干旱区年内降水分配不均会加剧旱涝灾害的发生，进而制约该地区生态系统功能和水资源管理。全球增暖背景下，中国西北干旱区自1980s降水量整体显著增多，但尚未充分明晰其年内分配特征有何变化。本研究基于CN05. 1降水格点数据，采用多个时间均匀性表征指标，系统考查了1961-2021年西北干旱区降水不同时间尺度均匀性的时空演变特征。基于月尺度降水集中指数（Precipitation Concentra‐tion Index，PCI）的分析表明，西北干旱区整体降水季节特征较为明显（平均PCI为17. 8）；从PCI的长期趋势来看，近1961-2021年约89. 1%的面积呈减小趋势［平均变化率为-0. 29·（10a）-1］，尤其极端干旱区下降速率最快［-0. 44·（10a）-1］。西北干旱区PCI整体减小主要是由于夏季降水量占比降低［-0. 6%·（10a）-1］而冬季占比增加［0. 35%·（10a）-1］所致，反映出该地区年内降水的季节集中程度有所减弱。基于日尺度降水集中度（Precipitation Concentration Degree，PCD）和集中期（Precipitation Concentration Period，PCP）的结果与月尺度一致，西北干旱区 PCD呈显著下降趋势［-0. 008·（10a）-1］，PCP变化不显著，仅在部分地区有所前移［最大-1. 54 d·（10a）-1］。平均而言，西北干旱区年降水量的一半（50%）可由日降水量最多的11天贡献，在湿润区达到一半年降水量所需的最湿日呈减少趋势［-1. 8 d·（10a）-1］，而在极端干旱区呈增加趋势［0. 9 d·（10a）-1］。本研究可为西北干旱区极端旱涝灾害的应对管理和政策制定提供有效的科学依据。

Uneven intra-annual precipitation distribution in arid regions can intensify both drought and flood events，thereby inhibiting ecosystem functioning and water resource management. Under global warming，total precipitation in arid Northwest China（NWC）has significantly increased since the 1980s. Yet，it is insufficient to understand the spatio-temporal variations in its intra-annual distribution patterns. Based on the CN05. 1 gridded precipitation dataset，we comprehensively examined the spatio-temporal variations in the temporal homogeneity of precipitation across multiple time scales from 1961 to 2021. As revealed by the Precipitation Concentration In‐ dex（PCI）at monthly scale，NWC exhibits pronounced seasonal precipitation patterns，with an average PCI of 17. 8. From 1961 to 2021，PCI show a decreasing trend over 89. 1% areas of NWC with an overall tendency of -0. 29·（10a）-1，especially in the hyper-arid sub-region［-0. 44·（10a）-1］. The reduction in PCI is primarily attrib‐ uted to the decreasing proportion of summer precipitation［-0. 6%·（10a）-1］and the increasing proportion of win‐ ter precipitation［0. 35%·（10a）-1］，indicating a weakening seasonal concentration of intra-annual precipitation. At daily scale，the long-term changes in the Precipitation Concentration Degree （PCD） and Precipitation Concentration Period（PCP）agree with the monthly-scale PCI. PCD presents a significant decreasing trend ［-0. 008·（10a）-1］，and PCP generally varies insignificant with slight decreasing in some regions［maximum -1. 54 d·（10a）-1］. On average，50% of annual precipitation in NWC is contributed by the 11 wettest days. The wettest days contributing to half of annual precipitation decrease at a rate of -1. 8 d·（10a）-1 in humid sub-region but increase at 0. 9 d·（10a）-1 per decade in the hyper-arid sub-region. Our findings provide critical scientific in‐ sights in climate adaptation，risk mitigation and strategy making for drought and flood extremes in arid NWC.