# Quantifying Climate Change and Ecological Responses within the Yangtze River Basin, China
## 3 Results  
### Trends of the Climatic Parameters in the Yangtze River Basin (YRB) during 1961-2013  
Figure 2 shows the annual average temperature variation trend of temperature and precipitation in the YRB. The annual mean air temperature was 12.79 \({}^{\circ}\)C during 1961-2013, with a maximum of 13.82 \({}^{\circ}\)C in 2006 and a minimum of 12.15 \({}^{\circ}\)C in 1984. The annual mean temperature shows a significant upward trend and the correlation significant is at 0.01 level (Figure 2a); it increased by 0.82 \({}^{\circ}\)C during 1961-2013, a rate of 0.016 \({}^{\circ}\)C decade\({}^{-1}\), and this rate increased to 0.42 \({}^{\circ}\)C decade\({}^{-1}\) during the 1980s. The decadal mean air temperature during 1961-2013 increased: 12.54 \({}^{\circ}\)C (1961-1970), as follows: 12.54 \({}^{\circ}\)C (1971-1980), 12.51 \({}^{\circ}\)C (1981-1990), 12.85 \({}^{\circ}\)C (1991-2000), and 13.40 \({}^{\circ}\)C (2001-2010). However, there is no significant trend in annual mean precipitation (Figure 2b). The annual mean precipitation during 1961-2013 fluctuates 1031.15 mm, with a maximum of 1239 mm in 1973 and a minimum of 854.68 mm in 1978. The decadal mean precipitation varied over the last five decades, as follows: 1008 mm (1961-1970), 1055 mm (1971-1980), 1071 mm (1981-1990), 1022 mm (1991-2000), and 1148 mm (2001-2010). The seasonal mean value of observed air temperature during 1961-2013 shows a similar spatial distribution pattern in every season (Figure 3), with lower air temperatures in the high-altitude areas in the upper reaches of the YRB [44]. The spatial patterns of the linear trends in air temperature are illustrated in Figure 4. Spring temperatures increased more rapidly mostly in the lower altitude areas of the middle and lower reaches of the YRB (MLYRB). Summer and winter temperatures have similar distributions, where the temperature is increasing rapidly are mainly in the source region of the Yangtze River (SRYR), in eastern Tibet and in the Yunnan Plateau. The areas of rapid temperature increase in autumn are chiefly distributed across the higher altitude areas of the YRB and in the densely populated areas of the Yangtze River Delta (YRD). Figure 2: Temporal trends in annual mean air temperature and precipitation in the YRB during 1961–2013. (**a**) Temporal trends in average air temperature; (**b**) temporal trends in precipitation. \(b\) is the regression coefficient. Significance level: ** means the significant of the 99% confidence interval, \(p\) < 0.01, * means the significant of the 95% confidence interval, \(p\) < 0.05. The spatial distributions of the seasonal mean value of observed precipitation during 1961-2013 exhibit a differentiated spatial pattern (Figure 5). Precipitation in the SRYR during the years was relatively low compared to other areas in the YRB. The areas with more precipitation in spring are mainly located in the lower elevations of the hilly regions of south-eastern China reflect the influence of the monsoon (Figure 5a). The regions with less precipitation in summer are mostly distributed across the SRYR and in the Hanzhong Basin (Figure 5b). The areas with increased autumn precipitation are principally distributed within the Sichuan Basin (Figure 5c), and the areas with increased winter precipitation are mainly concentrated in the south-eastern region of the Xiang-Gan Mountains (Figure 5d). Figure 4: Spatial distribution of (**a**) the linear trends in observed spring air temperature, (**b**) the linear trends in observed summer air temperature, (**c**) the linear trends in observed autumn air temperature and (**d**) the linear trends in observed winter air temperature for the YRB during 1961–2013. Figure 3: Spatial distribution of (**a**) the mean value of observed spring air temperature, (**b**) the mean value of observed summer air temperature, (**c**) the mean value of observed autumn air temperature and (**d**) the mean value of observed winter air temperature in the YRB during 1961–2013.