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Xi Chen
Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China

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Journal article
Published: 15 August 2021 in Water
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The amount of water taken from groundwater for agricultural irrigation is often not observed, while hydrological models have been extensively proposed to investigate the irrigation dynamics and impacts in agricultural areas. In this work, we propose an agro-hydrological model that integrates agricultural irrigation with the traditional Xin’anjiang (XAJ) hydrological model. In particular, the proposed model incorporates the FAO guidelines on crop evapotranspiration into hydrological routing of water balance and flow fluxes in unsaturated and saturated zones. The model was used to calibrate the groundwater irrigation amounts in terms of both the observed river discharge and the groundwater depth in the Xuanwu plain area of the Huaihe River Basin in China. The calibration and sensitivity analyses were performed by the shuffled complex evolution (SCE-UA) method. This method can be applied to a single-objective optimization of model parameters, based on either the river discharge or the groundwater depth, or to a multi-objective optimization of model parameters based on both of these objectives. The results show that the multi-objective calibration is more efficient than the single-objective method for capturing dynamics of the river discharge and the groundwater depth. The estimated means of the annual groundwater withdrawal for wheat and maize irrigations were found to be about 140.5 mm and 13.7 mm, respectively. The correlation between the groundwater withdrawal and the change in groundwater depth during crop growing seasons demonstrated that the groundwater withdrawal is the dominant factor for the groundwater depth change in the river basin, particularly in the winter wheat season. Moreover, model simulations show that the combined effects of the reduced precipitation and the increased groundwater withdrawal would lead to a decrease of the average annual runoff and an increase of the average groundwater depth. These estimates can greatly help in understanding the irregular changes in the groundwater withdrawal and offer a quantitative basis for studying future groundwater demands in this area.

ACS Style

Yimeng Sun; Xi Chen; Xi Chen; Liu Yang. Modeling Groundwater-Fed Irrigation and Its Impact on Streamflow and Groundwater Depth in an Agricultural Area of Huaihe River Basin, China. Water 2021, 13, 2220 .

AMA Style

Yimeng Sun, Xi Chen, Xi Chen, Liu Yang. Modeling Groundwater-Fed Irrigation and Its Impact on Streamflow and Groundwater Depth in an Agricultural Area of Huaihe River Basin, China. Water. 2021; 13 (16):2220.

Chicago/Turabian Style

Yimeng Sun; Xi Chen; Xi Chen; Liu Yang. 2021. "Modeling Groundwater-Fed Irrigation and Its Impact on Streamflow and Groundwater Depth in an Agricultural Area of Huaihe River Basin, China." Water 13, no. 16: 2220.

Journal article
Published: 30 July 2021 in Science of The Total Environment
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Preserving groundwater-dependent terrestrial ecosystems through environmental water allocation is critical for sustainable development in arid inland basins. Assessing the environmental water requirement is challenging due to the complex relationship between vegetation growth and groundwater depth. This study proposed a new assessment method by combining the copula joint distribution function and the dual objective optimization. The copula joint distribution function was used to describe the relationship between vegetation and groundwater depth instead of the traditional regression analysis. Given an ecological protection target, the conditional probability of achieving the target was estimated using the copula joint distribution. The groundwater depth interval with relatively high probability was suitable for vegetation growth and correspondingly conducive for ecological protection. In addition to ecological protection, the socio-economic water requirement was incorporated into the environmental water assessment, resulting in a dual optimization problem that could be resolved by the ideal point method. The optimization analysis revealed a groundwater depth with a high probability of successful ecological protection and low groundwater evapotranspiration to balance vegetation and human demands for groundwater. The proposed method of environmental water assessment by combing copula joint distribution function and dual objective optimization was applied in the Turpan Basin, an arid inland basin in Northwest China. The environmental groundwater depth ranged between 6 and 20 m, and the optimized interval was 7–8 m. The optimal environmental groundwater depth resulted in a probability of 0.46 to achieve the ecological protection target and annual evapotranspiration of 983 mm. The proposed method was practical and reliable and could be an effective tool for assessing the environmental water requirement of groundwater-dependent vegetation in arid inland basins.

ACS Style

Feng Huang; Carlos G. Ochoa; Xi Chen. Assessing environmental water requirement for groundwater-dependent vegetation in arid inland basins by combining the copula joint distribution function and the dual objective optimization: An application to the Turpan Basin, China. Science of The Total Environment 2021, 799, 149323 .

AMA Style

Feng Huang, Carlos G. Ochoa, Xi Chen. Assessing environmental water requirement for groundwater-dependent vegetation in arid inland basins by combining the copula joint distribution function and the dual objective optimization: An application to the Turpan Basin, China. Science of The Total Environment. 2021; 799 ():149323.

Chicago/Turabian Style

Feng Huang; Carlos G. Ochoa; Xi Chen. 2021. "Assessing environmental water requirement for groundwater-dependent vegetation in arid inland basins by combining the copula joint distribution function and the dual objective optimization: An application to the Turpan Basin, China." Science of The Total Environment 799, no. : 149323.

Journal article
Published: 16 April 2021 in Journal of Geophysical Research: Atmospheres
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Knowledge of the interplays between soil moisture (SM) and precipitation (P) across different temporal scales is crucial to understand the land‐atmosphere interactions. To examine the factors influencing SM‐P coherences, observed long‐term SM and P datasets were obtained from two regional networks (i.e., the Nebraska Mesonet and part of the Soil Climate Analysis Network in Utah) within the continental United States. We evaluated the intricate SM‐P interactions by checking high‐ and low‐frequency components using wavelet analysis. The analysis revealed that the global coherence coefficients (GCCs) between SM and P at all frequencies tended to be greater under wetter climatic conditions, suggesting that higher P could promote the SM‐P interactions. Moreover, GCCs were more correlated with meteorological factors in Nebraska with wetter climates (e.g., positively with mean annual P and negatively with aridity index at high‐frequency periodicities (daily to 3 monthlies), and opposite interactions at low‐frequency periodicities (3 monthlies to yearly)); whereas, significant correlations emerged between GCCs and soil texture at all frequency periodicities in Utah (e.g., positively with sand fraction while negatively with silt and clay fractions). Part of the reason for the impact of soil texture in Utah was that as the P periodicities weakened with increasing climatic dryness in Utah, soil texture played a more important role in controlling infiltration processes, which directly affected SM‐P coherences. Overall, this study demonstrates that SM‐P interactions at regional scales were possibly affected by the relative importance of meteorological and local land surface conditions in controlling SM dynamics.

ACS Style

Dongdong Wu; Chongli Di; Tiejun Wang; Lichun Wang; Xi Chen. Characterization of the Coherence Between Soil Moisture and Precipitation at Regional Scales. Journal of Geophysical Research: Atmospheres 2021, 126, 1 .

AMA Style

Dongdong Wu, Chongli Di, Tiejun Wang, Lichun Wang, Xi Chen. Characterization of the Coherence Between Soil Moisture and Precipitation at Regional Scales. Journal of Geophysical Research: Atmospheres. 2021; 126 (8):1.

Chicago/Turabian Style

Dongdong Wu; Chongli Di; Tiejun Wang; Lichun Wang; Xi Chen. 2021. "Characterization of the Coherence Between Soil Moisture and Precipitation at Regional Scales." Journal of Geophysical Research: Atmospheres 126, no. 8: 1.

Original paper
Published: 31 March 2021 in Theoretical and Applied Climatology
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Water use efficiency (WUE) is an important link between carbon and water cycles, which is critical for the forests under future global climatic changes. WUENDVI was calculated by accumulated normalized difference vegetation index (NDVI) and actual evapotranspiration (ET) and could reflect the impacts of climatic changes and human activities on WUE. The three forestry regions of China are the northeast, southwest, and southeast areas. Among them, the northeast forest region is a natural forest region with forest stock accounting for more than 1/4 of China, and the southwest mountainous forest region is another natural forest region in China, with forest stock accounting for more than 1/3 of China, while the southeast forest area is mainly plantations. In 2018, the forest areas over three forestry regions of China were around 1,725,988 km2. This paper evaluated the changes in forest WUE and their relationships with climatic change and human activities over three forestry regions of China during 1961–2019. The main findings of this study were summarized as follows: (1) the spatial changes of WUE were gentle in the artificial forest region but fluctuant sharply in the natural forest regions. In the southwest forest region, the WUE increased with elevation, while it showed the opposite trends in the artificial forest region. Overall, the annual mean forest WUE increased in almost all regions of the study areas during 1961-2019; (2) in the northeast and southeast forest regions, the WUE presented a negative relationship with the temperature. In the southwest forest region, the WUE was positively correlated with the temperature and its increase rate slowed down significantly when the temperature increases by more than 1 °C. The WUE was negatively correlated with precipitation in the three regions and was more sensitive to the decrease of precipitation. The sensitivity of WUE to precipitation reduction was highest in the artificial forest region and lowest in the northeast forest region; (3) the forest WUE and WUENDVI were lowest in the artificial forest region but highest in the northeast forest region, while the net increase in forests area during 1980–2018 was largest in the artificial forest region (155,975 km2) but lowest in the northeast forest region (78,766 km2). In general, human activities had the greatest impact on the forest WUE in the northeast forest region. Human activities and climatic change had quite complex and interactive effects on forest WUE. Therefore, more attention should be paid to the joint influences of climate change and human activities on WUE.

ACS Style

Jiaxi Tian; Zengxin Zhang; Rui Kong; Bin Zhu; Fengying Zhang; Shanshan Jiang; Xi Chen. Changes in water use efficiency and their relations to climate change and human activities in three forestry regions of China. Theoretical and Applied Climatology 2021, 144, 1297 -1310.

AMA Style

Jiaxi Tian, Zengxin Zhang, Rui Kong, Bin Zhu, Fengying Zhang, Shanshan Jiang, Xi Chen. Changes in water use efficiency and their relations to climate change and human activities in three forestry regions of China. Theoretical and Applied Climatology. 2021; 144 (3-4):1297-1310.

Chicago/Turabian Style

Jiaxi Tian; Zengxin Zhang; Rui Kong; Bin Zhu; Fengying Zhang; Shanshan Jiang; Xi Chen. 2021. "Changes in water use efficiency and their relations to climate change and human activities in three forestry regions of China." Theoretical and Applied Climatology 144, no. 3-4: 1297-1310.

Journal article
Published: 17 November 2020 in Journal of Hydrology
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To achieve sustainable development, ecological water diversion has been implemented as a management tool to recover degraded oasis ecosystems in arid endorheic basins. Aiming to explore oasis response and identify appropriate objectives for oasis restoration, this study used a conceptual lumped ecohydrological model. Qingtu Oasis in the Shiyang River basin, Northwest China, was used as a case study to test this model. The model coupled groundwater budget, oasis response, and evapotranspiration dynamic modules. The model structure was clear and reasonable, and the calculation was of low cost. The application in Qingtu Oasis verified the model's effectiveness. The model was able to effectively capture the ecohydrological response attributed to the recovering of Qingtu Oasis in response to ecological water diversions occurring during the last decade. Combined with scenario analysis, the simulation indicated that Qingtu Oasis was fragile and largely dependent on ecological water diversion. Ecological responses were positive and non-linearly correlated with water input, resulting in an optimal water input that produced maximum water benefit by minimum water consumption. The ideal point method was useful in identifying this cost-effective water volume for oasis restoration. For Qingtu Oasis, the optimal water diversion was 45 million m3, which would recover the oasis to 29.16 km2 with an NDVI of 0.41. The current oasis conditions approach the optimal status, and ecological water diversion was suggested to continue and maintain the current oasis status. The volume of 45 million m3 could be taken as an upper threshold of water diversion, because above this threshold, water consumption would not result in water benefits effectively. This study proposed a practical tool for ecohydrological process simulation.

ACS Style

Feng Huang; Carlos G. Ochoa; Xi Chen; Danrong Zhang. Modeling oasis dynamics driven by ecological water diversion and implications for oasis restoration in arid endorheic basins. Journal of Hydrology 2020, 593, 125774 .

AMA Style

Feng Huang, Carlos G. Ochoa, Xi Chen, Danrong Zhang. Modeling oasis dynamics driven by ecological water diversion and implications for oasis restoration in arid endorheic basins. Journal of Hydrology. 2020; 593 ():125774.

Chicago/Turabian Style

Feng Huang; Carlos G. Ochoa; Xi Chen; Danrong Zhang. 2020. "Modeling oasis dynamics driven by ecological water diversion and implications for oasis restoration in arid endorheic basins." Journal of Hydrology 593, no. : 125774.

Journal article
Published: 12 November 2020 in Science of The Total Environment
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The extension-induced rift systems on the Tibetan Plateau (TP) may convey large amount of groundwater to rivers, but sources and flow paths of such groundwater are unknown. The Yarlungzangbo River (YR) is the only large river that traverses the southern Tibetan plateau from west to east, following one major suture zone that is cut by extensional normal faults. The faults could influence the flow paths of groundwater discharging to the river. In this study, O and H isotopes, major ions and 222Rn concentrations are analyzed along the YR, and interpreted in relation to structural geology and tectonics. The YR exhibits an abrupt change of isotopic and chemical compositions along with a large increase in flow where the middle reach intersects NE-SW-trending rifts. Low values of δD and δ18O and high concentrations of major ions and 222Rn in the middle reach show that waters are modified isotopically and chemically by a variety of possible water origins, such as recharge of high-altitude glacier melt and discharge from groundwater. Groundwater contributes 27 to 40% of the river flow in the middle reach. Isotopically-light meltwater from high-altitude glacier melt cannot account for the isotope composition of the present outflow of groundwater. The O and H isotope data in the YR and discharging groundwater can be well explained by the groundwater originated as paleo-precipitation during a cooler time, such as the late Pleistocene to early Holocene. The paleo-groundwater discharge can account for about 36 × 108 m3 water budget unbalance in the middle reach. The study provides the first clear isotope evidence for the source of groundwater discharge into a large river through favorable conduits in large-scale active tensile fault zones and confirms the regional scale of groundwater flow on the Tibetan Plateau. Understanding the characteristics and changes of streamflow and surface-groundwater circulation on the Tibetan Plateau will help to manage water resources under a changing environment.

ACS Style

Hongbing Tan; Xi Chen; Dongping Shi; Wenbo Rao; Jing Liu; Jintao Liu; Christopher J. Eastoe; Jiarong Wang. Base flow in the Yarlungzangbo River, Tibet, maintained by the isotopically-depleted precipitation and groundwater discharge. Science of The Total Environment 2020, 759, 143510 .

AMA Style

Hongbing Tan, Xi Chen, Dongping Shi, Wenbo Rao, Jing Liu, Jintao Liu, Christopher J. Eastoe, Jiarong Wang. Base flow in the Yarlungzangbo River, Tibet, maintained by the isotopically-depleted precipitation and groundwater discharge. Science of The Total Environment. 2020; 759 ():143510.

Chicago/Turabian Style

Hongbing Tan; Xi Chen; Dongping Shi; Wenbo Rao; Jing Liu; Jintao Liu; Christopher J. Eastoe; Jiarong Wang. 2020. "Base flow in the Yarlungzangbo River, Tibet, maintained by the isotopically-depleted precipitation and groundwater discharge." Science of The Total Environment 759, no. : 143510.

Original paper
Published: 27 August 2020 in Stochastic Environmental Research and Risk Assessment
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The probability distributions of hydrological series are primarily determined according to the best fitting of empirical probability from observation data. The fitted distribution functions are variable in different watersheds, and thus difficult to be applied to estimate probability of any discharge occurrence at other stations. In this study, chaotic characteristics of annual discharge series are analyzed by using correlation dimension analysis at 12 hydrological stations in the six main rivers in China. It is found that the correlation integral of annual discharge series represents the probability distribution of difference between any two annual discharges. The derived probability function can be perfectly fitted by the Pearson III function. Although the six basins have distinctively different climate conditions from the northern cold temperature zone to the southern subtropical zone, the correlation dimension of chaotic characteristics for annual discharges are similar at the 12 hydrological stations. The mean of difference between any two annual discharges, the maximum and minimum of annual discharge are found to be high correlation with the mean of annual discharge. Moreover, the derived probability distributions at 12 hydrological stations can be normalized by a universal distribution function, and the derived probability is high correlation with the probability distribution of annual discharge. This universal probability distribution can be easily applied to obtain probability distributions of annual discharge series over any stations.

ACS Style

Guangsheng Wang; Xi Chen; Chengpeng Lu; Junchao Shi; Jinfeng Zhu. A generalized probability distribution of annual discharge derived from correlation dimension analysis in six main basins of China. Stochastic Environmental Research and Risk Assessment 2020, 34, 2071 -2082.

AMA Style

Guangsheng Wang, Xi Chen, Chengpeng Lu, Junchao Shi, Jinfeng Zhu. A generalized probability distribution of annual discharge derived from correlation dimension analysis in six main basins of China. Stochastic Environmental Research and Risk Assessment. 2020; 34 (12):2071-2082.

Chicago/Turabian Style

Guangsheng Wang; Xi Chen; Chengpeng Lu; Junchao Shi; Jinfeng Zhu. 2020. "A generalized probability distribution of annual discharge derived from correlation dimension analysis in six main basins of China." Stochastic Environmental Research and Risk Assessment 34, no. 12: 2071-2082.

Research article
Published: 02 May 2020 in Hydrological Processes
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In cockpit karst landscapes, fluxes from upland areas contribute large volumes of water to low‐lying depressions and stream flow. Hydrograph hysteresis and similarity between monitoring sites is important for understanding the space‐time variability of hydrologic responses across the “hillslope‐depression‐stream” continuum. In this study, the hysteretic feature of hydrographs was assessed by characterising the loop‐like relationships between responses at upstream sites relative to subsurface discharge at the outlet of a small karst catchment. A classification of hydrograph responses based on the Multi‐Scale Smoothing Kernel (MUSS)‐derived distance classifies the hydrograph responses on the basis of similarities between hillslope and depression sites, and those at the catchment outlet. Results demonstrate that the temporal and spatial variability of hydrograph hysteresis and similarity between hillslope flow and outlet stream flow can be explained by the local heterogeneity of depression aquifer. Large depression storage deficits emerging in the highly heterogeneous aquifer produce strong hysteresis and multiple relationships of upstream hydrographs relative to the outlet subsurface discharge. In contrast, when depression storage deficits are filled during consecutive rainfall events, depression hydrographs at the high permeability sites are almost synchronous or exhibit a monotonous function with the hydrographs at the outlet. This reduced hydrograph hysteresis enhances preferential flow paths in fractured rocks and conduits that can accelerate the hillslope flow to the outlet. Therefore, classification of hydrograph similarities between any upstream sites and the catchment outlet can help to identify the dominant hydrological functions in the heterogeneous karst catchment. This article is protected by copyright. All rights reserved.

ACS Style

Runrun Zhang; Xi Chen; Zhicai Zhang; Chris Soulsby. Using hysteretic behaviour and hydrograph classification to identify hydrological function across the “hillslope–depression–stream” continuum in a karst catchment. Hydrological Processes 2020, 34, 3464 -3480.

AMA Style

Runrun Zhang, Xi Chen, Zhicai Zhang, Chris Soulsby. Using hysteretic behaviour and hydrograph classification to identify hydrological function across the “hillslope–depression–stream” continuum in a karst catchment. Hydrological Processes. 2020; 34 (16):3464-3480.

Chicago/Turabian Style

Runrun Zhang; Xi Chen; Zhicai Zhang; Chris Soulsby. 2020. "Using hysteretic behaviour and hydrograph classification to identify hydrological function across the “hillslope–depression–stream” continuum in a karst catchment." Hydrological Processes 34, no. 16: 3464-3480.

Journal article
Published: 01 May 2020 in Ecological Engineering
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An improved understanding of the response of oasis ecosystems to ecological water diversion is essential for sustainably managing water resources in arid inland river basins. This entropy-based investigation provides new insight into the ecohydrological impacts of ecological water diversions through a case study of Qingtu oasis in the lower Shiyang River basin in Northwest China. Since 2010, an ecological water diversion project was put in place by Water Resources Bureau of Shiyang River Basin to restore the degraded Qingtu oasis. Annual cumulative water releases from this water diversion project had reached 0.25 billion m3 in 2018. This contributed to an increase in shallow groundwater level of 1.2 m. A combination of land cover classification indices and an entropy approach were used to assess the ecohydrological response to water diversion inputs. Land cover was classified as sparsely, lowly, moderately, and highly vegetated areas using Normalized Difference Vegetation Index (NDVI) calculated from Landsat images and the Excess Green minus Excess Red Index that was estimated from unmanned aerial vehicle images. Land cover complexity was evaluated using component complexity and spatial complexity. The component complexity corresponds to land cover composition and was assessed using the Shannon's entropy. The spatial complexity corresponds to spatial configuration of different land cover compositions and was analyzed using spatial entropy methodology. The rise in groundwater level caused by ecological water diversion drove the land cover transition and enhanced the component complexity. Field survey data showed that tendency and randomness co-existed in the spatial pattern of groundwater depth and its relationship with NDVI, which jointly affected spatial complexity (i.e., dependence and independence in spatial co-occurrences of different land cover categories). Results from this study improve understanding of the impacts that ecological water diversions can have on land cover evolution in natural oasis in arid inland river basins.

ACS Style

Feng Huang; Carlos G. Ochoa; Xi Chen; Qinbo Cheng; Danrong Zhang. An entropy-based investigation into the impact of ecological water diversion on land cover complexity of restored oasis in arid inland river basins. Ecological Engineering 2020, 151, 105865 .

AMA Style

Feng Huang, Carlos G. Ochoa, Xi Chen, Qinbo Cheng, Danrong Zhang. An entropy-based investigation into the impact of ecological water diversion on land cover complexity of restored oasis in arid inland river basins. Ecological Engineering. 2020; 151 ():105865.

Chicago/Turabian Style

Feng Huang; Carlos G. Ochoa; Xi Chen; Qinbo Cheng; Danrong Zhang. 2020. "An entropy-based investigation into the impact of ecological water diversion on land cover complexity of restored oasis in arid inland river basins." Ecological Engineering 151, no. : 105865.

Journal article
Published: 30 April 2020 in Water Resources Research
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Understanding hydrological processes is essential for management of water resources and for promoting catchment sustainability. In karst regions, landscapes spatially heterogeneous and include discontinuous soil distribution, and complex networks of matrices and conduits in hillslopes and depressions, which result in variation in hydrological processes. However, most previous studies have mainly focused on the effects of the distribution of soil depth and the fast‐slow flow in the matrices and conduits on hydrological processes, and ignored the different hydrological processes related to hillslopes and depressions (HD). This study improved the VarKarst model by adding randomly distributed soil and epikarst depths (RSE), fast‐slow flow (FS) and HD. The improved model was calibrated and validated in six large catchments (1,213‐5,454 km2) and one small catchment (1.25 km2). Results showed by adding a combination of FS and HD (Scenario FS+HD) and a combination of RSE, FS, and HD (Scenario RSE+FS+HD) improved model performance (calibrated and validated KGE ranged from 0.54 to 0.89 and AIC ranged from ‐336.49 to 669.77) compared models that included other scenarios (original VarKarst, Scenario RSE, Scenario FS, Scenario HD, and Scenario RSE +FS), especially when reproducing discharge of peaks and recessions. These results suggest that there is a need to separate the hillslopes and depressions when modeling karstic hydrological processes.

ACS Style

Chaohao Xu; Xianli Xu; Meixian Liu; Zhenwei Li; Yaohua Zhang; Jingxuan Zhu; Kelin Wang; Xi Chen; Zhicai Zhang; Tao Peng. An Improved Optimization Scheme for Representing Hillslopes and Depressions in Karst Hydrology. Water Resources Research 2020, 56, 1 .

AMA Style

Chaohao Xu, Xianli Xu, Meixian Liu, Zhenwei Li, Yaohua Zhang, Jingxuan Zhu, Kelin Wang, Xi Chen, Zhicai Zhang, Tao Peng. An Improved Optimization Scheme for Representing Hillslopes and Depressions in Karst Hydrology. Water Resources Research. 2020; 56 (5):1.

Chicago/Turabian Style

Chaohao Xu; Xianli Xu; Meixian Liu; Zhenwei Li; Yaohua Zhang; Jingxuan Zhu; Kelin Wang; Xi Chen; Zhicai Zhang; Tao Peng. 2020. "An Improved Optimization Scheme for Representing Hillslopes and Depressions in Karst Hydrology." Water Resources Research 56, no. 5: 1.

Journal article
Published: 11 March 2020 in Hydrology and Earth System Sciences
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Climate warming is changing streamflow regimes and groundwater storage in cold alpine regions. In this study, the Yangbajain headwater catchment in the Lhasa River basin is adopted as the study area to assess streamflow changes and active groundwater storage in response to climate warming. The results show that both annual streamflow and the mean air temperature increase significantly at respective rates of about 12.30 mm per decade and 0.28 ∘C per decade from 1979 to 2013 in the study area. The results of gray relational analysis indicate that the air temperature acts as a primary factor for the increased streamflow. Due to climate warming, the total glacier volume has retreated by over 25 % during the past 50 years, and the areal extent of permafrost has degraded by 15.3 % over the last 20 years. Parallel comparisons with other subbasins in the Lhasa River basin indirectly reveal that the increased streamflow at the Yangbajain Station is mainly fed by the accelerated glacier retreat. Using baseflow recession analysis, we also find that the estimated groundwater storage that is comparable with the GRACE data increases significantly at rates of about 19.32 mm per decade during the abovementioned period. That is to say, as permafrost thaws, more spaces have been made available to accommodate the increasing meltwater. Finally, a large water imbalance (of more than 5.79×107 m3 a−1) between the melt-derived runoff and the actual increase in runoff as well as the groundwater storage is also observed. The results from this study suggest that the impacts of glacial retreat and permafrost degradation show compound behaviors on the storage–discharge mechanism due to climate warming, and that this fundamentally affects the water supply and the mechanisms of streamflow generation and change.

ACS Style

Lu Lin; Man Gao; Jintao Liu; Jiarong Wang; Shuhong Wang; Xi Chen; Hu Liu. Understanding the effects of climate warming on streamflow and active groundwater storage in an alpine catchment: the upper Lhasa River. Hydrology and Earth System Sciences 2020, 24, 1145 -1157.

AMA Style

Lu Lin, Man Gao, Jintao Liu, Jiarong Wang, Shuhong Wang, Xi Chen, Hu Liu. Understanding the effects of climate warming on streamflow and active groundwater storage in an alpine catchment: the upper Lhasa River. Hydrology and Earth System Sciences. 2020; 24 (3):1145-1157.

Chicago/Turabian Style

Lu Lin; Man Gao; Jintao Liu; Jiarong Wang; Shuhong Wang; Xi Chen; Hu Liu. 2020. "Understanding the effects of climate warming on streamflow and active groundwater storage in an alpine catchment: the upper Lhasa River." Hydrology and Earth System Sciences 24, no. 3: 1145-1157.

Journal article
Published: 04 February 2020 in Journal of Hydrology
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Water storage in the Tibetan Plateau (TP) is extremely sensitive to climate change. Observations in TP have revealed warming and moistening trends before 2004 and weakening of those trends after 2004. These changes in the course of climate warming altered hydrological components in TP from the early years of 1992–2003 to the recent decade of 2004–2015, resulting in strong changes of the terrestrial water storage (TWS) in TP. In this study, hydrological and climatic data that determine the budget of TWS in TP were compiled from multiple data sources for 1992–2015. An empirical formula was developed by correlation analysis of TWS from these data with TWS derived from GRACE data for 2003–2015 in TP. The estimated TWS by the formula highly agrees with GRACE data in describing TWS variations across TP, even though it underestimates the absolute value of annual TWS in north TP. The formula was used to estimate TWS variations in 1992–2003, which were compared to those in 2004–2015. Major results show that (1) in the warm and wet region of south TP, the recently reduced rate of climate warming and moistening reversed the trend of annual TWS from increase in 1992–2003 to significant decrease in 2004–2015. This change is largely caused by decreases of soil water and groundwater storage and increased runoff. (2) In the cold and dry region of north TP, the increase of TWS in 1992–2003 accelerated in 2004–2015 because of increases of soil moisture and lake storage. (3) The difference of TWS change in the north and south TP altered the multi-year balance of water storage over the entire TP. Decreasing TWS from 2004 to 2015 lowered multi-year mean TWS in south TP, while increasing TWS in north TP raised its multi-year mean TWS. The reduction of TWS in south TP, with decrease of streamflow and groundwater storage, could threaten the sustainability of surface and subsurface water resources for this critical source region of Asia’s large rivers. The accumulation of TWS following the rise of surface water in north TP could increase spilling of lakes and thus risks of floods and debris flows.

ACS Style

Jiarong Wang; Xi Chen; Qi Hu; Jintao Liu. Responses of terrestrial water storage to climate variation in the Tibetan Plateau. Journal of Hydrology 2020, 584, 124652 .

AMA Style

Jiarong Wang, Xi Chen, Qi Hu, Jintao Liu. Responses of terrestrial water storage to climate variation in the Tibetan Plateau. Journal of Hydrology. 2020; 584 ():124652.

Chicago/Turabian Style

Jiarong Wang; Xi Chen; Qi Hu; Jintao Liu. 2020. "Responses of terrestrial water storage to climate variation in the Tibetan Plateau." Journal of Hydrology 584, no. : 124652.

Journal article
Published: 18 December 2019 in Science of The Total Environment
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Forest carbon stocks has an important role in the global carbon budget. Based on the satellite-observed and LPJ model simulated aboveground biomass carbon (ABC) data, the spatial and temporal changes of subtropical forest carbon storage in the Yangtze River basin and its relations to the climate variation and human activities were analyzed by using the methods of cumulative curve analysis and climate sensitivity analysis during 1993–2012. The results revealed that: (1) In general, the forest ABC increased obviously in the Yangtze River basin during the past 20 years, and the ABC rose from 2563.91 Tg C in 1993 to 2893.17 Tg C in 2012, with a growth rate of 12.84%. The higher ABC distribution was mainly concentrated in the Jialing River basin and Hanjiang River basin and the significantly increasing trends could be found in most area of the Yangtze River basin; (2) The forest ABC was sensitive to the changes of temperature and precipitation. When the temperature increases by 1 °C, the ABC in the Yangtze River basin will increase by 3.32%, while it will decrease by −6.12% when the precipitation increases by 10%; (3) The forest ABC growth rate had accelerated from 3.15% in 1993–2000 to 8.01% in 2001–2012. The cumulative curve of the forest ABC was generally higher than the temperature or the precipitation after 2000. The total areas induced by climate variation and human activities accounted for 30.5% and 52.59% with an increases in ABC by 67.52 Tg C and 188.74 Tg C from 1993 to 2012, respectively. The implementation of major forestry projects might be the main reason for the rapid increase of forest ABC in the Yangtze River basin. This study suggested human activities such as ecological projects might contribute to the accelerated greening trend and highlighted the pivotal role of subtropical forest ABC in the carbon budget in China.

ACS Style

Rui Kong; Zengxin Zhang; Fengying Zhang; Jiaxi Tian; Juan Chang; Shanshan Jiang; Bin Zhu; Xi Chen. Increasing carbon storage in subtropical forests over the Yangtze River basin and its relations to the major ecological projects. Science of The Total Environment 2019, 709, 136163 .

AMA Style

Rui Kong, Zengxin Zhang, Fengying Zhang, Jiaxi Tian, Juan Chang, Shanshan Jiang, Bin Zhu, Xi Chen. Increasing carbon storage in subtropical forests over the Yangtze River basin and its relations to the major ecological projects. Science of The Total Environment. 2019; 709 ():136163.

Chicago/Turabian Style

Rui Kong; Zengxin Zhang; Fengying Zhang; Jiaxi Tian; Juan Chang; Shanshan Jiang; Bin Zhu; Xi Chen. 2019. "Increasing carbon storage in subtropical forests over the Yangtze River basin and its relations to the major ecological projects." Science of The Total Environment 709, no. : 136163.

Journal article
Published: 16 December 2019 in Science of The Total Environment
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Overexploitation of water resources at middle reaches has threatened downstream oasis in arid inland river basins. To achieve sustainable development, ecological water conveyance is one effective measure to reallocate water resources between socio-economic and natural systems. A comprehensive impact assessment of ecological water conveyance on groundwater-dependent ecosystems that are common in downstream inland river basins is needed. The present study integrated the technologies of remote sensing analysis, trend detection, and numerical simulation into a technical framework that identifies the spatial response and temporal dynamics of vegetation to groundwater changes induced by ecological water conveyance. The Normalized Difference Vegetation Index (NDVI) was used as a proxy to estimate vegetation. The structure of the framework we used is clear and reasonable. We used remote-sensing data and ground truth information, and a decision tree that incorporates an iterative self-organizing data analysis technique. The decision tree classifies the land cover into affected and unaffected areas, and the results indicate the spatial range of impact. The Mann-Kendall algorithm and Sen's slope detect the tendency in NDVI series that indicates the temporal response of vegetation. The Verhulst logistic function, combined with environment carrying capacity function, constitutes a simplified vegetation dynamic model that can be used to predict potential impact through scenario analysis. An application in the Shiyang River basin in Northwest China evaluated the performance and usefulness of the framework; the accuracy of the results suggested that the framework is effective and practical. Additional case studies are required to assess the reliability and applicability of the framework and identify the factors that affect assessment results beyond our case study in the Shiyang River basin.

ACS Style

Feng Huang; Xunzhou Chunyu; Danrong Zhang; Xi Chen; Carlos G. Ochoa. A framework to assess the impact of ecological water conveyance on groundwater-dependent terrestrial ecosystems in arid inland river basins. Science of The Total Environment 2019, 709, 136155 .

AMA Style

Feng Huang, Xunzhou Chunyu, Danrong Zhang, Xi Chen, Carlos G. Ochoa. A framework to assess the impact of ecological water conveyance on groundwater-dependent terrestrial ecosystems in arid inland river basins. Science of The Total Environment. 2019; 709 ():136155.

Chicago/Turabian Style

Feng Huang; Xunzhou Chunyu; Danrong Zhang; Xi Chen; Carlos G. Ochoa. 2019. "A framework to assess the impact of ecological water conveyance on groundwater-dependent terrestrial ecosystems in arid inland river basins." Science of The Total Environment 709, no. : 136155.

Journal article
Published: 10 October 2019 in Water
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The spatiotemporal evolution of meteorological droughts in Guizhou Province, Southwest China is analyzed based on a new set of the Standardized Precipitation Index series that mainly includes drought events that occurred from 1961 to 2004 at 81 meteorological stations. The cluster analysis shows that the study region can be classified into six homogeneous sub-regions where the drought characteristics and their temporal evolutions are quite different. The trend test and periodicity analysis indicate that Guizhou Province experienced a drier trend, which was most significant in the western parts of the region. It was found that the intensified drought severity was not always coincident with the drier trend but relied on the occurrence of extreme drought events. The trends of drier climate and drought severity were highly coincident with the temporal evolution of the drought periodicities, which were shortened from 1–4 years to less than one year. The shortened drought periodicity was found to be associated principally with a shift of the large-scale dominant climate indices from the North Atlantic Oscillation to the Indian Ocean Dipole after the late 1970s, and variations of the extreme drought events were mostly related to NINO34 in the study region.

ACS Style

Liying Xiao; Xi Chen; Runrun Zhang; Zhicai Zhang. Spatiotemporal Evolution of Droughts and Their Teleconnections with Large-Scale Climate Indices over Guizhou Province in Southwest China. Water 2019, 11, 2104 .

AMA Style

Liying Xiao, Xi Chen, Runrun Zhang, Zhicai Zhang. Spatiotemporal Evolution of Droughts and Their Teleconnections with Large-Scale Climate Indices over Guizhou Province in Southwest China. Water. 2019; 11 (10):2104.

Chicago/Turabian Style

Liying Xiao; Xi Chen; Runrun Zhang; Zhicai Zhang. 2019. "Spatiotemporal Evolution of Droughts and Their Teleconnections with Large-Scale Climate Indices over Guizhou Province in Southwest China." Water 11, no. 10: 2104.

Journal article
Published: 14 July 2019 in Water
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The purpose of this study is to quantitatively evaluate the accuracy of the GPM IMERG v5 and the TRMM 3B42 v7, with the reference of 224 rain gauge stations over the Yangtze River basin in China from April 2014 to December 2017. The results showed that: (1) The changing pattern of IMERG v5 was similar to the 3B42 v7, and higher correlations can be found between the satellite-based precipitation products (SPPs) and observed precipitation for the monthly and annual time scale; (2) the IMERG v5 tended to overestimate the distribution range of the main rain band while the 3B42 v7 underestimated the precipitation in Sichuan basin, and the largest differences were found for the precipitation less than 1 mm/d for two SPPs; (3) both of the IMERG v5 and 3B42 v7 overestimated the precipitation in the lower elevation areas (

ACS Style

Yifan Wu; Zengxin Zhang; Yuhan Huang; Qiu Jin; Xi Chen; Juan Chang. Evaluation of the GPM IMERG v5 and TRMM 3B42 v7 Precipitation Products in the Yangtze River Basin, China. Water 2019, 11, 1459 .

AMA Style

Yifan Wu, Zengxin Zhang, Yuhan Huang, Qiu Jin, Xi Chen, Juan Chang. Evaluation of the GPM IMERG v5 and TRMM 3B42 v7 Precipitation Products in the Yangtze River Basin, China. Water. 2019; 11 (7):1459.

Chicago/Turabian Style

Yifan Wu; Zengxin Zhang; Yuhan Huang; Qiu Jin; Xi Chen; Juan Chang. 2019. "Evaluation of the GPM IMERG v5 and TRMM 3B42 v7 Precipitation Products in the Yangtze River Basin, China." Water 11, no. 7: 1459.

Article
Published: 21 June 2019 in Climatic Change
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Elevated atmospheric CO2 concentration alters vegetation growth and composition, increases plant water use efficiency (WUE), and changes surface water balance. These changes and their differences between wet and dry climate are studied at a mid-latitude experiment site in the Loess Plateau of China. The study site, the Jinghe River basin (JRB), covers an area of 43,216 km2 and has a semiarid climate in the north and a semi-humid climate in the south. Two simulations from 1965 to 2012 are made using a site-calibrated Lund–Potsdam–Jena dynamic global vegetation model: one with the observed rise of the atmospheric CO2 from 319.7–391.2 ppmv, and the other with a fixed CO2 at the level of 1964 (318.9 ppmv). Analyses of the model results show that the elevated atmospheric CO2 promotes growth of woody vegetation (trees) and causes a 6.0% increase in basin-wide net primary production (NPP). The NPP increase uses little extra water however because of higher WUE. Further examination of the surface water budget reveals opposite CO2 effects between semiarid and semi-humid climates in the JRB. In the semiarid climate, plants sustain growth in higher CO2 because of the higher level of intracellular CO2 and therefore WUE, thus consuming more water and causing a greater decrease of surface runoff than in the fixed-lower CO2 case. In the semi-humid climate, NPP also increases but by a smaller amount than in the semiarid climate. Plant transpiration (ET) and total evapotranspiration (E) decrease in the elevated CO2 environment, yielding the increase of runoff. This asymmetry of the effects of elevated atmospheric CO2 exacerbates drying in the semiarid climate and enhances wetness in the semi-humid climate. Furthermore, plant WUE (=NPP/ET) is found to be nearly invariant to climate but primarily a function of the atmospheric CO2 concentration, a result suggesting a strong constraint of atmospheric CO2 on biophysical properties of the Earth system.

ACS Style

Richao Huang; Xi Chen; Qi Hu. Changes in vegetation and surface water balance at basin-scale in Central China with rising atmospheric CO2. Climatic Change 2019, 155, 437 -454.

AMA Style

Richao Huang, Xi Chen, Qi Hu. Changes in vegetation and surface water balance at basin-scale in Central China with rising atmospheric CO2. Climatic Change. 2019; 155 (3):437-454.

Chicago/Turabian Style

Richao Huang; Xi Chen; Qi Hu. 2019. "Changes in vegetation and surface water balance at basin-scale in Central China with rising atmospheric CO2." Climatic Change 155, no. 3: 437-454.

Journal article
Published: 19 June 2019 in Remote Sensing
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Net Primary Productivity (NPP) is a basis of material and energy flows in terrestrial ecosystems, and it is also an important component in the research on carbon cycle and carbon budget. This paper evaluated the spatial distribution pattern and temporal change trends for forest NPP simulated by the LPJ (Lund-Potsdam-Jena) model and NDVI (normalized difference vegetation index) in the Yangtze River basin from 1982 to 2013. The results revealed that: (1) the spatial distribution of the forest NPP and NDVI in the Yangtze River basin has gradually decreased from the southeast coast to the northwest. The forest NPP and NDVI in the mid-lower Yangtze were higher than that of the upper Yangtze; (2) the forest NPP and NDVI in most areas of the Yangtze River basin were positively correlated with the temperature and precipitation. Moreover, the correlations among the temperature with the forest NPP and NDVI were stronger than that of correlations among precipitation with forest NPP and NDVI. Moreover, the extreme drought event in the year of 2004–2005 led the NPP to decrease in the middle and lower Yangtze River basin; (3) human activity such as major ecological projects would have a certain impact on the NPP and NDVI. The increase in forest areas from 2000 to 2010 was larger than that from 1990 to 2000. Moreover, the increasing rate for the NDVI was higher than that of NPP, especially after the year 2000, which indicates that the major ecological projects might have great impacts on the vegetation dynamics. Moreover, more attention should be paid on the joint impacts of human activity and climate change on terrestrial NPP and NDVI.

ACS Style

Fengying Zhang; Zengxin Zhang; Rui Kong; Juan Chang; Jiaxi Tian; Bin Zhu; Shanshan Jiang; Xi Chen; Chong-Yu Xu. Changes in Forest Net Primary Productivity in the Yangtze River Basin and Its Relationship with Climate Change and Human Activities. Remote Sensing 2019, 11, 1451 .

AMA Style

Fengying Zhang, Zengxin Zhang, Rui Kong, Juan Chang, Jiaxi Tian, Bin Zhu, Shanshan Jiang, Xi Chen, Chong-Yu Xu. Changes in Forest Net Primary Productivity in the Yangtze River Basin and Its Relationship with Climate Change and Human Activities. Remote Sensing. 2019; 11 (12):1451.

Chicago/Turabian Style

Fengying Zhang; Zengxin Zhang; Rui Kong; Juan Chang; Jiaxi Tian; Bin Zhu; Shanshan Jiang; Xi Chen; Chong-Yu Xu. 2019. "Changes in Forest Net Primary Productivity in the Yangtze River Basin and Its Relationship with Climate Change and Human Activities." Remote Sensing 11, no. 12: 1451.

Preprint content
Published: 17 June 2019 in Hydrology and Earth System Sciences Discussions
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Climate warming is changing streamflow regimes and groundwater storage in cold alpine regions. In this study, a headwater catchment named Yangbajain in the Lhasa River Basin is adopted as the study area for quantifying streamflow changes and active groundwater storage in response to climate warming. The changes in streamflow regimes and climate factors are evaluated based on hydro-meteorological observations from 1979 to 2013. The results show that annual streamflow increases significantly at a rate of about 12.30 mm/10a during this period. Through baseflow recession analysis, we also find that the estimated groundwater storage that is comparable with the GRACE data increases significantly at the rates of about 19.32 mm/10a during these years. The rising of air temperature is the main factor for the increase in streamflow and groundwater storage, which has led to a loss of over 25 % of the total glacier volume for half century in this catchment. Parallel comparisons with other sub-basins in the Lhasa River Basin reveal that the increased streamflow at the Yangbajain station is mainly fed by the accelerated glacier retreat rather than frozen ground degradation. However, the increase of active storage capacity is caused by frozen ground degradation, which can accommodate the increasing meltwater in the valley. The huge gap between the melt-derived runoff and the increased water volume in groundwater storage and streamflow suggests that more than 60 % of the total ablation of glaciers should be discharged downstream through deep fault. This study provides a perspective to clarify the impact of glacial retreat and frozen ground degradation on hydrological processes, which fundamentally affects the water supply and the mechanisms of streamflow generation and change.

ACS Style

Lu Lin; Man Gao; Jintao Liu; Jiarong Wang; Shuhong Wang; Xi Chen; Hu Liu. Quantifying streamflow and active groundwater storage in response to climate warming in an alpine catchment, upper Lhasa River. Hydrology and Earth System Sciences Discussions 2019, 2019, 1 -41.

AMA Style

Lu Lin, Man Gao, Jintao Liu, Jiarong Wang, Shuhong Wang, Xi Chen, Hu Liu. Quantifying streamflow and active groundwater storage in response to climate warming in an alpine catchment, upper Lhasa River. Hydrology and Earth System Sciences Discussions. 2019; 2019 ():1-41.

Chicago/Turabian Style

Lu Lin; Man Gao; Jintao Liu; Jiarong Wang; Shuhong Wang; Xi Chen; Hu Liu. 2019. "Quantifying streamflow and active groundwater storage in response to climate warming in an alpine catchment, upper Lhasa River." Hydrology and Earth System Sciences Discussions 2019, no. : 1-41.

Review
Published: 24 May 2019 in International Journal of Environmental Research and Public Health
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Groundwater depth is an important environmental factor affecting vegetation growth and landscape dynamics in arid environments. This study applied a science mapping approach to visualize the development of groundwater-vegetation-related research, synthesized the vegetation response to changes in groundwater depth, and analyzed the change rate of the response curve to identify the groundwater threshold that is essential to conserve the groundwater-dependent terrestrial ecosystems. These ecosystems emerged as a research hotspot due to climate change, groundwater overexploitation, and the recognition of these ecosystems' importance for sustainable development. There are two main types of response functions of vegetation to changes in groundwater depth-monotone and bell-shaped functions-among which the monotone function includes linear, curvilinear, and stepwise response. The shape of a response curve is mainly determined by the combined effects of oxygen stress, salinization, and water stress; oxygen stress and salinization dominate in shallow groundwater depth, while water stress dominates in deep groundwater depth. On a non-linear vegetation metric-groundwater depth response curve, the change rate analysis method is effective to identify the breakpoint that can be taken as a candidate threshold of groundwater depth. The results will add insight into the intellectual structure of the groundwater-vegetation interactions and provide practical reference for groundwater resource management, ecological conservation, and sustainable development in arid environments.

ACS Style

Feng Huang; Danrong Zhang; Xi Chen. Vegetation Response to Groundwater Variation in Arid Environments: Visualization of Research Evolution, Synthesis of Response Types, and Estimation of Groundwater Threshold. International Journal of Environmental Research and Public Health 2019, 16, 1849 .

AMA Style

Feng Huang, Danrong Zhang, Xi Chen. Vegetation Response to Groundwater Variation in Arid Environments: Visualization of Research Evolution, Synthesis of Response Types, and Estimation of Groundwater Threshold. International Journal of Environmental Research and Public Health. 2019; 16 (10):1849.

Chicago/Turabian Style

Feng Huang; Danrong Zhang; Xi Chen. 2019. "Vegetation Response to Groundwater Variation in Arid Environments: Visualization of Research Evolution, Synthesis of Response Types, and Estimation of Groundwater Threshold." International Journal of Environmental Research and Public Health 16, no. 10: 1849.