摘要:

Rainfall is the most important water resource in central and western Sudan, a region affected by the recent drought in Africa. A general methodology for studying the annual rainfall process is presented and applied to data from central and western Sudan. It is assumed that certain time series models adequately describe the annual rainfall process in the region. Based on this assumption, the drought frequencies are calculated in the subregions with stationary series. The theory of runs is applied in calculating drought frequencies using a data generation method.

ISSN:0262-6667    

DOI:10.1080/02626669209492581

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

EPSAT-NIGER (Estimation of Precipitation by SATellite—NIGER experiment) has been designed to improve the understanding of the precipitation systems of Sudano-Sahelian Africa and to develop operational rainfall estimation algorithms for this region. It is based on the combined use of a very dense raingauge network (93 gauges over a study area of 16 000 km2) and a C-band weather radar system. The experiment is scheduled to last three years, 1990–1992. The network pattern, a regular grid with nodes spaced at 12.5 km and a 16 gauge target area where the distance between stations is decreased to 1 km, has allowed for some preliminary studies on the rainfall distribution at various space and time scales. Whereas the long term average rainfall gradient is uniform, rainfall increasing north to south, a single rainy season can be markedly different. The local variability may be extremely large. That variability is enhanced at smaller sampling time steps and the computation of reference areal rainfall for satellite imagery validation is extremely sensitive to the design of the ground-based validation system. The joint processing of gauge and radar data has led to the identification of a few typical features of the drop size distribution of the African squall lines, which could lead to deriving specific algorithms for radar calibration in this region. The data provided by EPSAT-NIGER will be used in various international projects for the assessment of water input from the atmosphere to the continent over the Sahel.

ISSN:0262-6667    

DOI:10.1080/02626669209492582

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In this analysis, a semi-distributed conceptual runoff model was applied in five basins varying in area between 43 and 195 km2, lying in different physiographic regions of Switzerland (lowland, alpine, heavily glaciated high alpine basins) representing various runoff regimes. An objective, labour-intensive optimization procedure was developed and found suitable for deriving optimal parameter values. A separate calibration procedure was employed in the heavily glaciated basin, as glacier mass balance data measured at different elevations were deemed very helpful for finding plausible parameter values. The results show that this conceptual runoff model can be successfully applied in various physiographic regions, without structural changes, to calculate daily discharge. However, no conclusive relationships between parameter values and basin characteristics could be found. One reason may be that the investigated sample was too small. It is also felt that the inherent structure of this type of conceptual model is not suited to relating parameter values representing lumped model characteristics with physical basin characteristics. The advantages of conceptual models are such that they can be readily applied in various physiographic regions and therefore constitute a valuable tool for operational hydrology.

ISSN:0262-6667    

DOI:10.1080/02626669209492583

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

This paper asserts that the traditional method for reservoir routing is unnecessarily complicated. It requires the solution of a transcendental equation at each time step. Reservoir routing is actually simply the numerical solution of a differential equation. Any standard method can be used, and all are simpler than the traditional method. The paper also shows that the alternative form of the governing equation in terms of the reservoir surface elevation has some advantages over the usual form involving storage volume. The presentation incorporates the case where reservoir outflow may be varied by control of valves or spillway gates. Numerical methods for reservoir routing are examined and compared, and it is concluded that simple standard methods for solving differential equations are to be preferred to the traditional method for flood routing, and should replace it.

ISSN:0262-6667    

DOI:10.1080/02626669209492584

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

An attempt has been made to provide a basis on which the amounts of deficit storage occurring in the natural hydrographs of small catchments can be estimated as a function of yield and the frequency of occurrence. The yield levels envisaged constitute only small proportions of the mean flow and the deficits arise due to seasonal fluctuations only. It is presumed that any deficits built up during the dry periods of the year are made up by the winter flows, so that there is no year to year carry over. The streamflow data of 26 catchments in Ireland are analysed to obtain the series of annual maxima storages on each catchment. Assuming that they are distributed according to the extreme value type 1 distribution, the relationship between the deficit storage and its frequency of occurrence is calculated for various levels of yield on each catchment. A simple model is described which expresses this relationship in terms of a few parameters. For use on ungauged catchments, those parameters are related to the physical characteristics of the catchments by multiple linear regression.

ISSN:0262-6667    

DOI:10.1080/02626669209492585

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Snowmelt and runoff in urban areas in Luleå, north Sweden, are discussed and compared with rural conditions. The uneven snow distribution in cities is quantified. Energy fluxes at the snow surface in different environments are estimated. It is shown that, mainly because of increased absorbed radiative energy in the snow, the daily melt is about 10 mm higher in the city than in rural environments. In the course of prolonged snowmelt, the infiltration capacity of most soils in urban areas becomes so reduced that melt-induced peak flows from grassed and gravelled surfaces are similar to those from asphalted surfaces. When rain falls on snow, overland flow may take place from the entire area of a basin.

ISSN:0262-6667    

DOI:10.1080/02626669209492586

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A comparison between two analytical techniques commonly used for the determination of sulphur concentrations in natural water samples is reported. Significant differences in the sulphur values obtained using inductively coupled plasma atomic emission spectrometry and ion chromatography are described. The contribution of a sulphur fraction (presumed to be organic S) not detected by ion chromatography is identified. This contribution varies considerably between individual samples and is highly correlated to the concentration of dissolved organic carbon. The results are explained in terms of an organic S component which is of environmental importance.

ISSN:0262-6667    

DOI:10.1080/02626669209492587

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669209492588

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669209492589

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669209492590

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor