Multivariate analysis as a tool to infer hydrologic response types and controlling variables in a humid temperate catchment

We assess the ability of multivariate statistical analyses applied to event hydrographs parameters, to characterize a catchment hydrological behaviour. Motivation for such an approach lies in the fact that streamflow records have yet to be exploited to their full potential towards hydrological interpretation and can be used to infer a catchment state of connectivity from a qualitative standpoint. We have therefore processed 96 event hydrographs from a small headwater temperate humid forested catchment using principal component analysis, variation partitioning and classification tree analysis. These techniques prove to be promising in discriminating contrasted types of hydrologic responses (e.g. low‐ vs high‐magnitude events, slow vs quick timing events), identifying the main hydro‐meteorological variables that control these responses and determining thresholds values of the hydro‐meteorological variables leading to a switch between catchment response types. Copyright © 2010 John Wiley & Sons, Ltd.     

Application of a regionalized Clark IUH model with limited hydrologic data availability

To aid prediction of the flow hydrograph in a basin with limited data, a practical approach to determining a regionalized Clark instantaneous unit hydrograph (IUH) model is presented. The proposed model is described in terms of the synthetic time–area concentration curve, the concentration time, and a special regional similarity value that is valid in the whole basin. The latter was estimated from a Monte Carlo testing procedure based on the normal probability distribution of transformed regional similarity values composed of the time of concentration and the storage coefficient in gauged basins. The time–area concentration curve and the concentration time were calculated from a rational equation as in conventional methods. The method of transformation adopted was the Box–Cox power transformation, which is known to make non‐normal values resemble normal data. By introducing the regional similarity value into a Clark IUH, a statistically best estimate of IUH for given data conditions and its quantified degree of uncertainty were realized. The Wi River basin in Korea was used to test the applicability of the regionalized Clark IUH. The performance of the suggested methodology was evaluated by assuming an ungauged sub‐basin at the site. The results showed that the IUH model developed in this work was an effective tool, predicting a reliable hydrograph within the study area even though only limited data were available. Copyright © 2008 John Wiley & Sons, Ltd.     

夏季金塔绿洲及邻近戈壁的冷湿舌及边界层特征分析

利用2004年7月金塔“绿洲系统能量与水分循环过程观测与数值研究”重点项目加强期系留梯度探测资料,对该绿洲边缘的冷湿舌现象及边界层特征进行了分析。结果表明,戈壁绿洲边缘的确存在冷湿舌;白天从09时至18时都有冷湿舌出现,高度一般维持在0～600m之间;冷湿舌受风速、风向、太阳对地面加热强度等因素的影响很大,也与午后绿洲辐散风有密切关系。这一发现对深入研究戈壁绿洲能量与水分循环,尤其是对绿洲与周围沙漠戈壁的水热交换研究具有重要意义,也为进一步研究绿洲的维持和发展提供了很好的基础。     

基于规则格网DEM的地形特征提取算法

提出并实现了一种基于规则格网DEM的地形特征线提取算法,该算法在现有地表水流模拟方法的基础上将矢量操作与栅格操作结合起来对规则格网DEM中的洼地进行填平处理,采用邻域格网分组扫描方法确定平地水流方向,与以往算法相比在提取效率和结果准确性等方面都有了明显的改进,从而也使其更加适合于对大规模的DEM数据进行处理,采用各种尺度的DEM进行试验的结果验证了以上结论.     

Scaling effects of proximate desertification drivers on soil nutrients in northeastern Tanzania

We tested the scaling effects of proximate desertification drivers (i.e. soil erosion, bush encroachment and grazing pressure) on soil nutrients in northeastern Tanzania. We analyzed nutrient concentrations in the desertified and non-degraded benchmark. For the desertified landscapes we analyzed nutrient concentrations at the coarse (landscape), medium (micro-landscape) and sampling unit (fine scale) levels. Further, for the desertified micro-landscapes, we used the differences in total nutrient concentrations to identify moderately dysfunctional and dysfunctional micro-landscapes. The desertified micro-landscapes had an overall lower soil organic matter, total nitrogen and exchangeable phosphorus, and soil water, but had elevated cation exchange capacity and soluble bases compared with the benchmark. Different intensities of desertification processes, mediated by the three proximate desertification drivers, produced varied amounts of nutrients corresponding with moderately dysfunctional and dysfunctional micro-landscapes. The dysfunctional micro-landscapes had the lowest nutrient availability. The effects of proximate desertification drivers on pooled nutrients were scale-independent. For individual nutrients only pH, soil water and Mg⁺⁺ showed scaling effects at the coarse or medium scales for soil erosion, while for grazing pressure pH, soil water, CEC, Na⁺, Mg²⁺⁺ and Ca²⁺⁺ showed scale dependence. The scaling effects were interlinked with landscape processes that operated simultaneously and interactively with different drivers.     

广西凤山岩溶国家地质公园典型地质遗迹景观价值

广西凤山岩溶国家地质公园是我国西南喀斯特旅游资源的富集带,岩溶遗迹景观种类多、规模宏大、特色鲜明。园区内的岩溶洞穴、天生桥、天坑和天窗等4类典型地质遗迹景观与国内外同类景观对比,洞穴通道规模世界最大、巨型洞穴厅堂数量多、密度大;形态巨大、景观奇特的地下河三门海天窗、以高大石笋为代表的洞穴沉积物世界罕见,世界上最大的洞内天生桥,均具有很高的美学观赏价值和科学价值,地质遗迹景观资源的典型性、稀有性、自然性均在同类地质遗迹中名列前茅。     

Distributed hydrologic and hydraulic modelling with radar rainfall input: Reconstruction of the 8–9 September 2002 catastrophic flood event in the Gard region,France

On 8–9 September 2002, an extreme rainfall event caused by a stationary mesoscale convective system (MCS) occurred in the Gard region, France. Distributed hydrologic and hydraulic modelling has been carried out to assess and compare the various sources of data collected operationally and during the post-event field surveys. Distributed hydrological modelling was performed with n-TOPMODELs and assessed for ungauged basins with the discharge estimates of the post-event surveys. A careful examination of the occurrence in time and space of the flash floods over the head watersheds indicates that flooding was controlled by the trajectory of the convective part of the MCS. Stationarity of the MCS over the Gardon watershed (1858 km² at Remoulins) for 28 h was responsible for the exceptional magnitude of the flood at this scale. The flood dynamics were characterized by an extensive inundation of the Gardonnenque plain upstream of the Gardon Gorges resulting in a significant peak flow reduction downstream. One-dimensional unsteady-flow hydraulic modelling was found to be required to reproduce these dynamics. Hydraulic modelling also proved to be potentially useful for the critical analysis and extrapolation of operational discharge rating curves.     

Thermal Remote Sensing of Near Surface Environmental Variables: Application Over the Oklahoma Mesonet

Many recent studies have applied satellite remote sensing data to large‐scale hydrologic and biospheric modeling. It is widely accepted that the thermal infrared observations from the Advanced Very High Resolution Radiometer (AVHRR) have the potential to estimate land surface conditions, such as surface temperature, near surface air temperature, and near surface water vapor. In this study, algorithms to estimate all three variables are presented and applied to an area covering the state of Oklahoma for a six day period in August, 1994. The results were validated using ground observations from the 111 station Oklahoma Mesonet. Validation of the remote sensing algorithms with Mesonet observations produced comparable results to previous validation studies. In addition, the validation process revealed inadequacies in thermal modeling that had not been detected in previous validation studies leading to the development of a new approach to estimate atmospheric water vapor.     

Predicting landscape sensitivity to present and future floods in the Pacific Northwest,USA

Floods are the most frequent natural disaster, causing more loss of life and property than any other in the USA. Floods also strongly influence the structure and function of watersheds, stream channels, and aquatic ecosystems. The Pacific Northwest is particularly vulnerable to climatically driven changes in flood frequency and magnitude, because snowpacks that strongly influence flood generation are near the freezing point and thus sensitive to small changes in temperature. To improve predictions of future flooding potential and inform strategies to adapt to these changes, we mapped the sensitivity of landscapes to changes in peak flows due to climate warming across Oregon and Washington. We first developed principal component‐based models for predicting peak flows across a range of recurrence intervals (2‐, 10‐, 25‐, 50‐, and 100‐years) based on historical instantaneous peak flow data from 1000 gauged watersheds in Oregon and Washington. Key predictors of peak flows included drainage area and principal component scores for climate, land cover, soil, and topographic metrics. We then used these regression models to predict future peak flows by perturbing the climate variables based on future climate projections (2020s, 2040s, and 2080s) for the A1B emission scenario. For each recurrence interval, peak flow sensitivities were computed as the ratio of future to current peak flow magnitudes. Our analysis suggests that temperature‐induced changes in snowpack dynamics will result in large (>30–40%) increases in peak flow magnitude in some areas, principally the Cascades, Olympics, and Blue Mountains and parts of the western edge of the Rocky Mountains. Flood generation processes in lower elevation areas are less likely to be affected, but some of these areas may be impacted by floodwaters from upstream. These results can assist land, water, and infrastructure managers in identifying watersheds and resources that are particularly vulnerable to increased peak flows and developing plans to increase their resilience. Copyright © 2015 John Wiley & Sons, Ltd.     

Modeling the effects of climate change projections on streamflow in the Nooksack River basin,Northwest Washington

The Nooksack River has its headwaters in the North Cascade Mountains and drains an approximately 2000 km² watershed in northwestern Washington State. The timing and magnitude of streamflow in a snowpack‐dominated drainage basin such as the Nooksack River basin are strongly influenced by temperature and precipitation. Projections of future climate made by general circulation models (GCMs) indicate increases in temperature and variable changes in precipitation for the Nooksack River basin. Understanding the response of the river to climate change is crucial for regional water resources planning because municipalities, tribes, and industry depend on the river for water use and for fish habitat. We combine three different climate scenarios downscaled from GCMs and the Distributed‐Hydrology‐Soil‐Vegetation Model to simulate future changes to timing and magnitude of streamflow in the higher elevations of the Nooksack River. Simulations of future streamflow and snowpack in the basin project a range of magnitudes, which reflects the variable meteorological changes indicated by the three GCM scenarios and the local natural variability employed in the modeling. Simulation results project increased winter flows, decreased summer flows, decreased snowpack, and a shift in timing of the spring melt peak and maximum snow water equivalent. These results are consistent with previous regional studies, but the magnitude of increased winter flows and total annual runoff is higher. Increases in temperature dominate snowpack declines and changes to spring and summer streamflow, whereas a combination of increases in temperature and precipitation control increased winter streamflow. Copyright © 2013 John Wiley & Sons, Ltd.