容县2010年6月滑坡灾害降雨阈值研究

大暴雨常引起群发性滑坡灾害的发生,对大暴雨引起的滑坡进行预警显得尤为重要,而确定诱发群发性滑坡的降雨阈值是预警的关键。在容县2010年6月初暴雨及其诱发的滑坡数据基础上,分析降雨和滑坡发生数量的相关性;采用降雨强度-降雨历时模型的统计分析方法,建立不同滑坡发生概率的降雨强度-降雨历时阈值线,且用ROC方法对阈值线进行检验。研究结果表明:滑坡发生数量和降雨量相关性为0.507;采用ROC方法分析得到滑坡发生概率为10%、50%、90%,阈值线的准确率分别为0.70、0.75、0.39,漏报率分别为0.05、0.23、0.93,误报率分别为0.75、0.29、0.04;综合以上指标,将50%阈值线作为研究区的阈值线,并进一步分析该线在不同日数下诱发滑坡的降雨阈值,作为容县群发性降雨型滑坡灾害预警分析。

西部典型侏罗系富煤区地下水补径排的同位素特征

以位于吐哈盆地的大南湖矿区为例,结合该区侏罗系含煤地层渗透性好、富水性强、静储量大等典型水文地质特征,通过野外调查,沿区域主要补给方向共采取了9个地表水及地下水样,开展了氢氧同位素及水化学分析与测试;在获取研究区水样氢氧同位素特征并首次构建哈密地区氢氧同位素降雨线的基础上,系统研究了天山东段南麓区域地下水的补径排条件;结合研究区所处的干旱区域特征及主要构造的控水作用研究,基本阐明了大南湖凹陷特殊地下水系统的形成原因及水循环条件。研究结果表明:天山东段南麓雪融水是区域地下水的惟一远程补给水源,通过深渗透方式进行补给,主径流方向为由北东向南西,补给途径长;受研究区北部沙尔湖隆起、西部及南部觉罗塔格隆起、东部边界断层等隔水构造的控制,研究区总体水文地质条件较为封闭,地下水循环交替差,进而形成了大南湖矿区上侏罗系含水层具有以静储量为主、高矿化度的特殊水文地质特征。

Analysis of ‘9.4' unusual rainfall in Beijing during autumn 2015

In this paper, an unusual rainfall in Beijing that occurred on 4 September(‘9.4') 2015 is studied to clarify the reasons for such a strong rainfall in autumn. It was indicated that various factors, including stationary westerlies disturbance(i.e. low in the west and high in the east), forward-titling trough,warm shear line, unstable stratification and convective available potential energy release, low level jet as well as a series of mesoscale convective systems produced the strong rainfall. Ordinarily, this situation is uncommon in autumn.

Precipitation and Rainwater pH Spatial Distribution in Bahia Blanca and Tandil, Argentina

While the occurrence of rainfall is a regional scale phenomenon, cities influence on precipitation spatial distribution patterns and their characteristics. These influences had been studied for a very long time especially in the Northern Hemisphere. Tandil and Bahia Blanca are middle cities of Argentina located in the south of Buenos Aires province. Both present continental template climate. The aim of this research is to analyze the spatial distribution patterns of precipitation and the rainwater pH values for the period October 2010-September 2011 in Tandil and Bahia Blanca. Gauge rain nets were installed in both cities. In each event of precipitation, amount and pH values were collected. Isohyets plotting were included in the thematic cartography that was made using ArcGis 9.3~ software. Although natural rains are generally considered as being weakly acid, the rainwater pH measurements demonstrated that in both cities the rain is alkaline. Regarding to the spatial distribution of the precipitation amounts, the isohyets of the annual records showed that the highest values were registered in areas of higher elevation while the lowest values were presented in both cities downtown, where the high buildings are concentrated.

Impact of Rainfall Temporal Heterogeneity on Relationship between Curve Number and Rainfall Depth in the Zagros Mountain Region,Iran

The impact of temporal variation of rainfall on the relationship between rainfall and catchment response is investigated in a catchment with high temporally variable rainfalls and a high percentage of permeable soils in the southwest of Iran.Twenty-nine storm events are classified into two classes, High Temporal heterogeneous(HT) and Low Temporal heterogeneous(LT) events using the variogram technique and the storm events of each class are analyzed to detect the relationship between Curve Number(CN) and rainfall depth. It is found that there is not a similar correlation between CN values and rainfall depths for both temporally variable classes, and hence, two different responses can be observed in the catchment according to rainfall temporal heterogeneities. For HT events, a complacent behavior is detected in which the CNs decline as rainfall depth increases while a different response, violent behavior, is observed for LT events in which the CNs rise and asymptotically approach a constant value with increasing storm size. This considerable difference between CN-P relationships derived from the two temporally variable classes of rainfall is attributed to the provocation of different runoff generation mechanisms, infiltration-excess and saturation-excess caused by rainfall temporal heterogeneities. Moreover, the results support the validity of variogram technique to classify storm events into two LT and HT classes.

Experimental investigation on rainfall infiltration and solute transport in layered porous and fractured media

Layered structures with upper porous and lower fractured media are widely distributed in the world. An experimen- tal investigation on rainfall infiltration and solute transport in such layered structures can provide the necessary foundation for effectively preventing and forecasting water bursting in mines, controlling contamination of mine water, and accomplishing ecological restoration of mining areas. A typical physical model of the layered structures with porous and fractured media was created in this study. Then rainfall infiltration experiments were conducted after salt solution was sprayed on the surface of the layered structure. The volumetric water content and concentration of chlorine ions at different specified positions along the profile of the experiment system were measured in real-time. The experimental results showed that the lower fractured media, with a considerably higher permeability than that of the upper porous media, had significant effects on preventing water infil- tration. Moreover, although the porous media were homogeneous statistically in the whole domain, spatial variations in the features of effluent concentrations with regards to time, or so called breakthrough curves, at various sampling points located at the horizontal plane in the porous media near the porous-fractured interface were observed, indicating the diversity of solute transport at small scales. Furthermore, the breakthrough curves of the outflow at the bottom, located beneath the underlying fractured rock, were able to capture and integrate features of the breakthrough curves of both the upper porous and fractured media, which exhibited multiple peaks, while the peak values were reduced one by one with time.

Rainfall Forecasting Using Fourier Series

The need for accurate rainfall prediction is readily apparent when considering many benefits in which such information would provide for river control, reservoir operation, forestry interests, flood mitigation, etc.. Due to importance of rainfall in many aspects, studies on rainfall forecast have been conducted since a few decades ago. Although many methods have been introduced, all the researches describe the study as complex because it involves numerous variables and still need to be improved. Nowadays, there are various traditional techniques and mathematical models available, yet, there are no result on which method provide the most reliable estimation. AR （auto-regressive）, ARMA （auto-regressive moving average）, ARIMA （auto-regressive integrated moving average） and ANNs （artificial neural networks） were introduced as a useful and efficient tool for modeling and forecasting. The conventional time series provide reasonable accuracy but suffer from the assumptions of stationary and linearity. The concept of neurons was introduced first which then developed to ANNs with back propagation training algorithm. Although certain ANNs） models are equivalent to time series model, but it is limited to short term forecasting. This Paper presents a mathematical approach for rainfall forecasting for Iran on monthly basic. The model is trained for monthly rainfall forecasting and tested to evaluate the performance of the model. The result Shows reasonably good accuracy for monthly rainfall forecasting.

Method to determine parameters in the rainstorm intensity formula

This paper presents a new method to determine parameters in the nonlinear mathematical model of the urban rainfall intensity formula. The method transforms the nonlinear equation into a linear one, and incorperates a damping factor and a step factor to improve the precision of the calculated results. It works out the parameters based on given rainstorm intensity, period of the recurrence of rainstorm and lasting time of the rainfall. The results turns out to have the smallest residual error compared with those obtained by several other methods and satisfy the related standard. The method proves of fast convergence, desirable generality, stability and accuracy, which overcomes the defects of other existing numeral methods.

Modeling Runoff from Semi-Arid Agricultural Lands in Northwest Iran

Transformation of rainfall into runoff over an area is a very complex process which exhibits both temporal and spatial variability;runoff in a defined area can be affected by factors such as topography, vegetation, rainfall characteristics and soil properties. This study was conducted to develop an empirical model using the rainfall characteristics and soil properties for predicting runoff from dry-farming lands in a semi-arid agricultural area in Hashtroud, Northwest Iran. Runoff plots(1.83 m × 22.1 m) in triplicate were installed in thirty-six sloped dry-farming lands in the study area. Runoff under natural rainfalls was measured in each plot during a2-year period. The results showed that runoff for 41 runoff-producing rainstorm events with duration longer than 30 min was largely associated with a rainfall index obtained by multiplying the positive square root of rainfall depth(h0.5) by the logarithm of the maximum 30-minute intensity(LogI30)(R2= 0.81). Runoff significantly varied among the plots(P < 0.001), which was considerably related to the effective soil properties(R2= 0.74), i.e., soil permeability(Per) and aggregate stability(AS). A multiple linear regression model was developed between runoff and the rainfall index(h0.5logI30) and the effective soil properties(AS and Per). Evaluation of the model using 34 runoff-producing rainstorm events that occurred during the next two years resulted in high values of the efficiency coefficient and R2(0.88 and 0.91, respectively), which revealed that the model developed in this study could be used in predicting runoff from the dry-farming lands in the semi-arid regions.