This study focuses on an extreme precipitation event that occurred in North China from July 28 to August 1， 2023， referred to as the "23.7" extreme precipitation event.The purpose of this research is to assess the performance of various parameterization schemes within the WRF model in simulating this event， identify the optimal scheme combinations， and diagnose the physical causes of simulation biases.Using the Weather Research and Forecasting （WRF-ARW） model version 4.5.1， a total of 24 sensitivity experiments were conducted with six different microphysics schemes and four cumulus parameterization schemes.The precipitation simulation results were systematically evaluated using various spatial-temporal verification metrics， including the Threat Score （TS）， the Fractions Skill Score （FSS） and so on.The results indicate that： （1） The dynamical downscaling simulations effectively reproduced the orientation and area of rainfall associated with this extreme precipitation event， with accuracy improving as model resolution increased.（2） Among all scheme combinations， the combination of the WSM6 microphysics scheme and the Kain-Fritsch cumulus scheme （WSM6-KF） demonstrated the highest overall skill in simulating the precipitation area， intensity， and evolution trend， particularly excelling in the simulation of heavy rainfall events and above.In-depth diagnosis revealed that this combination's strength lies in its ability to accurately reproduce the distribution of deep graupel and intense updrafts corresponding to the heavy precipitation center， thereby capturing the key microphysical and dynamical features of this extreme precipitation event.（3） Despite the strong performance of the optimal scheme （WSM6-KF）， systematic biases were still present.Comparisons with ERA5 reanalysis data indicated that this scheme underestimated the water vapor transport pathways and moist layer thickness in the terrain-forced uplift regions of the Taihang Mountains during the later stages of precipitation， which directly resulted in an underestimation of peak precipitation and a westward shift of some rainfall areas.This study provides references for future operational forecasting of extreme precipitation in this region and insights for model improvement.
Under the process of climate warming and humidification， extreme precipitation events have occurred frequently in the arid and semi-arid regions of northwest China.The fragility of the ecological environment in this area makes it highly vulnerable to secondary disasters induced by extreme precipitation， resulting in strong disaster-causing effects.Using daily precipitation data and atmospheric reanalysis data， this study focuses on extreme precipitation events in the arid and semi-arid regions of northwest China during the summer （June-August） from 1980 to 2022.Based on the K-means clustering method， these extreme precipitation events are classified into three types， which occur in the mid-eastern Loess Plateau， the Ili River Valley Basin， and the Qilian Mountains respectively.Additionally， an analysis is conducted on their frequencies， large-scale circulation patterns， and water vapor transport of each type of extreme precipitation.The main results show that： （1） Over the past 40 years， the frequency of summer extreme precipitation in the arid and semi-arid regions of northwest China has shown an increasing trend.While a slight decreasing trend and amplified interannual oscillation occurred since the 21st century.Among these events， the extreme precipitation occurring in the mid-eastern Loess Plateau has the strongest intensity but the lowest cumulative days， whereas that in the Ili River Valley Basin has the weakest intensity but the highest cumulative days.（2） The large-scale circulation patterns corresponding to the three types of extreme precipitation exhibit a "low pressure in west and high pressure in east" pattern over the East Asian continent， however， significant differences exist in their intensity and location.Furthermore， anomalous anticyclone of the Western Pacific Subtropical High， along with water vapor transport via the Southwest Monsoon， the southerly winds on the eastern side of the Qinghai-Tibet Plateau， and the mid-latitudes， serves as important sources of water vapor affecting the three types of extreme precipitation.（3） Since the 21st century， extreme precipitation frequencies have increased in the eastern part of the arid and semi-arid regions of northwest China， while it has decreased rapidly in the western part.The frequency variations of mid-eastern Loess Plateau， the Ili River Valley Basin extreme precipitation are significantly influenced by the mid-latitude quasi steady Rossby wave activities， whereas， Type of the Qilian Mountains is notably affected by anomalous low pressure over the Tibetan Plateau.The above results provide a certain theoretical basis and application value for deeply understanding of the spatiotemporal Characteristics of extreme precipitation in northwest China， improving the accuracy of summer extreme precipitation prediction， and enhancing disaster prevention and mitigation efforts.
To investigate the specific effects and extent of the influence of soil temperature and soil moisture content-particularly soil temperature variations-on soil thermal conductivity， so as to provide a reference for land surface models to consider the influence of soil temperature changes on thermal conductivity.This study utilizes observational data from grassland and forest underlying surfaces collected at the Pingliang Land Surface Process and Severe Weather Observation Station， Chinese Academy of Sciences， from December 2017 to July 2021， to comparatively analyze the relationships among soil thermal conductivity， soil water content， and soil temperature.Partial correlation analysis was employed to quantify the independent effects of water content and temperature on thermal conductivity.The results show that： （1） The grassland typically enters the freezing phase 1~7 days earlier than the forest and initiates thawing 1~6 days later， the grassland has 1~4 additional days of freeze-thaw events compared to the forest areas.（2） Both surfaces exhibit pronounced seasonal cycles， with soil thermal conductivity， water content， and temperature peaking in summer and reaching minima in winter.Thermal conductivity closely tracks variations in water content.At 5 cm depth， the grassland shows higher annual mean soil water content （~0.12 m³·m⁻³） and temperature （~1.3 ℃） than the forest， along with greater seasonal and diurnal variability.（3） The peak soil temperature at 5 cm depth in the forest lags behind that of the grassland by approximately 2 hours， and the diurnal amplitudes of thermal conductivity， water content， and temperature are all larger in the grassland than in the forest.（4） Under dry conditions （soil water content ≤ 0.12 m³·m⁻³）， soil temperature remains significantly， albeit weakly， correlated with thermal conductivity （partial correlation coefficient r=0.169， p<0.001）， indicating that both water content and temperature should be jointly considered in land surface models for arid and semi-arid regions.
Based on statistical analysis of elevated convection cases during the 2010 -2024 cold seasons in Henan Province using conventional observations and ERA5 reanalysis data， this study examines spatiotemporal distributions， synoptic configurations， and formation mechanisms. Results indicate that： （1） Characteristic configurations feature prominent 500 hPa troughs， intense 700 hPa southwesterly warm-moist jets， and a deep cold dome with northeasterlies below 850 hPa. Key sounding signatures include pronounced cold domes exceeding 150 hPa thickness and frontal inversions with tops at 850~700 hPa where over half of cases exhibit inversion-layer temperature differences greater than 4 °C. Thermodynamic instability is best characterized by elevated most unstable energy and thermal contrast between 700 hPa and 500 hPa. （2） Moisture transport at 700 hPa and its associated high specific humidity provide essential vapor conditions for elevated convection during the cold season. Strong upward motion is observed above 800 hPa， with its core centered at 500~400 hPa. Intense deep-layer vertical wind shear （>20 m·s-1） and pronounced baroclinicity develop between the northerly flow beneath the inversion layer and the southwesterly jet atop the inversion layer. Such vertical wind shear configuration proves conducive to the sustenance and development of cold-season convection. （3） Cold season elevated convective instability mechanisms encompass four distinct types. The dominant conditional instability type exhibits deep vertical convection characterized by the strongest updraft intensity， with convective penetration extending significantly above the -20 ℃ level， frequently triggering thunderstorms and hailstorms. The hybrid mechanism type integrates conditional instability with conditional symmetric instability， displaying the most extensive updraft coverage at moderate intensity and capable of producing multiphase hazards including thunderstorms， hail and freezing precipitation mixtures such as freezing rain and sleet. Both the conditional symmetric instability type manifested through narrow slantwise convection and the frontogenesis circulation type featuring broad multicellular updraft structures demonstrate lower convective development heights with weaker intensities， predominantly generating thunderstorms and convective heavy winter precipitation events.
Under the background of frequent extreme weather and increasing serious secondary disasters such as geological disasters and floods in small and medium-sized rivers， it is of great significance to enhance the ability to forecast and early warning of flood meteorological risk in small and medium-sized basins. The Yiluo River Basin in the middle reaches of the Yellow River was selected as the study area. Based on multi-source data such as geographical information， meteorological and hydrological observations， and combined with digitized remote sensing information of the actual river network at fourth- to fifth-order streams， the Yiluo River Basin was precisely divided into 19 subbasins. Utilizing the localized SWAT distributed hydrological model， the key hydrological sections of Yiluo River and the daily runoff series of Heishiguan， Baimasi and Longmenzhen Hydrological stations in past 44 years were reconstructed to classify the flood grades. Taking the warning flood as an example， the statistical methods such as correlation coefficient analysis， P-III frequency curve and quadratic function fitting were used to establish the fitting curves of the maximum cumulative areal rainfall and the maximum runoff increase of the above three key hydrological stations and their sections， thus the critical thresholds of areal rainfall for different grades were obtained. On this basis， the areal rainfall threshold transplantation scheme was adopted to clarify the different grades flood-inducing critical surface rainfall thresholds for the 19 sub-basins of the Yiluo River， and ultimately obtained a set of graded flood-inducing critical area rainfall threshold indicators for small and medium-sized basins in the study area. The threshold indicators were applied and verified in the Yiluo River Basin during the flood season in 2024， showing that the overall hit rate of flood based on the research threshold was 55. 6%， among them， the early warning hit rate of single-day heavy rainfall was 100%， for continuous precipitation processes， using 48-hour cumulative area-rainfall early warning， the hit rate reached 88. 9%. This study provides research ideas and references for flood prevention， forecasting and early warning services in areas with insufficient or no hydrological data in the small and medium-sized river basins， and provides a valuable reference and technical support for flood disaster prevention and mitigation.
