| Based on the measured data of average temperature,average precipitation,extreme maximum temperature and minimum temperature in Dujiangyan and Wenchuan from 1965 to 2015,the characteristics of climate change in the transition zone between Chengdu Plain and Northwest Sichuan Plateau are analyzed by using linear tendency estimation,Mann-Kendall mutation test and Morlet wavelet analysis.In addition,two stations,Wenjiang and Barkam,were selected respectively in the plain and plateau areas on both sides of the study area.The data and the same method were used to analyze the climate change characteristics of the study area and the plain and plateau areas on both sides of the study area.The results show that:(1)During the study period,the average annual temperature and the average temperature of the four seasons in the study area showed a significant warming trend.In the 1990 s and later,the warming was more obvious,and the warming rate in Wenchuan area was higher than that in Dujiangyan area.According to the comparison results,the annual and four seasons average temperature growth rate of the study area is significantly higher than that of the two sides.In addition,the annual average temperature of the four areas in 30 years is gradually warming;except for the fluctuating and rising state of temperature in spring in Barkam,the average temperature of Barkam in summer,autumn,winter and four seasons temperature of the other three places is gradually warming.(2)The abrupt change of annual and four seasons temperature in the study area is different.Although the time of abrupt change point or intersection is in the late 1990 s or the early 21 st century,the significant warming time of mean annual and four seasons temperature in Wenchuan is earlier than that in Dujiangyan.Compared with the plain and plateau areas on both sides,the difference between Wenchuan area and the two sides is the most obvious.The time of mutation and warming in Wenchuan is the earliest in four seasons,and the plateau area is later.The change characteristics of Dujiangyan area are similar to the eastern plain area.(3)The main periods of annual average temperature in Dujiangyan and Wenchuan are 4a,8a,19 a and 24 a,8a,respectively.The time scale of main period in Dujiangyan area is smaller.According to the comparison of cycle characteristics,the main cycle time scale of annual average temperature increases gradually from east to west.In plain area and Dujiangyan area,the main period in summer and winter is more obvious,and the periodic oscillation is dominated by small time scale;in Wenchuan area and plateau area,The time scale of the main period of mean temperature in four seasons is relatively large,but the main period in Wenchuan area is relatively not obvious,and there are obvious periodic changes in Barkam area.(4)Except for winter in Wenchuan,the average annual precipitation and the four seasons precipitation in the study area show a weak decreasing trend.In the early 21 st century,the precipitation is relatively small,and the precipitation rate of Dujiangyan is higher than that of Wenchuan.The average annual precipitation of the study area and the plain area show a decreasing trend in 51 years.Dujiangyan has the fastest annual precipitation deceleration rate,the decreasing trend in Wenchuan is the slowest,and the average annual precipitation of the plateau area increases with a weak trend.According to the change of annual average precipitation in 30 years in four regions,the annual average precipitation in Wenjiang and Dujiangyan decreased fluctuatly,the annual average precipitation in Wenchuan decreased gradually,while that in Barkam increased.The precipitation of the four seasons is obviously different.On the whole,the precipitation of the study area and plain area shows a decreasing trend in spring,summer and autumn,and the decreasing trend of Dujiangyan area is more obvious;the precipitation of plateau area has a significant growth,only decreased in autumn.In addition,the changes of precipitation in the four regions in 30 years are different.(5)There are two abrupt change points in the annual precipitation of Dujiangyan and Wenchuan in 1998,2000 and 1996,2013,respectively.The abrupt change of annual precipitation in plain and plateau area is more frequent,especially in plateau area,and the mutation time is earlier than that in study area.The abrupt change of spring precipitation in the study area is more frequent,the spring,summer and autumn precipitation decreased slightly,and the winter precipitation mainly increased.Compared with the areas on both sides,the annual and summer precipitation abrupt changes are more frequent in plain and plateau areas;the spring precipitation abrupt changes are frequent but weaker in summer and winter in the study area.The summer,autumn and winter precipitation abrupt changes are the weakest in Wenchuan area,also,the mutation situation in winter decreased in all regions.(6)According to the results of wavelet analysis,the main periods of annual precipitation in Dujiangyan and Wenchuan are 11 a,3a,16 a and 4a,11 a,18a,respectively.Compared with the regions on both sides,the time scale of the main periods in study area is relatively large.The main period of precipitation in the four seasons in the study area is also in small and medium scale,and the main period time scale of Dujiangyan is relatively smaller.The main period of precipitation in four seasons in Dujiangyan area is closer to that in the east plain area;the main period of Wenchuan area is more similar to that in the west plateau area;the main period time scales of summer and winter in four regions are larger.(7)The extreme minimum and maximum temperature in the study area showed a significant warming trend,and the overall growth range of the maximum and minimum temperature in the study area was significantly larger than that in plain and plateau areas.According to the change of 30-year extreme temperature in the four regions,the extreme temperature in the four regions showed a gradual warming trend in each period,and the temperature was obviously warming.In Dujiangyan area,there is no mutation point in the maximum temperature,and the mutation point in the minimum temperature is in 2006.In Wenchuan area,the mutation point in the maximum temperature is in 1996,and there is no mutation point in the minimum temperature.The occurrence time and significant warming time of extreme temperature mutation point in the study area and plain area are earlier than those in the western plateau area,especially in Wenchuan.The main periods of extreme maximum and minimum temperature in Dujiangyan are 4a,8a,17 a and 4a,11 a,18a,respectively.The main periods of extreme maximum and minimum temperature in Wenchuan are 4a,8a and 8A respectively.The main periods of extreme temperature in Wenchuan are relatively small and smaller than those in plain and plateau areas,the temperature changes more frequently. |
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