Inuence of Climate Change and Anthropogenic Activities on Groundwater Level in the Northern Huangqihai Basin, China Jing Jin ( [email protected] ) Institute of Water Resources for Pastoral Area,MWR https://orcid.org/0000-0001-6166-1804 Zihe Wang Institute of Water Resources for Pastroal Area,MWR Yiping Zhao Institute of Water Resources for Pastoral Area,MWR Huijun Ding Geological Environment Monitoring Insititute of Inner Mongolia Yufei Chen Housing and Urban Rual Development Bureau of Saihan District,Hohht Research Article Keywords: Variation in groundwater level, Quantitative assessment, Climate change, Anthropogenic activities, Northern Huangqihai basin. Posted Date: August 4th, 2021 DOI: https://doi.org/10.21203/rs.3.rs-523965/v1 License: This work is licensed under a Creative Commons Attribution 4.0 International License. Read Full License 1 Influence of climate change and anthropogenic activities on groundwater 2 level in the northern Huangqihai basin, China 3 4 Jing Jin1,2*, Zihe Wang2, Yiping Zhao2, Huijun Ding3, Chen Yufei4 5 1 Yinshanbeilu National Field Research Station of Desert Steppe Eco-hydrological System, 6 China Institute of Water Resources and Hydropower Research, Beijing 100038, China 7 2 Institute of Water Resources for Pastoral Area, MWR, Hohhot 010020, China; 8 3 Geological Environment Monitoring Institute of Inner Mongolia, Hohhot 010020, China 9 4 Housing and Urban-Rural Development Bureau of Saihan District, Hohhot 010020, China 10 *Corresponding author: [email protected] (Jing Jin) 11 Abstract: The variation in the groundwater level, which is an indicative factor that can reflect 12 changes in both groundwater level and groundwater quantity, was selected as the factor to be analyzed. 13 Rainfall and groundwater exploitation were chosen as the representative factors of climate change and 14 anthropogenic activities, respectively. By applying the elastic coefficient method and other 15 mathematical statistical methods, the influence of climate change and anthropogenic activities on 16 groundwater was analyzed qualitatively and quantitatively. The northern Huangqihai basin was chosen 17 as the study area. The rainfall in the study area showed an increasing trend from 1996-2020, while most 18 variations in groundwater level were negative. This result indicated that the positive influence of 19 rainfall on the variation in the groundwater level in the study area was not enough to offset the negative 20 influence of groundwater exploitation. The correlation between anthropogenic activities and variations 21 in the groundwater level was lower in wet years than in normal years but the highest in dry years. 22 Based on the comparative method of the slope changing ratio of cumulative quantity and the elastic 23 coefficient method, it was determined that the contribution rate of climate change to the variation in 24 groundwater level was 22.08% and that of human activities was 77.92%. Thus, the sustainable 25 development of the groundwater environment can be realized by positively guiding anthropogenic 26 activities and minimizing negative influences. 27 Keywords: Variation in groundwater level; Quantitative assessment; Climate change; 28 Anthropogenic activities; Northern Huangqihai basin. 29 1 30 Introduction 31 Groundwater is an important resource for human survival and development, especially in the arid 32 and semiarid areas of Northwest China, where water resources are scarce and the ecological 33 environment is sensitive and fragile (Wang et al. 2020; Wu et al. 2019, 2020; Ren et al. 2021; Wei et 34 al. 2021). In the past 100 years, the increase in temperature and rainfall variability, as well as changes 35 in natural environment, has changed the quantity, quality and spatiotemporal distribution of 36 groundwater resources (Li et al., 2019; Cui et al, 2020). Simultaneously, the interference of 37 anthropogenic activities on groundwater has increased (Acharyya and Achiransu 2014; Yihdego et al., 38 2017b; Li et al., 2018b; He and Wu 2019a; He and Li 2020; Khan et al., 2020), which has changed 39 the evolution of the groundwater environment from a single naturally driven model to a dual 40 naturally-artificially driven mode (Wang et al., 2006). Quantitative research on the influence of climate 41 change and anthropogenic activities on groundwater is a hot but challenging topic in the field of 42 hydrology and water resources (Wang et al., 2011; Li 2014; Li et al., 2018b), and is of great 43 significance for protecting groundwater resources and promoting the sustainable development of the 44 groundwater environment. 45 Previous studies on the influence of climate change and anthropogenic activities on the 46 groundwater level have mainly focused on qualitative analyses (Liao et al., 2014; Shi et al., 2014; Jin et 47 al., 2020), while the quantitative analyses in this field have been based on mathematical statistics 48 methods and simulation model (Su et al. 2020). Some researchers (Hotta et al., 2010; Kearns et al., 49 2015; Wilopo et al., 2021) have analyzed the influence of urbanization and groundwater exploitation on 50 groundwater level by using mathematical statistical methods, such as correlation analysis and wavelet 51 coherence analysis. Malaka et al. (2021) considered groundwater exploitation as the dominant factor in 52 groundwater level change based on mathematical statistical methods. By applying multivariate linear 53 regression analysis, Yihdego et al. (2017a) concluded that the rise in the groundwater level in coastal 54 areas of New South Wales was caused by a long-term cumulative land-use change. Wei et al. (2016) 55 used the bidirectional regression mutation analysis method to analyze the response relationship 56 between a decrease in the groundwater level and the irrigation area in the Jiansanjiang region of 57 Heilongjiang Province. The Mann-Kendall ( M-K) test is commonly utilized to evaluate the influence 58 of climate change and anthropogenic activities on changes in groundwater depth (Zhu et al., 2017; Cui 59 et al., 2020). Gemitzi and Stefanopoulos (2011) applied the autoregressive integrated moving average 2 60 (ARIMA) model based on abundant basic data to analyze the influence of irrigation and rainfall on the 61 groundwater level. He and Wu (2019b) and He et al. (2020) investigated the relationship between land 62 use/land cover and groundwater quality, and concluded that the change in land use/land cover was an 63 indicator representing integrated human activities and that its impact on groundwater can be quantified 64 using the curved streamline searchlight shaped model. Fei et al. (2009) considered that groundwater 65 exploitation played an important role in the decrease in groundwater level through correlation analysis. 66 From the perspective of hydrogeology, the variation in groundwater level is an intuitive indicator 67 of not only the change in groundwater level but also the change in groundwater storage, as shown in Eq. 68 (1) (China Geological Survey 2018). 69 (1) 푊̅ ∆푄 =3 휇 × 퐹 × ∆푡 70 where Q is the variation in groundwater storage (m ), μ is the specific yield of phreatic water, F is the 71 area of△ the phreatic aquifer (m2), is the average variation in groundwater level (m), and t is time 72 (a). 푊̅ △ 73 Therefore, the variation in groundwater level, which can directly reflect the changes in 74 groundwater level and groundwater storage, was selected as the analysis factor of groundwater in this 75 study. Rainfall, which is important to groundwater recharge, was selected as the factor of climate 76 change that influences groundwater, and groundwater exploitation was chosen as the factor of 77 anthropogenic activities that directly influences groundwater. First, the characteristics of annual rainfall, 78 groundwater exploitation and the variation in groundwater level from 1996-2020 were qualitatively 79 analyzed. Second, the influences of climate change and anthropogenic activities on groundwater were 80 quantitatively analyzed by using the comparative method of the slope changing ratio and the elastic 81 coefficient method. This study is very meaningful for the protection and management of groundwater. 82 Materials and Methods 83 Study area 84 The northern Huangqihai basin (113°2′-113°28′ E, 40°43′-41°3′ N), in Right Chahaer County and 85 the Jinning District of Wulanchabu city in Inner Mongolia, China, is located in the middle of the 86 northern farming-pastoral ecotone and covers nearly 521 km2 in area (Fig. 1). The study area is an 87 important ecological barrier in the northern Beijing-Tianjin-Hebei region, where water resources are 88 rare and the ecological environment is sensitive and fragile. The development of the regional social 3 89 economy is highly dependent on groundwater and mainly exploits a shallow aquifer, which is the 90 Quaternary aquifer that consists of sand and gravel of varying sizes. The basin is surrounded by 91 mountains on three sides, and the terrain around Huangqihai Lake is relatively low. Thus, groundwater 92 generally flows from the surrounding area to Huangqihai Lake. There is a thick clay layer under the 93 Quaternary aquifer, which results in a weak hydraulic relationship between the Quaternary aquifer and 94 the deeper aquifer. 95 96 The recharge sources of groundwater are rainfall infiltration and groundwater lateral inflow, and 97 rainfall infiltration accounts for approximately 60% of the total recharge. The discharge sources are 98 exploitation, evaporation and discharge into the lake, and groundwater exploitation