How well will the Surface Water and Ocean Topography (SWOT) mission observe global reservoirs?

Abstract:

Accurate observations of global reservoir storage are critical to understand the global availability of managed water resources. By taking measurements at a 250-m² spatial resolution and minimum frequency of every 22-days, the NASA SWOT mission will greatly improve the coverage of global reservoir monitoring. With a given 2020 launch date and projected orbit lifetime of only three years, it is essential that the measurement uncertainty is known in advance to maximize the applicability of SWOT data in monitoring systems or models as it is being acquired. We use in-situ measurements of California reservoirs as a ‘truth’ dataset to be compared to simulated SWOT data. Estimates of both temporal and spatial uncertainty will be determined by analyzing how much information is lost when using synthetic records over gauged measurements to generate time series of monthly reservoir storage and by evaluating changes in observations after perturbing satellite flight paths within the range of expected swaths. Based on similar studies that investigated expected SWOT measurement errors for lakes, anticipated uncertainty in SWOT reservoir storage estimates vary from a low of 5% for large reservoirs (>1 km²) to 20% for small reservoirs (<0.01 km²) with negligible impacts due to variations in orbit. The feasibility of using SWOT estimates of storage in large-scale hydrologic models will then be assessed by using synthetic SWOT storage to calibrate RES-ADAPT, a newly developed climate adaptive reservoir model that was tested in California and designed to evaluate global reservoir management impacts on the climate system.