| It has become a common social phenomenon that Floods and drought gradually arouse people’s more wide attention just because that the frequency of extreme climate events caused by global warming is more and more high. Thus, Preparing the judgment for the trend in the next drought and flood disaster is the premise of disaster risk assessment and prevention. Northwest of the central region, located in the hinterland of the Eurasian, having large amount of arid and semiarid place, is the confluence of three natural geographical regionalization in China where it have complex terrain, diverse climate and uneven spatial distribution of precipitation. So, as a sensitive area of climate change and fragile ecological environment, it is more significant to study the spatial and temporal distribution of drought and flood in the region of the northwest central.This paper mainly contains such contents that the characteristics of space and time for drought and flood disasters, symmetry rules and related mechanism analysis in the northwest of the central region under the background of recent 54 years climate change. Besides, This paper also discuss the time evolution for disasters in different scale, forecast the next time which disasters will possibly occur in the future and analysis the relationship between the drought and flood disasters and ENSO events and the relative abundance of sunspots in the northwest central region by using the method such as linear trend, Mann-Kendall mutation test, ordinary Kriging interpolation, precipitation Z index method, symmetry、relation analysis and others. The main conclusions as follows:(1)The average of annual temperature showed upward trend with the rate of 0.34℃/10a in center of northwest from 1960 to 2013 and the temperature mutated in 1994. Besides, the temperature changes may be experienced such different period that slight decline period, smooth fluctuation period, significant rise and fell slightly. The degree of temperature show different character in each season that the highest of degree occurs in winter with the ratio of 0.44℃/10 a while the lowest occurs in spring and summer with the ratio of 0.30℃/10 a. Meanwhile, the annual average temperature show reduced trend from east to west and temperature trend rate show different spatial distribution that the low value occurs in the middle while the high value occurs in both sides in the Northwest central.(2)The precipitation showed an increasing trend at rate of 0.37 and 5.25 mm/10a in the central of northwest china and in the cold region on Qinghai-Tibetan plateau while it showed reducing trend with the ratio of 0.62 and 11.12mm/10a in northern arid areas and eastern monsoon zone form 1960 to 2013. Besides, the main type of warm and dry occurs in northern arid areas and eastern monsoon zone while the main style of warm and wet occurs in Qinghai-Tibetan plateau. Overall, it have experienced diverse stage that relative stable period mainly occurred in 1960 to 1980, the decreased period occurred in 1980 to 21st century and then upward period occurred in the last of 21st century. In addition, the annual precipitation show reduced trend from southeast to northwest in spatial distribution and precipitation show rising trend in spring, summer and winter respectively with the ratio of 0.69,1.67 and 0.51mm/10a, but precipitation in autumn show decreased trend with the ratio of 0.82mm/10a.(3) From 1960 to 2013, the region in Northwest central district, Northern arid areas and Qinghai-Tibetan plateau have witnessed change trend from drought to waterlog while the region of the east monsoon have witnessed opposite change trend. The proportion of drought and waterlog showed little difference in the last 54 years in the central of northwest. Generally, except autumn, other seasons have also appears changed trend from drought to waterlog. The heavy flood events relatively concentrated in summer and the frequency of waterlog is high in 1980-1990.(4) Based on commensurability method, symmetry, the butterfly structure and the structure, the characteristics of drought and flood disasters were investigated. Central northwest drought, flood catastrophe disaster, drought in arid areas in northern, the symmetry of large floods was better, the flood catastrophe in arid areas in northern, qinghai-tibet GaoHan District flood catastrophe disaster had no obvious symmetry Overall, the symmetry rules of drought was better than waterlog’s.The next time of drought might happen in 2015, the region of large floods is in year of 2014 and 2020, among of them 2014 have been verified. The spring drought is in 2015, the summer drought is in 2019, summer waterlog is in 2015. The summer flood catastrophe is in 2015. The region of northern for drought is in 2017. Waterlog is in 2018. The eastern monsoon region for drought in the year of 2019, the waterlog in the year of 2018.The Tibetan Gaohan District drought in the year of 2016, the waterlog in the year of 2015.(5) The drought and flood disasters mainly occurred in the period of ENSO events in Northwest central district, Northern arid areas, east monsoon and Qinghai-Tibetan plateau from 1960 to 2013. Overall, the proportion for the drought years was higher than the flood catastrophe in the period of ENSO events and it was more influenced by ENSO events in east monsoon than Qinghai-Tibetan plateau. The drought disasters mainly occurred at the sunspots, peak year and the cycle of decreased for large and medium scale of time in this place. The floods disasters have also appeared similar law. Besides, the drought and flood disasters also mainly occurred at the sunspots, peak year and the cycle of decreased for small scale of time while it seldom occurred in the cycle of increased. Especially for drought disasters, it have never happened in the cycle of increased.The study have discussed the climate change and the space-time characteristics of drought and flood disasters in the central of northwest china, and have forecasted the future trend for drought and flood disasters, which can enrich the existing research results and provides certain theory basis when the future industrial and agricultural production and relevant government decision in the study area will be made. |
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