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From 2 August to 4 August in 2023, a prolonged and extensive extreme heavy rainfall event occurrs in the southeast of Heilongjiang Province. Utilizing multiple observations and ERA5 reanalysis data, characteristics of the precipitation process are analyzed focusing on large-scale circulation background, mesoscale circulation system evolution, environmental conditions from perspectives of climate statistics, weather analysis, and physical quantity diagnosis. Factors contributing to the prolonged extreme heavy rainfall event are explored. Main causes for the long duration of this heavy precipitation event are the stable maintenance of favorable large-scale conditions, such as the persistent divergence of the upper troposphere, the stable location of the west Pacific subtropical high (WPSH) and Northeast China cold vortex (NCCV), and continuous water vapor transport by the southwest jet. Due to the strong southwest jet, there is abundant moisture transfer, primarily through the advection of water vapor, which is the primary source for heavy rainfall. The process can be divided into two stages due to significant differences of rainfall, atmospheric stratification, and local circulation characteristics. In the first stage, the meridional water vapor inflow layer and the saturated layer are thick, resulting in high tropospheric humidity. The atmospheric condition is characterized by weak convective instability. Under the control of the northwest airflow at 500 hPa, the development of southwest jet, along with the influence of a weak eastward-moving vortex system at 850 hPa, results in horizontal wind speed convergence and systematic upward motion, leading to widespread and prolonged precipitation. The heavy rainfall area is mainly composed of cumulus embedded stratus, with a large coverage area of the cloud system, low echo centroid height, and high precipitation efficiency. With weak convective instability that promotes the development of convection and train effect in some periods, extreme hourly precipitation and large cumulative precipitation occur. In the second stage, the meridional water vapor inflow is concentrated in the lower troposphere with high intensity. The lower troposphere is close to saturation, with high humidity and temperature, while the middle and upper troposphere is dry and cold, and the atmospheric condition is more unstable than that in the first stage. Convection is developed and strengthened by the combined action of systematic uplift by a trough at 500 hPa, warm shear at 850 hPa, topographic convergence, and uplift. The cloud system is dominated by local strong cumulus clouds, and the distribution of precipitation intensity is uneven. At the beginning of this stage, convective cells continue to form at the trumpet-shaped terrain and move towards the eastern mountainous areas, organizing into linear convection. This is accompanied by the development and southward movement of surface convergence lines, leading to the generation of new convection and continuously causing localized intense short-duration rainfall.

Beijing, Tianjin, Hebei and neighbouring areas (34°-43°N, 113°-123°E) are located at the north edge of the East Asian summer monsoon, and they are also the main heavy-rain areas in northern China. The hourly precipitation data of 87 national meteorological stations from 1966 to 2021 are used for the analysis of spatial distribution and interannual variations, while the data of 298 stations from 1980 to 2021 are used to statistically analyze the diurnal variations and interannual variations of light precipitation (0.1-20 mm·h-1) and short-time heavy precipitation (no less than 20 mm·h-1) for the warm season (May-September) over the region. The results show that the annual average light precipitation and frequency in Beijing, Tianjin, Hebei and neighbouring areas during the warm season are much higher than those of short-time heavy precipitation. However, there is an area in the west of the Bohai Sea Region (37°-41°N, 115°-119.5°E) with high short-time heavy rainfall intensity but weak rainfall amount and frequency, which means the convective characteristics of short-time precipitation over this area are more extreme and significant. The interannual variations of two kinds of precipitation amount, frequency, and intensity in Beijing, Tianjin, Hebei and neighbouring areas excluding the west of Bohai Sea Region both present an overall growing trend in the warm season, in which the increasing trend of short-time heavy precipitation is more obvious, but the trend in the west of the Bohai Sea Region is not obvious. The diurnal variation amplitudes of light precipitation amount and frequency in Beijing, Tianjin, Hebei and neighbouring areas excluding the west of the Bohai Sea Region are significantly weaker than those of short-time heavy precipitation, but the peak durations are significantly longer. Compared to Beijing, Tianjin, Hebei and neighbouring areas excluding the west of the Bohai Sea Region, two types of precipitation in the west of the Bohai Sea Region from July to September are more frequent and the rainfall peak durations are longer. The interannual variations of precipitation in different periods of the whole day show that the light precipitation in two regions both decrease in the afternoon, while the short-time heavy precipitation has weakened significantly in the afternoon since 2005, but increased significantly from midnight to early morning.

Maize (Zea mays L.) is one of the most important grain crops in the world. Drought caused by climate change in recent years may greatly threaten water supply and crop production, even if the drought only lasts for a few days or weeks. Therefore, effective daily drought monitoring for maize is crucial for ensuring food security. A pivotal challenge in current related research may be the selection of data collection and the methodologies in the construction of these indices. Therefore, orthorectified reflectance in the short-wave infrared (SWIR) band, which is highly sensitive to variations in vegetation water content, was daily obtained from the MODIS MCD43A4 product. Normalized Difference Water Index (NDWI) calculated using the NIR and SWIR bands and days after planting (DAP) were normalized to obtain the Vegetation Water Index (VWI) and normalized days after planting (NDAP), respectively. The daily dynamic threshold model for different agricultural drought grades was constructed based on the VWI and NDAP with double-logistic fitting functions during the maize growing season, and its specific threshold was determined with historical drought records. Verification results indicated that the VWI had a good effect on the daily agricultural drought monitoring of spring maize in the "Golden Maize Belt" in northeast China. Drought grades produced by the VWI were completely consistent with historical records for 84.6% of the validation records, and 96.2% of the validation records differed by only one grade level or less. The VWI can not only daily identify the occurrence and development process of drought, but also well reflect the impact of drought on the yield of maize. Moreover, the VWI could be used to monitor the spatial evolution of drought processes at both regional and precise pixel scales. These results contribute to providing theoretical guidance for the daily dynamic monitoring and evaluation of spring maize drought in the "Golden Maize Belt" of China. [ABSTRACT FROM AUTHOR]