Spatial-Temporal Distribution of Summer Extreme Precipitation in South China and Response of Tropical Ocean

In the study, the summer extreme precipitation in South China is divided into early rainy season (MJ) and late rainy season (JA). The percentile method (95%) is used to define the extreme precipitation threshold. Based on the international general definition method of extreme precipitation threshold: percentile method (95%), the extreme precipitation thresholds in flood season before and after South China are defined respectively. The total amount and frequency of extreme precipitation in flood season before and after 1979-2014 are calculated in this paper. The change trend of the two indicators is basically the same, and the two indicators have obvious interannual variation and an upward trend. According to the results of wavelet analysis of extreme precipitation frequency, the frequency of extreme precipitation in the first flood season mainly has a period of 3 - 5 years, while the frequency of extreme precipitation in the later flood season has a significant period of 6 - 8 years. The spatial distribution of extreme precipitation before and after the flood season shows that the extreme precipitation in the former flood season is mainly distributed in the central part of Guangdong, the northeast of Guangxi and the western part of Fujian, and the extreme precipitation in the latter flood season mainly occurs in the southern coastal area. The results show that there are different tropical SST regions affecting the extreme precipitation in South China. The former flood season is mainly the tropical Indian Ocean warm SST, and the latter flood season is mainly the tropical Pacific warm SST. The tropical Indian Ocean SST stimulates the anticyclonic anomaly over the South China Sea, which brings the southwest warm and humid air flow into South China, resulting in the increase of extreme precipitation in the first flood season of South China;the tropical Pacific SST stimulates the cyclonic anomaly over the South China Sea, which reduces the water vapor outflow caused by the seasonal northward jump of the subtropical high in South China, resulting in the increase of extreme precipitation in the later flood season of South China.

Construction of Forecast and Early Warning System of Meteorological and Geological Disasters in Qinghai Province

Based on the meteorological and geological disaster data, ground observation data set, CLDAS grid point data set, and EC, BJ and other model product data during 2008-2020, the temporal and spatial distribution characteristics of meteorological and geological disasters and precipitation were analyzed, and the causes of the occurrence of meteorological geological disasters and the deviation of model precipitation forecast were revealed. Besides, an objective precipitation forecast system and a forecast and early warning system of meteorological and geological disasters were established. The results show that meteorological and geological disasters and precipitation were mainly concentrated from May to October, of which continuous precipitation appeared frequently in June and September, and convective precipitation was mainly distributed in July-August;the occurrence frequency of meteorological and geological disasters was basically consistent with the distribution of accumulated precipitation and short-term heavy precipitation, and they were mainly concentrated in the southern and eastern parts of Qinghai. Meteorological and geological disasters were basically caused by heavy rain and above, and meteorological and geological disasters were divided into three types: continuous precipitation(type I), short-term heavy precipitation(type II) and mixed precipitation(type III). For type I, the early warning conditions of meteorological and geological disasters in Qinghai are as follows: if the soil volumetric water content difference between 0-10 and 10-40 cm is ≤0.03 mm^(3)/mm^(3), or the soil volumetric water content at one of the depths is ≥0.25 mm^(3)/mm^(3), the future effective precipitation reaches 8.4 mm in 1 h, 10.2 mm in 2 h, 11.5 mm in 3 h, 14.2 mm in 6 h, 17.7 mm in 12 h, and 18.2 mm in 24 h, and such warning conditions are mainly used in Yushu, Guoluo, southern Hainan, southern Huangnan and other places. For type II, when the future effective precipitation is up to 11.5 mm in 1 h, 14.9 mm in 2 h, 16.2 mm in 3 h, 19.9 mm in 6 h, 25.3 mm in 12 h, and 26.3 mm in 24 h, such precipitation thresholds are mainly used in Hainan, Huangnan, and eastern Guoluo;as it is up to 13.3 mm in 1 h, 15.5 mm in 2 h, 16.6 mm in 3 h, 19.9 mm in 6 h, 31.1 mm in 12 h, and 34.0 mm in 24 h, such precipitation thresholds are mainly used in Hehuang valley. The precipitation thresholds of type III are between type I and type II, and closer to that of type II;such precipitation thresholds are mainly used in Hainan, Huangnan, and northern Guoluo. The forecasting ability of global models for heavy rain and above was not as good as that of mesoscale numerical prediction model, and global models had a wet bias for small-scale precipitation and a dry bias for large-scale precipitation;meso-scale models had a significantly larger precipitation bias. The forecast ability of precipitation objective forecast system constructed by frequency matching and multi-model integration has improved. At the same time, the constructed grid forecast and early warning system of meteorological and geological disasters is more precise and accurate, and is of instructive significance for the forecast and early warning of meteorological and geological disasters.