Exploring the factors controlling the performance of the Surface Water and Ocean Topography mission discharge algorithms
Abstract
Openly available measurements of river flow are essential to allocation of water resources, flood and drought forecast and mitigation efforts, for our understanding of the hydrologic cycle and for many other applications. Access to high quality local measurements is not ubiquitous and is particularly difficult for rivers flowing on remote locations or across country boundaries. Measurements taken from satellite missions such as upcoming the Surface Water and Ocean Topography (SWOT) mission offer data that can be freely downloaded by anyone; however, such platforms often measure either water level or inundated areas and how they change over time, which are not sufficient to directly quantify river flow. Methods to estimate discharge based on satellite measurements have been or are in development and knowledge of the uncertainty of their estimates is essential for wide application of such methods. We conducted a comprehensive assessment of the accuracy and precision of five methods designed to estimate discharge based on SWOT measurements under three conditions: ideal, that is if the measurements were available once a day and contained no error, with no measurement error but changing how frequently the measurements were taken, and a third scenario containing different levels of measurement error. We found that the precision of the estimates is related to the precision in the prior guess of the mean annual flow rate. However, the assessed methods consistently improved over the prior, especially when reach where the methods operate have distinct characteristics in space. We also found that despite the use of very similar discharge equations, the subtle differences in equations among the methods can be important. Finally, we found at least two methods can work well with the expected amount of measurement error and frequency.
