# Changes in Meteorological Elements and Its Impacts on Yunnan Plateau Lakes
## 3 Results
### Analysis of Sudden Changes in Air Temperature  
Sudden changes in climate are ubiquitous in the climatic system and occur when the climate changes from one stable state to another, which is a specific manifestation of the non-linearity of the climate system [25]. In our analysis of the trends in climatic factors over the 40 years from 1980 to 2019, we found that the air temperature was the only factor showing a significant upward trend, and we performed a Mann-Kendall analysis to determine the point at which the air temperature underwent an abrupt change among the Yunnan Plateau lakes. The data presented in Figure 5 indicates that the abrupt change in the annual average air temperature of the Yunnan Plateau lakes occurred in the early 2000s, and the year in which this abrupt change occurred was earlier for lakes in northwest Yunnan than for the central lakes. Specifically, this change was initially detected in the northwest lakes in 2001, whereas for most lakes in central Yunnan, the change took place 2002, the exception being Lake Yilong, where air temperatures rose abruptly in 2004. This is later than the time point proposed by [PERSON] et al. [26], who reported that the annual average ground air temperature in Yunnan showed a significant abrupt warming commencing in 2000. We suspect that this disparity in findings could be attributable to the use of different time series data. In their comparison of the times of abrupt changes in air temperature in different regions of China, [PERSON] et al. [27] identified clear geographical differences, with changes occurring earlier in higher latitude areas than in those at lower latitudes. This is consistent with our finding of the later abrupt change for Lake Yilong, which among the Yunnan Plateau lakes lies at the lowest latitude. In addition, we found that the air temperature of the Yunnan Plateau lakes showed an initial downward trend from the early 1980s until 1985, at which point the trend reversed. In 1997, we detected a sudden change from cold to warm in the lakes of central Yunnan, which is consistent with the findings of [PERSON] et al. [28], thereby indicating that the annual average air temperature in Yunnan has increased significantly in the past 46 years, and there was a sudden change from cold to warm in 1997. Table 4 lists the maximum, minimum, and average values of air temperature for each of the four decades during the period from 1980 to 2019, which reveal that for almost all lakes, air temperatures have been increasing continuously, and that the magnitude of change has been increasing since 1980, reaching the fastest growth rate of 0.2 \({}^{\circ}\)C per decade over the past 10 years. In addition, these data reveal considerable differences in change among the individual lakes, with the rates of annual average air temperature rise ranging from 0.08 \({}^{\circ}\)C per decade for Lake Yilong to 0.34 \({}^{\circ}\)C per decade for Lake Lugu, with the rates of air temperature rise per decade being greater among the lakes located in northwest Yunnan (0.2 to 0.23 \({}^{\circ}\)C) than those of lakes located in central Yunnan (0.14 to 0.17 \({}^{\circ}\)C). Overall, the rate of annual average air temperature rise has been 0.18 \({}^{\circ}\)C per decade. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Climate Factor** & **Lake** & **Spring** & **Summer** & **Autumn** & **Winter** \\ \hline \multirow{6}{*}{Precipitation} & Chenghai Lake & 3.96296 ** & \(-\)0.82457 & \(-\)2.47601 & \(-\)1.06519 ** \\  & Dianchi Lake & 1.75127 & \(-\)4.83401 ** & \(-\)5.67196 ** & \(-\)0.51708 ** \\  & Erhai Lake & 4.57181 ** & \(-\)2.43614 & \(-\)5.70940 ** & \(-\)2.12645 ** \\  & Fuixian Lake & 0.76844 ** & \(-\)3.72356 & 0.16865 ** & 0.24276 \\  & Lugu Lake & 4.14140 ** & 1.13157 & \(-\)2.73790 ** & \(-\)0.17256 ** \\  & Yangzonghai Lake & 0.40433 & \(-\)2.08926 & \(-\)7.39131 ** & \(-\)1.13807 ** \\  & Yilong Lake & 1.73657 & \(-\)5.55325 ** & \(-\)7.35147 ** & 0.62853 \\ \hline \end{tabular}  
* Significant at the 95% level, ** Significant at the 99% level.  
\end{table}