Quantifying and attributing recent changes in global lake and reservoir storage using satellite observations and hydrological modeling

Abstract:

Lakes and reservoirs are essential components of the global hydrological cycle. They function as sentinels of climate change, and provide indispensable water supply, energy generation, aquatic ecosystems for meeting agricultural, industrial, and domestic needs. Despite the importance of lakes and reservoirs to natural systems and human societies, their water storage dynamics are poorly understood on a global scale. This is further exacerbated by the declining gauging measurements across the world. The resulting knowledge gap prevents a fundamental understanding of the surface water availability, and thus impedes effective water resource management. Here, we provide a comprehensive assessment of recent changes in global lake/reservoir storage and the attributions to climate and anthropogenic forces using a combination of satellite observations and hydrological modeling. First, we use a newly developed water mapping algorithm to leverage the entire Landsat archive (including cloudy images) to generate monthly water areas for about 1,000 major lakes and reservoirs worldwide from 1990s to the present. Second, the water areas are combined with water levels derived from satellite-based altimetry to deduce the storage changes in each of the major water bodies. Storage uncertainty in missing smaller lakes is estimated using empirical geo-statistical approaches. The quantified lake storage changes will be used to investigate the direction and magnitude of the lake storage trends across the globe. The global patterns of lake water storage trends are analyzed and composited based on different climate regions (dry versus wet) and waterbody types (saline, natural freshwater, and artificial reservoirs). Furthermore, they will be linked to changes in regional and global climate to identify the forcings of lake level variability. Using statistical models that incorporate observed changes in lake water storage, simulated/observed climate variables (e.g., precipitation, potential evapotranspiration, runoff, near-surface soil moisture), and simulated human water withdrawal, we will attempt to attribute recent lake water storage changes to natural and anthropogenic causes. These results will advance the understanding of surface water storage dynamics and the implications for the water cycle.