The influence of elevation error on the morphometrics of channel networks extracted from DEMs and the implications for hydrological modelling

Stream network morphometrics have been used frequently in environmental applications and are embedded in several hydrological models. This is because channel network geometry partly controls the runoff response of a basin. Network indices are often measured from channels that are mapped from digital elevation models (DEMs) using automated procedures. Simulations were used in this paper to study the influence of elevation error on the reliability of estimates of several common morphometrics, including stream order, the bifurcation, length, area and slope ratios, stream magnitude, network diameter, the flood magnitude and timing parameters of the geomorphological instantaneous unit hydrograph (GIUH) and the network width function. DEMs of three UK basins, ranging from high to low relief, were used for the analyses. The findings showed that moderate elevation error (RMSE of 1·8 m) can result in significant uncertainty in DEM‐mapped network morphometrics and that this uncertainty can be expressed in complex ways. For example, estimates of the bifurcation, length and area ratios and the flood magnitude and timing parameters of the GIUH each displayed multimodal frequency distributions, i.e. two or more estimated values were highly likely. Furthermore, these preferential estimates were wide ranging relative to the ranges typically observed for these indices. The wide‐ranging estimates of the two GIUH parameters represented significant uncertainty in the shape of the unit hydrograph. Stream magnitude, network diameter and the network width function were found to be highly sensitive to elevation error because of the difficulty in mapping low‐magnitude links. Uncertainties in the width function were found to increase with distance from outlet, implying that hydrological models that use network width contain greater uncertainty in the shape of the falling limb of the hydrograph. In light of these findings, care should be exercised when interpreting the results of analyses based on DEM‐mapped stream networks. Copyright © 2007 John Wiley & Sons, Ltd.     

ENSO indices and analyses

New ENSO indices were developed and the spatial variability and temporal evolution of ENSO were analyzed based on the new indices and modeling experiments, as well as multiple data resources. The new indices, after being defined, were validated with their good diagnostic characteristics and correlation with wind and SST. In the analysis after the definition and validation of the new indices, ENSO feedbacks from wind, heat fluxes, and precipitation were spatially and temporally examined in order to understand ENSO variability and evolution with some emphasized points such as the interaction among the feedbacks, the role of westerly wind bursts and the transformation between zonal and meridional circulations in an ENSO cycle, and the typical pattern of modern ENSO.     

天津滨海新区中全新世以来地形地貌演化

根据最新获得的多项天津滨海新区海岸带地质调查资料,分别利用海区的浅地层剖面成果反演海底古地形、利用海区沉积钻孔了解沉积物时代、利用陆区的贝壳堤,埋藏牡蛎礁,古墓葬和埋藏砂体分布等,研究各时期古岸线的位置与形态,并与海区的沉积环境和地形地貌进行对比,对天津滨海新区中全新世以来的地形地貌演化进程及演化机制概括性介绍.自中全...     

Responses of spatial-temporal variation of Karst ecosystem service values to landscape pattern in northwest of Guangxi,China

The responses of spatiotemporal variation of ecosystem service values (ESVs) to landscape pattern from 1985 to 2005 in a typical Karst area of the northwest Guangxi Zhuang Autonomous Region,China,were examined us-ing remote sensing and geographic information system techniques in this paper.The total ecosystem service values de-clined significantly from 1985 to 1990,and then increased slowly from 1990 to 2005,almost equaled to the 1985 level.The ecosystem service values tended to decline from the west to the...     

六棱山北麓中段冲沟地貌发育的定量研究及其新构造意义

利用地貌形态指标对六棱山北麓断层中段的5条冲沟进行定量化研究,流域的冲沟比降指标(SL)、面积--高度积分值(HI)和流域盆地形态因子(Bs)的异常值表明5条冲沟的发育对六棱山北麓断层活动性有明显的响应,流域发育处于壮年期.秋林沟口野外实测数据验证并揭示了六棱山北麓断裂晚第四纪以来的活跃性.     

An analysis of the trophic network of a macrotidal estuary: the Seine Estuary (Eastern Channel, Normandy, France)

A steady state, mass balance, trophic network has been constructed to illustrate the flow of energy in the Seine Estuary by using Network Analysis and Ecopath methods. This ecosystem shows 15 compartments from primary producers to the top consumers (fish and birds). This study has been compared with other ecosystems of comparable nature located in North America (Narragansett, Chesapeake, Delaware Bays), Europe (Ems Estuary, Dublin Bay and Bay of Somme), and South Africa (Swartkops Estuary) in which analysis of trophic network has been applied with similar methods.The Seine Estuary shows values of some global parameters and indices either close to large North American bays and a South African estuary characterised by the complexity of their trophic network, or values near European bays and estuaries, or else remain typical of the Seine estuary. All of this reflects specific functioning of the Seine Estuary which can be explained by the analysis of the dominant food web. In the upstream sector an important pelagic food web was found correlated with highest primary production, especially planktonic, which is rapidly consumed by an abundant zooplankton and suprabenthos (Mysidacae and Decapoda Crustacea). This reveals the dominant consumer role of this sector. The external fluvial inputs (277.80 gC m⁻² y⁻¹) are transferred to the downstream sector which produces the major export (548.43 gC m⁻² y⁻¹), in parallel with the low consumption and efficiency of dominant benthos component from its bentho-pelagic food web. This reflects the dominant exporter role of this sector.In the Seine Estuary low values of detritivory index D/H (2.52), recycling index FCI (16.1%) and connectance (0.24) were found associated with high values of P/B ratio (38.2%), sum of exports (548.43 gC m⁻² y⁻¹) and the great difference between ratio of ascendency to capacity development A/C and internal ratio A_i/C_i. This shows the lack of a dominant resource as in Delaware Bay, that the state of development is different from a mature ecosystem, and the dependance on external connections similar to the Bay of Somme, another ecosystem of Eastern Channel, France.     

1962–2011年长江流域极端气温变化（英文）

Based on daily maximum and minimum temperature observed by the China Meteorological Administration at 115 meteorological stations in the Yangtze River Basin from 1962 to 2011,the methods of linear regression,principal component analysis and correlation analysis are employed to investigate the temporal variability and spatial distribution of temperature extremes.Sixteen indices of extreme temperature are selected.The results are as follows:(1) The occurrence of cold days,cold nights,ice days,frost days and cold spell duration indicator has significantly decreased by –0.84,–2.78,–0.48,–3.29 and –0.67 days per decade,respectively.While the occurrence of warm days,warm nights,summer days,tropical nights,warm spell duration indicator and growing season length shows statistically significant increasing trends at rates of 2.24,2.86,2.93,1.80,0.83 and 2.30 days per decade,respectively.The tendency rate of the coldest day,coldest night,warmest day,warmest night and diurnal temperature range is 0.33,0.47,0.16,0.19 and –0.07℃ per decade,respectively.(2) The magnitudes of changes in cold indices(cold nights,coldest day and coldest night) are obviously greater than those of warm indices(warm nights,warmest day and warmest night).The change ranges of night indices(warm nights and cold nights) are larger than those of day indices(warm days and cold days),which indicates that the change of day and night temperature is asymmetrical.(3) Spatially,the regionally averaged values of cold indices in the upper reaches of the Yangtze River Basin are larger than those in the middle and lower reaches.However,the regionally averaged values of most warm indices(except warm spell duration indicator) and growing season length in the middle and lower reaches are larger than those in the upper reaches.(4) The extreme temperature indices are well correlated with each other except diurnal temperature range.     

利用单台地磁数据估算Ap和Kp指数的可行性分析

通过分析单台长期地磁场扰动幅度和地磁行星指数Ap和Kp关系,对1小时磁扰幅度rH的日平均与Ap进行拟合,快速估算Ap指数.对3小时内rH的平均与Kp进行对数拟合,估算Kp指数.采用肇庆地震台2003-2008年地磁H分量分钟值数据,估算行星Ap和Kp指数,与世界数据中心(WDC)给出的Ap和Kp指数进行统计分析.结果发...     

Assessing benthic health under multiple human pressures in Bohai Bay (China), using density and biomass in calculating AMBI and M‐AMBI

In recent decades, China has undergone an impressive development, which has produced increasing human pressures including coastal degradation. Bohai Bay, located in the west of the Bohai Sea (north of China), has been affected by various human pressures, including waste water discharges, land reclamation and oil exploitation. To monitor the effects of these pressures on this ecosystem, benthic macroinvertebrates and environmental variables (dissolved oxygen, nutrients, metals, etc.) were sampled in 2009 and 2011. To assess the ecological status of the benthic communities, the AZTI Marine Biotic Index (AMBI) and multivariate‐AMBI (M‐AMBI) were used, including both density and biomass in the calculation. This is the first research in which M‐AMBI based on biomass (M‐bAMBI) is applied. Both methods showed that the nearshore areas, especially close to the Haihe and Jiyun estuaries, were affected by human pressures, with a clear gradient of decreasing impacts offshore. The ecological status as assessed using density and biomass was quite similar. Significant relationships were also found between both methods and environmental variables. The use of AMBI and M‐AMBI, based upon density and biomass, in assessing the ecological status of water bodies in China seems to be promising.     

Impact of the central Pacific zonal wind divergence and convergence on the central Pacific El Nio event

The central Pacific(CP) zonal wind divergence and convergence indices are defined, and the forming mechanism of CP El Nio(La Nia) events is discussed preliminarily. The results show that the divergence and convergence of the zonal wind anomaly(ZWA) are the key process in the forming of CP El Nio(La Nia) events. A correlation analysis between the central Pacific zonal wind divergence and convergence indices and central Pacific El Nio indices indicates that there is a remarkable lag correlation between them. The central Pacific zonal wind divergence and convergence indices can be used to predict the CP events. Based on these results, a linear regression equation is obtained to predict the CP El Nio(La Nia) events 5 months ahead.