Baofu Li

Variations of temperature and precipitation of snowmelt period and its effect on runoff in the mountainous areas of Northwest China

Water resources in the arid land of Northwest China mainly derive from snow and glacier melt water in mountainous areas. So the study on onset, cessation, length, temperature and precipitation of snowmelt period is of great significance for allocating limited water resources reasonably and taking scientific water resources management measures. Using daily mean temperature and precipitation from 8 mountainous weather stations over the period 1960–2010 in the arid land of Northwest China, this paper analyzes climate change of snowmelt period and its spatial variations and explores the sensitivity of runoff to length, temperature and precipitation of snowmelt period. The results show that mean onset of snowmelt period has shifted 15.33 days earlier while mean ending date has moved 9.19 days later. Onset of snowmelt period in southern Tianshan Mountains moved 20.01 days earlier while that in northern Qilian Mountains moved only 10.16 days earlier. Mean precipitation and air temperature increased by 47.3 mm and 0.857°C in the mountainous areas of Northwest China, respectively. The precipitation of snowmelt period increased the fastest, which is observed in southern Tianshan Mountains, up to 65 mm, and the precipitation and temperature in northern Kunlun Mountains increased the slowest, an increase of 25 mm and 0.617°C, respectively, while the temperature in northern Qilian Mountains increased the fastest, increasing by 1.05°C. The annual runoff is also sensitive to the variations of precipitation and temperature of snowmelt period, because variation of precipitation induces annual runoff change by 7.69% while change of snowmelt period temperature results in annual runoff change by 14.15%.

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.

Climate System in Northwest China

A comparative analysis for detecting temperature and precipitation changes in the period 1960–2010 was conducted using data from 74 meteorological stations in China’s arid northwest. Significant increasing trends (P < 0.01) were revealed through the investigation, showing rates of 0.343 °C/10a and 6.07 mm/10a, which is higher than the global average. The winter temperature rate increased 0.486 °C/10a, while the summer temperature changed at a rate of 0.232 °C/10a. However, although precipitation increased 2.51 mm/10a in summer, it slowed in winter to a rate of 1.16 mm/10a. Regionally, the highest increasing rates of temperature and precipitation occurred in northern Xinjiang, and the lowest rates were recorded in southern Xinjiang and the Hexi Corridor. We found that, among the four seasons, winter saw the greatest temperature changes. We also found that the winter temperature in this region had a strong association with the Siberian High (correlation coefficient: R = − 0.715) and greenhouse gas emissions (R = 0.51).

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.

Impacts of land cover change and water management practices on the Tarim and Konqi river systems, Xinjiang, China

Abstract. The Tarim and Konqi Rivers in western China have experienced dramatic changes in streamflow and riparian vegetation due to climatic variability, land cover change, and water management including interbasin water transfers. To assess the extent and evolution of vegetation dynamics along these rivers, we use Landsat and MODIS images for land cover classification, spectral mixture analysis, and landscape phenology analysis. From 1998 to 2011, agriculture nearly tripled in extent, from 1376 to 3742  km2. Natural riparian vegetation persisted in aggregate but experienced losses (to agriculture) in some areas while expanding into barren land elsewhere. Spectral mixture analysis suggests that interbasin water transfers from the Konqi to the Tarim River increased near-channel riparian vegetation on the Tarim at the expense of vegetation on the Konqi. A time-series of MODIS images reveals a pattern of increasing and decreasing greenness across the region, including loss of vegetation in distal regions that were formerly subject to sporadic seasonal flooding but now are cut off from their water supply due to water management. These results suggest that satellite remote sensing may play a valuable role in monitoring the effects of changing land use and hydrology on riparian systems in Central Asia and other arid regions.