Influences of Tropical Cyclones on China During 1965-2004

Using the Joint Typhoon Warning Center （JTWC） and China Meteorological Administration （CMA） tropical cyclone track datasets, variations in frequency and intensity of the affecting-China tropical cyclones （ACTCs） are studied for the period of 1965-2004. First, the differences between the two tropical cyclone datasets are examined. The annual frequencies of tropical cyclones in the western North Pacific basin are reasonably consistent to each other, while the intensity records are less reliable. The annual numbers of ACTCs based on different datasets are close to each other with similar interdecadal and interannual variations. However, the maximum intensity and the annual frequency of ACTCs for strong categories show great dependence on datasets. Tropical cyclone impacts on China show the same variations as the annual number of ACTCs and also show dependence on datasets. Differences in tropical cyclone impacts on China are mainly caused by datasets used. The annual frequency of ACTCs, especially the length of lifetime of ones that make landfall, and the intensity estimates all have effects on the value of impacts on China.

Comparison of Two Drought Indices in Studying Regional Meteorological Drought Events in China

The composite-drought index （CI）, improved weighted average of precipitation index （IWAP）, and the objective identification technique for regional extreme events （OITREE） were employed to detect China＇s regional meteorolo- gical drought events （CRMDEs） during 1961-2010. Compared with existing references, CI and IWAP both showed strong ability in identifying CRMDEs. Generally, the results of CI and IWAP were consistent, especially for extreme and severe CRMDEs. During 1961-2010, although the frequencies of extreme and severe CRMDEs based on C! and IWAP both showed weak decreasing trends, the two mean-integrated indices both showed increasing but not signifi- cant trends. However, the results of IWAP were more reasonable than CI＇s in two aspects. Firstly, the monthly fre- quency of extreme and severe CRMDEs based on IWAP showed a clear seasonal variation, which coincided with the seasonal variation of the East Asian monsoon over central-eastern China, whereas the frequency based on CI presen- ted a much weaker seasonal variation. Secondly, the two sets of results were sometimes inconsistent with respect to the start and end times of a CRMDE, and CRMDEs based on CI generally showed two unreasonable phenomena： （1） under non-drought conditions, a severe drought stage could suddenly occur in a large area; and （2） during the follow- ing period, drought could alleviate gradually in cases of non-precipitation. Comparative analysis suggested that the IWAP drought index possesses obvious advantages in detecting and monitoring regional drought events.