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.

Research of Hydrochemical Properties of Hyporheic Zone along the WeiHe River in Shanxi Segment

By sampling the undercurrent belts of riverfront, shoal and riverbed at Xianyang, Xi’an, Lintong and Huaxian in Weihe basin of Shaanxi province in the summer and winter of 2014 and analyzed the water chemical character through Piper trilinear chart, This thesis has come to the following conclusions: (1) PH in shoal range from 7.42 to 7.98, and in riverfront, the average is 7.58, present alkaline. The TDS in riverfront is higher than that of river water, it range from 506.5 to 824, 616.06 mg?L?1 in average. (2) All of the water at riverfront, shoal and riverbed under the influence of carbonate. The concentration of ionic concentration at shoal is between riverbed and riverfront, by contrast, it close to riverfront. This result means the shoal recharged by both surface and river water, and the groundwater recharge is more conspicuous than surface water. Besides, from upstream to downstream, the two kinds of main ions ( and Ca2+) have little change in the same river, it related to such factors as river evaporation, the exchange interaction of surface and underground water and so on.

Analysis on the Changing Trends of Surface Water Quality and Their Causes of Weihe River in Shaanxi Province during Recent Ten Years

[ Objective] The study aimed to analyze the changing trends of surface water quality and their causes of Weihe River in Shaanxi Province over past ten years. [ Method] Based on the available monitoring data of water quality of Weihe River in Shaanxi Province from 2001 to 2010, the changing trends of surface water quality of Weihe River in Shaanxi Province during recent ten years were assessed by using the assessment method of surface water quality according to the Assessment Method of Surface Water Quality and Environmental Quality Standards for Surface Water （GB 3838-2002）. Moreover, the possible reasons for the trends were also proposed. [ Result] From 2001 to 2010, there was a relatively decrea- sing trend of water pollution in Weihe River due to the considerable decline in the content of the main environmental pollutants like permanganate in- dex, 5-day biochemical oxygen demand （ BOD5 ）, ammonia nitrogen, oil and volatile phenol. Meanwhile, the comprehensive pollution index fell by 62.7%, eliminating Weihe River＇s black and stink on schedule. However, the overall surface water quality of Weihe River was still polluted heavily in each year, and the pollution control of Xi＇an section should be paid more attention to. [ Conclusion] The research could provide scientific refer- ences for the comprehensive environmental control of Weihe River in Shaanxi Province.

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.

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.

Major elements in the Holocene loess-paleosol sequence in the upper reaches of the Weihe River valley,China

Palaeohydmlogical investigations were carried out in the Guchuan Basin in the upper reaches of the Weihe River valley, China. A set of palaeoflood slackwater deposits （SWDs） was found interbedded in the Holocene Ioess-paleosol sequence at the Guchuanzhen site （GCZ）. These palaeoflood SWDs were studied by field observations and laboratory analyses including concentrations of chemical elements and optically stimulated luminescence （OSL） dating. The results showed that the palaeoflood SWDs were the result of the secondary separations of the surface soil and weathered soil layers during the process of water transport and deposition, and without obvious weathering during soil development. These extraordinary flood events were dated back to 3,200-3,000 a B.P. with the OSL method and checked by archaeological dating of the human remains retrieved from the profile. These extraordinary flood events were therefore considered as regional expression of known climatic events and demonstrated the climatic instability in the Holocene. This result is important for understanding the effects of global climate change on the dynamics of river systems.

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.

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.

Multi-Fractal Characteristics of Daily Runoff Series of Weihe River Watershed

Application of fractal theory on the evolution of nonlinear study of the hydrological system, which found its internal rules from the complex hydrologic system, could make us more fully understand the hydrodynamic characteristics of the complex motion of this system. Taking Weihe River as study area, this paper analyzes daily runoff series’ multi-fractal character and relative fluctuation feature by using the De-trended Fluctuation Analysis (DFA) method. Result shows that the daily runoff series of main channel and branches of Weihe river all shows multi-fractal characteristics clearly, and the turns of multi-fractal intensity of daily runoff series in Weihe river are: Xianyang station (1.388) > Yingge station (0.697) > Linjiacun station (0.665) > Zhangjiashan station (0.662) > Zhuangtou station (0.635). Rainfall, evaporation, water income and human activity and other factors affect the fluctuation character and multi-fractal intensity of daily runoff series through these factors’ superimposition and pining down mutually. This study could provide a theoretical supply for obtaining the quantitative indicators on multi-fractal characteristics about eco-environment situation of watershed, and for runoff forecasting.

Evapotranspiration Estimation and Influence on Water Change in the Weihe River Basin,China

As the largest sub-basin of the middle reaches of the Yellow River with an obvious decreasing trend in annual runoff in recent years,the Weihe River basin is a significant region with regard to the protection and improvement of the environment in West China.Evapotranspiration(ET)is the loss of water from the Earth’s surface to the atmosphere and plays an important role in the regional water cycle,especially when considering water resource shortages.In this study,through analyzing the grid precipitation data after interpolation from 39 meteorological stations in and around the Weihe River basin from 1981 to 2011,certain periods during 1987,1993,1999,2001,2002 and 2009 with similar precipitation characteristics had been chosen for estimating the ET in the Weihe River basin.To illustrate ET’s influence on the water budget,these estimations are calculated based on an improved Penman-Monteith equation as well as remote sensing data and meteorological data.The results show that:(1)the annual ET in the Weihe River basin ranged from 350mm to 400mm in 1987,1993,1999,2001,2002 and 2009,accounting for more than 70%of the corresponding annual precipitation.There is a definite increasing trend in different decades that is primarily distributed during the summer.(2)The spatial distribution patterns of the ET in the six years mentioned area unique set,and the years are roughly identical with more than 500mm in the middle and lower reaches of the Weihe River in the southeastern region and less than 400mm in upper reaches of the Jinghe River in the northwestern area.(3)At the single-point scale,the coefficient of determination(R2)is 0.618 compared to the eddy correlation measurements in 2009 at the Changwu site,showing good agreement between the estimated ET and the observed ET.At the basin scale,the model-estimated ET is slightly lower than the actual ET with regard to the surface water budget.Additionally,the estimated ET in 2001,2002 and 2009 is close to the MODIS ET product.(4)For similar precipitation conditions,the regional amount of water shows a decreasing tendency with increasing ET,which may result from the rise in NDVI and improvements in vegetation coverage caused by human activities.This research suggests the influence of ET on water change at the basin level,which can also explain the decreasing runoff and can provide necessary information for improved water resource management.

Analysis on Strategic Future of Application of Agricultural Ecological Source in Control on Agricultural Nonpoint Source Pollution in Xi River Area in Guangxi

Non-point source pollution has become a hot issue on aquatic ecological environment at home and abroad. The research analyzed the challenges confronted by Xi River and proposed to construct agricultural ecological source in middle and upper reaches of the Xi River from the perspectives of scientific layout, legal construction, routine monitoring, technology integration, and coordination system in order to promote sustainable development of eco-environment in Xi River.

Discussion of Design Concepts of the Peach Blossom Lake Waterfront Park on the Chan River of Xi'an City

The construction of Peach Blossom Lake Waterfront Park on the Chan River in Xi'an City gives tourists and Xi'an citizens a waterfront park.By participating the field investigation,feasibility study,demonstration of design scheme as well as extended preliminary design and construction drawing design of the project,the author studied the "maintenance" and "innovation" in constructing modern urban waterfront parks by combining landscape design knowledge and practices,that is to say,how to inherit Chinese traditional culture and gardening art while making innovations,and achieve the organic integration of traditional cultural elements and modern functional elements.

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.

变化环境下渭河流域土壤水储量模拟及影响因素

[目的]随着气候变化和人类活动影响加剧,流域气候和下垫面条件发生改变,为准确模拟土壤水分变化过程并分析其影响因素对于地区的水资源管理和植被建设的重要意义。[方法]以黄土高原地区渭河流域为研究对象,基于ABCD水文模型,采用EFAST法分析模型参数敏感性,构建常参数和时变参数模型,比较不同参数模型的径流深和土壤水储量模拟精度,探讨气候变化和植被恢复对渭河流域土壤水储量变化的影响,明确土壤水储量变化的主导因素。[结果]土壤水层补给地下水的比例参数c最为敏感,地下水储放系数d、流域实际蒸散发量与土壤蓄水量之和的上限参数b次之,表征土壤完全饱和前径流的倾向性参数a最不敏感;与ABCD常参数模型相比,时变参数模型将率定期径流深模拟结果的NSE、KGE、R^(2)分别提高19%,10%,19%,验证期的NSE、KGE、R^(2)分别提高7%,7%,9%,时变参数模型显著改善径流深模拟效果;基于时变参数模型模拟的渭河流域土壤水储量与ERA5-Land 0—100 cm土层土壤水储量的相关关系最强,二者的变化过程基本相同;不同影响因素对渭河流域土壤水储量变化的影响程度由强到弱依次为潜在蒸散发>降水>NDVI。[结论]研究成果为该地区水资源规划和管理、植被建设提供科学依据,也为其他类似地区的土壤水储量研究提供参考。

2000—2021年渭河流域NDVI变化及其影响因素

渭河流域是黄河中游重要的生态涵养地,同时也是黄土高原水土流失的典型区域,监测该地区植被生长变化趋势,并分析其与气候变化和人类活动的关系,对科学评估区域生态建设成效、黄土高原植被恢复和生态修复具有重要意义。基于2000—2021年归一化植被指数(NDVI)、气温、降水量、人口密度、土地利用数据,分析了渭河流域NDVI的时空变化特征,探究了气候变化和人类活动对NDVI变化趋势的影响。结果表明,2000—2021年,渭河流域植被生长季NDVI呈增加趋势,全区年平均增速为0.004。年际尺度上,NDVI与年平均降水量呈正相关关系,与年平均气温的相关性不显著;月尺度上,NDVI与4月和8月的气温、降水量均呈正相关关系,与7月气温呈弱的负相关关系。人口密度变化与NDVI变化趋势呈负相关,流域人口密度的减小有利于植被的恢复和改善。土地利用类型内部变化是植被NDVI变化的主要原因。NDVI显著减少区NDVI的减少趋势主要由关中平原耕地NDVI的减少引起,NDVI显著增加区NDVI的增加趋势主要由草地、林地以及黄土丘陵区、黄土残塬区耕地NDVI的增加引起。

渭河陕西段干支流多环芳烃分布特征及潜在生态风险研究

【目的】为研究渭河陕西段干支流多环芳烃的时空分布特征,分析其来源与潜在的生态风险,【方法】采用气相色谱-质谱法(GC-MS)连续2 a对研究区内30个采样点水体的15种多环芳烃进行了定量检测分析,使用异构体比值法解析其来源种类及贡献程度,并运用苯并(a)芘毒性当量生态风险评价(TEQBap)和终生致癌风险评价(ILCR)分析其潜在风险。【结果】结果显示:渭河陕西段水体中ΣPAHs范围为0~93.00 ng·L^(-1),检出平均值为9.67 ng·L^(-1);单体浓度范围为0~30.50 ng·L^(-1),其中苯并蒽和芴的检出浓度最高,检出平均值分别为3.25 ng·L^(-1)、2.83 ng·L^(-1);在环数占比上,多环芳烃主要以三环、四环和五环的中高环形态存在。【结论】结论表明:渭河陕西段平水期各多环芳烃浓度相比丰水期有所增加,丰水期各多环芳烃种类分布相比平水期较为单一;各采样点处多环芳烃小于轻污染水平,与国内外其他河流相比处于较低水平;多环芳烃主要来源为煤等化石燃料及生物质的燃烧,并具有一定的生态风险,致癌风险不容忽视。

渭北旱塬不同年限撂荒地土壤酶活性及其化学计量变化特征

[目的]探究渭北旱塬区不同年限撂荒地的土壤养分、胞外酶活性及其化学计量的变化特征及影响因素,以期为渭北旱塬区撂荒地的改善与管理提供一定的理论依据。[方法]以渭北旱塬不同年限(5 a, 10 a, 20 a, 25 a和33 a)的撂荒地为研究对象,测定了土壤养分和参与土壤碳(C)、氮(N)和磷(P)循环的5种胞外酶活性,随后利用单因素方差分析、土壤胞外酶化学计量学模型和主坐标分析(PCoA)研究不同撂荒年限下土壤养分和胞外酶活性及其生态化学计量的变化规律及影响因子。[结果]随着撂荒年限的增加,土壤C和N获取酶活性显著减小,而P获取酶活性显著增加;土壤C、N和P含量变化与酶活性变化趋势相反。随撂荒年限延长,土壤微生物的C限制得到缓解,P限制逐渐加强。PCoA拟合环境因子分析结果显示:土壤可溶性有机碳(DOC)、总磷(TP)、速效氮(AN)和速效磷(AP)含量是驱动酶活性及其计量比变化的关键因子。[结论]撂荒对土壤养分状况具有显著改善作用,但随撂荒时间延长(20 a以上)会加剧微生物P限制,因此对经过长年撂荒的土地应当适量施用磷肥,以改善其土壤状况。

黄河-渭河交汇处水流结构与河道演变实测结果分析

黄河-渭河交汇处是黄河流域典型的大型河道交汇处之一,亦是中下游水动力和泥沙输移的重要控制节点。为进一步认识该处大宽深比、高含沙、复杂地形条件下的三维水流结构及河道演变规律,运用声学多普勒流速剖面仪(ADCP)对该交汇处15个横断面的流场进行现场测量,采用动能校正系数(α)和动量校正系数(β)分析水动力调整过程。通过遥感影像数据提取河道平面形态,分析交汇处及上下游的河道演变规律。结果表明,黄河-渭河交汇处可观测到明显的停滞区、最大流速区、流速恢复区等水动力特征区;拐角处未发现明显分离区,主要是因为该处河道过渡平顺。黄河与渭河交汇初期,由于流速差异大和河道缩窄导致流速不均匀性较强,α、β分别约为1.5、1.2,随着河道向下游展宽,流速不均匀性迅速减小。交汇处断面内存在较强的二次流,其流速可达主流流速的1/8,并向下游衰减。遥感研究表明交汇处所属黄河河段不稳定,且存在顶点的岸线淤长和对岸的岸线后退现象。

河南省主要河川径流变化归因

为相对全面客观地分析气候变化和人类活动对河南省主要河川径流变化的影响,基于河南省内卫河、伊洛河、洪汝河和唐河流域1961—2022年径流和降水资料,以及国家气候中心根据Penman-Monteith公式计算的年潜在蒸散发资料,比较4个蒸发对比站年潜在蒸散发和蒸发皿年蒸发值,运用Mann-Kendall突变检验法和累积双曲线法分析4个研究流域控制水文站年径流序列的变化趋势和突变年份,以及4个流域年降水和潜在蒸散发的变化趋势。采用基于Budyko假设的弹性系数法对径流变化开展归因分析。结果表明:4个蒸发对比站年潜在蒸散发与蒸发皿年蒸发变化趋势基本一致,4个水文站年径流深及4个流域年降水和年潜在蒸散发均呈下降趋势。4个水文站年径流深分别在1977年、1985年、2008年和2010年发生了突变。气候变化对径流减少的贡献率在卫河和伊洛河流域为7%以下,在洪汝河和唐河流域约为12%~18%,降水减少不显著和潜在蒸散发呈下降趋势是贡献率小的原因,可见人类活动是影响4个流域径流变化的主要驱动因素。