## 4 Results and Analysis
### Climate Change since 1990 in the TRH Region  
According to the variations of annual average temperature in the TRH region (Figure 6a), the average temperature had shown an obvious upward trend since 1990, from -4.2 \({}^{\circ}\)C in 1990 to -3.3 \({}^{\circ}\)C in 2012,  
Figure 4: The distribution of wetland changes in the TRH region from the early 1990s to 2004 (humidity Region I: 0.3–0.4; II: 0.4–0.5; III: 0.5–1; and IV: \(>\)1). Figure 5: The distribution of wetland changes in the TRH region from 2004 to the early 2012 (humidity Region I: 0.3–0.4; II: 0.4–0.5; III: 0.5–1; and IV: \(>\)1). an increase of 0.9 \({}^{\circ}\)C in total. The annualized growth rate of temperature varied in different time periods. The warming rate was 0.68 \({}^{\circ}\)C/10 years from 1990 to 2004, faster than that during 2004-2012, when it decreased to 0.27 \({}^{\circ}\)C/10 years. As the temperature increased, the change of annual precipitation (Figure 6b) also showed an increasing trend from 1990 to 2012 in the TRH region. Annual precipitation was 430.63 mm in 1990 and 532.6 mm in 2012 respectively, an increase by 102.0 mm. On the other hand, the increase of annual precipitation also showed significant periodic differences. The annual precipitation grew slowly during 1990-2004 at 1.8 mm/year, while the growth rate increased to 8.0 mm/year during 2004-2012 with significant fluctuations. For example, the annual precipitation shrank to 399.2 mm in 2006 due to a severe drought. In conclusion, the temperature and precipitation showed a general upward trend from 1990 to 2012. During 1990-2004, the temperature rose fast while precipitation grew slowly. During 2004-2012, the temperature growth trend slowed down and the upward trend of precipitation became more obvious. Based on the general upward trend of temperature and precipitation, the change trend of temperature and precipitation also showed spatial differences (Figure 7). During 1990-2004, the spatial distribution of annual average temperature trend rate showed an increasing trend in all over the TRH region. The average temperature trend rate was 0.82 \({}^{\circ}\)C/10 years in the Yellow River basin which was the most significant in the three major source areas. In particular, the temperature of the eight counties in the eastern Yellow River basin had a greater growth rate between 0.6 \({}^{\circ}\)C/10 years and 1.2 \({}^{\circ}\)C/10 years. In addition, the temperature increased relatively significantly in Yushu, between 0.8 \({}^{\circ}\)C/10 years and 1.0 \({}^{\circ}\)C/10 years, and gradually decreased from Yushu to the periphery. The temperature growth in the extensive region of western Tuotuohe in the Yangtze River basin was relatively low, under 0.6 \({}^{\circ}\)C/10 years. From 2004 to 2012, the variation tendencies of temperature had evident regional differences. The temperature growth rate in the central TRH was the most significant, between 0.6 \({}^{\circ}\)C/10 years and 0.8 \({}^{\circ}\)C/10 years, and decreased gradually from the center to the periphery. On the contrary, the temperature had decreasing tendency in Yushu in southern TRH, Banma and Xinghai in eastern TRH, and Zhiduo in northwestern TRH. During 2004-2012, the average temperature trend rate was 0.38 \({}^{\circ}\)C/10 years in the Yellow River basin, which was the most obvious warming basin, while it was only 0.16 \({}^{\circ}\)C/10 years in the Lancang River basin. Figure 6: Change of average annual (**a**) temperature and (**b**) precipitation in the TRH region. The annual trend rate of precipitation (Figure 8), during 1990-2004, in Tanggulashanxiang, Zhiduo, and Zaduo counties in the southwestern TRH region presented an obvious increasing tendency, with a trend rate of 5-11 mm/year. While the range of change in vast areas of central TRH is relatively small, with trend rate was between \(-\)1 mm/year and 1 mm/year.