Modelling Land Use/Land Cover Change of River Rwizi Catchment, South-Western Uganda Using GIS and Markov Chain Model

Analysis of catchment Land use/Land cover (LULC) change is a vital tool in ensuring sustainable catchment management. The study analyzed land use/land cover changes in the Rwizi catchment, south western Uganda from 1989-2019 and projected the trend by 2040. Landsat images, field observations, key informant interviews and focus group discussions were used to collect data. Changes in cropland, forestland, built up area, grazing land, wetland and open water bodies were analyzed in ArcGIS version 10.2.2 and ERDAS IMAGINE 14 software and a Markov chain model. All the LULC classes increased in area except grazing land. Forest land and builtup area between 2009-2019 increased by 370.03% and 229.53% respectively. Projections revealed an increase in forest land and builtup area by 2030 and only built up area by 2040. LULCC in the catchment results from population pressure, reduced soil fertility and high value of agricultural products.

Runoff Modeling in Ungauged Catchments Using Machine Learning Algorithm-Based Model Parameters Regionalization Methodology

Model parameters estimation is a pivotal issue for runoff modeling in ungauged catchments.The nonlinear relationship between model parameters and catchment descriptors is a major obstacle for parameter regionalization,which is the most widely used approach.Runoff modeling was studied in 38 catchments located in the Yellow–Huai–Hai River Basin(YHHRB).The values of the Nash–Sutcliffe efficiency coefficient(NSE),coefficient of determination(R2),and percent bias(PBIAS)indicated the acceptable performance of the soil and water assessment tool(SWAT)model in the YHHRB.Nine descriptors belonging to the categories of climate,soil,vegetation,and topography were used to express the catchment characteristics related to the hydrological processes.The quantitative relationships between the parameters of the SWAT model and the catchment descriptors were analyzed by six regression-based models,including linear regression(LR)equations,support vector regression(SVR),random forest(RF),k-nearest neighbor(kNN),decision tree(DT),and radial basis function(RBF).Each of the 38 catchments was assumed to be an ungauged catchment in turn.Then,the parameters in each target catchment were estimated by the constructed regression models based on the remaining 37 donor catchments.Furthermore,the similaritybased regionalization scheme was used for comparison with the regression-based approach.The results indicated that the runoff with the highest accuracy was modeled by the SVR-based scheme in ungauged catchments.Compared with the traditional LR-based approach,the accuracy of the runoff modeling in ungauged catchments was improved by the machine learning algorithms because of the outstanding capability to deal with nonlinear relationships.The performances of different approaches were similar in humid regions,while the advantages of the machine learning techniques were more evident in arid regions.When the study area contained nested catchments,the best result was calculated with the similarity-based parameter regionalization scheme because of the high catchment density and short spatial distance.The new findings could improve flood forecasting and water resources planning in regions that lack observed data.

Soil erosion differences in paired grassland and forestland catchments on the Chinese Loess Plateau

In this study,two adjacent gauged catchments on the Chinese Loess Plateau were selected,in which one catchment was afforested and one was restored with natural vegetation in 1954.The distributions of soil erosion rates were estimated between 2010 and 2020 with a high spatial resolution of 2 m in the paired catchments based on the Revised Universal Soil Loss Equation model(RUSLE)and Geographic Information Systems(GIS).The results showed that the simulated soil erosion rates in 2010-2020 averaged 12.58 and 8.56 t ha^(-1)a^(-1)for the grassland and forestland catchment,respectively.Moreover,areas with high soil erosion rates(>80t ha^(-1)a^(-1))were mainly distributed in the topography with steep slope gradients(>45°).Comparisons between simulated soil erosion rates and observed annual sediment loads indicated that the simulation results of the grassland catchment were lower than the observed values,while it was reversed in the forestland catchment.We conclude that the RUSLE model cannot simulate the gravity erosion induced by extreme rainfall events.For the forestland catchment,insufficient streamflow and dense vegetation coverage are crucial factors resulting in hindering the movement of sediments.

Sediment-Loading Processes in a Forested Catchment: Modeling and Observations

In order to investigate sediment-loading processes in a catchment, the daily time series of river discharge and sediment load were applied to a semi-distributed model, the Soil and Water Assessment Tool (SWAT). The time series of discharge and sediment load were obtained by monitoring the river stage and water turbidity of the Oikamanai River, Hokkaido, Japan, in the rainfall season (April-November) of 2011-2014. The catchment is forested (ca 90% area) but underlain by the Neogene sedimentary rocks with currently active faults and forest soils with tephra layers, which tend to frequently produce slope failure such as landslide and bank collapse by rainfall or snowmelt. The water turbidity, T, in ppm was converted into suspended sediment concentration, SSC, in g/L by applying the linear relationship between T and SSC. The acquisition of the time series of discharge, Q (m3/s) and sediment load, L (=Q·SSC in g/s) of the river allowed us to distinguish the fluvial sediment transport, accompanied by slope failure in the upstream, from that under no slope failure. The SWAT was used to simulate soil erosion and identify the region prone to the soil erosion in the Oikamanai River basin. The model’s results showed a satisfactory agreement between daily observed and simulated sediment load as indicated by the high Nash-Sutcliffe efficiency. This evidences that the upper mountainous region of the catchment provides a main sediment source, accompanied by slope failure.

Water yield and biomass production for on a eucalypt-dominated Mediterranean catchment under different climate scenarios

Worldwide,forests are vital in the regulation of the water cycle regulation and in water balance allocation.Knowledge of ecohydrological responses of production forests is essential to support management strategies,especially where water is already scarce.Shifting climatological patterns are expected to impact thermopluviometric regimes,water cycle components,hydrological responses,and plant physiology,evapotranspiration rates,crop productivity and land management operations.This work(1)assessed the impacts of different predicted climate conditions on water yield;(2)inferred the impacts of climate change on biomass production on eucalypt-to-eucalypt succes sion.To this end,the widely accepted Soil and Water Assessment Tool(SWAT)was run with the RCA,HIRHAM5 and RACMO climate models for two emission scenarios(RCP 4.5 and8.5).Three 12-year periods were considered to simulate tree growth under coppice regime.The results revealed an overall reduction in streamflow and water yield in the catchment in line with the projected reduction in total annual precipitation.Moreover,HIRHAM5 and RACMO models forecast a slight shift in seasonal streamflow of up to 2 months(for2024-2048)in line with the projected increase in precipitation from May to September.For biomass production,the extreme climate model(RCA)and severe emis sion scenario(RCP 8.5)predicted a decrease up to 46%.However,in the less extreme and more-correlated(with actual catchment climate conditions)climate models(RACMO and HIRHAM5)and in the less extreme emission scenario(RCP 4.5),biomass production increased(up to 20%),and the growth cycle was slightly reduced.SWAT was proven to be a valuable tool to assess climate change impacts on a eucalypt-dominated catchment and is a suitable decision-support tool for forest managers.

Hydrogeological Investigations of Groundwater and Surface Water Interactions in the Berg River Catchment, Western Cape, South Africa

The Berg River Catchment based in the Western Cape Province,South Africa services the greater Cape Town area with water,subsequent to supplying the vast agricultural activities that exist in the middle and the lower reaches.This study thus investigates the hydrogeochemical interactions between surface and groundwater in the Berg River Catchment with the aim of establishing trends and transfer of constituents between the surface and groundwater systems,investigates the role that geology plays in water chemistry as well as identifies the geochemical processes controlling surface and groundwater chemistry in the catchment.This study was carried out using three types of research designs namely i)experimental research design;ii)field research design and meta-analysis research design.Furthermore,the study made use of hydrochemical data ranging from 2003 to 2013 obtained from the National Water Monitoring Database owned and maintained by the Department of Water and Sanitation and data that were sampled in 2016 by authors and analyzed using the ICP-MS Technique Ground Water Chart,Arc-GIS and Geosoft(Oasis Montaj)were further employed to model the data.The results indicated that:i)in the Upper Berg there is not much interaction and transfer of constituents between surface and groundwater;ii)the Middle Berg,however,indicated a degree of interaction with the sharing of constituents between the two water systems and iii)the Lower Berg indicated only NaCl water type also noting that the area situated near the river mouth whereby there is the mixing of river and seawater.

土壤厚度演化模型理论方法研究进展

全球平均土壤厚度仅约为1 m,但土壤厚度的空间分布信息在地貌、生态及水文科学等领域的研究和实践中具有重要价值。由于其具有显著的空间异质性,基于现有土壤制图产品、地球物理勘测及经验统计模型难以获取流域尺度土壤厚度分布信息,亟待发展土壤厚度预测的过程机理模型。本文回顾了土壤厚度演化模型理论方法的研究进展,评价了不同土壤生成及输移模型的适用性。研究指出土壤化学风化成土等机理仍不清晰是制约模型发展的理论瓶颈。此外,模型的方法体系仍需完善,亟待进一步发展描述土壤生成和输移的函数形式及其参数的估计方法等,指出物理与随机结合的模拟方法以及基于数学物理途径的参数确定方法等有望解决模型应用中遇到的难题。最后,在土壤厚度演化模型基础上,提出发展基于流域协同演化理论的土壤发生学模型是定量预测土壤理化全要素发生所亟需突破的难点之一。

巢湖流域水生态系统状况变化研究

基于已开展的巢湖流域水域生物资源调查,综合2013、2023年水质、浮游植物、着生藻类、底栖动物和大型水生植物等资料,分析巢湖水域生物环境状况变化。结果表明:经过10年治巢项目的实施,巢湖流域整体水质有了明显改善,以南淝河和十五里河的水质改善最为明显。浮游植物群落组成发生较大变化,蓝藻门密度比由33.33%降为2.76%,硅藻门、金藻门密度比由11.43%、0.83%分别上升为26.62%、1.76%。底栖动物多样性呈上升趋势,耐污类群密度呈下降趋势。着生硅藻多样性指数总体呈增长趋势,优势群类依然主要为双壳缝目、无壳缝目和单壳缝目,大型水生植物群落优势种组成变化相对较小。本研究可为山水工程生态修复效果科学评估和生态修复方案制定提供数据支撑。

降雨时空不确定性对小流域洪峰模拟的影响评估

山丘区小流域洪峰模拟结果与降雨时空分布密切相关。以河南省荥阳市王宗店流域“7·20”山洪灾害为例,构建了15种时空分布的10 min尺度降雨情景,综合采用中国山洪水文模型和方差分析理论评估降雨时空情景变化对洪峰模拟的影响。结果表明:中国山洪水文模型可以较好地模拟“7·20”暴雨洪水过程。不同时间情景下10 min降雨量均匀分布模拟得到的洪峰流量较小、峰现时间较晚;非均匀分布时最大10 min降雨量发生时间越晚,模拟得到的洪峰流量越大、峰现时间越晚。空间情景变化主要影响洪峰流量模拟,采用泰森多边形法模拟得到的洪峰流量最大。时间情景变化是洪峰流量和峰现时间模拟结果不确定性的最主要来源,空间情景变化和时空情景耦合变化仅影响洪峰流量模拟。

秦汉新城渭河1#雨水出口系统优化方案研究与实践

针对西安市西咸新区秦汉新城渭河1#雨水出口流域面积过大,存在系统内涝安全风险的问题,研究1#雨水出口系统优化方案。依据陕西省省级城市内涝治理实施方案,分析1#雨水出口系统存在的一系列问题以及优化原则和目标,重点分析了大汇水分区下雨水系统安全以及雨污分流改造的思路,为解决城市水安全、水环境以及水资源利用提出了应对措施与建议。

供需协调视角下城市应急救援可达性评估--以郑州“7·20”特大暴雨为例

日益频繁的特大暴雨对城市造成愈加严重的影响,亟须关注应急救援需求的变化特征以及与之对应的应急救援可达性水平,以此提升城市应急救援的动态响应能力。以郑州市中心城区为例,通过社交媒体数据识别求救点和道路阻碍点,分析“7·20”特大暴雨背景下应急救援需求的时空分布特征。基于供需协调的视角,利用高斯两步移动搜寻法评估城市应急救援可达性。研究结果表明,应急救援需求具有动态集聚分布特征,同时应急救援可达性存在供需错位。最后,从完善应急救援通道网络、建立应急救援可达性智能评估平台、优化应急救援资源的空间布局三方面提出优化策略。

基于就医活动推断的老年人公交就医可达性研究

为准确评估老年人公交就医出行的实际可达性,本文基于老年卡数据构建公交出行链,提出基于公交出行链的老年人就医活动推断方法,获取老年人的实际就医出行需求和出行时间。引入公交实时到站数据以反映公交实际运营水平对就医可达性的影响,构建面向出行全过程的实际出行成本矩阵,包括等候时间、乘车时间、换乘时间。考虑不同医院服务供给能力差异构建综合服务能力指标,引入分级服务半径和高斯距离衰减函数,提出基于改进两步移动搜索法的老年人公交就医可达性计算方法。以北京市六环内区域为例进行实证分析,结果表明:老年人公交就医可达性整体呈现由中心向外围递减的趋势,在城市外围区域其分布也存在空间异质性,五环路外的东部和西部区域可达性较好,而北部、东北部区域的可达性相对较差;各区域高峰时段的平均可达性均明显低于平峰时段的平均可达性。本文可为提升老年人就医出行可达性和公交系统适老化水平提供支撑。

基于改进高斯两步移动搜索法的西南山地乡村居民医疗设施可达性评价——以重庆市九龙坡区为例

近年来,乡村医疗资源的数量和质量都有显著提升,但不同地区乡村居民在获得医疗机会、就医成本等方面存在较大差异,医疗设施布局不合理问题仍存在。医疗设施可达性作为衡量医疗设施空间布局是否合理的关键指标,为解决医疗资源分配不合理和改善医疗资源分配不公等问题提供了重要依据。针对传统高斯两步移动搜索法(Gaussian-Based 2SFCA)对于山地乡村地区医疗资源可达性在供给与需求思考不足的问题,将其进行改进,从而更为科学客观地评价可达性。研究选取重庆市九龙坡区乡村地区为研究对象,借助Arcgis平台分析乡村医疗设施供需情况,引介改进高斯两步移动搜索法分析设施可达性,在此基础上,借助SPSS软件进行K聚类分析,揭示乡村医疗设施可达性影响因素。研究发现:第一,各类医疗设施的可达性数值综合层面上的高可达性区域主要是由于临近医疗资源高供给能力的县综合医院和乡镇卫生院所贡献的,而村级医疗设施对综合可达性空间差异影响较小;第二,山地乡村地区公共医疗设施配置存在医疗资源与人口分布的空间不匹配的情况,主要体现在村级医疗设施;第三,区域可达性水平与交通通达性高低没有必然联系,受人口需求(人口规模、人口密度)、医疗设施供给服务能力及分布的影响更大。最后针对不同可达性区域提出优化策略。本研究为西南山地乡村地区医疗设施可达性评价提供了一套具有实践操作性的方法体系。

中国水文区划及水文分区方法综述

水文区划是水资源规划的重要依据,也是无资料地区水文研究的有效手段。中国早期的水文区划工作主要是适应水资源规划的需求,全国性的水文区划主要出现在1950s,20世纪末集中出现了更精细、完善的省级水文区划研究。水文分区是水文区划工作的核心内容,主要包括分区指标和分区方法的确定。当前采用的水文分区指标主要包括气候、水文、下垫面三类,水文分区方法以聚类方法为主。目前主要用于解决水文缺资料问题,同时也发展出生态水文分区方法,提高了生态性评价的合理性。基于当前研究进展,提出未来研究重点如下:(1)在水文分区中纳入水文相似理论;(2)水文区域性规律研究及其在水资源、环境、生态等领域的应用;(3)水文分区结果的检验与科学解释。本研究可为区域水资源规划、水文模型参数移植、生态环境保护等提供理论依据。

基于改进两步移动搜索法的合肥市中心城区综合公园可达性评价

为提高城市综合公园布局均衡性地定量评估的准确性,以合肥市中心城区为例,提出一种基于改进多出行模式的两步移动搜索法,利用高德地图的路径规划模型,结合双变量局部空间自相关、洛伦兹曲线以及基尼系数等方法,在手机信令数据的基础上对不同时间阈值下的城市综合公园的可达性及供需情况进行分析,进一步揭示中心城区综合公园布局的合理性。结果显示:合肥市中心城区综合公园的可达性空间差异显著,可达性较高区域通常分布在新城区以及综合公园周边地区,并且随着时间阈值的提高,可达性水平的空间分布呈现均衡态势;合肥市中心城区在15 min与30 min时间阈值下均只有近5%的居住网格处于供需匹配状态;近7%的居住网格处于供需显著不匹配状态,主要集中于老城区西部以及滨湖区北部区域,居住区密度与综合公园数量是影响供需匹配的重要原因。研究结果表明,通过利用手机信令数据与高德路径规划数据作为数据源对传统可达性的计算方法以及两步移动搜索模型进行改进,建立微观尺度下城市综合公园的可达性评价框架,能够精确地评估城市综合公园的可达性;通过优化城市交通的通达程度以提高居民综合公园游憩出行的阈值,能够显著促进城市综合公园整体的空间分布合理性。

基于两步移动搜索法的福州市公园绿地主客观可达性研究

公园绿地的可达性对于提升民生福祉、环境公平及城市高质量发展具有深远意义。综合考虑公园绿地的主观和客观供给能力,基于公园绿地规模、网络好评度、高德地图API路径规划等数据,运用高斯两步移动搜索法测度了居民单一出行及多交通出行模式下福州市公园绿地的客观和主观可达性,得出以下结论:(1)同一出行模式下公园绿地的主客观可达性差异大,客观可达性的高值区主要分布在非中心城区,而主观可达性的高值区大多分布在中心城区;(2)不同交通出行模式下主观和客观可达性也存在差异,步行出行模式下的公园绿地可达性低于驾车和公共交通出行模式的可达性,综合出行模式的可达性分布与驾车可达性分布相似,尚未形成公共交通主导的公园绿地发展模式;(3)公园绿地主客观供需平衡的县域少,供需不平衡的县域多,高人口密度县域存在公园绿地供给小于需求问题,非中心城区县域公园绿地主客观供需比普遍较低;(4)步行、驾车、公共交通出行模式下的高客观供需比-高主观供需比的公园绿地仅三坊七巷和福州市贵安新天地休闲旅游度假区,超过70%的公园绿地属低客观供需比-低主观供需比类型。本研究不仅关注公园绿地的空间可达性,也基于人的感受对公园绿地的主观可达性加以测度,为可达性评价提供新的研究思路,同时也为福州市公园绿地资源配置和存量绿地的质量提升提供建议。

全球气象预报驱动流域水文预报研究进展与展望

全球气象模型及新兴人工智能模型为流域水文预报提供了日、次季节、季节等不同时间尺度的海量气象预报数据。与此同时,基于气象预报开展水文预报,涉及到数据获取、模型构建、评估检验等技术问题。本文以全球气象预报相关的研究计划为切入点,调研现有的1 d至2周小时尺度中短期天气预报、1~60 d次季节尺度气象预报、1~12个月季节尺度气象预报以及新兴的人工智能气象预报;梳理气象预报驱动下流域水文预报模型方法,阐述气象预报订正、水文模型设置和预报评估检验等技术环节。基于全球气象预报生成实时和回顾性流域水文预报,定量检验不同预见期下预报精度以评估相关模型方法的预报性能,为水利工程预报-调度实践应用打下坚实的基础。

城市内涝灾害对应急救援服务可达性的影响评估

【目的】城市化进程加快和气候变化导致内涝积水频发,造成道路封闭和交通堵塞,给城市应急救援响应的时效性带来严重影响。为了准确评估暴雨内涝下的城市应急救援响应能力,【方法】以荔湾区为例,通过构建内涝水动力模型,模拟不同设计降雨情景下的内涝积水,识别道路积水风险,明确阻断道路,并结合两步移动搜寻法(2SFCA)对不同脆弱性的兴趣点(POI)的应急救援服务可达性进行评估。【结果】结果显示:随着降雨重现期从1 a一遇增大到100 a一遇,内涝积水面积增大,平均积水深度从0.08 m增大到0.20 m。受积水影响道路数量持续增加,阻断道路长度从11 km上升至49 km,增长了超过300%。随着阻断道路的增多,应急救援可达的POI数量呈现下降趋势,并且在不同时间阈值内平均下降40%以上,可达性呈明显下降趋势。【结论】内涝模型耦合城市路网得到的道路积水可以揭示阻断道路的总体格局,可达性模型可以快速估算出应急救援的时效性。结果可为应急救援响应能力的评估提供参考。

梅大高速公路路基边坡失稳条件与滑坡机理初探

文章对广东梅大(梅州—大埔)高速公路路基边坡失稳和滑坡的成因机制进行了初步研究和分析,基于香港地区路基边坡失稳滑坡调查研究资料、成果和现场勘察获得了失稳路基边坡附近完全风化花岗岩土的颗粒分布和液限塑限含水率,定量计算、分析了该段路基边坡稳定性。通过Google地形图分析了失稳路基边坡附近的几个可能汇水区域和汇水量,对该路基边坡失稳与滑流的成因机制进行了分析。研究认为山坡公路建设需要开挖削坡和填土,可完全改变自然山坡汇水流域;公路可成为瞬态河流,将大量雨水跨流域调流到其他公路边坡或山坡,导致边坡失稳和滑坡,形成公路坍塌丢失。这种路基边坡失稳模式亟待深入研究并加强防范。

降雨集流渗灌条件下红梅杏根系分布研究

为了明确降雨集流渗灌技术在宁南山区红梅杏种植中解决缺水问题的实际效果,以5年生红梅杏果树为研究对象,设置自然条件(NAT)和覆膜安装渗灌器(RCII)两种处理,采用分层分段挖掘法挖掘根系,并对比分析根长密度分布。结果表明:通过降雨集流渗灌技术所集蓄的水量可以促进红梅杏根系更好的生长,解决缺水问题。在RCII条件下,在地表以下0~100 cm内,根长密度随深度的增加而减少。此外,在RCII条件下,沿行距方向和45°方向的根长密度的对比,证明了渗灌器集流对根系进行水分补充的有效性。通过对行距、株距、深度、根长密度进行偏相关分析和多独立样本非参数检验,发现行距(安装渗灌器)、株距(未安装渗灌器)对根长密度在水平方向的分布并未产生明显区别(显著性P>0.05);地下深度60~80 cm是影响根长密度分布的关键区间。综上,降雨集流渗灌技术对解决宁南山区红梅杏旱地种植过程中的缺水问题具有积极作用,具有较好的推广前景。