Yaning Chen

Effects of climate change on water resources in Tarim River Basin, Northwest China

Based on hydrology, temperature, and precipitation data from the past 50 years, the effects of climate change on water resources in Tarim River Basin in Northwest China were investigated. The long-term trends of the hydrological time series were detected using both parametric and nonparametric techniques. The results showed that the increasing tendency of the temperature has a 5% level of significance, and the temperature increased by nearly 1 degree C over the past 50 years. The precipitation showed a significant increase in the 1980s and 1990s, and the average annual precipitation exhibited an increasing trend with a magnitude of 6.8 mm per decade. A step change occurred in both the temperature and precipitation time series around 1986. The streamflow from the headwater of the Tarim River exhibited a significant increase during the last 20 years. The increase in temperature, precipitation, and streamflow may be attributed to global climate change.

Changes in Central Asia's Water Tower: Past, Present and Future.

The Tienshan Mountains, with its status as “water tower”, is the main water source and ecological barrier in Central Asia. The rapid warming affected precipitation amounts and fraction as well as the original glacier/snowmelt water processes, thereby affecting the runoff and water storage. The ratio of snowfall to precipitation (S/P) experienced a downward trend, along with a shift from snow to rain. Spatially, the snow cover area in Middle Tienshan Mountains decreased significantly, while that in West Tienshan Mountains increased slightly. Approximately 97.52% of glaciers in the Tienshan Mountains showed a retreating trend, which was especially obvious in the North and East Tienshan Mountains. River runoff responds in a complex way to changes in climate and cryosphere. It appears that catchments with a higher fraction of glacierized area showed mainly increasing runoff trends, while river basins with less or no glacierization exhibited large variations in the observed runoff changes. The total water storage in the Tienshan Mountains also experienced a significant decreasing trend in Middle and East Tienshan Mountains, but a slight decreasing trend in West Tienshan Mountains, totally at an average rate of −3.72 mm/a. In future, water storage levels are expected to show deficits for the next half-century.

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.

Environmental hazards in Xinjiang Line of New Eurasian Continental Bridge

Xinjiang Line of New Eurasian Continental Bridge is the important lifeline project in western China. Various disasters, such as flood, strong wind, sandstorm, and roadbed disasters, have been seriously affecting the railway transportation. The field investigation and analysis on the data collected since 1959 show that: serious floods often occurred when the rain intensity reached 25 mm/h or 30 mm/d; the critical wind speed for turning over a train is between 35 m/s and 67 m/s, and such cases happened in draught places of mountain opening and trunk valley; the angle between wind direction and railway is closely related to the thickness of accumulative sand along the lines; roadbed disasters taking the form of side-slope sliding, roadbed sinking and silt turning up took place in spring when the temperature rapidly rose to 10–15°C from zero and precipitation came forth or when the thickness of snow cover on shade slope reached above 20 cm in winter; the disasters taking place in the 1990s were far stronger than those of the 1980s and the order of hazard intensity along the Xinjiang Line is Urumqi>Shihezi>Kuitun>Liuyuan>Shanhan>Hami.

Regional disparities in warm season rainfall changes over arid eastern–central Asia

Multiple studies have reported a shift in the trend of warm season rainfall over arid eastern–central Asia (AECA) around the turn of the new century, from increasing over the second half of the twentieth century to decreasing during the early years of the twenty-first. Here, a closer look based on multiple precipitation datasets reveals important regional disparities in these changes. Warm-season rainfall increased over both basin areas and mountain ranges during 1961–1998 due to enhanced moisture flux convergence associated with changes in the large-scale circulation and increases in atmospheric moisture content. Despite a significant decrease in warm-season precipitation over the high mountain ranges after the year 1998, warm season rainfall has remained large over low-lying basin areas. This discrepancy, which is also reflected in changes in river flow, soil moisture, and vegetation, primarily results from disparate responses to enhanced warming in the mountain and basin areas of AECA. In addition to changes in the prevailing circulation and moisture transport patterns, the decrease in precipitation over the mountains has occurred mainly because increases in local water vapor saturation capacity (which scales with temperature) have outpaced the available moisture supply, reducing relative humidity and suppressing precipitation. By contrast, rainfall over basin areas has been maintained by accelerated moisture recycling driven by rapid glacier retreat, snow melt, and irrigation expansion. This trend is unsustainable and is likely to reverse as these cryospheric buffers disappear, with potentially catastrophic implications for local agriculture and ecology.