摘要:

The spatial variability of the factors of the universal soil loss equation is examined on the mediterranean basin of Conca de Tremp covering 43.1 km2in Spain. The evaluation of the rainfall erosivityRand the soil erodibilityKis relatively straightforward and spatially-averaged values of these parameters can be applied to the entire basin. Conversely, the spatial variability of annual soil erosion losses on large basins depends primarily on the factorsL, SandCdescribing topographic, vegetation and land use parameters. A grid size analysis of soil erosion losses from the Conca de Tremp basin under mediterranean climatic conditions in Spain shows excellent agreement with the earlier results on the Chaudière basin in Canada. It is concluded for both basins that unbiassed estimates of soil erosion losses are obtained for grid sizes less than about 0.125 km2. The analysis of the Conca de Tremp basin validates the use of the grid size factor proposed by Julien & Frenette (1987). It is also found that the grid size factor primarily depends on the average slope gradient which decreases with increasing grid size or drainage area. On the other hand, the grid size factor does not depend on the spatial variability of the factorsR, K, LandC.

ISSN:0262-6667    

DOI:10.1080/02626669109492541

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The long term hydrological response of a medium-sized mountainous catchment to climate changes has been examined, The climate changes were represented by a set of hypothetical scenarios of temperature increases coupled with precipitation and potential evapotranspiration changes. Snow accumulation and ablation, plus runoff from the study catchment (the Mesochora catchment in central Greece) were simulated under present (historical) and altered climate conditions using the US National Weather Service snowmelt and soil moisture accounting models. The results of this research obtained through alternative scenarios suggest strongly that all the hypothetical climate change scenarios would cause major decreases in winter snow accumulation and hence increases in winter runoff, as well as decreases in spring and summer runoff. The simulated changes in annual runoff were minor compared with the changes in the monthly distribution of runoff. Attendant changes in the monthly distribution of soil moisture and actual evapotranspiration would also occur. Such hydrological results would have significant implications on future water resources design and management.

ISSN:0262-6667    

DOI:10.1080/02626669109492542

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

This paper reviews simplified methods for evaluating the rainfall erosivity index and proposes two relationships for estimating the annual value of Wischmeier's rainfall erosivity index at sites equipped with recording and non-recording raingauges. For the Sicilian region, the FAO index was also found to represent the erosion risk. A regional relationship to estimate the standard deviation of the annual erosivity index is proposed. The isoerosivity map is plotted by using 41 values of the rainfall erosivity index calculated by Wischmeier's procedure and 128 values estimated according to a relationship proposed by the authors. Finally, for each of 169 sites, an erosion risk index is calculated and an erosion risk map is plotted.

ISSN:0262-6667    

DOI:10.1080/02626669109492543

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Long term research has been conducted into the hydrological effects of different land usage of a wetland mire in southern Germany. Drainage for agriculture lowered the water table and reduced evaporation from about 110% of open water losses to just under the Penman short grass potential rate. The runoff regime was altered and peak flows increased. Afforestation of agricultural land increased evaporation losses to much higher levels than open water evaporation, and annual runoff was nearly halved. Forest growth reduced soil water and baseflows. Peak flows became smaller; the rate of reduction was particularly rapid in the early years of tree growth.

ISSN:0262-6667    

DOI:10.1080/02626669109492544

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Statistics of seasonal and daily rainfall in nine regions covering the United Kingdom are presented, together with the best currently available predictions of changes in rainfall and evaporation, based on various general circulation model (GCM) assessments of the climate 40 years ahead. On that basis, runoff sequences are generated for the region of northwest England with north Wales (NWE & NW, humid temperate) and for southeast England (SEE, temperate but less humid), both for the current climate and for the year 2030 estimate, the latter incorporating higher evaporation losses. The future annual runoff is reckoned as 8% less than the current average in the SEE region and 4% less than that in the NWE & NW region. Direct supply reservoir yield versus storage graphs are then derived in each case for a range of duration-based probability of emptiness, their yields (i.e. sustained draw-off rates) and storage capacities being expressed as proportions of current annual runoff. The year 2030 graphs fall systematically below those for the current climate, representing 8% to 15% loss of yield from existing storage in the SEE region and 4% to 25% loss of yield in the NWE & NW region.

ISSN:0262-6667    

DOI:10.1080/02626669109492545

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A numerical algorithm for computation of gamma frequency factors is given and verified in the ranges of −9.0 ≤ skewness coefficient ≤ 9.0 and 10−8≤ non-exceedance probability ≤ 1—10−8, which are wide enough for all hydrological applications.

ISSN:0262-6667    

DOI:10.1080/02626669109492546

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

In many mountainous areas of the Pacific coast of North America, rainfall onto snowpacks causes massive floods, probably the single greatest cause of changes in channel morphology and lotie habitats. To understand and model this hydrometeorological phenomenon better, process-response hypotheses were developed for snowpack outflow amount, duration and rate and the time lags from the beginning of rainfall to initial and peak outflow. The hypotheses were evaluated by correlation and regression analyses based on measurements of 20 rainon-snow events monitored between 1984 and 1990 at forested and open plots near Lake Tahoe, California. Outflow amount correlated significantly with precipitation amount, duration and rate, snow depth and melt potential. Many of these variables also correlated significantly with outflow duration and rate and lag time to peak outlfow. Regression models expalined 80–90% of the variation in outflow amount and duration. Significant differences were not identified between the forest and open plots for any of the outflow attributes.

ISSN:0262-6667    

DOI:10.1080/02626669109492547

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A physically based model of moisture transfer in the soil-canopy-atmosphere system, fitted to measured data in wheat fields, was applied to calculate the sensitivity of evapotranspiration to the combined effect of possible CO2-induced climate changes and the direct impact of doubling CO2content in the atmosphere. The impact of carbon dioxide was taken into account by changing the stomatal resistance and the leaf area index. Several climate change scenarios were used. Simulation studies showed that when the changes of a number of climatic and plant factors are considered, evapotranspiration responses can differ greatly from those that consider only temperature change. The temperature effect of the increase in CO2content in the atmosphere can be compensated by changes in the physiological parameters of vegetation. Thus, under certain conditions, one can expect a decrease in evapotranspiration instead of an increase such as is predicted by a number of models which neglect the direct effects of CO2on plant behaviour.

ISSN:0262-6667    

DOI:10.1080/02626669109492548

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669109492549

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0262-6667    

DOI:10.1080/02626669109492550

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor