Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere最新文献

Water resources management is a contentious challenge in Southern Africa. Scarce resources, often poor quality, unfavourable temporal and spatial distribution and competing stakeholders characterise the water resources in this region. The following general objectives and techniques are investigated: (a) Development of dynamic water balance and erosion models for three study catchments using remotely sensed and other data, (b) assessment of water demand and usage of the different user sectors and stakeholders, (c) design and simulation of “What if?” scenarios to investigate trends and interactions of the complex water resources planning process, and (d) development and implementation of strategies to solve water allocation conflicts. The product of the project, the prototype IWRMS, is an innovative computer based toolset designed as an assembly of tested, validated and well documented procedures comprising techniques of database management, remote sensing, GIS, process modelling, decision support and implementation strategies. The modelling results and first prototype installations in Southern Africa show the applicability of this system.

River flow forecasting is required to provide basic information on a wide range of problems related to the design and operation of river systems. The availability of extended records of rainfall and other climatic data, which could be used to obtain stream flow data, initiated the practice of rainfall-runoff modelling. While conceptual or physically-based models are of importance in the understanding of hydrological processes, there are many practical situations where the main concern is with making accurate predictions at specific locations. In such situation it is preferred to implement a simple “black box” (data-driven, or machine learning) model to identify a direct mapping between the inputs and outputs without detailed consideration of the internal structure of the physical process. Artificial neural networks (ANNs) is probably the most successful machine learning technique with flexible mathematical structure which is capable of identifying complex non-linear relationships between input and output data without attempting to reach understanding as to the nature of the phenomena. In this study the applicability of ANNs for downstream flow forecasting in the Apure river basin (Venezuela) was investigated. Two types of ANN architectures, namely multi-layer perceptron network (MLP) and a radial basis function network (RBF) were implemented. The performances of these networks were compared with a conceptual rainfall-runoff model and they were found to be slightly better for this river flow-forecasting problem.

Aerosols collected between 1994 and 1999 at more than 45 different sites in Europe have been measured for Pb isotopic composition and Pb concentrations by Thermal Ionisation Mass Spectrometry (TIMS). With respect to ²⁰⁶Pb/²⁰⁷Pb and ²⁰⁸Pb/²⁰⁷Pb ratios a change in isotopic composition compared with earlier measurements was detected in parts of Europe. Also, seasonal variations were observed at some sites. This was most probably due to a relative increase (due to the phasing out of leaded petrol) of both industrial Pb in the atmosphere and pollution from long- or meso-scale transport.

Global freshwater assessments tend to focus primarily on water flow in perennial rivers, lakes, and groundwater, so called blue water in the hydrological cycle. Little attention is paid to the role of green water, or vapour flows, in sustaining the generation of terrestrial ecosystem services, including biomass production. Ecosystem services (such as carbon sequestration, nutrient retention, pollination and pest control) are generated by ecological processes in different biomes of the World and essential for socio-economic development. In this paper we critically assess the limitations of the past blue water bias for future ecohydrological landscape management. We present results from an effort of quantifying continental green water fluxes for major terrestrial biomes indicating that the large biomes, generating essential ecosystem services depend on more than 90 % of the total average terrestrial return flow of green water to the atmosphere. The paper discusses the future implications of such large dependence on green water fluxes, and options of improving efficiency in water resources management. It points at the need of avoiding sectoral management and calls for an ecohydrological landscape management based on both ecological and hydrological knowledge.

Numerical model for simulation and evaluation of summer episodes of anthropogenic surface ozone (summer smog episodes) is presented in this article. This model has been used for special air-pollution studies in the region of Prague (central part of Bohemia - the Czech Republic). It is based on so called “puff model” technology and lagrangian method of trajectories construction in the boundary layer of atmosphere is applied. Processes of turbulent dispersion of puffs, photochemical and other chemical transformations and deposition of compounds on the earth surface are also taken into account. System of equations used for chemistry description of the model is presented here in details and a brief informative presentation of model results is also included.

The main objective of the present study is to detect and assess empirical relationships between river discharge and catchment characteristics to support the simulation of nitrogen losses on the regional and national scale. The empirical model derived provides the basis for a comprehensive and harmonized tool for the calculation of annual river discharge and nutrient loads from 49 Danish catchments to coastal waters. The model was applied for the years 1994 and 1995. Results from this application indicate that the simulated values are generally lower than the corresponding values from previous estimations. The main explanation is that precipitation as the most important model parameter shows a distinct gradient towards the coastal areas. This gradient has not been considered by the previously applied regional methods. Although the model results are generally reasonable, improvements are necessary, particularly with respect to the representation of subsurface properties.

Current research suggests that strategies to control nitrogen as well as sediment and phosphorus loss from nonpoint sources should focus on different runoff components and their spatial and temporal variation within the catchment. Therefore nonpoint source models, especially in humid climatic regions, should consider variable hydrological active source areas. These models should also be able to consider runoff generation by saturated overland flow as well as Horton overland flow. A combination of the hydrologic model WaSiM-ETH and the erosion and P-transport model AGNPS Version 5 was chosen for this study. The models were run in the WaSiM-ETH runoff generation mode (Topmodel and Green a. Ampt approach) and the SCS curve number mode, modified by Lutz (1984), to assess these different runoff calculation procedures. A medium sized catchment in the lower Hessian uplands of Germany was selected for the present investigation. The results show that the combined Topmodel/Green and Ampt runoff approach produce reasonabe results for the simulation of runoff volume for single runoff events at the catchment outlet. The more physically based model approach computed a much more realistic distribution of runoff and P yield producing areas than the SCS curve number method, modified by Lutz (1984). Reasonable results were achieved for sediment yield calculations. Particulate P calculations showed larger deviations between measured and calculated values.

The regional chemistry transport model REM3 has been applied operationally to forecast ozone since 1997 at the FU - Berlin. Within a forecast system REM3 is utilized to predict the large scale ozone situation in Central Europe. The paper gives an overview about the application of the model and assess the model performance with respect to the objective of the model application.

In the framework of the GEWEX / Rhone project, which aims at developing a regional model of the surface energy and water cycle in the Rhone basin, the flow of the Saone river basin (30000) km2 was modelled with the MARTHE model. The paper first describes the functionalities of MARTHE and then the modelling of the Saone basin with a 2 km grid at a daily time step over a 14 years (August 1981 to July 1995) using different surface hydrological models (soil models) : these soil models require from 3 to 91 parameters over the entire basin. A comparison of the results shows that the daily flows at the 52 gauging stations of the Saone are best modelled with the GR4 soil model using only 3 parameters. This advocates the gathering of additional data namely aquifer data and soil saturation in order to avoid over-parameterisation.