Study On Dry And Wet Climate Changes In The Valleys Of The Hengduan Mountains In Western Sichuan In Recent 59 Years

The daily average temperature,maximum temperature,minimum temperature,precipitation,sunshine hours,relative humidity,and average wind speed of Xiaojin,Kangding,Xichang,and Huili near 59a(1960-2018)in the valley of the Hengduan Mountains in western Sichuan were selected.Climatic data,as well as geographic factors such as altitude,latitude and longitude,are used to analyze the climate change characteristics of the area using the linear tendency estimation method;the MK test method is used to analyze the abrupt climate change characteristics of the area and comprehensively determine the time of the abrupt climate change;calculated by the Penman-Monteith model recommended by FAO Reference crop evapotranspiration and wet-dry index are analyzed and their wet-dry changes are analyzed.Partial correlation analysis discusses the main climatic factors affecting reference crop evapotranspiration in this area.Research indicates:1.Characteristics of climate change in the valley area of the Hengduan Mountains in western Sichuan in recent 59a(1960-2018):(1)From the perspective of inter-decadal changes: the average temperature of the area has generally increased in the past 59 years,and the temperature linear tendency rate Kangding(1.743°C/10a)= Xichang(1.743°C/10a)> Huili(1.429°C/10a)> Xiaojin(0.486?/10a),the climate warming trend is obvious.Precipitation generally shows an upward trend.Kangding(252.79mm/10a)> Xichang(156mm/10a)> Xiaojin(101.96 mm /10a)> Huili(12.597mm/10a),the warm and humid climate in the north is obvious.Except for Huili(320.13h/10a),the hours of sunshine in the other three places showed a downward trend,with the decline rate high in the north and low in the south,and Xiaojin the highest,with a propensity rate of-857.35h/10 a.(2)From the perspective of seasonal changes: in the past 59 years,the average temperature of the four seasons increased in the low-latitude regions in the south than in the high-latitude regions in the north.The most obvious season in the four seasons was winter.In spring,the precipitation in the area as a whole increased,increasing from north to south,the largest is Huili(944.09mm/10a);in summer,the precipitation in Xiaojin and Huili showed a downward trend,and the precipitation in Kangding and Xichang showed The upward trend;in autumn,the precipitation mainly shows a downward trend,and Huili(-806.71mm/10a)has the largest;in winter,the precipitation except Xichang(-121.74mm/10a)shows an upward trend.The sunshine hours in the four seasons are mainly decreasing.The most obvious seasons in the northern high latitudes are spring and winter,and the southern low latitudes are summer and autumn.(3)From the characteristics of abrupt changes: the average annual temperature in Kangding,Xichang,and Huili showed significant upward abrupt changes in 2005,2000,and 2008,respectively,and Xiaojin's climate abrupt changes were not obvious.In 1986,the annual precipitation in Kangding showed a relatively obvious ascending mutation.The mutation time of Xiaojin and Xichang was very short,the mutation characteristics were not obvious,and there were no obvious mutation points.The annual sunshine hours of Kangding and Xichang showed a more obvious declining mutation in 1988.Xiao Jinhe's reason was that the mutation time was too short and the mutation characteristics were not obvious.(4)Judging from the changes before and after the mutation: the average temperature changes slowly in the area 31a(1960-1990)before the mutation;the precipitation as a whole shows an upward trend,the upward trend is larger in the north and the lower,and the rising trend in Kangding is the largest(30.89mm/10a);The hours of sunshine are increasing in the north and decreasing in the south.The tendency is Xiaojin(37.57h/10a)> Kangding(11.21h/10a)> Xichang(-8.04h/10a)> Huili(-58.21h/ 10a).After the abrupt change in this area,the average temperature showed an upward trend except Xiaojin(-0.15?/10a)in the recent 28a(1991-2018),and the largest increase in the southern Huili(0.5?/10a);precipitation in the northern Xiaojin(4.17mm/10a)He Kangding(17.35mm/10a)mainly showed an upward trend,while Xichang(-24.37mm/10a)and Huili(-34.80mm/10a)in the south mainly showed a downward trend.The sunshine hours in the north showed a downward trend.Xiaojin The most significant(-251.87h/10a);the southern part shows an upward trend,and the Huili rise is the most significant(121.86h/10a).2.The characteristics of wet and dry climate changes in the valley area of Hengduan Mountains in western Sichuan in recent 59a(1960-2018):(1)From the perspective of reference crop evapotranspiration: The average reference crop evapotranspiration over the years has gradually decreased from south to north.Huili(1075.0mm)> Xichang(946.0mm)> Xiaojin(923.6mm)> Kangding(782.5mm).Xiaojin and Kangding in the north have large evapotranspiration in summer and Xichang and Huili in the south have large evapotranspiration.Nearly 31a(1960-1990)before the mutation,there was no significant change in the evapotranspiration of the reference crops except for Xichang(88.02mm/10a);after the mutation,nearly 28a(1991-2018)except Xiaojin(-9.83mm/10a)showed an overall upward trend,Kangding's rising trend was the most significant(the propensity rate changed from-9.14 mm / 10 a before the mutation to 248.82mm/10 a after the mutation).(2)From the perspective of wet and dry indexes: the inter-decadal dry and wet indexes in Xiaojin and Kangding in the north are mainly increasing and the degree of humidity is increasing;Xichang and Huili in the south are mainly decreasing and showing trends.The multi-year averages of the dry and wet index in spring are respectively Xiaojin(0.53)and Kangding(0.87)belong to the semi-humid range,and Xichang(0.38)and Huili(0.32)are in the semi-range;the multi-year averages of the summer wet and dry index are respectively Xiao Jin(1.01),Kangding(1.48),Xichang(2.76),and Huili(2.17)all belong to the humid range;the multi-year averages of the autumn wet and dry indices are Xiaojin(0.85),Kangding(1.31),Xichang(1.68),Huili(1.47),except for small metals in the sub-humidity,are in the humid range;the multi-year averages of the winter wet and dry indices are(0.07),Kangding(0.22),Xichang(0.10),and Huili(0.12),except Kangding Outside semi-all belong to range.Nearly 31a(1960-1990)before the abrupt change,the climate became humid in the north and dry in the south.Except for Xiaojin(0.013/10a),the wet and dry index showed a decreasing trend in nearly 28a(1991-2018)after the mutation,and the humidity of the climate decreased.3.Characteristics of correlation degree between reference crop evapotranspiration and major climate factors in the valley area of Hengduan Mountains in western Sichuan in recent 59a(1960-2018):The reference crop evapotranspiration in this area in the past 59 years has a significant positive correlation with average temperature and a significant negative correlation with relative humidity.Before the abrupt climate change(before 1990),the reference crop evapotranspiration was significantly positively related to the single climate factor of the average temperature.After the mutation(since 1991),the reference crop evapotranspiration was significantly positively correlated with the average temperature and wind speed,and the relative humidity was significantly negatively correlated.From the perspective of regional differences,the main climatic factors affecting the reference evapotranspiration of the region in the past 59 years were Xiaojin(average wind speed),Kangding(average temperature),Huili(average wind speed),and Xichang(sunshine hours).The main climatic factors affecting the evapotranspiration of reference crops in the area before the mutation(before 1990)and after(from 1991)were Xiaojin(average wind speed;mean wind speed),Kangding(sunshine hours;relative humidity),and Xichang(average wind speed;Average wind speed),Huili(sunshine hours;sunshine hours).