Increased southerly and easterly water vapor transport contributed to the dry-to-wet transition of summer precipitation over the Three-River Headwaters in the Tibetan Plateau

The Three-River Headwaters(TRH)region in the Tibetan Plateau is vulnerable to climate change;changes in summer(June–August)precipitation have a significant impact on water security and sustainability in both local and downstream areas.However,the changes in summer precipitation of different intensities over the TRH region,along with their influencing factors,remain unclear.In this study,we used observational and ERA5 reanalysis data and employed a precipitation categorization and water vapor budget analysis to quantify the categorized precipitation variations and investigate their possible linkages with the water vapor budget.Our results showed an increasing trend in summer precipitation at a rate of 0.9 per year(p<0.1)during 1979–2020,with a significant dry-to-wet transition in 2002.The category‘very heavy precipitation’(10 mm d−1)contributed 65.1%of the increased summer precipitation,which occurred frequently in the northern TRH region.The dry-to-wet transition was caused by the effects of varied atmospheric circulations in each subregion.Southwesterly water vapor transport through the southern boundary was responsible for the increased net water vapor flux in the western TRH region(158.2%),while southeasterly water vapor transport through the eastern boundary was responsible for the increased net water vapor flux in the central TRH(155.2%)and eastern TRH(229.2%)regions.Therefore,we inferred that the dry-to-wet transition of summer precipitation and the increased‘very heavy precipitation’over the TRH was caused by increased easterly and southerly water vapor transport.

数值天气预报模式对雅砻江下游强降水预报能力检验研究（英文）

目的:检验数值天气预报模式(WRF)在雅砻江下游对强降水的预报能力,并找出表现最优的参数化方案组合。创新点:首次针对雅砻江流域检验WRF模式对强降水的预报能力,并加入了计算时间作为评价的重要参考。方法:通过三场强降水事件,利用七种常用的云微物理参数化方案(Kessler,Lin et al.(Lin),SingleMoment 3-class(WSM3),Single-Moment 5-class(WSM5),Ferrier,Single-Moment 6-class(WSM6),和New Thompson et al.(NTH))和3种积云对流参数化方案(Kain-Fritsch(KF),Betts-Miller-Janjic(BMJ)和Grell-Devenyi(GD))的组合,对WRF模式在雅砻江下游的降水预报能力进行检验。为了评价WRF模式的预报能力,引入探测率(POD),空报率(FAR),BIAS和公平预报评分(ETS),对比不同方案组合的降水空间分布和站点预报的有效性。同时,均方根误差(RMSE)等指标被用来评价面雨量预报的精确性。除常规评价外,还将计算时间作为方案评价的重要参考,在满足精度需求的前提下优先选择计算效率高的方案组合。结论:1.WRF模式能够适用于雅砻江下游强降水预报;2.WSM3以及GD参数化方案组合的表现最为有效和稳定。