Deciphering Reservoir Dynamics: From Hydrology to Water Resources Management

Reservoir flow regulation represents the most intensive human-induced alteration of the hydrological cycle. These extensive reservoirs have significantly enhanced our capacity to manage Earth's freshwater resources. With a growing population and a changing climate, reservoirs are increasingly relied upon to meet rising demands. However, holistic knowledge about reservoir dynamics is severely limited across spatiotemporal scales. In situ storage measurements are often not shared, particularly across international river basins. While the evaporation losses from reservoirs in arid/semi-arid regions are substantial, water managers are typically dependent on crude loss estimates obtained from evaporation pans. The absence of large-scale, consistent, and comprehensive reservoir observations has posed a significant challenge in quantitatively assessing the humans influence on these waterbodies and accurately representing them in land surface and hydrologic models. Consequently, reservoir estimates with large uncertainties are inadequate for supporting decisions related to water resources management.

During the past two decades, both reservoir remote sensing and modeling capabilities have rapidly evolved, bridging a critical knowledge gap between reservoir impoundment and the changing environment. Primarily based upon the research from my group, this lecture will aim towards revealing reservoir dynamics in the context of climate, hydrology, and water management. First, we will introduce several newly developed (publicly available) remote sensing datasets (elevation, surface area, bathymetry, storage change, and evaporative water loss) spanning across regional to global scales. By relating the variability and the long-term trends of these lake/reservoir variables to climate forcings and anthropogenic activities, the key drivers behind them can be identified. Second, we will show that the remotely sensed reservoir datasets can be adopted to support modeling in different ways, from model parameterization to calibration/validation. One other promising use of remotely sensed reservoir information is data assimilation, which has been widely implemented in many land surface and hydrological models (but with variables such as satellite soil moisture). Third, we will present a few applications which can support water resources management. One example is near real-time daily reservoir evaporation monitoring in the western US, which helps water managers with reservoir flow regulation. Another example is the projection of surface water availability through integrated climate-hydrology-management modeling at a basin scale under future climate change scenarios. The lecture will conclude with a further discussion on unresolved challenges and unprecedented opportunities (e.g., the SWOT mission).