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Bao Y.,Nanjing University of Information Science and Technology | Meng C.,Nanjing University of Information Science and Technology | Shen S.,Nanjing University of Information Science and Technology | Qiu X.,Nanjing University of Information Science and Technology | And 2 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2011

Jiangsu Province is located in the middle of East China and the lower reaches of the Yangtze River, with plains covering about 68 percent of its total area. The province spans the subtropical/ humid and warm-temperate/ semi-humid climate zones. The climate is damp and four seasons are clear. The rainfall is concentrated in spring and summer. However, drought events are often observed across the entire province in autumn especially late autumn. It is important to understand the physical formation mechanisms, temporal and spatial distribution patterns of drought events in the province. This may provide decision-makers scientific evidence to design or examine a monitoring network and forewarning system of drought event in the province. In this study, a heavy drought event occurring in October and November 2006 is analyzed using the surface observational data from 54 stations across the province and the National Aeronautics Space Administration (NASA) satellite products. The surface meteorological observation data include daily precipitation, daily mean temperature, daily maximum temperature, daily minimum temperature, solar radiation reaching the surface, sunshine duration, wind speed and relative humidity. The daily composite drought index (CI) is calculated using the two-month observational data. The calculated CI is used to determine the beginning and ending dates, duration and severity of the drought event in the different regions of the province and analyze their temporal and spatial evolving patterns. The change in vegetation pattern during the drought event is described by vegetation water supply index (VWSI) and examined by using 8-day composited surface albedo and surface temperature. Both surface albedo and surface temperature are retrieved from MODerate resolution Imaging Spectroradiometer(MODIS) data and their horizontal resolutions are 500 meters and 1 kilometer, respectively. The soil spatial and temporal patterns of the drought event are investigated with the soil relative humidity (SRH) data. The SRH was measured on the surface and at 10 centimeters below the ground surface on the 8th day per ten days during the period from October to November in 2006 at 16 agro-meteorological observational stations across the province. The spatial distribution of the drought is analyzed by using a software of geographic information system called ArcGIS9.3 in which the inverse distance weighted interpolation is used. Several results are obtained from this study. First, there is no conflict among the evolutions of atmosphere, vegetation, soil moisture during the drought as indicated by different indices such as CI, VWSI, SRH. Second, the drought event starts from the northwest part of the province and spread southeastward whereas the ending date shows an opposite direction. The event presents a similar evolution pattern in the different regions, which is weak at the beginning, strong at the next, and weak again in the final across the entire province. The duration decreases from the northern part to the southern part of the province successively. Third, the drought severity is heavier in the northern part than in the southern part of the province. The evolving processes of drought event are very different and highly dependent on the meteorological and geographic conditions. Fourth, CI, VWSI and SRH are three useful parameters for describing the duration and severity of drought events. Source


Bao Y.,Nanjing University of Information Science and Technology | Meng C.,Nanjing University of Information Science and Technology | Shen S.,Nanjing University of Information Science and Technology | Qiu X.,Nanjing University of Information Science and Technology | And 2 more authors.
Acta Geographica Sinica | Year: 2011

In this paper, the observed meteorological data of 54 meteorological stations from 1960 to 2009 in Jiangsu Province of China were collected and a composite index (CI) of meteorological drought was used to analyze the temporal and spatial characteristics of droughts in the province. Based on the daily CI values of each station in the 50 years, the drought processes of each station were confirmed one by one and the occurrence frequencies, scopes and severities of the meteorological droughts were computed and analyzed to reveal the temporal and spatial occurrence pattern of the meteorological droughts in different parts of Jiangsu Province. The results were showed as follows. (1) The annual and seasonal occurrence frequencies of the meteorological drought in the province decreased from north to south. In all the seasons, the occurrence frequency of the winter droughts was the highest. (2) The years of drought occurrence in a large scope (more than 90% of the total area of the province) were most in winter and least in summer. (3) In the 50 years, there was a notable inter-annual wave of the annual average lasting days and the annual average occurrence severities of meteorological droughts in the whole province but their linear changing tendencies were not obvious. (4) The drought lasting days of different grades in Jiangsu reduced from north to south in general. The drought lasting days of different grades were most in winter and least in summer. Source

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