Diverse flood characteristics over southern High Mountain Asia under different synoptic patterns

High Mountain Asia (HMA) supplies abundant natural and human water demands in Asia, nourishing about 30% of global population, which is of vital importance to sustainable water resources management. However, the space-time pattern of flood characteristics and its related synoptic conditions in this region remains unclear. This study illuminates the discrepancy of flood characteristics in two stages of warm season over the southern HMA, particularly the spatial propagation, scale and frequency of floods. In the first stage, more local-scale floods occur and propagate from the downstream to the upstream, while in the second stage, there would be more widespread and high-magnitude floods in this region. The tributaries are characterized by local-scale floods, but with a higher frequency in the first stage than the second stage. Diverse synoptic patterns of Indian Low Pressure (ILP) and Western Pacific Subtropical High (WPSH) are responsible for the individual characteristics of floods. The WPSH is favorable for facilitating a massive amount of moisture from the Pacific and Indian Ocean to southern HMA, and thus tends to induce the intensive and widespread floods in the second stage. A shift of earlier and later flood peak dates in the historical period is shown in the first and second stage, respectively. Effective measures need to be implemented to cope with the spatial and temporal variability in flood characteristics by integrating the tradeoffs between freshwater management and flood risks mitigation.