Temperature changes on different flanks in the QDM from 1969 to 2018
The Mann-Kendall test revealed 91.53% (108 stations) of stations presenting a significant increasing trend in spring temperature (Fig. 2), while 51.69% (61 stations), 77.12% (91 stations) and 86.44% (102 stations) of weather stations showed substantial trend in summer, autumn and winter temperatures, respectively. The greater proportion of stations showed significant temperature trends on the west Qinling-Daba Mountains than on the other flanks in different seasons. In this case, 97.06%, 88.24%, 94.12% and 97.06% of stations were found to have a notable warming trend on the West Qinling Mountains in spring, summer, autumn, and winter, respectively, while stations are less than 89.29%, 35.71%, 69.05%, 80.95% on the other flanks. The northern flanks have had more proportion of weather stations showing significant warming trend in different seasons as compared to the southern flank in the Qinling Mountains. For instance, 95%, 40%, 75% and 95% of stations significant warming trend in the former in spring, summer, autumn, and winter, respectively, while 93.55%, 35.48%, 64.52% and 87.10% of stations showing significant warming trend in the latter in the four seasons, respectively. The southern flank in Daba Mountains, with 7.69% stations depicted a significant negative trend in summer, autumn and winter.
The trend analysis for the mean temperature of different seasons revealed that there was a significant warming trend on different flanks in the QDM from 1969 to 2018 (Fig.3, Table1). However, the increasing rate varied greatly from different seasons and flanks. The temperature increasing rate was greater on the northern flank of the Qinling Mountains and the Daba Mountains as compared to the southern flanks in the four seasons (Fig. 3). Among them, the temperature tendency is greater in spring and winter than in summer and autumn on different flanks in the QDM. Climate warming was least in summer with temperature increasing rate as low as 0.123°C/10a, 0.074°C/10a, 0.085°C/10a, 0.056°C/10a, and 0.285°C/10a, respectively, on the northern flank of Qinling Mountains, the southern flank of Qinling Mountains, the northern flank of Daba Mountains, the southern flank of Daba Mountains, and the West Qinling-Daba Mountains.
Table 1. Seasonal temperature trends (°C/10a) on different flanks in the QDM during 1969-2018. Notes: ** indicates that the climate trends are significant at the level of 0.05 and 0.01, respectively.
Different
flanks
|
Spring Temperature
(°C/10a)
|
Summer Temperature
(°C/10a)
|
Autumn Temperature
(°C/10a)
|
Winter Temperature
(°C/10a)
|
Southern flank of Qinling Mountains
|
0.342**
|
0.074**
|
0.181**
|
0.267**
|
Northern flank of Qinling Mountains
|
0.479**
|
0.123**
|
0.205**
|
0.374**
|
Southern flank of Daba Mountains
|
0.224**
|
0.056**
|
0.112**
|
0.234**
|
Northern flank of Daba Mountains
|
0.338**
|
0.085**
|
0.194**
|
0.274**
|
West Qinling-Daba Mountains
|
0.350**
|
0.285**
|
0.308**
|
0.362**
|
Temperature changes into different elevations in the QDM from 1969 to 2018
The significance statistics of trends in mean temperature showed that stations detected significant increasing trend varies greatly varied on different seasons and altitudes in the QDM (Fig.4). In the QDM, 89.77% (79 stations), 35.23% (31 stations), 69.32% (61 stations), and 81.82% (72 stations) of stations were detected to have a significant warming trend at 0-1000m altitude in spring, summer, autumn, and winter, while the proportion of stations with a significant increasing trend was greater than 98.68%, 92.50%, and 100% at other elevations (1000-2000m, 2000-3000m). In different seasons, it was discovered that high altitude areas have a higher proportion of warming area than low altitude areas.
The temperature trend analysis for different seasons revealed that there was a significant warming trend at different elevations in the QDM from 1969 to 2018. (Fig. 5, Table 2). However, the rate of increase in mean temperature varied greatly depending on the season and elevation. In higher elevation, we detected an increasing rate in the mean temperature of summer, autumn, and winter (Fig. 5, Table 2). At elevations of 3000-4000m, the increasing rate could reach 0.440°C/10a, 0.39°C/10a, and 0.456°C/10a, respectively, while at 0-1000m, it was 0.205°C/10a, 0.218°C/10a, and 0.303°C/10a, respectively. The increasing rate in spring is higher in the lower altitude areas (at 0-1000m and 1000-2000m) than in the higher altitude areas (at 2000-3000m and 3000-4000m).
Table 2. Seasonal mean temperature increasing rates (°C/10a) at different elevations in the QDM during 1969-2018. Notes: * and ** indicate that the climate trends are significant at the level of 0.05 and 0.01, respectively, by the Mann-Kendall test for the long-term trend.
Elevation classification(m)
|
Spring Temperature(°C/10a)
|
Summer
Temperature(°C/10a)
|
Autumn
Temperature(°C/10a)
|
Winter
Temperature(°C/10a)
|
0-1000
|
0.369**
|
0.205**
|
0.218**
|
0.303**
|
1000-2000
|
0.405**
|
0.281**
|
0.308*
|
0.384**
|
2000-3000
|
0.351**
|
0.359**
|
0.339**
|
0.405**
|
3000-4000
|
0.317**
|
0.440 **
|
0.390**
|
0.456**
|
Precipitation changes into different flanks and elevations in the QDM from 1969 to 2018
The Mann-Kendall test did not show a significant trend in precipitation. However, some stations exhibited notable trends in spring, summer, and winter precipitations (Fig. 6). Weather stations were distributed at different elevations. For instance, Mount Hua station was present at 2000-3000m on the northern flank of the Qinling Mountains. Shiquan station location was at 0-1000m on the southern flank of the Qinling Mountains. Taibai station at 1000-2000m on the southern flank of Qinling Mountains, Zigui stations at 0-1000m on the southern flank of Daba Mountains, Beichuan station at 0-1000m, Diebu, Songpan and Hezuo stations at 2000-3000m on the west Qinling-Daba Mountains.
As shown in Fig.7 and Table 3, there were two weather stations, Zigui and Shiquan, that showed significant increasing trends in precipitation in summer, and 1 weather station (Diebu) that showed significant decrease trends, with change rates as high as 47.36mm/10a, 22.91mm/10a, and-19.43mm/10a, respectively, which were higher than other stations in other seasons. In contrast, four weather stations (Zigui, Beichuan, Taibai, and Hezuo) indicated increasing and decreasing changes in precipitation in winter. It is important to note that Mount Hua weather station recorded a significant decrease in precipitation in spring and autumn, with rates of -14.60mm/10a and -11.50mm/10a, respectively. Only in spring, the Songpan weather station depicted an increasing trend, i.e., 7.63mm/10a in precipitation.
Table 3. Seasonal mean precipitation change rates (mm/10a) at the weather station with significant trend in different seasons in the QDM during1969-2018. Notes: * and ** indicate that the climate trends are significant at the level of 0.05 and 0.01 levels, respectively, by the Mann-Kendall test for the long-term trend.
Stations
Name
|
Latitude
(N°)
|
Longitude
(E°)
|
Altitude
(m)
|
Spring Precipitation
(mm/10a)
|
Summer Precipitation (mm/10a)
|
Autumn
Precipitation
(mm/10a)
|
Winter Precipitation (mm/10a)
|
Zigui
|
30.83
|
110.97
|
295.50
|
-
|
47.36**
|
-
|
6.33*
|
Shiquan
|
33.05
|
108.27
|
484.90
|
-
|
22.91*
|
-
|
-
|
Beichuan
|
31.63
|
104.45
|
597.20
|
-
|
-
|
-
|
1.65*
|
Taibai
|
34.03
|
107.32
|
1543.60
|
-
|
-
|
-
|
2.13**
|
Mount Hua
|
34.48
|
110.08
|
2064.90
|
-14.60**
|
|
-11.5*
|
-
|
Diebu
|
34.07
|
103.23
|
2374.20
|
-
|
-19.43*
|
-
|
-
|
Songpan
|
32.67
|
103.60
|
2881.30
|
7.63*
|
-
|
-
|
-
|
Hezuo
|
35.00
|
102.90
|
2910.00
|
-
|
-
|
-
|
1.19*
|