江苏省典型干旱过程特征

为了研究江苏省重大干旱过程的生消和演变特征,选取2006年10-11月覆盖全省的一次严重秋旱事件作为典型个例,收集54个气象台站的逐日气象观测资料,计算逐日复合气象干旱指数CI值,以此为基础统计干旱发生的开始日期、结束日期、持续日数和逐日旱强,研究全省和各地区的旱情生消和演变特征；选用MODIS产品数据,利用植被供水指数法,反演干旱发展过程；利用实测土壤相对湿度数据,在ArcGIS9.3中采用反距离权重插值法,分析干旱事件中土壤湿度的空间变化特征.研究结果表明:(1)在这一典型秋旱事件中,由CI指数、VWSI指数和土壤相对湿度反映的大气、植被、土壤干旱的生消和演变过程基本一致.(2)干旱的发生是由西北到东南逐渐扩展蔓延,结束则由东南向西北逐渐收缩消失,持续天数从北向南递减.(3)旱情总体上北重南轻,但不同地区因大气背景和自然地理条件不同发展过程差异较大.(4)利用CI指数、VSWI指数和土壤湿度可以较全面而系统地监测干旱过程的生消、演变和强度变化.

Analysis on characteristics of a typical drought event in Jiangsu Province

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.