Analysis On Urban Spatial Expansion And Driving Forces Of Changsha

Global warming has already attracted the attention of scholars at home andabroad, through the analysis of,such as global sea level height, surface temperatureand so on, the IPCC said that in the context of global warming has become anaccepted fact, the global precipitation also has spatial and temporal changes. Inrecent years, the floods of the Yangtze River basin shows an increasing trend, at thesame time,, Dongting Lake watershed as an extremely significant region to globalclimate change of the Yangtze River basin,its floods also become one of the mostserious area. Therefore, this article aims to analyze extreme precipitation events inthe past50years as well as the temporal and spatial distribution of the DongtingLake basin trends in the past110years and its droughts and floods evolutionchanges, in order to further explore how the trend affects the natural environmentand social life.This paper uses1960to2010,103sites of daily precipitation and1901to2010,the CRU monthly precipitation with the regional mean, anusplin interpolation,theMann-Kendall mutation inspection and so on to analysis the trends and mutation inDongting Lake Basin. Taking into account the uneven distribution of sites acrossthe region, the research done in this article are all based on evenly distributed grids.The results shows that:(1) the past50years, the Dongting Lake watershed insummer and winter the extreme precipitation are in increase,while in spring andautumn are in decrease, and within the region,there are a clear spatialdifferentiation,too;(2)The80to90years of the20th century are the ages ofprecipitation mutations increasing, in which the year1986and1997are the typical,it means precipitation has increase in recent years in Dongting Lake watershed,andthe intensity of extreme precipitation is also increasing;(3) The precipitation of theDongting Lake watershed mainly has four types on the spatial distribution in thepast110years：the southeast more than the northwest type (November to nextApril as the representative),the South more than North type (May, June and Augustas the representative), the West more than East type (July as the representative) andthe northwest more than southeast pattern (September to October as therepresentative), this phenomenon mainly dues to its geographical location easing tosuffer from the high pressure which comes from the Pacific Ocean;(4) Theevolution of droughts and floods in the past110years, found that there are frequent alternating drought and flood disasters in the Dongting Lake watershed, even in theearly20th century and the early21st century, the ranges are large,but the late20thcentury are slightly too small, and in recent20years, the climate begin to showinga continuous water logging or persistent drought, such as the continuous partialfloods situation in the1990s, but from the2003the climate starts to be a partialdrought, so it is useful for us to prepare enough adequate to resist the naturaldisasters;(5) using Hunan Province on behalf of regional and selecting severalareas to focus on the impact of rainfall on floods and crop production, pointed outthat if the excessive precipitation, the strength is too large or the precipitation timeis relatively long all may lead to floods, and if not, the drought appears likely toincrease, and also precipitation in this uneven spatial and temporal distribution hasa great impact on grain, cotton and citrus production.