Modeling stream flow and sediment yield using the SWAT model: a case study of Ankara River basin,Turkey

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.     

1950—2014年印度粮食单产对气候变化的响应

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。     

基于霍顿下渗公式超渗产流计算几个问题的探讨

用霍顿下渗公式进行超渗产流计算,用迭代算法根据流域土壤含水量计算相应的下渗能力时发现:当土壤含水量较小时,迭代计算正常;当土壤含水量居中时,易发生迭代震荡现象;当土壤含水量较大时,极易发生迭代计算出错情况。对此,分析了迭代震荡和迭代计算出错的原因;提出了用算术平均法减小迭代震荡的问题;用限制震荡幅度结合算术平均法解决迭代计算出错的问题;同时,推导出了超渗产流模式下流域平均蓄水容量与霍顿下渗公式中三参数间的经验关系式。     

河南省棉花产量的灰色-马尔柯夫预测模型

灰色－马尔柯夫预测模型对波动较大序列比较适合，根据该组合模型，用ＧＭ（１，１）灰色模型预测河南省棉花单产，再用马尔柯夫模型转移概率预测系统未来发展方向和修正预报产量。经拟合和预报，效果较好。     

灵台塬区烤烟丰产栽培试验

１９９２年灵台县什字塬烤烟栽培试验表明，这里光照条件好，气温、降水条件不理想，但采取保墒增温措施后，也可获得较高产量。单株留叶１８片、种植密度２．４万株／ｈｍ￣２时，烤烟产值最高。     

A DIAGNOSTIC EXPERIMENTAL STUDY OF EFFECTS OF CO2 ENRICHMENT ON COTTON GROWTH, DEVELOPMENT AND YIELD

A series of experiments were conducted about the effects of different CO₂ concentrations and ventilating time on cotton using OPT-1 open top chambers.The results show that.for all the ventilating treatments,the development stages of cotton were advanced,plant height increased,the biomass of root and stalk increased when CO₂ concentration increased:the number of bolls formed in summer was more than 85% of the total for the treatment of 700 ppm CO₂ concentration;single boll weight,the number of bolls per plant,ginned and unginned cotton weights,and stalk weight increased obviously when CO₂ concentration increased,but the influences of CO₂ enrichment on the ratio of ginned weight to the total weight of ginned and unginned cotton,fibre length and ginned weight of 100-seed were small.     

Identification and comparison of perennial yield estimation models using Mt. Amiata Aquifer (southern Tuscany,Italy) as an example

With the principal aim of identifying and comparing suitable evaluation and forecasting models of perennial yield, detailed hydrogeological research was conducted on the cold phreatic aquifer located in the volcanites of Mount Amiata, southern Tuscany's most important water reservoir. The study was based on spring discharge, precipitation, and temperature data. It permitted the identification of the following models: (1) ratios between discharge values measured at the springs, (2) depletion urve analysis of the springs, (3) multiple regression with climatic data, and (4) water balance, coefficients of potential infiltration and runoff coefficients derived on a physiographic basis. Analysis of the results obtained using these models shows their excellent ability to forecast in the medium and long term; for short-term (yearly) forecasts, highly satisfactory results have been obtained for most of the methods used. With regard to Mt. Amiata's average perennial yield, it is estimated at 55×10⁶ m³/yr (the maximum deviation among the various evaluations performed varies from 4 to 8 percent), and it presents a decreasing trend, which is proportional to the reduction of local precipitation.     

Rainfall,runoff and erosion on bare arable soils in east Shropshire,England

The magnitude, frequency, and duration of erosive rainfall on bare arable soils is investigated within an area of sandy soils in east Shropshire. Rainfall parameters are compared with runoff and erosion from ten 25 m² runoff plots, maintained in a bare condition on slopes of varying steepness. On rain-drop compacted (capped) soils measured erosion rates of ≦ 42.7t ha^?1 occur during individual storms. Erosion rates increase markedly with slope and on slopes > ? 13° are largely attributable to rill erosion. Prolonged duration, low intensity events cause relatively little erosion; most is accomplished by short duration, high intensity (> 10 mm h^?1) convective rainstorms. Comparison of measured erosion-producing events and long-term rainfall records indicate that potentially erosive storms are quite frequent, and are most likely to cause erosion in late spring/early summer.     

岳西县改造中低产田初步尝试

岳西是典型的贫困山区县,由于低产土壤分布广,自然灾害频繁,物化投入少等原因导致粮食生产水平低,广大群众没有摆脱贫困。通过耕作制度改革,优化种植结构等措施,已取得显著效果。对于山区低温冷害类型和生理机制等方面研究,也取得较大进展,同时也闯出一条具有山区特色发展高效农业的路子。     

Sediment yield and delivery in the blanket peat moorlands of the southern Pennines

In contrast to much previous research on blanket peat moorland, which has concentrated upon studies of the form and causes of gully erosion, this paper attempts to investigate sediment transport and to estimate both short-term and long-term sediment yields in such terrain. The research was conducted on Wessenden Head Moor to the west of Huddersfield, Yorkshire, where automatic stream sampling continued over a period of two years. Use of corrected rating curves (Ferguson, 1988) provided a mean estimate of sediment yield over this period of 55 t km^?2 yr^?1. In addition an estimate of longer-term sediment yield was derived from four reservoir sediment surveys in the Wessenden Valley. Total yield was 203.69 t km^?2 yr^?1, including an organic fraction of 38.82 t km ^?2 yr^?1. Stream sampling at three sites on Shiny Brook, including headwaters and the outflow to the reservoir, suggested that there is great temporal and spatial variability in mineral and organic inputs to the reservoirs. Although not excessive in gravimetric terms, the low density of peat means that there is a serious erosion problem. Estimates of erosion rates for the peat gully network at Shiny Brook appear to confirm earlier evidence concerning the relatively recent occurrence of this erosion, within the last two centuries.