Based on daily MCI and identification method of persistent regional drought events, the persistent regional drought events in summer and autumn were identified in Hunan Province from 1961 to 2017. And on this basis, the spatio-temporal characteristics of evaluation indexes including frequency, duration, intensity and start date, end date of persistent regional drought evens were analyzed. The results show that the persistent regional drought events occurred 1.4 times per year on average in Hunan Province in summer and autumn from 1961 to 2017, and the annual variation trend of drought events wasn’t obvious. The decadal variation characteristic was obvious, the drought frequency was the least in the 2000s, but the accumulative intensity of drought was the strongest and lasting days of drought were the longest. The drought events were fewer and weaker in the 1990s. The continuous droughts from summer to autumn dominated in Hunan Province, and occurred more frequently from July 28 to October 14. The drought events persisted mainly from 15 d to 30 d, and the longest lasted 183 d. The duration of general drought events was less than 40 days, while for severe drought events and above it was more than 110 days. The spatial distributions of persistent regional drought events mainly appeared three patterns including the whole province pattern, northwestern pattern and southern pattern in Hunan Province. The drought events with the whole province pattern were the most, and drought grades reached mostly heavy level and above. The persistent regional drought events were less in the north and more in the south of Hunan Province, and the accumulative intensity of drought increased gradually from northwest to southeast. The drought degree in northwestern Hunan was lighter, while in Dongting Lake, central and southern Hunan it was heavier.

Based on daily precipitation, mean air temperature, maximum and minimum air temperature, wind speed and direction (four times a day) data during 1961-2018, and hourly precipitation data during 1978-2018 from 6 national meteorological stations around the Poyang Lake as well as the reanalysis data of European Center during 1979-2018, the climate difference between the east and the west side of the Poyang Lake caused by the cold-heat source effect on different time scales was analyzed. The results are as follows: (1) There was an obvious cold-heat source effect in the Poyang Lake. The diurnal temperature range in the Poyang Lake area was 2-4 ℃ smaller than that in mountainous areas, and the high temperature days was half of that in other areas of the same latitude in Jiangxi Province. (2) The precipitation in the Poyang Lake was also less than other areas of Jiangxi. The precipitation in the east and the west side of the lake presented the cyclical fluctuation in a year, there were more precipitation from August to October in the west side of the lake, while there were more rainfall in other months in the east side of the lake, the difference was obvious especially in middle of winter and summer. (3) There were differences of precipitation between the east and the west of the lake at day and night. The precipitation in the east of the lake was more obvious at night in January, while in September it was more obvious in the west of the lake at day. (4) Lake-land wind existed in the Poyang Lake. The average wind speed at 02:00 BST in January at Yongxiu station in the west side of the lake was higher than that of Duchang station in the east side of the lake, and the west wind component occurred more. In August, the average wind speed at Duchang station was higher than that of Yongxiu station at 14:00 BST, and the south wind occurred more frequently. (5) Compared with 14:00 BST, the atmospheric ascending motion was more obvious at 02:00 BST in the main area of the Poyang Lake in January, the near-surface wind field converged. While compared with 02:00 BST in August, subsidence movement was more obvious at 14:00 BST, and near-surface wind field diverged.

Based on the conventional observation data, Doppler radar products at Kashi station, FY-2D satellite cloud images and NCEP/NCAR reanalysis data, the formation mechanism and mesoscale weather system of four rainstorm processes under the anomalous circulation background in the west of Southern Xinjiang in August 2016 were analyzed comparatively. The results show that the more rainstorms in the western part of Southern Xinjiang in August 2016 occurred under the circulation background of the strong Ural Mountains high ridge on 500 hPa and Polar lows, anomalous water vapor convergence zone on 700 hPa over Tibetan Plateau and longitudinal oscillation of South Asia high. And the establishment, development and decline of the Ural Mountain high ridge on 500 hPa were closely related with rainstorms in the western part of Southern Xinjiang in August 2016. The intensity of rainstorm was closely related with 850 hPa warm ridge and temperature difference above 28 ℃ between 500 hPa and 850 hPa, while the differences of humidity layer thickness below 500 hPa, easterly airflow below 700 hPa, surface shear line and dry line resulted in different intensity, falling area and duration of rainstorm. The water vapor transport at the southern boundary was important source of rainstorm in the western part of Southern Xinjiang, while at the eastern boundary it was important supply of short-term heavy rainfall in the area. The humidity gradient on satellite images was conductive to the occurrence of convective weather, while the structures of the strong echo, low centroid and high cloud top of radar were beneficial to the occurrence of short-term heavy rainfall.

Abstract:Results from the data of meteorological disasters in 2008 in Langfang show that the torrential rain and flood disasters are the
most damageable．From 1949 to 2007，the direct economic losses caused by the torrential rain and flood disasters are 198．673 billion，
which are 82．2%of those caused by all the meteorological disasters．The sustainable development of national and local economic is
significantly affected by the torrential rain and flood disasters．Based on the system theories and principles of natural disasters evaluation，8 indexes are calculated，including topographic index(H)，intensity(C)and frequency(R)index of the torrential rain and lood disasters，onomical disaster bearing capacity index(E)，economic loss index(E')，life vulnerability index(L)，life damage ndex(L')and disaster relief index(K)，respectively．Combined disaster index were obtained for each county after systematically assessed the regional differences in risks of the torrential rain and flood disasters in Langfang，and 4 grades(extremely high，high，medium and low)were used to divide the torrential rain and flood disasters．Studies on the division of the torrential rain and flood disasters an provide us scientific basis for the precaution of the torrential rain and flood disasters and reduction of their economic losses and taking effective measures to these disasters．