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991.
Sergio Grauso Andrea Pagano Grazia Fattoruso Piero De Bonis Filippo Onori Pasquale Regina Carlo Tebano 《Environmental Geology》2008,54(2):219-234
In the present work on-going research is discussed whose primary goal is to test some statistical methods to estimate the
average yearly area-specific sediment yield (SSY). Using geomorphological and climatic parameters various multiple regression
formulae have been set up based on SSY observed data from 16 catchments of Sicily. Three distinct techniques were adopted
to select the parameters to be used in the equations: simple correlation, stepwise regression analysis and a supervised geomorphological–statistical
correlation. The comparison of the results showed the effectiveness of the stepwise analysis, which led to a regression equation
with a coefficient of determination (r
2) of 0.87. Nevertheless, even this methodology showed some elements of uncertainty that have caused, in some cases, appreciable
differences between observed and predicted values (mean percentage error equal to 26%). These differences are likely either
due to the hydraulic regime of most of Sicilian watercourses (typical of semi-arid regions) or to hidden factors (e.g., topography,
human impact and concentrated erosion), which can greatly affect the processes of sediment production and transport. The study
has pointed out the need to take into account a larger number of observations and to perform the analysis of relations between
suitable variables and SSY at a more detailed time resolution. 相似文献
992.
993.
利用1950—2014年印度粮食单产统计资料及气候变化资料,从实证的角度,定量分析了小麦、水稻单产对气候的年际变化和年代内趋势性变化的响应。结果表明:1)年际变化方面,粮食单产与降水量和雨日数呈显著正相关,与温度和潜在蒸发量呈显著负相关,其中小麦单产与四者的相关系数分别为0.35(P<0.01)、0.24(P<0.10)、-0.32(P<0.05)和-0.41(P<0.001),水稻的相关系数分别为0.32(P<0.05)、0.32(P<0.05)、-0.26(P<0.05)和-0.33(P<0.01)。这表明,高温、少雨导致的水分胁迫不利于粮食增产。2)在年代内趋势性变化方面,1996—2005年印度气候呈现暖、干化趋势,全国平均粮食单产呈下降趋势;从变化速率的空间分异看,单产下降速率与暖、干化速率的空间分异规律基本吻合,单产快(慢)速下降区域与降水量快(慢)速减少、潜在蒸发量快(慢)速增加区域基本一致。水稻和小麦单产变化速率与降水量变化速率的空间分异均呈正相关,与潜在蒸发量变化速率的空间分异均呈负相关。由此表明,降水减少和温度升高导致的水分胁迫是印度粮食单产时空变化的主要气象成因。 相似文献
994.
Modeling stream flow and sediment yield using the SWAT model: a case study of Ankara River basin,Turkey 总被引:1,自引:0,他引:1
The Soil and Water Assessment Tool (SWAT) was tested for prediction of stream flow and sediment yield in the Ankara basin, Turkey. The overall objective of this study was to evaluate the performance and applicability of the SWAT and generate a soil erosion map. Thirteen years of daily/monthly flow and monthly sediment data were used for calibration and validation. Model performance was evaluated using statistical measures to assess the applicability of the model in simulating stream flow and sediment yield during calibration (1989–1996) and validation (1982–1984) periods. Nash Sutcliffe efficiency (NSE), relative error (RE), and R² (coefficient of determination) for daily flow were computed as 0.61, ?0.55, and 0.78, respectively; and as 0.79, ?0.58, and 0.89 for monthly flow during the calibration. Statistical comparisons of sediment yield produced values for NSE, RE, and R² of 0.81, ?1.55, and 0.93, respectively, during the calibration. The resulting map suggests that significant portions of urbanized and highly cultivated areas in the vicinity of stream channels are particularly vulnerable to soil erosion. SWAT satisfactorily simulated hydrology and sediment yield and can be used as a tool in decision-making for water resources planning in a basin with similar characteristics. 相似文献
995.
A shallow landslide erosion and sediment yield component, applicable at the basin scale, has been incorporated into the physically
based, spatially distributed, hydrological and sediment transport modelling system, SHETRAN. The component determines when
and where landslides occur in a basin in response to time-varying rainfall and snowmelt, the volume of material eroded and
released for onward transport, and the impact on basin sediment yield. Derived relationships are used to link the SHETRAN
grid resolution (up to 1 km), at which the basin hydrology and final sediment yield is modelled, to a subgrid resolution (typically
around 10–100 m) at which landslide occurrence and erosion is modelled. The subgrid discretization, landslide susceptibility
and potential landslide impact are determined in advance using a geographic information system (GIS), with SHETRAN then providing
information on temporal variation in the factors controlling landsliding. The ability to simulate landslide sediment yield
is demonstrated by a hypothetical application based on a catchment in Scotland.
Received: 30 October 1996 · Accepted: 25 June 1997 相似文献
996.
柴达木盆地盐湖卤水层给水度分布变化特征 总被引:2,自引:1,他引:1
选择柴达木盆地马海盐湖作为研究对象,在研究区布置给水度采样点11处,采样深度1.61~148.5 m,采集给水度样品75件。结合研究区以往37处采样点的72个测试数据,共计取得48处采样点145个测试数据。根据给水度实测数据,采用数理统计方法分析了柴达木盆地马海盐湖卤水层给水度分布变化。其主要特征表现为:① 给水度在水平方向上表现出较大的差异性,卤水层WⅠ至WⅤ的给水度分别介于0~0.263 5、0.009 4~0.209 9、0~0.277 8、0.006 2~0.135 9、0~0.107 7。在采样点MHK-022~MHK-026处,各卤水层给水度值较小,均小于0.06。在盐湖东北部,各卤水层给水度值较大,均大于0.08。② 给水度在垂直方向上受地层静压力的影响随着深度的增加而减小,上部卤水层WⅠ的给水度均值为0.105,下部卤水层WⅤ的给水度均值已降至0.038 7,不足卤水层WⅠ给水度均值的40%。③ 给水度在垂直方向上还表现出旋回性的变化特征,这种沉积旋回的出现可能是对成盐期间气候波动的反映。 相似文献
997.
This paper firstly analyzes the land use - land cover (LULC) in Lake Ziway watershed (Ethiopia) and quantifies the changing patterns from 1973 to 2014 using Landsat images. Secondly, the paper estimates sediment yields using the Soil and Water Assessment Tool (SWAT model). It also assesses and estimates water abstraction from Lake Ziway using survey data. The study shows that the conversions from woodlands into agricultural lands and settlement areas are the major detected LULC changes. Of the total area of the watershed, agricultural lands and settlement areas together increased from 57% in 1973 to 75% in 2014 at the expense of woodlands whose areas decreased from 26.16% to 6.63% in the study periods. The study also shows that water abstraction and sediment loads are increasing at Lake Ziway watershed. The major driving forces behind these LULC changes and the impacts on the lake natural condition are anthropogenic factors such as population growth, land policy changes and deforestation. Increasing demands for more land and water resources, i.e., land for settlements and cultivation, wood for fuel and charcoals, and water for irrigation and municipal water supply, are the underlying causes for the observed changes on the watershed resources. Thus, if the existing scenarios of human pressures are left neglected without management interventions, severe watershed degradations will continue to further affect the watershed's resources including the hydrology. Therefore, responsible government institutions should start mobilizing the local communities along with providing financial and material supports for watershed rehabilitation through afforestation and soil and water conservation activities. Additionally, the free-access practices for water use should be replaced by user-charge policy to regulate water abstractions in order to adequately sustain the water level of Lake Ziway and its feeder rivers. In this respect, this study provides firsthand information to policy makers and planners to put in place a comprehensive land and water use plan and regulations against the unruly human actions in the watershed before irreversible losses might happen to Lake Ziway and its watershed resources. 相似文献
998.
999.
1000.