Analysis on the Variations of Annual Runoff Distribution in the Weihe Basin

With the impact of climate change and the increasing intensity of human activities,the hydrological regime had changed,including annual runoff distribution,which was related with water resources management and ecological construction. Based on the monthly runoff data for more than 40 years of the Beidao,Xianyang,Huaxian station on Weihe Basin,the annual distribution characteristics of runoff were studied. Several indices related to attributes of uneven,concentrate degree and variation amplitude were calculated,and the results showed that there had obvious fresh and drought seasonal changes in 1990s. The annual runoff distribution had changed a lot,mainly because of runoff decrease in the wet season. The Huaxian station,which locates at the upper reaches,had a higher unevenness,concentration and relative variation rate than that of the Beidao and Xianyang station.

Characteristics of horizontal crustal movement in Weihe basin and adjacent zones by GPS observation

Based on the GPS data provided by CMONOC during 1999~2002 and observed by Seismological Bureau of Shaanxi Province during 2001~2002, we have obtained the crustal movement velocity field in Weihe basin and adjacent regions. The results show that the motion velocity in Weihe basin and adjacent zones is characterized by distinct NE-directional stripped variation. The south border of Ordos block seems to show an discontinuous anti-clockwise rotation on the whole with an average velocity of about 5.7 mma-1 relative to Yulin site on the Ordos block. There is a left-lateral shear belt on both sides of Binxian-Xi'an-Lantian zone in the central Weihe basin, and its northern area has a better corresponding relationship with the dense zone of small earthquakes in Tong-chuan-Jingyang-Lintong-Weinan.

Lateral migration of fault activity in Weihe basin

Lateral migration of fault activity in Weihe basin is a popular phenomenon and its characteristics are also typical. Taking the activity migrations of Wangshun Mountain piedmont fault toward Lishan piedmont fault and Weinan platform front fault, Dabaopi-Niujiaojian fault toward Shenyusi-Xiaojiazhai fault, among a serial of NE-trending faults from Baoji city to Jingyang County as examples, their migration time and process are analyzed and discussed in the present paper. It is useful for further understanding the structure development and physiognomy evolution history of Weihe basin.

The Lithofacies Paleogeography and Paleoenvironmental evolution of the Cenozoic in the Weihe Basin, China

The Weihe Basin,which is known as a Cenozoic rift Basin,is special for its location where not only enrich oil,gas and water,but also is a"sweet"for environment evolution research.It sits in the transition area between the ordos basin with full of oil and gas resources in the north and the Qinling Orogenic Belt with rich mineral

Driving forces behind the spatiotemporal heterogeneity of land-use and land-cover change:A case study of the Weihe River Basin,China

The impact of socioeconomic development on land-use and land-cover change(LUCC)in river basins varies spatially and temporally.Exploring the spatiotemporal evolutionary trends and drivers of LUCC under regional disparities is the basis for the sustainable development and management of basins.In this study,the Weihe River Basin(WRB)in China was selected as a typical basin,and the WRB was divided into the upstream of the Weihe River Basin(UWRB),the midstream of the Weihe River Basin(MWRB),the downstream of the Weihe River Basin(DWRB),the Jinghe River Basin(JRB),and the Luohe River Basin(LRB).Based on land-use data(cultivated land,forestland,grassland,built-up land,bare land,and water body)from 1985 to 2020,we analyzed the spatiotemporal heterogeneity of LUCC in the WRB using a land-use transfer matrix and a dynamic change model.The driving forces of LUCC in the WRB in different periods were detected using the GeoDetector,and the selected influencing factors included meteorological factors(precipitation and temperature),natural factors(elevation,slope,soil,and distance to rivers),social factors(distance to national highway,distance to railway,distance to provincial highway,and distance to expressway),and human activity factors(population density and gross domestic product(GDP)).The results indicated that the types and intensities of LUCC conversions showed considerable disparities across different sub-basins,where complex conversions among cultivated land,forestland,and grassland occurred in the LRB,JRB,and UWRB,with higher dynamic change before 2000.The conversion of other land-use types to built-up land was concentrated in the UWRB,MWRB,and DWRB,with substantial increases after 2000.Additionally,the driving effects of the influencing factors on LUCC in each sub-basin also exhibited distinct diversity,with the LRB and JRB being influenced by the meteorological and social factors,and the UWRB,MWRB,and DWRB being driven by human activity factors.Moreover,the interaction of these influencing factors indicated an enhanced effect on LUCC.This study confirmed the spatiotemporal heterogeneity effects of socioeconomic status on LUCC in the WRB under regional differences,contributing to the sustainable development of the whole basin by managing sub-basins according to local conditions.

East Asian paleoclimate change in the Weihe Basin (central China) since the middle Eocene revealed by clay mineral analysis

Obtaining a continuous sedimentary record of Cenozoic East Asian paleoclimate change is key to understand the origin,evolution and driving mechanism of the East Asian monsoon and climate change.Based on the continuous Cenozoic fluvial and lacustrine sedimentary sequence in the Weihe Basin,central China,we carried out research on the content and crystal parameters of clay minerals.The paleoclimate change since the middle Eocene was reconstructed accordingly.The results show that smectite and illite are the dominant clay minerals in fluvial-lacustrine sediments of Weihe Basin.The crystallinity of illite,the chemical index of illite,the ratio of smectite to illite and chlorite decrease gradually,which indicates that chemical weathering in the Weihe River watershed stepwise weakened since the middle Eocene,under the background of a semi-arid and semi-humid climate.The formation of palygorskite may be affected by a weak diagenesis.In this case,the content of smectite and the illite crystallinity caused by the weathering in the corresponding period may be actually higher than that of the current,which indicates that the climate in the Weihe Basin region was relatively warm and humid from the middle Eocene to Pliocene.With the decrease of Cenozoic global temperature and the continuous accumulation of sediments,the intensity of chemical weathering in the Weihe Basin gradually weakened,and the East Asian monsoon climate gradually evolved until becoming dry in the Quaternary.Evidence from clay minerals also indicates that the aridification in the Weihe Basin from the late Eocene to the Oligocene may be a response to the global cooling event at the Eocene-Oligocene transition.

Distribution of Helium Resources in Weihe Basin,Central China:Insight from 3D Magnetic Inversion

There is promising indication of helium-rich natural gas in Weihe Basin.However,the lack of a detailed investigation on the origin and the spatial distribution of helium source rocks(mainly Yanshanian granites)limits the helium potentiality evaluation in Weihe Basin(WB).We performed three-dimensional(3 D)inversions of magnetic data in Weihe Basin and its adjacent areas to figure out the crustal thermal structure and the temporal-spatial distribution of deep granite in the basin.Based on this,we have proposed a geological model of helium accumulation and predicted the potential area of helium distribution.The results of 3 D magnetic inversion indicate that the granites in the deep Weihe Basin are mostly located at the central and southern parts of the basin,which are connected spatially with the granites in the North Qinling Orogenic Belt.These granites were all derived from largescale intra-continental orogeny in the Qinling area during the mid-Mesozoic,providing a good material basis for crust-derived helium in the basin.The local uplift of the Curie surface makes the thermal fluid more actively,which contributes to helium accumulation.The faults developed in the WB are the migration pathway of crust-derived helium and the upward migration of the mantle-derived helium.The wells with high percentage helium are mostly located near the Weihe fault and the areas on the south of it.The Wugong-Xi’an-Lantian area in the central and the Lintong-Weinan-Tongguan area in the eastern Weihe Basin are the most promising helium distribution areas.Furthermore,the region from the north of Taibai Mountain to Baoji City in the western Weihe Basin may also be another potential area of Helium resource.

Quantitative Estimation on Contributions of Climate Changes and Human Activities to Decreasing Runoff in Weihe River Basin, China

Human activities and climate changes are deemed to be two primary driving factors influencing the changes of hydrological processes, and quantitatively separating their influences on runoff changes will be of great significance to regional water resources planning and management. In this study, the impact of climate changes and human activities was initially qualitatively distinguished through a coupled water and energy budgets analysis, and then this effect was further separated by means of a quantitative estimation based on hydrological sensitivity analysis. The results show that: 1) precipitation, wind speed, potential evapotranspiration and runoff have a significantly decreasing trend, while temperature has a remarkably increasing tendency in the Weihe River Basin, China; 2) the major driving factor on runoff decrease in the 1970 s and 1990 s in the basin is climate changes compared with that in the baseline 1960 s, while that in the 1980 s and 2000 s is human activities. Compared with the results based on Variable Infiltration Capacity(VIC) model, the contributions calculated in this study have certain reliability. The results are of great significance to local water resources planning and management.

Application of the InVEST model for assessing water yield and its response to precipitation and land use in the Weihe River Basin, China

With realizing the importance of ecosystem services to society, the efforts to evaluate the ecosystem services have increased. As the largest tributary of the Yellow River, the Weihe River has been endowed with many ecological service functions. Among which, water yield can be a measure of local availability of water and an index for evaluating the conservation function of the region. This study aimed to explore the temporal and spatial variation of water yield and its influencing factors in the Weihe River Basin(WRB), and provide basis for formulating reasonable water resources utilization schemes. Based on the InVEST(integrated valuation of ecosystem services and tradeoffs) model, this study simulated the water yield in the WRB from 1985 to 2019, and discussed the impacts of climatic factors and land use change on water yield by spatial autocorrelation analysis and scenario analysis methods. The results showed that there was a slight increasing trend in water yield in the WRB over the study period with the increasing rate of 4.84 mm/10a and an average depth of 83.14 mm. The main water-producing areas were concentrated along the mainstream of the Weihe River and in the southern basin. Changes in water yield were comprehensively affected by climate and underlying surface factors. Precipitation was the main factor affecting water yield, which was consistent with water yield in time. And there existed significant spatial agglomeration between water yield and precipitation. Land use had little impact on the amount of water yield, but had an impact on its spatial distribution. Water yield was higher in areas with wide distribution of construction land and grassland. Water yield of different land use types were different. Unused land showed the largest water yield capacity, whereas grassland and farmland contributed most to the total water yield. The increasing water yield in the basin indicates an enhanced water supply service function of the ecosystem. These results are of great significance to the water resources management of the WRB.

Spatial-temporal Analysis and Prediction of Precipitation Extremes: A Case Study in the Weihe River Basin, China

Extreme precipitation events bring considerable risks to the natural ecosystem and human life.Investigating the spatial-temporal characteristics of extreme precipitation and predicting it quantitatively are critical for the flood prevention and water resources planning and management.In this study,daily precipitation data(1957–2019)were collected from 24 meteorological stations in the Weihe River Basin(WRB),Northwest China and its surrounding areas.We first analyzed the spatial-temporal change of precipitation extremes in the WRB based on space-time cube(STC),and then predicted precipitation extremes using long short-term memory(LSTM)network,auto-regressive integrated moving average(ARIMA),and hybrid ensemble empirical mode decomposition(EEMD)-LSTM-ARIMA models.The precipitation extremes increased as the spatial variation from northwest to southeast of the WRB.There were two clusters for each extreme precipitation index,which were distributed in the northwestern and southeastern or northern and southern of the WRB.The precipitation extremes in the WRB present a strong clustering pattern.Spatially,the pattern of only high-high cluster and only low-low cluster were primarily located in lower reaches and upper reaches of the WRB,respectively.Hot spots(25.00%–50.00%)were more than cold spots(4.17%–25.00%)in the WRB.Cold spots were mainly concentrated in the northwestern part,while hot spots were mostly located in the eastern and southern parts.For different extreme precipitation indices,the performances of the different models were different.The accuracy ranking was EEMD-LSTM-ARIMA>LSTM>ARIMA in predicting simple daily intensity index(SDII)and consecutive wet days(CWD),while the accuracy ranking was LSTM>EEMD-LSTM-ARIMA>ARIMA in predicting very wet days(R95 P).The hybrid EEMD-LSTM-ARIMA model proposed was generally superior to single models in the prediction of precipitation extremes.

Runoff characteristics and its sensitivity to climate factors in the Weihe River Basin from 2006 to 2018

Exploring the current runoff characteristics after the large-scale implementation of the Grain for Green(GFG)project and investigating its sensitivities to potential drivers are crucial for water resource prediction and management.Based on the measured runoff data of 62 hydrological stations in the Weihe River Basin(WRB)from 2006 to 2018,we analyzed the temporal and spatial runoff characteristics in this study.Correlation analysis was used to investigate the relationships between different runoff indicators and climate-related factors.Additionally,an improved Budyko framework was applied to assess the sensitivities of annual runoff to precipitation,potential evaporation,and other factors.The results showed that the daily runoff flow duration curves(FDCs)of all selected hydrological stations fall in three narrow ranges,with the corresponding mean annual runoff spanning approximately 1.50 orders of magnitude,indicating that the runoff of different hydrological stations in the WRB varied greatly.The trend analysis of runoff under different exceedance frequencies showed that the runoff from the south bank of the Weihe River was more affluent and stable than that from the north bank.The runoff was unevenly distributed throughout the year,mainly in the flood season,accounting for more than 50.00%of the annual runoff.However,the trend of annual runoff change was not obvious in most areas.Correlation analysis showed that rare-frequency runoff events were more susceptible to climate factors.In this study,daily runoff under 10%-20%exceeding frequencies,consecutive maximum daily runoff,and low-runoff variability rate had strong correlations with precipitation,aridity index,and average runoff depth on rainy days.In comparison,daily runoff under 50%-99%exceeding frequencies,consecutive minimum daily runoff,and high-runoff variability rate had weak correlations with all selected impact factors.The sensitivity analysis results suggested that the sensitivity of annual runoff to precipitation was always higher than that to potential evaporation.The runoff about 87.10%of the selected hydrological stations were most sensitive to precipitation changes,and 12.90%were most sensitive to other factors.The spatial pattern of the sensitivity analysis indicated that in relatively humid southern areas,runoff was more sensitive to potential evaporation and other factors,and less sensitive to precipitation.

Study of crustal seismic velocity in the Weihe fault depression basin by seismic tomographic imaging

This paper gives a study of 3 D crustal seismic velocity changes in the Weihe fault depression basin, in which the overlapping sphere iterative reconstruction method of tomographic image was used in connection with the two point fast ray tracing technique. By means of theoretical modeling, the monitoring function of the observatory network system of Shaanxi Province was tested. Using the seismic data of the network, seismic tomographic inversion imaging of the crustal seismic velocity in the Weihe fault basin was studied. The results are as follows: In the Tongchuan Yaoxian area to the north of Jingyang, there is a high velocity region extending nearly in NS direction, the highest velocity value is around Tongchuan. To the southwest of Shangxian and Lantian, there is a low velocity zone about 100 km long and about 50 km wide, inside which there are two regions of the lowest velocity 50 km apart. The epicenters of historical strong earthquakes are mainly on the boundary of high velocity regions or in regions of fairly high velocity. In the eastern and western parts of the south margin of the Qinling Mountains, there is an obvious lateral nonhomogeneity of seismic velocity.

Drought monitoring and reliability evaluation of the latest TMPA precipitation data in the Weihe River Basin, Northwest China

The high resolution satellite precipitation products bear great potential for large-scale drought monitoring, especially for those regions with sparsely or even without gauge coverage. This study focuses on utilizing the latest Version-7 TRMM Multi-satellite Precipitation Analysis （TMPA 3B42V7） data for drought condition monitoring in the Weihe River Basin （0.135×10^6 km2）. The accuracy of the monthly TMPA 3B42V7 satellite precipitation data was firstly evaluated against the ground rain gauge observations. The statistical characteristics between a short period data series （1998-2013） and a long period data series （1961-2013） were then compared. The TMPA 3B42V7-based SPI （Standardized Precipitation Index） sequences were finally validated and analyzed at various temporal scales for assessing the drought conditions. The results indicate that the monthly TMPA 3B42V7 precipitation is in a high agreement with the rain gauge observations and can accurately capture the temporal and spatial characteristics of rainfall within the Weihe River Basin. The short period data can present the characteristics of long period record, and it is thus acceptable to use the short period data series to estimate the cumulative probability function in the SPI calculation. The TMPA 3B42V7-based SPI matches well with that based on the rain gauge observations at multiple time scales （i.e., 1-, 3-, 6-, 9-, and 12-month） and can give an acceptable temporal distribution of drought conditions. It suggests that the TMPA 3B42V7 precipitation data can be used for monitoring the occurrence of drought in the Weihe River Basin.

The Spatio-temporal Evolution of Ecological Risk and Its Drivers in the Weihe River Basin Landscape from 1990 to 2020

The Weihe River Basin has a significant number of tributaries and a delicate ecological environment.Understanding the spatial and temporal evolution and determinants of landscape ecological risk in the Weihe River Basin(WRB)can improve the scientific protection and development of its watershed ecosystems.This study is based on land use statistics from the WRB for a 30-year period represented by 1990,2000,2010,and 2020.An initial model for the assessment of landscaping ecological hazards was created using the software that was also used to generate the landscape ecological risk index,such as ArcGIS 10.4 and Fragstats 4.2-64.Next,the spatial and temporal evolution of landscape ecological risk in the vicinity of the study area was characterized by the trajectory of the center of gravity migration and the spatial autocorrelation of GeoDa.Finally,Geodetector was used to analyze ecological risk drivers in the landscapes.According to the findings,the high-risk and relatively high-risk regions are steadily expanding,while the low-risk and relatively low-risk areas dominate the ecological risk landscape in the WRB.Within the Weihe River Basin,Xianyang and Xi'an are the areas to which the high-risk centers of gravity are migrating.Positive spatial correlations were found between the landscape ecological hazards in the study area,most prominently in the form of high-high and low-low aggregations.The primary drivers are the interplay between the GDP component,temperature,and elevation as a single factor.

One feature of the activated southern Ordos block:the Ziwuling small earthquake cluster

Small earthquakes （Ms〉2.0） have been recorded from 1970 to the present day and reveal a significant diffrence in seismicity between the stable Ordos block and its active surrounding area. The southern Ordos block is a conspicuous small earthquake belt clustered and isolated along the NNW direction and extends to the inner stable Ordos block; no active fault can match this small earthquake cluster. In this paper, we analyze the dynamic mechanism of this small earthquake cluster based on the GPS velocity field （from 1999 to 2007） , which are mainly from Crustal Movement Observation Network of China （CMONOC） with respect to the north and south China blocks. The principal direction of strain rate field, the expansion ratefield, the maximum shear strain rate, and the rotation rate were constrained using the GPS velocity field. The results show that the velocity field, which is bounded by the small earthquake cluster from Tongchuan to Weinan, differs from the strain rate field, and the crustal deformation is left-lateral shear. This left-lateral shear belt not only spatially coincides with the Neo-tectonic belt in the Weihe Basin but also with the NNW small earthquake cluster （the Ziwuling small earthquake cluster）. Based on these studies, we speculate that the NNW small earthquake cluster is caused by left-lateral shear slip, which is prone to strain accumulation. When the strain releases along the weak zone of structure, small earthquakes diffuse within its upper crust. The maximum principal compression stress direction changed from NE-SW to NEE-SWW, and the former reverse faults in the southwestern margin of the Ordos block became a left-lateral strike slip due to readjustment of the tectonic stress field after the middle Pleistocene. The NNW Neo-tectonie belt in the Weihe Basin, the different movement character of the inner Weihe Basin （which was demonstrated through GPS measurements） anti the small earthquake cluster belt reflect the activated southern margin of the Ordos block, which was generated through readjustment of the tectonic stress field after the middle Pleistocene.

Identification of impacts of climate change and direct human activities on streamflow in Weihe River Basin in Northwest China

Climate change and human activities make major influences on hydrology,which are known to have important impacts on streamflow variation.Therefore,it is critically important to identify how climate change and human activities will impact streamflow variation.Thus,the goal of this study is to identify the impacts of climate change and direct human activities on annual streamflow at four hydrologic stations in the Weihe River basin of China,with the estimation of evaporation based on the Budyko hypothesis.The Mann-Kendall test was employed to detect the break points of the four stations.According to the occurrence time of break points,the data series were divided into two periods:pre-change period(1960-1984)and post-change(1985-2010)period.The parameter of one-parameter Budyko-type model was calibrated with observed data during the pre-change period,with the R^(2) values ranged from 0.95 to 0.97 and the NSE values ranged from 0.80 to 0.94,and the high R^(2) and Nash-Sutcliffe Efficiency coefficient shows the model has good performance.The contribution ratios of climate change impacts on decreasing streamflow were 37%,23%,57%and 43%,and those of the impacts of direct human activities were 63%,77%,43%and 57%for the Linjiacun,Xianyang,Lintong and Huaxian station,respectively.Both the climate change and direct human activities have positive impacts on streamflow decrease at all of the four stations,and the direct human activities are the main factor causing the decrease of annual streamflow.