摘要:

The natural variability of precipitation in agricultural regions both in time and space is modelled using extensions of Box & Jenkins (1976) methodology based on the ARMA procedure. This broad class of aggregate regional models belongs to the general family of Space-Time Autoregressive Moving Average (STARMA) processes. The paper develops a three-stage iterative procedure for building a ST ARMA model of multiple precipitation series. The identified model is STMA (13). The emphasis is placed on the three stages of the model building procedure, namely identification, parameter estimation and diagnostic checking. In the parameter estimation stage the polytope (or simplex) method and three further classical nonlinear optimization algorithms are used, namely two conjugate gradient methods and a quasi-Newton method. The polytope method has been adopted and the developed model performed well in describing the spatio-temporal characteristics of the multiple precipitation series. Application has been attempted in a rural watershed in southern Canada.

ISSN:0262-6667    

DOI:10.1080/02626669509491444

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The spatio-temporal variability of daily precipitation series was investigated in a semiarid region of central Macedonia in northern Greece, Ten years of daily rainfall records for seven stations in the region constituted the data base. The spatial characteristics were examined by drawing composite correlation diagrams for the cool (October-March) season and the warm (April-September) season, and the results confirmed the regional homogeneity of the data sets. Furthermore, the temporal analysis indicated that the non-rainy days constituted the major portion of days throughout the year at all the stations. Similarly, light rainfall represented the majority of rainy days. Moreover, the annual rainfall variation showed high values in March, April and November with low values occurring in the summer and autumn. A sharp increase of rainfall between the 185th and the 195th day of the year must be taken into account when the harvest is scheduled. Harmonic and Power Spectrum analyses applied to the annual variation of rain depths using 5-day intervals revealed significant periodicities of 26, 122, 365 and 55 days. Finally the analysis of the annual variation of rain occurrences. revealed periodicities of 365 and 122 days.

ISSN:0262-6667    

DOI:10.1080/02626669509491445

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

An important characteristic of a river flow regime type is the time of year when high and low flows are likely to occur. How likely is it, however, to observe an identified seasonal pattern each individual year? Stability is an often neglected property of a flow regime, though shifts in the seasonal behaviour of flows affect both environmental and economic activities. An approach to characterize objectively the stability of a flow regime type, based on the concept of entropy, is presented. The stabilities of river flow maxima and minima are studied separately to investigate their respective contributions to the stability character of a particular regime type. A quantitative “instability index” permits a study of the development of a flow regime's stability in time, especially important in the context of a possible climate change. The method is presented using the example of a quantitative flow regime classification developed for Scandinavia and western Europe.

ISSN:0262-6667    

DOI:10.1080/02626669509491446

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A composite model for real time forecasting of flash floods in the Ayalon stream in central Israel has been constructed. The model is composed of four kinds of sub-models: an autoregressive model for discharges at upstream stations on the two major tributaries; a travel-time model for the flow from these stations to the downstream station located on the main stem of the stream; a time-area concentration curve for subwatershed drainage between the upstream and downstream stations; and a recession curve for the downstream station. The model incorporates an adaptive mechanism for continuous correction of forecast errors. This mechanism is calibrated during an initial period of operation, and is subsequently operated throughout a flow event. The model issues simultaneous forecasts for seven lead times ranging from 0.5 to 3.5 h. This provides a proper input for a flood warning system which is required for safe operation of a major highway running along the banks of a torrent stream in the metropolitan area of Tel-Aviv.

ISSN:0262-6667    

DOI:10.1080/02626669509491447

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The effects of changes in climate on aquifer storage and groundwater flow to rivers have been investigated using an idealized representation of the aquifer/river system. The generalized aquifer/river model can incorporate spatial variability in aquifer transmissivity and is applied with parameters characteristic of Chalk and Triassic sandstone aquifers in the United Kingdom, and is also applicable to other aquifers elsewhere. The model is run using historical time series of recharge, estimated from observed rainfall and potential evaporation data, and with climate inputs perturbed according to a number of climate change scenarios. Simulations of baseflow suggest large proportional reductions at low flows from Chalk under high evaporation change scenarios. Simulated baseflow from the slower responding Triassic sandstone aquifer shows more uniform and less severe reductions. The change in hydrological regime is less extreme for the low evaporation change scenario, but remains significant for the Chalk aquifer.

ISSN:0262-6667    

DOI:10.1080/02626669509491448

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The effects of climatically deviating periods of at least four years on discharge were investigated employing flow duration curves in the Upper Loire basin, France. The periods were determined using the standardized cumulative yearly deviation from the mean precipitation for ten climate stations. Flow duration curves from 27 catchments were determined and parameterized for each period. Results show that the effect of precipitation on discharge is more pronounced than the effect of temperature. They also show that the parameter values that determine the flow duration curve differ significantly between dry and wet periods. Furthermore the effect of drought on discharge is larger than the effect of wetness. Catchments with a high variability of discharge are more sensitive to changes of precipitation than catchments with a low variability of discharge.

ISSN:0262-6667    

DOI:10.1080/02626669509491449

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Les crises sismiques peuvent provoquer des modifications plus ou moins brutales et durables du niveau des nappes, particulièrement en milieu captif. Or les observations piézométriques faites dans des forages fournissent un signal brut. Celui-ci peut être en effet perturbé par les variations de la pression atmosphérique et par les marées terrestres. Une méthode de traitement du signal piézométrique brut est proposée (programme FIPAC). Deux exemples d'application sont analysés, par rapport à trois séismes historiques (Spitak en Arménie en 1988; Radia, 1991 Barysakho 1992, Géorgie), à partir de données acquises dans les chaînes du petit Caucase au pas de temps horaire et sur plusieurs années.

ISSN:0262-6667    

DOI:10.1080/02626669509491450

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Due to changes in physical characteristics, the valley side of a drainage basin may be represented by a series of overland planes. In such a situation, the downstream outflow from one plane becomes the upstream inflow for the subsequent plane. Based on the kinematic wave equations, two time of concentration (time to equilibrium) formulae are derived for planes subject to uniform rainfall excess and with a constant upstream inflow. For practical applications, the formulae are further developed in terms of the Manning resistance coefficient. The derived formulae are all consistent with those published for the case of zero upstream inflow.

ISSN:0262-6667    

DOI:10.1080/02626669509491451

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669509491452

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669509491453

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor