Zhongsheng Chen

Response of runoff to change of atmospheric 0°C level height in summer in arid region of Northwest China

Based on the daily observed data from eight sounding stations and the daily mountain runoff data from nine rivers in summer from 1960 to 2009 in four typical study areas located in arid region of Northwest China (ARNC), the change trends, abrupt change points, and their significance of runoff and 0°C level height (FLH) were analyzed in ARNC in the last 50 years by using Mann-Kendall (MK) nonparametric test, and the quantitative relationship between runoff and FLH in summer was also analyzed with the linear regression and elastic coefficient methods. The results are indicated as follows: (1) in recent 50 years, there is a similar changing trend between the summer runoff and FLH in ARNC and each region has its own unique feature. The summer runoff has been significantly ascending in the Tianshan Mountains and on the northern slope of the Qilian Mountains (NSQM) compared to that of the northern slope of the Kunlun Mountains (NSKM). Likewise, the FLH has been taking on a markedly rising trend on the northern slopes of the Tianshan and Qilian Mountains (NSTM and NSQM) in comparison with the southern slope of the Tianshan Mountains (SSTM). However, the FLH on NSKM has been decreasing with the speed of 2.33 m every year. (2) Abrupt change analysis indicates that the period of abrupt change happened for summer runoff and FLH is totally different among the four typical study regions, and even in same region. (3) There is a positive significant relation between the summer runoff and FLH in ARNC (NSQM P <0.05; other three regions P <0.01). Therefore, the ascending and descending of the summer FLH is a vital factor inducing the change of summer runoff in ARNC. (4) The elastic coefficient of summer runoff to the change of summer FLH on NSKM, NSTM, NSQM, and SSTM are 7.19, 3.80, 2.79, and 6.63, respectively, which indicates that there exists the regional difference in the sensibility of summer runoff to the change of summer FLH in ARNC. The distinct proportion of glacial meltwater runoff is an important cause resulting in the regional difference of sensibility.

Multiscale evolution of surface air temperature in the arid region of Northwest China and its linkages to ocean oscillations

The global climate has experienced unprecedented warming in the past century. The multiscale evolution of the warming is studied to better understand the spatial and temporal variation patterns of temperature. In this study, based on the yearly surface air temperature from the gridded CRU TS 3.22 dataset and the ensemble empirical mode decomposition method (EEMD), we investigated the multiscale evolution of temperature variability in the arid region of Northwest China (ARNC) from 1901 to 2013. Furthermore, the possible influences on the ARNC temperature change from the Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), and dipole mode index (DMI) were also discussed. The results indicated that in the past century, the overall temperature in the ARNC has showed a significant non-linear upward trend, and its changes have clearly exhibited an interannual scale (quasi-2–3 and quasi-6–7-year) and an interdecadal scale (quasi-14, quasi-24, and quasi-70-year). Compared with the reconstructed interannual variation, the reconstructed interdecadal variability plays a decisive role in the ARNC warming and reveals the climatic pattern transformation from the cold period to the warm period before and after 1987. Additionally, there were also regional differences in the spatial patterns of change trend in the ARNC temperature at a given time. We also found that the AMO and PDO had significant impacts on the ARNC temperature fluctuation at an interdecadal scale, whereas the DMI had a more important role in warming at the annual scale, which suggests that the importance of oceans cannot be ignored when considering climate change. Our findings deepen the understanding of the temperature changes all over the ARNC in the context of global warming.

Air Temperature Change in the Southern Tarim River Basin, China, 1964–2011

The temperature data from 3 meteorological stations (Kashi, Ruoqiang, and Hotan) in the South of Tarim River Basin (STRB) during 1964–2011 were analyzed by Mann-Kendall test and correlation analysis. The results from Mann-Kendall test show that the surface temperature (ST), 850 hPa temperature (T850), and 700 hPa temperature (T700) exhibited upward trends, while 300 hPa temperature (T300) revealed a downward trend. On the whole, the change rate of ST, T850, T700, and T300 was 0.26~0.46°C/10a, 0.15~0.40°C/10a, 0.03~0.10°C/10a, and −0.38~−0.13°C/10a, respectively. For the periods, ST and T850 declined during 1964–1997 and then rose during 1998–2011. T700 declined during 1964–2005 and then rose during 2006–2011, while T300 rose from 1964 to 1970s and then declined. The results from correlation analysis show that T850 and T700 positively correlated with ST (P < 0.01) at the all three stations and there was a negative correlation between T300 and ST at Hotan (P < 0.1), while the correlation is not significant at Kashi and Ruoqiang. The results indicate that there were gradient differences in the response of upper-air temperature (UT) to ST change.

Hydrologic System in Northwest China

Both the temperature and the precipitation in China’s arid northwestern zone have increased, eliciting corresponding changes in hydrological processes in the region’s inland basins. This chapter analyzes the characteristics of runoff and its components, the main findings are: (1) Runoff increased significantly at stations around the Tianshan Mountains. (2) The digital filtering method was used to separate baseflow from surface flow, after which the baseflow index (BFI) was calculated and analyzed. We find that baseflows of the four headstreams have increased considerably over the past 50 years. The baseflow and BFI showed obvious seasonal variations: The lowest baseflow and BFI typically occurred in December and January, and both increased gradually until reaching maximum values in August or July. And precipitation had a significant impact on runoff, whereas temperature strongly affected baseflow. In addition, in the Tizinafu River, the contribution of ice/snowmelt water varied from 25.96 to 68.87 % for spatial characteristics, and from 28.31 to 65.43 % for seasonal characteristics. The mean of the ice/snowmelt percentage is 43 %, which meant that ice/snowmelt water was the main supplying water source. (3) Using the data from 1960 to 2010, future runoff amounts were predicted. Some results can be concluded as follows: Runoff in the Aksu, Yarkand, and Hotan rivers will be low in 2010–2011 but will experience continued growth in 2017–2028.

Response of Runoff to Climate Change

Rising global temperatures have accelerated the water cycle, causing a redistribution of water resources that ranges from minor to extreme, arid areas are especially affected by this process due to the fragile nature of their eco-hydrology, which is more sensitive to climatic changes. The main effects of climate change to runoff are as follows: (1) The runoff in North Xinjiang has a strong positive relationship with precipitation, while that in the south slope of the Tianshan Mountains, the middle section of the north slope of the Tianshan Mountains and the Shule River has a strong positive relationship with air temperature; and there is a positive significant relation between summer runoff and 0 °C level height (FLH). (2) Human activities are presently the main driving forces behind runoff changes. In the Aksu, Kaidu, Shule and Heihe Rivers, the influence percentage of human activity on runoff is 90.4, 55.7, 63.1 and 78.8 %, respectively. (3) It was discovered that runoff in the Aksu and Yarkand Rivers is increasing with rising precipitation and temperature levels, and that runoff in the Hotan River is likewise increasing, but the rate of increase there is minimal. As runoff’s response to temperature is more sensitive to precipitation changes, runoff in the Aksu and Yarkand Rivers will increase 1.4–7.0 % with every 1 °C rise in temperature.