Water resources management, in particular flood control, in the Lancang‐Mekong River Basin (LMRB) faces two key challenges in the 21st century: climate change and dam construction. A large‐scale distributed Geomorphology‐Based Hydrological Model coupled with a simple reservoir regulation model (GBHM‐LMK‐SOP) is used to investigate the relative effects of climate change and dam construction on the flood characteristics in the LMRB. Results suggest an increase in both flood magnitude and frequency under climate change, which is more severe in the upstream basin and increases over time. However, stream regulation by dam reduces flood risk consistently throughout this century, with more obvious effects in the upstream basin where larger reservoirs will be located. The flood mitigation effect of dam regulation dominates over the flood intensification effect of climate change before 2060, but the latter emerges more prominently after 2060 and dominates the flood risk especially in the lower basin.

Electricity production by hydropower is negatively affected by drought. To understand and quantify risks of less than normal streamflow for hydroelectricity production (HP) at the global scale, we developed an HP model that simulates time series of monthly HP worldwide and thus enables analyzing the impact of drought on HP. The HP model is based on a new global hydropower database (GHD), containing 8,716 geo‐localized plant records, and on monthly streamflow values computed by the global hydrological model WaterGAP with a spatial resolution of 0.5°. The GHD includes 44 attributes and covers 91.8% of the globally installed capacity. The HP model can reproduce HP trends, seasonality, and interannual variability that was caused by both (de)commissioning of hydropower plants and hydrological variability. It can also simulate streamflow drought and its impact on HP reasonably well. Global risk maps of HP reduction were generated for both 0.5° grid cells and countries, revealing that 67 out of the 134 countries with hydropower suffer, in 1 out of 10 years, from a reduction of more than 20% of mean annual HP and 18 countries from a reduction of more than 40%. The developed HP model enables advanced assessments of drought impacts on hydroelectricity at national to international levels.

This study unveils regional patterns of dominant streamflow generation mechanisms across the conterminous United States and identifies their climatic and physiographic controls. Six signatures describing the characteristics of rainfall‐stormflow responses and the characteristics of base flow response are extracted from continuous rainfall‐streamflow time series for 432 US catchments. These study catchments are classified into eight classes based on similarities of the six signatures, and dominant streamflow generation mechanisms for each class are inferred based on the magnitudes of the six signatures. This catchment classification reveals geographically coherent regional patterns across the conterminous United States. Catchment climatic and physiographic characteristics most relevant to this catchment classification are identified using techniques such as correlation analysis and random forest modeling. The most relevant characteristics are climate aridity, median event rainfall volume, topographic slope, soil permeability, rock type, and vegetation density, which are found to be the main controlling factors governing the dominant streamflow generation mechanisms. The linkages between the inferred dominant streamflow generation mechanisms and specific combinations of the climatic and catchment physiographic characteristics identified above are synthesized in a conceptual diagram, as an extension of the classical Dunne diagram. The new findings, while largely consistent with the results of previous empirical and modeling studies, add rich process detail to the transferable understanding of regional patterns of dominant streamflow generation mechanisms and their climatic and physiographic controls.

Key Points: Modeling analysis of future hydrologic droughts over U.S. is provided Relative contributions from climate change and water managements are quantified Future hydrologic drought will be alleviated by reservoirs but intensified by local water extraction