A global, near real-time system measuring river, lake, and reservoir dynamics

Measuring and predicting the dynamics of discharge in rivers and water storage in lakes and reservoirs can inform water management and policy decisions, flood management and response, and help understand the influence of climate change and anthropogenic activities on hydrological, biogeochemical, and ecological processes. However, water body dynamics are often poorly observed on the ground. Gauging networks are unevenly distributed and in decline globally, and much gauging data is not publicly accessible in near real-time, if at all. Remote sensing technologies provide a unique alternative to monitor changes in water extent, level and volume in space and time. Our aim was to develop a global monitoring system that provides near real-time river discharge and lake and reservoir storage information from satellite observations. To estimate river discharge, we derived global surface water extent fraction from the 8-day 0.05° resolution reflectance data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and used recorded discharge at gauged sites and hydrological model estimates at ungauged sites to train MODIS-based satellite gauging reaches (SGRs) that can be used to estimate river discharge globally. In total, we were able to construct over 2,000 gauge-based and 11,000 model-based SGRs globally (Figure 1). To estimate volume changes in lakes and reservoirs, surface water extent dynamics for over 280 lakes and reservoirs (Figure 1) were derived from a daily 500-m resolution global surface water change dataset. Storage variations were calculated using surface water extent and height time series from the 10-day near real-time global lake and reservoir elevation dataset (G-REALM). As MODIS and G-REALM provide near real-time information, these data similarly allow estimation of river discharge and lake and reservoir storage in near real-time. It is hoped that the global monitoring system provides immediate and relevant information on rivers, lakes, and reservoirs, to inform government, the community and individuals on the current state of water resources in a historical context.