A Study On Objectively Identifying And Changes Of Persistent Regional Meteorological Drought Events In China During The Recent 50 Years

An objective identification method for persistent regional meteorological drought events was developed and the composite intensity index and classification of regional meteorological drought event based on this method was defined, and then the temporal and spatial distribution of persistent regional meteorological drought events in China during the recent 50 years and the cases of extreme drought events was analyzed.The main conclusions can be summarized as follows:(1)Objective Identification Method for Persistent Regional Meteorological Drought Events (OIMPRMDE) is the method which based on the daily weather data of stations. This method includes two steps:the daily natural belt drought separation and identification for persistent regional drought events. The method has good capability in identification of the drought events.(2) 4 indices of meteorological drought event, as the extreme intensity, cumulative intensity, cumulative area and duration, and a composite intensity index of drought events were defined. The composite intensity index is the Characteristic quantity about the duration, area and intensity that can reflect the continuous changes in time and space, strength of characteristics. Based on the composite intensity index defined: drought events and quasi-drought events. A number of 167 drought events occurred, are divided into four classification:the extreme drought events, severe drought events, general drought events and weak drought events.(3) Analyzed the temporal and spatial distribution of meteorological drought events in China from 1957 to 2008, including both as:Temporal distribution:a. From 1957 to 2008 the drought events have no significant increase in the overall trend. b. Nationwide drought events occurred each season, but the most frequently occurred in February to April and august to October following, while most likely to end in May to July. Of course, the droughts in different regions have distinct seasonal characteristics. The duration of drought events mainly between 30 to 40 days, the duration of extreme drought events are more than 100 days, the duration of over the general drought events are in 100 days or more, the duration of over the weak drought events are more than 30 days.Spatial distribution:The drought events have occurred in almost areas, and the most frequently occurred in North China which occurred almost each month, the highest in April, and the different intensity drought events have occurred in the region; followed by the southwest in the Southern and South China coastal areas, where the different intensity drought events have occurred in the region and the drought events have occurred in winter half year (October to next March), Northeast Midwest where the majority are general-droughts or weak droughts which have occurred in spring and summer to autumn, eastern part of Northwest where the different intensity drought events have occurred in the region and the drought events have occurred in summer half year (April to September).(4) Extreme drought events are defined as 10% of the strongest composite index of all drought events. There are the totals of 17 extreme drought events from 1957 to 2008. The frequency of extreme drought events occurred in 60 and 90's is highest, reaching more than 5th. Others occurred twice in 10 years. The North is the highest where the extreme drought events have occurred mainly have occurred from spring to summer or from winter to spring, and which the composite intensity index is larger. Second, Southwest where the extreme drought events have occurred almost in spring, Northeast in autumn, South, the Yangtze River basin and Northeast followed where the extreme drought events have occurred almost in autumn in the Yangtze River basin and South from spring to summer in northeast of China.(5) The extreme event which occurred from autumn 1998 to next spring 1999 is the most severe events during the recent 50 years in China, affecting the region including the north, northwest northeast, South, Southwest of China. The just ended extreme event, which occurred from autumn 2009 to next spring 2010 in the Southwest of China, becomes the most severe drought event in this region.