CryoSheds: a GIS modeling framework for delineating land-ice watersheds for the Greenland Ice Sheet

Choice of watershed delineation technique is an important source of uncertainty for cryo-hydrologic studies of the Greenland Ice Sheet (GrIS), with different methods yielding different watersheds for a common pour point. First, this paper explores this uncertainty for the Akuliarusiarsuup Kuua River Northern Tributary, Western Greenland. Next, a standardized, semi-automated modeling framework for generating land-ice watersheds for GrIS land-terminating ice (henceforth referred to as CryoSheds) using geographic information systems (GIS) hydrologic modeling tools is presented. The framework uses ArcGIS and the ArcPy geoprocessing library to delineate two types of land-ice watersheds, namely those defined by: (1) a hydraulic pressure potential with varying water to ice overburden pressure ratios (k-value), which determines theoretical flow paths from the hydrostatic equation, using surface and bedrock digital elevation models (DEMs) and (2) a surface topography DEM alone. Lastly, a demonstration of the CryoSheds method is presented for seven remotely sensed proglacial pour points along the Aussivigssuit River (AR), Western Greenland, and its largest tributaries. GrIS meltwater runoff from these seven nested land-ice watersheds is estimated using Modele Atmospherique Regional (MAR) v.3.2 and runoff uncertainties due to watershed delineation parameter selection is estimated.     

Spatial variability of soil erodibility and its correlation with soil properties in semi-arid mountainous watershed,Saudi Arabia

Soil erodibility values are best estimated from long-term direct measurements on runoff-plots; however, in lack of field tests, these values can be estimated using relationships based on physico-chemical soil properties. The study objective was to assess the erodibility and its correlation with soil properties. The average erodibility value was estimated 0.043 t ha h ha^?1 MJ^?1 mm^?1. The areas with heavy textured soil and low organic matter content had the lowest values of erodibility. The erodibility decreases as the sand content increases, whereas silt showed a positive correlation. The erodibility factors and its relation to soil properties were evaluated using multiple regression analysis. Results revealed that sand and organic matter content of soil combinedly explained 78% of variation. Altitudinal increases also seem to affect the soil texture. This study has demonstrated that soil properties and erodibility values can be used as assistance for soil conservation practices and modelling of landscape processes.     

太湖平原区河网结构变化对调蓄能力的影响

城镇化快速发展导致河网水系萎缩,连通性受阻,河网调蓄能力降低,加大了区域洪灾风险和洪涝损失.基于1960s,1980s,2010s的1:5万地形图水系及三个控制站的水位数据,选取河网密度(R_d),水面率(W_P),盒维数(D),水位Hurst指数(H),分析了近50年来太湖流域武澄锡虞地区的水系演变与河网调蓄能力变化;并借助代表性单元流域概念,以水位Hurst指数来表征河网调蓄能力,从河网调蓄的物理机理出发,探讨了河网调蓄与河网结构参数的关系.结果表明:① 受快速城镇化影响,1960s-2010s武澄锡虞地区河网密度,水面率及盒维数分别下降了18.87%,24.59%,7.60%,且1980s至2010s各水系指标的衰减率均高于1960s-1980s;② 1960-2010年,研究区年均及汛期的水位Hurst指数呈下降趋势,其所反映的河网调蓄能力与该地区河网水系各指标变化同步,这表明城镇化引起的河流水系衰减导致河网调蓄能力发生明显下降,非汛期水位Hurst指数先增加后降低,表现出一定的不确定性;③ 基于REW概念与水位Hurst指数值,初步构建了河网结构参数与调蓄能力的关系式,并对关系式进行了验证,基本可行,可在一定程度上揭示城镇化下水系变化对河网调蓄能力的影响,从而为评价平原水网区河网调蓄能力提供了一种相对简便的方法.     

基于从业者的旅游历史街区商业空间发展特征及机理——扬州“双东”案例

旅游商业化是历史街区复兴的重要途径。基于社会空间视角,旅游历史街区商业发展是以从业群体为日常运作核心,兼及居民、游客、恩庇者（管理者）等地域主体在内的空间生产过程。旅游历史街区演化是以“空间实践”为中心环节的社会建构,其发展状态是不同主体、不同层次的空间生产相互博弈的总体涌现。依托扬州“双东”案例,运用田野调查、统计检验、对应分析、模糊数学、逻辑回归等方法,以从业者空间生产为脉络,剖析旅游商业发展机理的杂合性与矛盾性,指出商业空间状态潜伏着不对称的利益博弈和不均衡的发展效应。“双东”旅游商业开发对城市中低产阶层自主就业有较强吸附效应,使之成为商业发展的主要依托。从业群体大致分化为乐观型、寓居型、保守型,分别对应于积极评价—业务扩张、温和评价—业务维持、消极评价—业务收缩生产机理,对“双东”空间演化具有不同的响应机制和影响效应。研究分析了主体、实践、环境特质对不同类型从业个体的影响特征以及对从业群体的总体影响,认为恩庇是统摄“好恶效应”、操控利益格局的多解方案。旅游历史街区商业发展利弊兼具、相因相生,统一于历史街区的自我演替过程。     

城市扩展对趵突泉泉域直接补给区保泉能力影响

直接补给区是趵突泉泉域重要的补给场所之一,随着城市发展其面积逐渐缩小。通过遥感手段解译60多年来济南城市发展趋势,分析揭示其对直接补给区面积及强渗漏小流域入渗功能的影响,采用大气降雨入渗系数法定量计算直接补给区面积削减对泉水保护的影响。结果表明,1954年—2015年,济南城市发展经历了平缓增长、快速增长、爆发式增长3个发展阶段,导致泉水直接补给区面积累计削减130km^2,约占总面积的29%,直接补给区内强渗漏小流域遭受不同程度破坏,6个渗漏功能完全丧失,9个渗漏功能部分丧失,仅9个渗漏功能保存近似完好,直接造成泉水入渗补给量减少约9.7万m^3/d(以多年平均降雨量648mm计)。直接补给区生态功能亟待保护与修复,应统筹管理小流域内山、水、林、土、草,加强小流域内山坡、山脚、山谷局部水循环的系统保护与修复,逐步恢复泉水补给能力。     

Geospatially based distributed rainfall‐runoff modelling for simulation of internal and outlet responses in a semi‐forested lower Himalayan watershed

This study presents a Geographic Information System (GIS)‐based distributed rainfall‐runoff model for simulating surface flows in small to large watersheds during isolated storm events. The model takes into account the amount of interception storage to be filled using a modified Merriam ( 1960 ) approach before estimating infiltration by the Smith and Parlange ( 1978 ) method. The mechanics of overland and channel flow are modelled by the kinematic wave approximation of the Saint Venant equations which are then numerically solved by the weighted four‐point implicit finite difference method. In this modelling the watershed was discretized into overland planes and channels using the algorithms proposed by Garbrecht and Martz ( 1999 ). The model code was first validated by comparing the model output with an analytical solution for a hypothetical plane. Then the model was tested in a medium‐sized semi‐forested watershed of Pathri Rao located in the Shivalik ranges of the Garhwal Himalayas, India. Initially, a local sensitivity analysis was performed to identify the parameters to which the model outputs like runoff volume, peak flow and time to peak flow are sensitive. Before going for model validation, calibration was performed using the Ordered‐Physics‐based Parameter Adjustment (OPPA) method. The proposed Physically Based Distributed (PBD) model was then evaluated both at the watershed outlet as well as at the internal gauging station, making this study a first of its kind in Indian watersheds. The results of performance evaluation indicate that the model has simulated the runoff hydrographs reasonably well within the watershed as well as at the watershed outlet with the same set of calibrated parameters. The model also simulates, realistically, the temporal variation of the spatial distribution of runoff over the watershed and the same has been illustrated graphically. Copyright © 2011 John Wiley & Sons, Ltd.     

Hydrologic impact of regional climate change for the snowfed and glacierfed river basins in the Republic of Tajikistan: hydrological response of flow to climate change

The warming of the Earth's atmosphere system is likely to change temperature and precipitation, which may affect the climate, hydrology and water resources at the river basins over the world. The importance of temperature change becomes even greater in snow or glacier dominated basins where it controls the snowmelt processes during the late‐winter, spring and summer months. In this study hydrologic responses of streamflow in the Pyanj and Vaksh River basins to climate change are analysed with a watershed hydrology model, based on the downscaled atmospheric data as input, in order to assess the regional climate change impact for the snowfed and glacierfed river basins in the Republic of Tajikistan. As a result of this analysis, it was found that the annual mean river discharge is increasing in the future at snow and glacier dominated areas due to the air temperature increase and the consequent increase in snow/ice melt rates until about 2060. Then the annual mean flow discharge starts to decrease from about 2080 onward because the small glaciers start to disappear in the glacier areas. It was also found that there is a gradual change in the hydrologic flow regime throughout a year, with the high flows occuring earlier in the hydrologic year, due to the warmer climate in the future. Furthermore, significant increases in annual maximum daily flows, including the 100‐year return period flows, at the Pyanj and Vaksh River basins toward the end of the 21st century can be inferred from flood frequency analysis results. Copyright © 2012 John Wiley & Sons, Ltd.     

Effects of reduced land cover detail on hydrological model response

Problems related to scale continue to be at the forefront of research in hydrology. Past research into issues of scale has focused mainly on digital elevation model grid size, the appropriate number and size of sub‐areas for subdividing a watershed, parameter transferability between watersheds and appropriate scales for linking hydrological and general circulation models. Much less attention has been given to the effects of scale on the representation of land cover and hydrological model response. Recent studies with respect to changes in land cover and hydrologic response have tended to focus on the issue of land cover maturity and the conversion of land through agricultural and forestry practices. The focus of this study is to examine the impact of the level of detail at which land cover is represented in modelling the hydrological response of Wolf Creek Basin in northwest Canada. A grid‐based land cover map with a spatial resolution of 30 m is coarsened or smoothed using several common grid‐based methods of aggregating categorical data, including: pixel thinning, modal smoothing and modal aggregation. A majority rule method based on polygons is also applied to the 30 m base cover. The SLURP hydrologic model is calibrated for the base cover and used as a reference for comparing simulations for the coarsened or ‘generalized’ land cover maps. Results of the simulations are compared to examine the sensitivity of hydrologic response to generalized land cover information. Comparisons of the SLURP model runs for Wolf Creek suggest that reducing the level of detail of land cover information generally has a limited effect on hydrologic response at the outlet. However, results for averages of water balance components across the basin suggest that the local variability of hydrologic response is affected in general. Copyright © 2007 John Wiley & Sons, Ltd.     

Effects of subsurface soil characteristics on wetland–groundwater interaction in the coastal plain of the Chesapeake Bay watershed

Ecosystem services provided by depressional wetlands on the coastal plain of the Chesapeake Bay watershed (CBW) have been widely recognized and studied. However, wetland–groundwater interactions remain largely unknown in the CBW. The objective of this study was to examine the vertical interactions of depressional wetlands and groundwater with respect to different subsurface soil characteristics. This study examined two depressional wetlands with a low‐permeability and high‐permeability soil layer on the coastal plain of the CBW. The surface water level (SWL) and groundwater level (GWL) were monitored over 1 year from a well and piezometer at each site, respectively, and those data were used to examine the impacts of subsurface soil characteristics on wetland–groundwater interactions. A large difference between the SWL and GWL was observed at the wetland with a low‐permeability soil layer, although there was strong similarity between the SWL and GWL at the wetland with a high‐permeability soil layer. Our observations also identified a strong vertical hydraulic gradient between the SWL and GWL at the wetland with a high‐permeability soil layer relative to one with a low‐permeability soil layer. The hydroperiod (i.e., the total time of surface water inundation or saturation) of the wetland with a low‐permeability soil layer appeared to rely on groundwater less than the wetland with a high‐permeability soil layer. The findings showed that vertical wetland–groundwater interactions varied with subsurface soil characteristics on the coastal plain of the CBW. Therefore, subsurface soil characteristics should be carefully considered to anticipate the hydrologic behavior of wetlands in this region.     

模型驱动数据空间分辨率对模拟生态水文过程的影响

设定两种独立的调参方案,检验将高/低分辨率下的调参值应用到低/高分辨率中驱动模型模拟的可行性;同时分析驱动数据分辨率的差异对模型模拟生态水文过程的影响;此外,设置9种集水面积阈值,分析驱动数据分辨率与集水面积阈值对模拟结果的影响。结果表明两种调参方案下模拟的水文与生态数据相关性强、差异小,说明调参方案受驱动数据分辨率的影响不明显;分辨率对土地覆被和土壤类型面积影响小,而对高程和坡度影响大;驱动数据分辨率降低,模拟径流的均值减小、峰值增大、生态变量值增大;驱动数据分辨与集水面积阈值之间不存在交互作用;集水面积阈值增大,模拟径流的均值、峰值均减小,生态变量值也减小,但阈值变化对峰现时间无影响。