Abstract
Warming in mountainous regions has experienced obvious elevation dependence (the warming rate of air temperature is amplified with elevation), which accelerates the melting of ice and snow, affecting glacier size and mass, and water resources in mountainous regions. Here, we used ERA5-Land monthly averaged datasets from 1979 to 2019 to analyze the elevation-dependent warming (EDW) variability, driving factor, and its implications to water resources in the Qilian Mountains (QLM). Results showed that: (1) Annual mean temperature shows a significant increasing trend in the QLM from 1979 to 2019 (0.31 °C/10a; p < 0.01), and the warming rate of annual mean temperature increased with elevation in the QLM in general. For seasonal scales, the most obvious EDW was found in summer. In the past 41 years, snow cover and snow depth showed a slight decreasing trend. There was a significant negative correlation between temperature and snow cover, which can explain that enhanced regional warming has caused decreases in snow cover and snow depth, largely controlling the pattern of EDW on the QLM. EDW has significant implications for water resources over QLM, especially above 5,000 m. Our study can provide a reference in understanding the importance of EDW to water resources in mountainous areas.
HIGHLIGHTS
ERA5-Land reanalysis 2 m temperature data are reliable in Qilian Mountains.
There is an obvious elevation-dependent warming (EDW) of annual mean temperature, especially above 5,000 m.
Snow cover in Qilian Mountain showed a decreasing trend.
Snow cover is an important mechanism driving EDW.
EDW has an important implication for water resources (especially above 5,000 m).
INTRODUCTION
Mountainous areas, such as Qinghai-Tibet Plateau (QTP), Tianshan, have unique environments with complex terrain conditions and fragile ecological environment (Yi et al. 2018; Pepin et al. 2019). Climate change affects the accumulation and melting of glaciers and snow in mountains areas (Sun & Liu 2013; Gao et al. 2018a, 2020; Fan et al. 2021; Jiao et al. 2021; Zuo et al. 2021). Rapid warming is expected to accelerate the melting of ice and snow, affecting glacier size and mass, and water resources (Guo et al. 2021; Shen et al. 2021). Elevation-dependent warming (EDW) occurs when the rate of warming increases with elevation (Pepin et al. 2015; You et al. 2020; Miller et al. 2021). Positive EDW accelerates soil moisture in mountain ecosystems, warming of the cryosphere, intensification of hydrological processes, and evolution of Phenological (Pepin et al. 2015; Río et al. 2021). Enhanced warming at high altitudes must be a considered for future climate adaptation strategies in sensitive mountainous regions (Johnston et al. 2018). Evidence for EDW has been obtained mainly from other high mountain ranges, such as the Swiss Alps (Rottler et al. 2019), Colorado Rocky Mountains (Minder et al. 2018), Tropical Andes (Aguilar-Lome et al. 2019; Toledo et al. 2021), and the Tibetan Plateau (Niu et al. 2021a, 2021b; Shen et al. 2021). The extent of EDW remains uncertain despite extensive research.
Many previous studies on EDW were based on observations and model simulations (Tudoroiu et al. 2016; Thakuri et al. 2019; Li et al. 2020; You et al. 2020). However, due to the scarcity of ground observation data, especially at elevations above 3,000 m, research on EDW in mountainous areas is limited (Rangwala & Miller 2012). A more comprehensive ground observation network is urgently needed, as well as reanalysis data, remote sensing data, and high-resolution climate modeling with better representation of both atmospheric and cryosphere processes to gain a greater understanding of EDW (Guo et al. 2019; You et al. 2020; Niu et al. 2021a). Palazzi et al. (2018) used Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations to assess EDW in the QTP, and results found that the warming rate in high-altitude areas has accelerated (Palazzi et al. 2018). Zhang et al. (2020) showed that air temperature increased at elevation ranges of 2,000–3,000 and 4,000–5,000 m, and cooled at 6,000–7,000 m. Gao et al. (2018b) used meteorological observations, ERA-interim reanalysis, and the Weather Research and Forecasting Mode (WRF) for the QTP to analyze EDW above 5,000 m, results showed that ERA-interim underestimated the increasing rate of temperature, and there was no obvious EDW above 3,000 m. Although satellite data can compensate for the lack of ground observation stations, the relatively short-time series, and long revisiting cycle limit the understanding of EDW variability. A high-resolution and long-time series air temperature dataset is necessary for more accurate EDW detection (Pepin et al. 2015).
The Qilian Mountains are an important ecological protection barrier and one of the most important sources of water in northwestern China. The mountain range is extremely important for assessing climatic and environmental changes across China (Lin et al. 2017; Wang et al. 2019). The QLM system is not only the source of many rivers but also hosts a unique desert oasis ecosystem (Sun & Liu 2013; Wang et al. 2019). However, most glaciers in the QLM exhibit an accelerated degradation due to recent climate warming (Qian et al. 2019). The warming rate of mean annual temperature in the entire QLM reached 0.33 °C/10a during 1960–2016, which is higher than the respective national mean (0.23 °C/10a) (Wang et al. 2019; Wen et al. 2019). However, the implications of EDW on water resources specialized in the QLM are unclear, perhaps due to the spare meteorological station, especially above 3,500 m. An evaluation of EDW in the QLM is critical for increased accuracy of estimates of the mass balance (and associated runoff) of high-altitude ice masses, and for understanding changes in the alpine environment of the QLM (Pepin et al. 2015).
Here, we analyzed the EDW variability, physical mechanism, and its implications for water resources based on the newest ERA5-Land reanalysis temperature datasets from 1979 to 2019 in the QLM. Section 2 describes the data and methods. Section 3 focuses on the EDW variability, driving factors, and implications of EDW to water resources. Section 4 concludes this study.
DATA AND METHODS
Data
Methods
Altitudes in the QLM were divided into seven ranges: 2,000 − 2,500 m, 2,500 − 3,000 m, 3,000 − 3,500 m, 3,500 − 4,000 m, 4,000 − 4,500 m, 4,500 − 5,000 m, and 5,000 − 5,500 m, respectively (Table 1). There are a total of 1983 grid points within the QLM, and the percentage of grid points in each altitude range to the total grid points is also shown in Table 1. The divided justification with 500 m interval was according to the literature (Williamson et al. 2020; Gao et al. 2021). Mann-Kendall (MK) trend test and Sen's slope approach were used to analyze the temperature trends (Tayfur & Yacoub 2019). Correlation analysis was used to analyze the relationship between temperature and snow cover as well as snow depth (Jiang et al. 2016).
Elevation range (m) . | Grid number . | Percentage (%) . |
---|---|---|
2,000 − 2,500 | 8 | 0.40 |
2,500 − 3,000 | 229 | 11.55 |
3,000 − 3,500 | 583 | 29.40 |
3,500 − 4,000 | 569 | 28.69 |
4,000 − 4,500 | 471 | 23.75 |
4,500 − 5,000 | 105 | 5.30 |
5,000 − 5,500 | 17 | 0.86 |
Elevation range (m) . | Grid number . | Percentage (%) . |
---|---|---|
2,000 − 2,500 | 8 | 0.40 |
2,500 − 3,000 | 229 | 11.55 |
3,000 − 3,500 | 583 | 29.40 |
3,500 − 4,000 | 569 | 28.69 |
4,000 − 4,500 | 471 | 23.75 |
4,500 − 5,000 | 105 | 5.30 |
5,000 − 5,500 | 17 | 0.86 |
RESULTS AND DISCUSSION
Temperature trend
Temperature (°C) . | MK (Z) . | Trend . | β (°C/10a) . |
---|---|---|---|
Annual | 4.62 | Yes (+) | 0.31** |
Spring | 3.74 | Yes (+) | 0.43** |
Summer | 3.96 | Yes (+) | 0.42** |
Autumn | 2.73 | Yes (+) | 0.25** |
Winter | 0 | No | 0.01 |
Temperature (°C) . | MK (Z) . | Trend . | β (°C/10a) . |
---|---|---|---|
Annual | 4.62 | Yes (+) | 0.31** |
Spring | 3.74 | Yes (+) | 0.43** |
Summer | 3.96 | Yes (+) | 0.42** |
Autumn | 2.73 | Yes (+) | 0.25** |
Winter | 0 | No | 0.01 |
**The significant test level at p < 0.01.
Snow cover and snow depth trends
Time scales . | Snow cover . | Snow depth . | ||||||
---|---|---|---|---|---|---|---|---|
MK (Z) . | Trend . | β (%/10a) . | Mutation time . | MK (Z) . | Trend . | β (m/10a) . | Mutation time . | |
Annual | 0 | No | −0.493 | No | 0 | No | −6.87 × 10−4 | No |
Spring | 0 | No | −0.797 | No | 0 | No | −1.65 × 10−3 | No |
Summer | 0 | No | −0.210 | 1984 | 0 | No | −1.94 × 10−4 | 1992 |
Autumn | 0 | No | −0.087 | No | 0 | No | −9.6 × 10−5 | No |
Winter | 0 | No | 0.312 | No | 0 | No | 4.25 × 10−4 | No |
Time scales . | Snow cover . | Snow depth . | ||||||
---|---|---|---|---|---|---|---|---|
MK (Z) . | Trend . | β (%/10a) . | Mutation time . | MK (Z) . | Trend . | β (m/10a) . | Mutation time . | |
Annual | 0 | No | −0.493 | No | 0 | No | −6.87 × 10−4 | No |
Spring | 0 | No | −0.797 | No | 0 | No | −1.65 × 10−3 | No |
Summer | 0 | No | −0.210 | 1984 | 0 | No | −1.94 × 10−4 | 1992 |
Autumn | 0 | No | −0.087 | No | 0 | No | −9.6 × 10−5 | No |
Winter | 0 | No | 0.312 | No | 0 | No | 4.25 × 10−4 | No |
Elevation (m) . | Snow cover (%/10a) . | Snow depth (m/10a) . | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
Annual . | Spring . | Summer . | Autumn . | Winter . | Annual . | Spring . | Summer . | Autumn . | Winter . | |
2,000 − 2,500 | −0.044 | −9.3 × 10−3 | 0 | −2.4 × 10−3 | −0.209 | −7.17 × 10−5 | 0 | 0 | 0 | −2.09 × 10−4 |
2,500 − 3,000 | −0.804 | −0.103 | −2.22 × 10−4 | −0.107 | −1.027 | −2.7 × 10−4 | −9.2 × 10−5 | 0 | −1.33 × 10−4 | −1.04 × 10−3 |
3,000 − 3,500 | −0.441 | −0.799 | −0.130 | −0.135 | −0.3211 | −2.67 × 10−4 | −8.62 × 10−4 | −1.19 × 10−4 | −1.47 × 10−4 | −6.46 × 10−5 |
3,500 − 4,000 | −0.377 | −0.902 | −0.275 | 0.052 | 0.181 | −7 × 10−4 | −2 × 10−3 | −2.9 × 10−4 | −2.66 × 10−5 | −2.27 × 10−4 |
4,000 − 4,500 | −0.489 | −1.597 | −0.494 | 0.386 | 0.258 | −6.77 × 10−4 | −2.55 × 10−3 | −4.86 × 10−4 | 4.4 × 10−4 | 8.7 × 10−4 |
4,500 − 5,000 | −0.325 | −1.580 | −0.518 | 0.263 | 0.506 | −7.1 × 10−4 | −3.3 × 10−3 | −5.7 × 10−4 | −1.14 × 10−4 | 9.77 × 10−4 |
5,000 − 5,500 | −0.160 | −4.026 | −0.630 | −1.018 | 0.114 | −1.68 × 10−2 | −7.2 × 10−3 | −5.9 × 10−4 | −1.15 × 10−3 | −5 × 10−4 |
Elevation (m) . | Snow cover (%/10a) . | Snow depth (m/10a) . | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
Annual . | Spring . | Summer . | Autumn . | Winter . | Annual . | Spring . | Summer . | Autumn . | Winter . | |
2,000 − 2,500 | −0.044 | −9.3 × 10−3 | 0 | −2.4 × 10−3 | −0.209 | −7.17 × 10−5 | 0 | 0 | 0 | −2.09 × 10−4 |
2,500 − 3,000 | −0.804 | −0.103 | −2.22 × 10−4 | −0.107 | −1.027 | −2.7 × 10−4 | −9.2 × 10−5 | 0 | −1.33 × 10−4 | −1.04 × 10−3 |
3,000 − 3,500 | −0.441 | −0.799 | −0.130 | −0.135 | −0.3211 | −2.67 × 10−4 | −8.62 × 10−4 | −1.19 × 10−4 | −1.47 × 10−4 | −6.46 × 10−5 |
3,500 − 4,000 | −0.377 | −0.902 | −0.275 | 0.052 | 0.181 | −7 × 10−4 | −2 × 10−3 | −2.9 × 10−4 | −2.66 × 10−5 | −2.27 × 10−4 |
4,000 − 4,500 | −0.489 | −1.597 | −0.494 | 0.386 | 0.258 | −6.77 × 10−4 | −2.55 × 10−3 | −4.86 × 10−4 | 4.4 × 10−4 | 8.7 × 10−4 |
4,500 − 5,000 | −0.325 | −1.580 | −0.518 | 0.263 | 0.506 | −7.1 × 10−4 | −3.3 × 10−3 | −5.7 × 10−4 | −1.14 × 10−4 | 9.77 × 10−4 |
5,000 − 5,500 | −0.160 | −4.026 | −0.630 | −1.018 | 0.114 | −1.68 × 10−2 | −7.2 × 10−3 | −5.9 × 10−4 | −1.15 × 10−3 | −5 × 10−4 |
Relationship between snow cover/snow depth and temperature
Elevation (m) . | Snow cover . | Snow depth . | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
Annual . | Spring . | Summer . | Autumn . | Winter . | Annual . | Spring . | Summer . | Autumn . | Winter . | |
2,000 − 2,500 | −0.159 | −0.396* | 0 | −0.455** | −0.185 | −0.152 | −0.356* | 0 | −0.461** | −0.189 |
2,500 − 3,000 | −0.351* | −0.489** | −0.383* | −0.621** | −0.363* | −0.320* | −0.472** | −0.301 | −0.613** | −0.332* |
3,000 − 3,500 | −0.319* | −0.634** | −0.644** | −0.682** | −0.328* | −0.174 | −0.545** | −0.401** | −0.662** | −0.212 |
3,500 − 4,000 | −0.349* | −0.670** | −0.699** | −0.650** | −0.258 | −0.298 | −0.600** | −0.654** | −0.625** | −0.201 |
4,000 − 4,500 | −0.481** | −0.685** | −0.641** | −0.665** | −0.423** | −0.390* | −0.577** | −0.480** | −0.584** | −0.314* |
4,500 − 5,000 | −0.443** | −0.655** | −0.584** | −0.637** | −0.451** | −0.350* | −0.511** | −0.373* | −0.502 | −0.287 |
5,000 − 5,500 | −0.759** | −0.803** | −0.586** | −0.816** | −0.749** | −0.559** | −0.523** | −0.484** | −0.616** | −0.480** |
Overall | −0.340* | −0.648** | −0.653** | −0.644** | −0.271 | −0.237 | −0.551** | −0.493** | −0.580** | −0.173 |
Elevation (m) . | Snow cover . | Snow depth . | ||||||||
---|---|---|---|---|---|---|---|---|---|---|
Annual . | Spring . | Summer . | Autumn . | Winter . | Annual . | Spring . | Summer . | Autumn . | Winter . | |
2,000 − 2,500 | −0.159 | −0.396* | 0 | −0.455** | −0.185 | −0.152 | −0.356* | 0 | −0.461** | −0.189 |
2,500 − 3,000 | −0.351* | −0.489** | −0.383* | −0.621** | −0.363* | −0.320* | −0.472** | −0.301 | −0.613** | −0.332* |
3,000 − 3,500 | −0.319* | −0.634** | −0.644** | −0.682** | −0.328* | −0.174 | −0.545** | −0.401** | −0.662** | −0.212 |
3,500 − 4,000 | −0.349* | −0.670** | −0.699** | −0.650** | −0.258 | −0.298 | −0.600** | −0.654** | −0.625** | −0.201 |
4,000 − 4,500 | −0.481** | −0.685** | −0.641** | −0.665** | −0.423** | −0.390* | −0.577** | −0.480** | −0.584** | −0.314* |
4,500 − 5,000 | −0.443** | −0.655** | −0.584** | −0.637** | −0.451** | −0.350* | −0.511** | −0.373* | −0.502 | −0.287 |
5,000 − 5,500 | −0.759** | −0.803** | −0.586** | −0.816** | −0.749** | −0.559** | −0.523** | −0.484** | −0.616** | −0.480** |
Overall | −0.340* | −0.648** | −0.653** | −0.644** | −0.271 | −0.237 | −0.551** | −0.493** | −0.580** | −0.173 |
*and **represent the significance level at p < 0.05 and p < 0.01, respectively.
Previous studies have shown that snow cover was mainly negatively correlated with temperature and positively correlated with precipitation (Jiang et al. 2016). Therefore, the decrease (increase) of snow cover was mainly related to the decrease (increase) of precipitation or warming (cooling). This is the reason why snow cover and snow depth did not change significantly but the negative correlation between temperature and snow cover was obvious and visible.
Driving mechanism of EDW
Previous studies have found that snow-albedo feedback, cloud-radiation effects, the downwelling effect of water vapor on longwave radiation, and aerosols can lead to EDW (Pepin et al. 2015). Snow/ice-albedo feedback is regarded as the most important mechanism for explaining EDW (Pepin et al. 2015; Johnston et al. 2018; Guo et al. 2021; Shen et al. 2021). This study mainly focuses on the influence of snow cover on the EDW. In general, there was a negative correlation between temperature and snow cover (Table 5). Warming reduces the amount of surface ice and snow in high-altitude areas, leading to a decrease in surface albedo and an increase in solar radiation absorbed by the surface, further increasing temperatures (Pepin et al. 2015). The decrease (increase) of snow cover was mainly related to the warming (cooling), which is roughly consistent with the results from a previous study (Zhang et al. 2021). Climate warming reduces the amount of surface ice and snow in high-altitude areas above 5,000 m, which leads to a decrease in surface albedo and an increase in solar radiation absorbed by the surface, further increases temperatures and reduces surface ice and snow (Pepin et al. 2015). Meanwhile, the accelerated melting of snow may affect temperature warming (Gao et al. 2021). The snow cover in winter increased, which would have increased the surface albedo, reduced solar radiation absorbed by the surface, and decreased surface temperature in winter (Shen et al. 2021). Shen et al. (2021) found that snow depth tends to decrease faster at higher elevations (p < 0.05) than at lower elevations, and warming rates are faster at higher elevations than at lower elevations. In high-altitude areas, the negative effects of temperature on snow cover have become greater. The decrease of snow cover and snow depth at higher altitudes (especially above 5,000 m) may indicate that continuous snow cover and glacier melting are intensified due to higher temperatures. This is consistent with the study that reported that temperatures have considerably increased around 5,000 m (Zhang et al. 2021).
Implications of EDW to water resources
CONCLUSION
The annual mean temperature showed a significant warming trend with a rate of 0.31 °C/10a. At the same time, the warming rate of annual mean temperature increased with elevation in the QLM in general. The EDW is distinctly seasonal, with the most obvious warming in summer, and the least obvious warming in winter.
The melt of snow cover has accelerated under regional warming in the QLM. Changes in snow cover were found to be an important factor contributing to the variability of EDW. Climate warming reduces the amount of snow cover in high-altitude areas, which leads to a decrease in surface albedo and an increase in solar radiation absorbed by the surface, further increasing temperatures. This new evidence can partly explain the EDW variability in the QLM, although the mechanisms remain to be determined.
EDW has a significant implication for water resources over the QLM, especially above 5,000 m. Water from snow melt is an important factor in the change of water resources in the Qilian Mountains. However, the actual impacts of EDW on regional water availability still need to be discussed in the future.
ACKNOWLEDGEMENTS
This study was supported by the National Key Research and Development Program of China (No. 2019YFC0507403), the National Natural Science Foundation of China (No. 41621001), and the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDA23060301).
DATA AVAILABILITY STATEMENT
Data cannot be made publicly available; readers should contact the corresponding author for details.
CONFLICT OF INTEREST
The authors declare there is no conflict.