Temporal And Spatial Trends Of Extreme Temperature And Precipitation In Coastal Areas Of Mainland China And Their Effects On Vegetation

Extreme weather will change the habitat of vegetation rapidly,which will impact the vegetation greatly.As the global temperature continues to rise,the frequency and intensity of the extreme climate will become more serious in the future.The China's coastal zone is the transition zone between land and sea.Coastal vegetation can reduce the impact of extreme weather events such as typhoons and floods.Therefore,studying the impact of extreme climate on the growth of vegetation in coast is of great significance for the coastal ecological safety.This study first analyzed the tempo-spatial variation of 6 extreme climate indices along the past 1956-2017 and normal difference vegetation index(NDVI)along the 1982-2015 of China coastal area.The climate indices included 3 temperature indices of the annual Minimum Temperature(TNn),the annual Mean Temperature(TMm)and the Annual Maximum Temperature(TXx)as well as 3 precipitation indices of the annual maximum Continuous Dry Day(CDD),the annual Simple Daily Intensity Index(SDII)and The annual Maximum 5-day Precipitation(Rx5day).Then a partial correlation analysis of extreme climate indices and 5 air circulation indices(Cold Air [CA,],Asian Polar Vortex Area [APVA],Eurasian Meridional Circulation [EAM],Eurasian Zonal Circulation [EAZ] and West Pacific Subtropical High Intensity [WPHI])as well as 2 human activity indices(General Population [GP] and the Gross Domestic Product [GDP])was taken to explore the influence of human and nature factors on extreme climate.The same method was used to research the influence of extreme climate on normal difference vegetation index(NDVI)on the annual scale.As the correlation between NDVI and extreme climate is not significant,a further step of analyzing time series change of NDVI change rate before and after the extreme climate month in the abnormal climatic region during typical year was taken.And there are mainly conclusions of this study:(1)There is a strong regularity showed in the tempo-spatial variation of extreme temperature indices in China coastal area,the TNn and TMm showed an increasing trend from north to south,while the TXx showed the same trend from coast to inland.At the same time,extreme precipitation indices indicated the character of wet in south and dry in north of China coastal area,CDD high value area(CDD > 50d),SDII low value area(SDII < 12.5mm/d)and Rx5 day low value area(Rx5day < 150mm)are mostly located in the north and northeast of China coastal area.While the low value area of CDD are mostly located near the Yangtze River Delta,the high value areas of SDII(SDII > 15mm/d)and the high value areas of Rx5day(Rx5day > 250mm)are concentrated in the coastal zone of South China.The extreme climate in coastal areas of China showed a trend of warming and wetting from 1956 to 2017,but some arid areas tended to be more arid.As to the extreme temperature indices,TNn,TMm and TXx in coastal areas increase at the rates of 0.18 ? /10 a,0.22 ? /10 a and 0.41 ? /10 a,respectively,and the warming rate in high latitude/high altitude areas is higher than that in low latitude/low altitude areas.The overall CDD in coastal areas decreases slightly at the rate of 0.02d/10 a,but only significant in the Yangtze River Delta(p<0.05).SDII and Rx5 day increased at the rates of 0.17 mm/(d·10a)and 0.8 mm/10 a overall respectively,which is only significantly in the south to Huaihe River(p <0.05),while they decreased in the north to Huaihe River.(2)Because of the large latitude span of coastal areas in China,the regional differences of the effects of atmospheric circulation on extreme climate in coastal areas were huge.The decrease of CA activity frequency may be related to the increase of TNn in the northeast China and north China coastal areas,as well as the decrease of CDD in the Northeast China coastal area.EAM was positively correlated with TNn in the east China coastal areas(p < 0.05),but negatively correlated with TMm in the coastal areas of south to Huaihe River(p < 0.05),and positively correlated with CDD in the coastal areas of Northeast China(p < 0.05).EAZ was positively correlated with TNn in the Yangtze River Delta(p < 0.05)and TMm in the coastal area north to Huaihe River(p < 0.05),no more than 10% of the total area had significant correlation with extreme rainfall.The correlation between WPHI and TXx was significant(p < 0.05),which accounted for 27.6% of the total coastal area.The correlation between WPHI and TXx was positive in the north China and northeast China coastal areas,but negative in the east and south China coastal areas.There is no significant correlation between APVA and extreme climate in coastal areas.There was a significant positive correlation between GDP and TMm in 41.55% of the coastal areas of mainland China(p<0.05),but no significant correlation with other extreme climate indices.The area with significant correlation between population size and TXx is the largest,but only accounts for 15.07%.They are positively correlated in the economically developed area such as Yangtze River Delta and Beijing-Tianjin-Hebei region,but negatively correlated in other regions.(3)Extreme high temperatures mostly occur in July and August,especially in Beijing,Tianjin,Hebei and Yangtze River Delta.Extreme low temperatures mostly occur in December to February of next year and were more likely to occur in the north to Huaihe River than in the south.Drought occurs mostly from November to February of next year,and are more serious in the north of China coastal area and west of Liaoning Province.Persistent heavy precipitation events are common in coastal areas.The occurrence time has a strong correlation with the movement of rain belts and typhoons,most of which occurred in May and lasted until October.Beijing-TianjinHebei region and the central part of Guangdong Province are high-risk areas of comprehensive extreme climate risk.The low-risk areas is relatively small,and most of them are distributed in high altitude areas of south to Huaihe River.Since 1990,there have been many turning points and mutation points of the extreme climate in the coastal areas of China,which indicated that the extreme climate in the coastal areas has fluctuated greatly in the past 30 years.(4)The vegetation in most coastal areas has been growing well for many years,and there is a clear trend of improvement,but the impact of extreme climate on vegetation can not be ignored.On the interannual scale,TNn and TXx are positively correlated with NDVI in the central of east China coastal area,but negatively correlated with NDVI in other areas.CDD is positively correlated with NDVI in most coastal areas of China,while Rx5 day is negatively correlated with vegetation NDVI in most areas.On the monthly scale,the vegetation growth in the Northeast and North China coastal areas became worse in the month of abnormal extreme low temperature,while the vegetation growth in the coastal areas south to Huaihe River did not change significantly.Before and after the occurrence of abnormal extreme high temperature,the vegetation growth in the Northeast China and North China coastal areas showed a trend of increase-decrease-increase,while in the eastern and southern China coastal area,the trend was opposite.The abnormal increase of Rx5 day promoted the growth of vegetation in the north of Huaihe River,but inverse in the south to Huaihe River.