Ji-wei Wng,Jin-ting Hung,*,Tuo Fng,Ge Song,Fng-qing Sun

a Xi’an University of Science and Technology, Xi’an 710054, China

b Xi’an Center, China Geological Survey, Xi’an 710054, China

Keywords:Groundwater level variation Global climate change Inland basin Golmud River Catchment Qaidam Basin Northeastern Qinghai-Tibet Plateau

ABSTRACT To identify the response of groundwater level variation to global climate change in Northwest China’s inland basins,the Golmud River Catchment was chosen as a case in this paper.Approaches of time series analysis and correlation analysis were adopted to investigate the variation of groundwater level influenced by global climate change from 1977 to 2017.Results show that the temperature in the Golmud River Catchment rose 0.57°C every 10 years.It is highly positive correlated with global climate temperature,with a correlation coefficient,0.87.The frequency and intensity of extreme precipitation were both increased.Generally,groundwater levels increased from 1977 to 2017 in all phreatic and confined aquifers and the fluctuation became more violent.Most importantly,extreme precipitation led to the fact that groundwater level rises sharply,which induced city waterlogging.However,no direct evidence shows that normal precipitation triggered groundwater level rise,and the correlation coefficients between precipitation data from Golmud meteorological station located in the Gobi Desert and groundwater level data of five observation wells are 0.13,0.02,−0.11,0.04,and −0.03,respectively.This phenomenon could be explained as that the main recharge source of groundwater is river leakage in the alluvial-pluvial Gobi plain because of the high total head of river water and goodness hydraulic conductivity of the vadose zone.Data analysis shows that glacier melting aggravated because of local temperature increased.As a result,runoff caused groundwater levels to ascend from 1977 to 2017.Correlation coefficients of two groundwater wells observation data and runoff of Golmud River are 0.80 and 0.68.The research results will contribute to handling the negative effects of climate change on groundwater for Northwestern China.

1.Introduction

Blue Book on Climate Change in China (2021)shows that global temperature has risen 1.2°C since industrialization.From 1951 to 2020,the annual mean temperature rose at 0.26°C every 10 years in China,which is obviously higher than global levels over the same period (0.15°C every 10 years).Environmental and ecological impacts occurred due to global warming,such as sea-level rise,permafrost degradation,glacier melting,water shortage,etc.Global warming is one of the major environmental problems,which possesses a wide range,long duration,complex constraints,and serious consequences.

Northwestern China is one of the sensitive areas to global climate change as well as ecological frail areas.It is a vital water source and ecological barrier zone of China (Jiang TL et al.,2021; Ding WG et al.,2010).Influenced by global warming,northwest China trend to be warming and wetting,where temperature rising and precipitation increasing (Li M,2021; Dang XY et al.,2019).Global warming accelerates glacier melting,increases precipitation and groundwater storage in Qaidam Basin (Jiao JJ et al.,2015).Inland basins in Northwest China are located in the semiarid or arid regions,and groundwater is an important water source for local production and living,also an important factor for balancing the fragile ecological environment (Tan H et al.,2009).Identifying the response of groundwater to climate change is the premise to ensure the industrial and agricultural water and residential water supply in the northwestern inland basin,maintain social and economic development and ecological balance.

To clarify the effect of climate change on groundwater,many studies have been carried out (Zheng XY,2012; Zhang N,2017; Guevara-Ochoa C et al.,2020; Li M,2015).Zhou PP et al.(2020) found significant impacts of global climate change on groundwater dynamics.Chen Z et al.(2003)concluded that there is a strong correlation among precipitation,temperature,and groundwater level in the Manitoba area by correlation analysis.Bekele E and Knapp V(2010) found that climate change in Fox Catchment had a significant impact on groundwater recharge sources using the SWAT hydrological model.Timothy R et al.(2011) studied the influence of climate warming on groundwater exploitation and predicted the dynamic change trend of groundwater level in extreme drought years.In recent years,researchers began to pay attention to the impact of climate change on groundwater resources.Zheng XY (2012) predicted the rainfall trend by wavelet analysis and studied the variation trend of groundwater in Guanzhong Basin under extreme climate by grey correlation degree,comprehensive index weighting approach,and numerical simulation.Lian YL et al.(2011)found the influence of climate change on groundwater temperature in Zhangye Basin based on the theory of basin water circulation.Ma YM (2015) discussed the relationship between groundwater level and precipitation in the center of Jilin Province and found that the dynamic changes of shallow groundwater level and precipitation are consistent.

Precipitation and temperature are the main driving factors of groundwater level change,but the response of groundwater level change to climate is different in the specific region.As a sensitive area of climate change,there were few studies on the relationship between global climate change and groundwater level dynamics in the northwestern inland basins of China.Taking all this into account,the authors chose the Golmud River Catchment as the study area.Based on the groundwater dynamics and meteorological data for a long period,groundwater level and global climate change were analyzed.The investigation provides a reference for the ecological environment protection and economic construction of inland basins in Northwest China.

2.Background of Golmud River Catchment

2.1.Geography

Golmud River Catchment locates at the south edge of the Qaidam Basin,under the jurisdiction of Golmud City,Haixi Mongolian,and Tibetan Autonomous Prefecture,Qinghai Province.Its geographical coordinates are 94°25′ to 95°19′E,36°07′ to 37°07′N,and area of the river catchment covers 4533 km2(Fig.1).The Golmud River is the second largest river in the Qaidam Basin,sourcing from Kunlun Mountain in the south,flowing northward through the Golmud alluvial fan and injecting to the terminal Dabuxun Salt Lake in the center of the basin.

2.2.Characters of the aquifer

Aquifer structures and hydraulic characteristics of Golmud River Catchment can be divided into a piedmont alluvial fan with coarse clastic structure phreatic aquifer system,alluvial plain with fine clastic layered structure confined aquifer system,and lacustrine plain multilayer structure confined aquifer system from south to north (Fig.2).

The main aquifer of alluvial fan in the study area is the huge thickness of Quaternary deposits and the groundwater ascribes to single loose rock pore water.The medium changes from coarse to fine and the groundwater table vary from deep to shallow.In the south area of the river catchment (Fig.2),the medium of the aquifer is coarse consisting of cobble,boulder,and gravel.The thickness of the aquifer is larger than 200 m.From south to the north,the depth to groundwater table decreases.The depth to groundwater table is larger than 100 m on the south edge of the alluvial plain.It decreases as 30 m to 50 m in the middle then less than 10 m finally close to the groundwater surface,then springs and rivers formed.In the northern study area,the medium of the aquifer is mainly sand and fine sand.The thickness of the aquifer varies from 30 m to 70 m and the water table is less than 3 m.Confined aquifer exists in fine soil plain and lake marshes plain with multi-layers of aquifers and aquitards (clay layers) interlaced.

2.3.Recharge and discharge

Groundwater is mainly recharged by the leakage of the Golmud River.In addition,it also includes gully flood infiltration,runoff recharge,and irrigation infiltration.The main discharge items of groundwater is the spring,evapotranspiration,human exploitation,and lateral outflow.

3.Data and Methods

3.1.Data

Global meteorological data from 1961 to 2019 was downloaded from the global surface temperature data updated by NASA in 2021 (Supplementary Tables; GISTEMP v4,https://data.giss.nasa.gov/gistemp/).It shows that the deviation of the data from 1951 to 1980 is the global average surface temperature (14°C).Golmud meteorological station was selected according to the location,to analyze the variation of climate in the Golmud River Catchment.Considering that climate change mainly performs as global warming and extreme climate events such as extraordinary precipitation,temperature and precipitation were chosen to investigate.For the convenience of analysis,the precipitation and temperature data of the Golmud station from 1961 to 2019 were pre-processed as the annual average.River runoff data from 1977 to 2017 recorded at Golmud hydrologic station was selected to investigate in this paper.

Long time-series data from 1977 to 2017 of G39,G47,G4,G5,and G23 groundwater observation wells were collected to study the groundwater change in the river catchment.G39 and G47 are located in the middle and upper alluvial-pluvial Gobi plain in the Golmud River Catchment.G5 and G4 are located at the intersection of alluvial and alluvial Gobi plain and fine soil plain,close to the Golmud water source.G23 is located near the groundwater overflow zone of the fine soil plain,where confined water is observed and the head is often close to the ground.The dynamic data of groundwater are processed the annual average in this paper to analyze the influence of groundwater on the long-term and large-scale global climate.The detailed data can be obtained from the Supplementary Tables.

Fig.1.The location of the Golmud River Catchment in the Qaidam Basin of Northwest China.

Fig.2.Aquifer character in Golmud River Catchment in the Qaidam Basin of Northwest China (after Huang JT et al.,2020).1-mild clay;2-sandy loam; 3-silt; 4-fine sand; 5-medium sand; 6-coarse sand; 7-sand-gravel; 8-sand-gravel with clay; 9-gravel with cobble; 10-gravel with clay; 11-gravel; 12-stratum boundary; 13-groundwater level; 14-granite; 15-freshwater; 16-saltwater; 17-brine.

3.2.Methods

Time-series of the meteorological data,river runoff data and groundwater dynamic data of the Golmud River Catchment were adopted in this case,and the trend of each element was analyzed by linear fitting method.The fitting parameters were estimated by the least square method.

Correlation analysis is a statistical analysis method to study the correlation of two or more random variables,and the closeness of the two variables is expressed by the correlation coefficient.The correlation coefficient is between −1 and 1,and the absolute value is closer to 1,indicating that the correlation of the two variables is stronger.In this paper,the correlation analysis method is used to analyze the relationship of Golmud meteorology and global meteorology,and the relationship of groundwater and precipitation in the Golmud River Catchment.

4.Monitoring results

4.1.Climate change in the Golmud River Catchment

The global annual average temperature,annual average precipitation,and annual average temperature in the Golmud River Catchment are shown in Fig.3.In 2019,the global average temperature was 1.2°C higher than the pre-industrial level.From 1961 to 2019,the annual average temperature rise rate in the Golmud River Catchment was 0.57°C every 10 years,which was significantly higher than the global average.The correlation coefficient calculated of the temperature in the Golmud River Catchment and the global temperature was 0.87,indicating the strong correlation.

The frequency and intensity of extreme precipitation events in the Golmud River Catchment from 1961 to 2019 were also related to global warming.Some researchers point out that atmospheric circulation is a direct factor affecting the dry-wet transformation in Northwest China.Li BF et al.(2015) found that Siberian high and North American subtropical high are the main reasons for the significant increase in precipitation in Northwest China.Peng D and Zhou T (2017) found that the subtropical westerly jet in Asia moves southward,resulting in the anomaly of positive vorticity advection over Northwest China,triggering the ascending motion of cyclone,and thus increasing the precipitation.It is also found that the periodic precipitation and temperature changes in Northwest China are related to the cold-warm phase transition of the Pacific Decadal Oscillation(Ma PL et al.,2020).Therefore,Climate change in the Golmud River Catchment is synchronized with global climate change.Global climate change directly affects local temperature and precipitation.Furthermore,the groundwater level is affected.

4.2.Relationship of groundwater level and precipitation

The correlation coefficients of groundwater level data from G39,G47,G4,G5,G23 observing wells and annual precipitation in the Golmud Basin were 0.13,0.02,−0.11,0.04,and −0.03,respectively.There is no correlation between the annual variation of groundwater level and precipitation.

Although the precipitation is not directly related to the variation of groundwater level in a long time-series,the interannual variation of groundwater level and precipitation in the Golmud River Catchment (Fig.4) shows that there is a certain consistency of the variation of groundwater level and the variation characteristics of precipitation in a period.From 1981 to 1989,the precipitation was abundant,and the groundwater levels rose.In 1990,precipitation fell abruptly and groundwater levels experienced a period of decline.After 2005,affected by global climate change,extreme precipitation events increased and groundwater levels fluctuated greatly.

4.3.Relationship of groundwater level and river runoff

To investigate the response of groundwater level to river runoff,G39 and G47 groundwater observation data were selected because of the distance of wells to the river.The short distance between wells and rivers ensured the stronger contribution of river runoff to groundwater.

Fig.3.Climate change in Golmud River catchment from 1961 to 2019.a-climate change; b-correlation between global temperature and Golmud temperature.

As the main recharge of groundwater in the alluvialpluvial Gobi plain of Golmud River Catchment,the annual average runoff of Golmud River and the groundwater level of observing wells in G39 and G47 have a significant correlation(Fig.5),with a correlation coefficient of 0.80 and 0.68.And the correlation decreases from south to north,that is,the correlation is relatively high in the alluvial-diluvial Gobi plain and weak in the fine soil plain.

4.4.Variation of groundwater level in Golmud River Catchment

There were familiar trends of groundwater levels variation at five observation wells in the study area in different aquifer structures (Fig.6).In the past 30 years,the groundwater level in Golmud has been on the rise.Specifically,the groundwater level rose slowly from 1980 to 1985 and gradually decreased from 1990 to 1995.After 1997,the groundwater level has experienced a relatively smooth and slow rise period.From 2008 to 2015,there was an intensive variation of groundwater level,with the largest rise and fall range of 18 m in G39.In general,the groundwater level in the Golmud River Catchment trends to rise which is common among different aquifer characters.Groundwater level fluctuation increased.In addition,the closer to the plain area,the less variation of groundwater level.

The rise of groundwater in the Golmud River Catchment has a significant impact on the local ecological environment and economic construction.The elevation of groundwater level leads to the movement of the overflow zone from the plain area to the mountains and enlargement of the vegetation coverage area,which is beneficial to the protection of the ecological environment.In the Golmud City,however,groundwater level results in urban waterlogging and threatening urban construction and residents’ lives.In recent years,the rise of groundwater level has caused many submerged disasters and urban waterlogging in Golmud City.For example,in 1983,affected by the superposition of floods,the groundwater level rose rapidly,which caused road flooding,house collapse,and large-scale flooding of farmland and grassland in Golmud City.In 1989,a larger flood occurred in the Golmud River,and the river channel regulation engineering facilities of the Golmud River were washed down.The rise of groundwater level led to the immersion damage of more than 200 houses,and the industrial production of the salt lake was affected at the same time (Wang SB and Wang XS,2019).The groundwater level in Golmud City increased continuously and significantly in 2008 and 2010,the area of swamped wetland expanded continuously,plenty of groundwater released from the surface,and waterlogging flooded into disaster,resulting in damage and collapse of buildings,flooded farmland,and water inflow into shopping malls,inducing big economic losses.

Fig.4.Annual variation of groundwater level and precipitation in Golmud River Catchment.

Fig.5.Annual variation of groundwater level and the river runoff in Golmud River Catchment.

5.Discussion

Global temperature increasing and frequent extreme precipitation events are the main characteristics of global climate change,which directly or indirectly affect the recharge of groundwater and cause the variation of groundwater,which are manifested in groundwater level rise and the intensification of groundwater level fluctuation.

There is no direct correlation between the annual variation of groundwater level and precipitation at five observation wells.This can be explained as that the meteorology station located in the Gobi Desert area on the lower edge of the alluvial fan.As the result,normal precipitation can’t recharge groundwater directly because of the small amount.However,precipitation increase in mountain area induced to the Golmud River runoff increase.As the main recharge of groundwater in the alluvial-pluvial Gobi plain of the catchment,more leakage of the river,influenced by the increased runoff,triggered the rise of groundwater level.Furthermore,annual precipitation observed by the meteorology station located in mountains,Wudaoliang station,for example,is much more than that in alluvial fan and the plain area within the basin (Huang JT et al.,2021),while further research is needed on the effect of uneven distribution of precipitation on groundwater.

The Golmud River originated from the Kunlun Mountains,whose main tributaries,the Kunlun River and the Snow River,are formed by melting glaciers.Fluctuation of the glacier is a vital influencing factor to river runoff (Jia YL et al.,2016).Glaciers in the Kunlun Mountains with huge volumes account for about two-thirds of total glacier reserves in the Qaidam Basin.Global warming,snowline retreating,Glacier surface melting intensified,meltwater gaining,eventually,the runoff of Golmud River increased continuously,which enhance the groundwater level by leakage recharge.Shi YF (2001) forecast that glacier meltwater will maintain increasing till 2050 influenced by global warming.Therefore,the groundwater level in the Golmud River Catchment will rise caused by global warming.

As stated above,the impact of climate change on groundwater in the Golmud River Catchment is mainly achieved by affecting the recharge of groundwater.River runoff increases,and groundwater level rises.As the temperature rises,the glacier melts,and a large amount of glacier meltwater flows into the Golmud River,the river runoff increases,causing the groundwater level rise recharged by river leakag.Besides,Extreme precipitation events lead to sharp fluctuations of groundwater level,which will be more likely to cause city disasters such as urban waterlogging.

Northwest China has been in the transformation to warming-wetting because of global climate change.As a typical arid sedimentary basin in Qaidam Basin,climate change characteristics in the Golmud River Catchment have a consistent trend with that in the northwest zone,presenting temperature rise and frequent precipitation.The inland basins in Northwest China are similar in climate,geological structure,hydrogeology,ecological distribution,and water cycle transformation.The distribution and combination characteristics of groundwater function have similar macroscopic zone distribution characteristics (Nie ZL et al.,2012; Xiao Y et al.,2018).The northwestern inland basin area belt can be divided into Gobi Desert belt formed by a piedmont alluvial-proluvial fan,oasis belt of fine soil plain,and downstream tail lake or desert belt.Golmud River Catchment is a typical region to study the response of groundwater dynamics to climate change in arid areas of Northwest China,which has a complete internal flow system from the mountainous area to the terminal lake.To a certain extent,the response of groundwater level in Golmud River Catchment to global climate change can reflect the variation of groundwater level in inland basins of Northwest China forced by global climate.With the background of global climate change and warming-wetting in Northwest China,the groundwater level of inland basins in Northwest China gradually rises and fluctuates more violently.

6.Conclusions

Taking the Golmud River Catchment as an example,this paper analyzed the groundwater level variation in inland basins of Northwest China driven by global climate.The following conclusions can be drawn from this study.

Fig.6.Annual variation of groundwater level in Golmud River Catchment.

(i) Climate in the Golmud River Catchment is warming and wetting.From 1961 to 2019,the temperature in the Golmud basin rose 0.57°C every 10 years,which is highly correlated with global climate,with a correlation coefficient of 0.87.Meanwhile,the frequency and intensity of extreme precipitation events are both increasing.

(ii) From 1977 to 2017,groundwater levels increased in all phreatic and confined aquifers.Meanwhile,the fluctuation became more violent.

(iii) Increased extreme precipitation and flood events led to the fact that groundwater level rises sharply,which induced city waterlogging.Confirmed by correlation analysis,there is no obvious correlation of groundwater level variation and precipitation multiplication from 1977 to 2017,correlation coefficients are 0.13,0.02,−0.11,0.04,and −0.03 in five observation wells,respectively.However,the aggravation of groundwater level fluctuation is related to the increase of extreme precipitation events.

(iv) Groundwater level rise in the Golmud River Catchment can be ascribed to Golmud River runoff.Glacier melting caused by global warming increases runoff of the Golmud River,groundwater level has been risen by recharge of leakage from Golmud River.Correlation coefficients of groundwater level change and runoff of Golmud River are 0.80 and 0.68 in two observation wells close to the river bank,respectively.

CRediT authorship contribution statement

Jin-ting Huang conceived of the presented idea.Jia-wei Wang and Tuo Fang verified the analytical methods.Jin-ting Huang encouraged Jia-wei Wang and Tuo Fang to investigate groundwater levels and supervised the findings of this work.All authors discussed the results and contributed to the final manuscript.

Declaration of competing interest

The authors declare no conflicts of interest.

Acknowledgment

This research was supported by the National Natural Science Foundation of China (41672250,42177076),the Key R & D Projects of Shaanxi Province (2021ZDLSF05-09),and the Natural Science Foundation of Shaanxi Province(2019JLZ-03).

Supplementary data

Supplementary dataset (Table S1,Table S2 and Table S3)to this article can be found online at doi: 10.31035/cg2021064.