Due to the uncertainty initiated from different data sources as well as the mismatch between the spatiotemporal resolutions of various satellite products, the validity of the results is examined through an innovative application of the First Order Reliability Method (FORM). Furthermore, the reliability sensitivity analysis also reveals that the failure probability of water budge closure is chiefly dependent on the accuracy of evapotranspiration estimations than the other components involved in the water budget equation.