Impacts of changing conditions on the ecological environment of the Shiyang River Basin, China Open Access

The Shiyang River Basin is one of the major inland river basins in China with the highest population density and most prominent water resources. The ecological environment of the river basin is extremely fragile and sensitive to climate change and human activities (Li et al. 2009; Jia et al. 2018). The excessive development and utilisation of water resources in the basin has caused a series of ecological and environmental problems over recent years, such as the continuous decline of regional groundwater levels and the deterioration of water quality, land desertification and salinisation (Chen et al. 2016; Hu et al. 2021), which are attributed to both natural and anthropogenic factors. Considering the fragile ecological environment of Shiyang River Basin, the national development and Reform Commission and the Ministry of water resources issued and implemented the ‘Key Management Plan of Shiyang River Basin in Gansu Province’ and the ‘Implementation Plan of Key Governance Adjustment of Shiyang River Basin.’ The implementation of the key plan and adjustment schemes of the drainage basin has also drawn significant attention to related research on the allocation and utilisation of regional water resources, improvement and management of the ecological environment, impact and adaptation of climate change, and countermeasures and regulation of human activities (Zhang et al. 2006; Zeng et al. 2015; Wei et al. 2016; Yao & Zeng 2016). This can help further understand the coupling relationship between the natural and ecological evolution process of the inland river basin and human activities in the arid zone. Understanding the changes in the ecological environment of the Shiyang River Basin under the changing environment can contribute to determining the human adaptation countermeasures to mitigate the ecological deterioration and ensure sustainable development of ecologically fragile areas.

The Shiyang River Basin is one of the largest inland river basins in the Hexi Corridor in Gansu Province (36 °29′–39 °27′ N and 101 °41′–104 °16′ E) (Figure 1), and the basin covers an area of 41,600 km². This area is linked to Baiyin City and Lanzhou City in the southeast and is adjacent to Zhangye City in the northwest. It is near the Qinghai Province in the southwest, and the Nei Monggol Autonomous Region in the northeast.

The Shiyang River Basin has 21 reservoirs and 3.81 × 10⁴ wells for underground water intake, with an intake capacity of 8.73 × 10⁸ m³ (Li et al. 2013; Zhao 2017). Vegetation types formed a significant vertical band spectrum. The topography of the watershed is high in the south and low in the north. Owing to the diverse vegetation and complex ecological area, the distribution of soil types is significantly affected by longitude and vertical zonality. The total population of the drainage basin was 2.71 million.

Meteorological data were obtained from the China Meteorological Data Service Center and coupled with data from related literature. Detailed information on the meteorological stations in the research area is shown in Table 1. Average temperature and precipitation data were obtained from four meteorological stations: Wushao Mountain, Wuwei, Minqin, and Yongchang. The hydrological data for the four hydrological stations, Za Mu Si, Nan Ying reservoir, Jiu Tiao Ling, and Sha Gou Si, were obtained from the Hydrological Bureau of Gansu Province.

The temperature in the Shiyang River Basin showed a significant upward trend over the past 50 years based on temperature and rainfall data from 1963 to 2016. The warming rate was 0.56 °C/10a, and the range of average temperature reached approximately 4 °C. The annual average temperature for 19 consecutive years was higher than that for 53 years (a value of 5.63 °C), particularly since 1996; thus, the rise in temperature was significant. However, the increasing trend in precipitation was small, and the rate of increase in precipitation was only 0.737 mm/10a (Figure 2). The results show that under the large-scale effects of global warming, the Shiyang River Basin had a considerably large temperature increase range and a comparatively small precipitation change range.

Wuwei City and Minqin County are the two regions in the lower reaches of the Shiyang River Basin where desertification and human intervention were found to be more severe, and Minqin County had a more fragile ecological environment. Both weather stations, Wuwei and Minqin, were selected to study the temperature and precipitation changes in the regions to detect the basic trends of climate change. Temperature showed a clear upward trend after the 1990s. The range of average temperature in spring was 2.38 and 2.33 °C in Wuwei and Minqin meteorological stations, respectively; summer: 2.10 and 1.80 °C, autumn: 2.39 and 2.19 °C, and winter: 2.61 and 3.12 °C, respectively. The highest temperatures in different seasons appeared after 2011 (Figure 3).

Table 2 shows that the changes in precipitation during the different seasons for different years were relatively stable. The maximum and minimum precipitation values in Wuwei were 25.21 and 2.61 mm, respectively. Similarly, in Minqin, the maximum and minimum precipitation values were 20.76 and 2.62 mm, respectively. The data show that a small change in precipitation occurred during winter and spring, and a slightly larger change occurred during summer and autumn. The annual change in precipitation was approximately 25–30 mm. From the perspective of seasonal distribution, the precipitation in the Shiyang River Basin was primarily concentrated in summer, followed by autumn and spring. Precipitation was very rare in winter, with clear spatial and temporal distribution characteristics.

The administrative division includes four cities and nine counties of the Shiyang River Basin. The population density is approximately 55 people/km², which belongs to a medium-density region, and is approximately 3.4 times the average population density in the Hexi Corridor. The population of the Shiyang River Basin (ten counties under Wuwei) was 76,419, with an average of less than 10,000 people per county. During the Tang Dynasty, the five counties to which Xiliang belonged had a total population of 128,192. The population has nearly doubled in the Hexi Corridor, and the population density has increased sharply from 6.19 people/km² in the 1950s to 16 people/km². In particular, the population of the Shiyang River Basin has increased sharply during the recent years. The population was 1.95787 million in 1987 and 2.8588 million in 2010. The population decreased slightly to 2.712 million in 2015, with the majority being agricultural population (Figure 4). The population of the region changed from positive to negative growth owing to the combined action of various factors, such as population policy and labour outflow.

Modern glaciers have developed in the Qilian Mountains owing to their tall mountains and abundant precipitation. The responses to different types of glacial changes differed with increasing temperature (Cao et al. 2010; Chen et al. 2017; Li et al. 2018). The increase in glacier accumulation caused by the increase in annual precipitation is not sufficient to offset the increase in glacial melting caused by the increase in temperature in the Qilian Mountains. As observed in Ningshanhe Glacier No. 3 in the Lenglongling area of the eastern Qilian Mountains, the area and volume of the glacier have decreased substantially by 13.1 and 35.3% (Liu et al. 2012), respectively, in the last 37 years. The area of 2684 glaciers in the Qilian Mountains has decreased by 20.88% over the past 50 years, and the storage of glaciers has decreased by 20.26%. The shrinking area of small glaciers is the main cause for the reduction in the total area of glaciers in the region. The increase in temperature is the main cause of the rapid shrinkage of the glaciers (Sun et al. 2015). This would inevitably affect the natural conditions of downstream water resource supply and the climate conditions with the change in snow cover of glaciers in high mountainous areas at different temperature and precipitation conditions (Han et al. 2011). Furthermore, this results in a decrease in the replenishment of glacial meltwater in the Qilian Mountains and a decline in upstream production flow. Glaciers have relatively weak regulatory functions in downstream rivers compared with the Shiyang River Basin, and the glacial melt water in the basin only accounts for 3.7% of the runoff in the upstream mountain area (Table 3) (Han et al. 2011; Liu et al. 2012; Sun et al. 2015; Li et al. 2018).

The sharp growth in population, increase in the intensity of human production activities, and unregulated destruction of watershed resources are the main reasons for the rapid reduction of water resources, which creates a contradiction between the supply and demand of these resources in the region. Precipitation in the Shiyang River Basin is the main source of replenishment of river runoff. The observation of the runoff in the Shiyang River Basin in the past 60 years revealed a relative downward trend in the runoff since 1960, with an average reduction rate of 0.11 × 10⁸ m³/10a. The average value of runoff decreased from 44.3 × 10⁸ to 42.1 × 10⁸ m³/10a before and after significant climate warming, respectively. The decline in precipitation in mountainous areas is one of the causes of the overall decrease in runoff from the mountain passes (Yang 2016). The groundwater level has shown a rapid downward trend in the plain since 1985. For example, the rate of decrease in the groundwater table depth was 4.1 m/10a in Minqin Oasis, which increases groundwater mineralisation. The water consumption in this area has increased sharply due to factors such as the expansion of artificial oases and the increase in population, which causes a significant decrease in the surface runoff of Minqin Oasis downstream (at a rate of 2.4 × 10⁸ m³/10a) (Wang et al. 2007). The spatial distribution was similar to the distribution of precipitation in the water production rate of each river. The runoff modulus of the deep mountain area was larger than that of the shallow mountain area (Table 4), and that of the western area was larger than that of the eastern area (Yang 2016).

The evolution of landscape patterns reflects the changes in regional natural and social factors, which are responses to the changes in the climate, resources, and the environment. The population of the river basin increased sharply in the 1980s, the primary industry developed rapidly, and consumption of water resources increased substantially. This led to changes in land use types with an increase in population and changes in the population structure, which had varying degrees of impact on the fragile ecological environment of the Shiyang River Basin. The proportion of upstream and downstream water use was severely unbalanced, and the difference in water use was large because the irrigation area had undergone continuous expansion in the middle and lower reaches of the Shiyang River Basin. The growth of cultivated land was mainly concentrated in the oasis areas in the middle and lower reaches of the river basin, and the desertification trend was completely concentrated in the downstream Minqin Oasis. The proportions of arable land, dry ditch, mobile sand land (Li et al. 2004), wind-eroded land, and residual hills increased continuously in Minqin County from 2000 to 2010, whereas the proportion of land, such as grassland and forest land, decreased with water and soil conservation. Changes in land use types occurred randomly (Yao et al. 2014; Zhang et al. 2014). Urban land and residential land expanded by 176.7 km² due to the influence of human activities, with an increase of 48.57% compared with 1986, whereas forest land and grassland decreased by 7.24 and 1.39% (Sun et al. 2016; Yao & Zeng 2016; Wei et al. 2017), respectively. The Shiyang River Basin is dominated by desertified land, bare rock, and bare soil, with low vegetation cover, and is susceptible to interference from climate change and human activities. As shown in the evolution trend of vegetation NDVI based on the Hurst index, the spatial evolution of vegetation cover was generally stable in the Shiyang River Basin, but with a large risk of degradation in the future. This is in good agreement with the wavelet analysis results for climatic factors. The climate is estimated to become cold and dry in the future, and vegetation might show a trend of degradation (Wei et al. 2012; Han & Wang 2017).

The amount of snowmelt in glaciers in high mountainous areas increases with the increase in temperature, which affects the amount of downstream water resources. Glacial meltwater has a significant regulatory effect on the rivers in areas with large upstream scales and high coverage, whereas the regulation of glacial runoff is weak in areas with small glaciers and low coverage, such as the eastern section of the Qilian Mountains (Li et al. 2011; Wang et al. 2011). The precipitation in the Shiyang River Basin has changed very slightly over the past 60 years. The runoff from the mountain pass generally shows a decreasing trend with increasing temperature, which in turn affects the downstream water resources. Large increases in temperatures were observed due to the increasing evaporation in the middle and lower reaches of the Shiyang River Basin, and high-intensity human activities led to serious deterioration of the ecological environment. Shiyang River Basin has areas with the most dense populations and the most significant disturbances caused by human activities among the three major river basins in the Hexi Corridor; therefore, it was selected for this research. This river basin was suitable to explore the impact of climate and human factors on the ecological environment, understand the complex relationship between oasis evolution and these two major factors, and guide sustainable development of the region. As indicated by Liu et al. (2013), the contribution rate of human factors to runoff loss was 50.50% from 1975 to 2009 in the middle oasis of the Shiyang River, the impact of runoff reached 0.5 × 10⁹ m³, and the contribution rate of natural factors was 49.5%. According to Dong et al. (2010) the intensity of human activities on downstream runoff exceeds 70%, and the impact of human activities on runoff cannot be ignored. Moreover, Wang et al. (2021) reported that the contribution rates of climate change and human activities to runoff changes were 45 and 55%, respectively, in the upper Shiyang River Basin. As shown in the principal component regression analysis by Jia et al. (2020), the influence of human factors reached 58.48% in the process of water resource change in the Shiyang River Basin, whereas the precipitation and temperature factors only accounted for 22.35 and 19.17%, respectively. The amount of sandy and inferior land types also showed an increasing trend because of unreasonable utilisation methods. The intense intervention of human activities has decreased vegetation cover, reduced the ability to retain water and soil, and strengthened the destructive impact of sandstorms in the Shiyang River Basin. However, ecological governance has received widespread attention in the Shiyang River Basin. Thus, the ecological environment would be gradually improved by actively promoting governance policies, transferring watershed and inter-basin water resources, establishing closed wells and pressured farms, transforming irrigation and water saving technology, adjusting the structure of the agricultural industry, and implementing ecological immigration measures, among other measures (Huang et al. 2017).

• (1)

  The Shiyang River Basin exhibited a larger temperature increase and a smaller change in precipitation from 1963 to 2016. From the perspective of seasonal changes over different time periods, temperature demonstrated a significant growing trend after the 1990s, and precipitation changes were relatively stable for different seasons in different years. A combined action of factors, such as population policies and labour outflows, has resulted in a change in the population of the region from positive to negative growth.

• (2)

  Changes in natural conditions and climate have resulted in a decline in the replenishment of glacial meltwater in the Qilian Mountains, and the snow glacier has a weak regulating effect on the downstream rivers. The runoff from mountain valleys has shown a slight downward trend since 1960, with a linear decrease rate of 0.11 × 10⁸ m³/10a. The upstream runoff decreased, and the supply of surface water resources was limited. Because high mountainous areas have little human impact, the analysis of export runoff can reveal the impact of climate change on runoff. The calculation of the typical river runoff modulus shows that the runoff modulus of the watershed above the station Jiu Tiao Ling in the deep mountain area is large, and the spatial distribution of the water production rate of each river is similar to that of precipitation. The spatial evolution of vegetation cover is generally stable in the Shiyang River Basin, and the area of vegetation improvement (including strong and weak continuous improvement areas) is larger than that of vegetation degradation (including strong and weak continuous degradation areas), and the spatial continuous improvement trend is stronger. The sharp growth in population and its impacts on production and living conditions have increased the pressure on the ecological environment of the river basin. Changes in natural and human factors have increased the proportion of arable land, dry ditch, mobile sand, wind-eroded land, and residual hills in the watershed, whereas the proportion of ecological land, such as grassland and forest land, is declining, and the ecological risks are increasing downstream.

• (3)

  Both climate change and human activities have a substantial impact on the ecological environment of the Shiyang River Basin, in which the impact of human factors is dominant.

This research was supported by the Gansu Youth Science and Technology Fund Project (21JR7RA547), the Higher Education Innovation Fund Project of Gansu Province (2021A-136), 2022 Longyuan Youth Innovation and Entrepreneurship Talent (Team) Project Funding, the Youth Foundation of Lanzhou City University (LZCU-QN2019-04), Doctor research launch aid of Lanzhou City University in 2019 (LZCU-BS2019-20). We would like to thank Senior Engineer YAO Jin-Zhong from water Resources Department of Gansu Province, Professor SHI Zheng-tao from Yunnan Normal University and Professor YUE Dong-Xia from Lanzhou University for their suggestions and comments that helped improve the scholarly quality of this paper.

All relevant data are included in the paper or its Supplementary Information.