# Impact of Climate Change on the Major Eco-Hydrological Parameters in the Dongting Lake Basin
## 3 Results and Discussion
### Spatial-Temporal Changes in Climate Variables, GPP and ET  
#### 3.2.1 Changes in Climate Variables  
Interdecadal variations of temperature and precipitation from 1980 to 2020 in Dongting Lake Basin are shown in Figure 5. The test results for sudden changes in temperature and precipitation are shown in Figure 6. The results show that the overall temperature in the Dongting Lake Basin exhibited an upward trend at 0.0339 \({}^{\circ}\)C/year from 1980 to 2020 with an R\({}^{2}\) of 0.5034 (\(p<0.05\)). According to the cumulative distance plot, 1997 was the time point when the sudden change in temperature occurred, which could be ascribed to the considerably large floods that occurred in the Dongting Lake Basin in 1998. Further, the temperature exhibited a more rapid response to the environmental conditions during this period. Such results are consistent with the Manner-Kendall test for abrupt changes in temperature. Figure 4: (**a**) The fit of the BESS model in Dongting Lake basin to GLASS products, respectively; (**b**) the fit of the BESS model and PLSH model ET results in Dongting Lake basin. Figure 5: Average temperature and precipitation trends in the Dongting Lake Basin from 1980 to 2020. In the Dongting Lake Basin, precipitation is highly fluctuating and is in an insignificant fluctuating downward trend. The precipitation was relatively stable from 1980 to 2001, before varying more drastically in the following years. Precipitation in the Dongting Lake Basin has changed abruptly five times in the last four decades, namely in 1981, 1982, 1983, 1990, and 2003, and no abrupt temperature changes occurred in the remaining years. An observation can be made that the precipitation in the Dongting Lake Basin was not considerably stable in the 1980s, with several abrupt changes occurring. According to the cumulative distance of precipitation, from 1980 to 1986, the precipitation in the basin underwent a process of significant increase to slow increase. From 1987 to 1993, the precipitation exhibited a decreasing trend. From 1994 to 2003, the precipitation in the basin increased significantly. Between 2004 and 2011, the rate of precipitation increase in the basin decelerated. Subsequently, from 2012 to 2020, the basin experienced a decrease in precipitation, which remained at a low level during this period. Variation trends of temperature and precipitation in different seasons were similar to that of mean annual temperature and precipitation, of which the characteristics are shown in Figure 7.  
The temperature and precipitation in Dongting Lake Basin fluctuated during four seasons, and the trend was not obvious. However, it can be seen that the temperature in the Dongting Lake Basin fluctuates and increases in the spring (March-May). In contrast, precipitation in the study area showed a fluctuating downward trend, with a larger precipitation decrease, which was especially obvious in the four seasons. The summer (June-August) showed a fluctuating downward trend in temperature, which was the only season in the Dongting Lake Basin that showed a downward trend in temperature. Precipitation changes in the study area showed a decreasing trend. In the fall (September-January), the temperature in the Dongting Lake Basin showed a fluctuating upward trend. On the contrary, precipitation changes showed a fluctuating downward trend. The temperature in winter (December-February of the following year) showed a fluctuating upward trend. Figure 6 shows a fluctuating downward trend in precipitation, with the smallest decrease in precipitation during the four seasons. Figure 6: Analysis of sudden changes in average temperature and precipitation in the Dongting Lake Basin from 1980 to 2020. (**a**) Temperature and precipitation of the cumulative distance level; (**b**) temperature of the Manner-Kendall mutation test; (**c**) precipitation of the Manner-Kendall mutation test.