降水预报产品在不同水文气象分区中小流域的适应性评估

以位于不同水文气象分区的屯溪流域和绥德流域为研究对象,选取TIGGE(THORPEX Interactive Garnd Global Ensemble)数据集中NCEP(National Centersfor Environmental Prediction)、ECMWF(European Centre for Medium-range Weather Forecasts)、CMA(China Meteorological Administration)3种预报产品的2010—2015年控制预报数据,基于分位数映射法中的QUANT(non-parametric quantile mapping using empirical quantiles)法和RQUANT(non-parametric quantile mapping using robust empirical quantiles)法进行预报降雨修正,并采用多分类预报检验、连续型预报检验和概率型预报检验等方法,对不同水文气象分区、不同预报产品和不同修正方法进行比较与适用性分析;同时,以屯溪流域实测降雨为例,通过增加噪声项对降雨重采样,基于新安江模型分析降雨不确定性对水文模拟结果的影响。结果表明:在研究流域,所选的预报产品对无雨和小雨期的预报精度都较高,但随着降雨量的增加,各产品的预报能力均出现较为明显的下降。多分类和连续型检验表明绥德流域的降雨预报效果更佳,NCEP和ECMWF在研究流域的整体预报精度较高,CMA的整体预报精度在研究流域略低于其他产品。各产品在修正后大部分检验指标预报精度提高,其中:ECMWF在绥德流域修正后预报精度最高,对两种修正方法都有很好的适用性;在屯溪流域,NCEP和ECMWF在不同修正方法后各指标预报精度各有高低,CMA在修正后仅在大雨量级的TS评分预报精度高于其他产品。降雨的不确定性会对水文模拟产生消极影响,并导致参数的不确定性和水文模拟精度的下降。

NMCP降水预报的适用性研究——以辽宁诺敏河为例

对高分辨率数值天气预报产品进行精度评估时考虑其时空不确定性是有必要的。从降水量级、空间分布和时间分布多角度出发建立降雨预报评估方法,选取2021年诺敏河流域的实测数据和预报数据,采用上述方法对NMCP模式进行了综合评价。结果表明:1) 在降水量级上,以相对误差作为评价指标。前36 h的NMCP模式相对误差在0.8以上,尤其对短时强降雨量预报精度较高;2) 在空间分布上,采用邻域法改善空间不确定性,结合FSS评分确定NMCP在该流域的最优邻域半径为60 km。3) 在时间分布上,引入时间域半径,结合TFSS评分确定最优时间域半径为2 h。前48 h的NMCP模式对大雨及以下的预报精度较高,FSS与TFSS评分均达到0.8以上,对于暴雨表现较差。该评价方法能够较好的反映降雨预报数据的时空分布,更加真实客观地评价降雨预报精度,为今后的多模式集成与气象水文耦合等应用提供理论基础。

Rapid assessment of regional superficial landslide under heavy rainfall

In order to establish a rapid method for regional slope stability analysis under rainfall,matric suction and seepage force were taken into account after obtaining explicit solution of infiltration depth.Moreover,simplified analysis model under 3D condition was put forward based on identification and division of slope units,as well as modification of sliding direction of each column.The result shows that explicit solution of infiltration depth is of good precision;for the given model,safety factors without taking seepage force into account are 1.82-2.94 times higher;the stagnation point of slope angle is located approximately in the range of(45°,50°);the safety factor changes insignificantly when wetting front is deeper than 2 m;when matric suction changes in the specified range,the maximum variations of safety factor are less than 0.5,which proves that matric suction plays an insignificant role in maintaining slope stability compared to the slope angle and infiltration depth.Incorporated with geographic information system,a practical application of regional slope stability assessment verifies the applicability of the proposed method.

Rapid Geometry Analysis for Earthquake-induced and Rainfall-induced Landslide Dams in Taiwan

Stability analysis of the dam is important for disaster prevention and reduction. The dam's geometry plays an important role in understanding its stability. This study develops a rapid landslide dam geometry assessment method for both earthquake-induced and rainfall-induced landslide dams based on nine real cases collected in Chinese Taipei and 214 cases collected worldwide. For simplification purposes, a landslide dam is classified into triangular or trapezoidal. The rapid landslide dam geometry assessment method in this paper uses only satellite maps and the topographic maps to get landslide area, and then analyze the dam geometry. These maps are used to evaluate the area of the landslide and the slope of the river bed. Based on the evaluation information, the proposed method can calculate dam height, the length of the dam, and the angles of the dam in both upstream and downstream directions. These geometry parameters of a landslide dam provide important information for further dam stability analysis. The proposed methodology is applied to a real landslide dam case at Hsiaolin Village. The result shows that the proposed method can be used to assess the landslide dam geometry.

Assessing the Seasonal Predictability of Summer Precipitation over the Huaihe River Basin with Multiple APCC Models

Seasonal rainfall predictability over the Huaihe River basin is evaluated in this paper on the basis of 23-year(1981-2003) retrospective forecasts by 10 climate models from the Asia-Pacific Economic Cooperation(APEC) Climate Center(APCC) multi-model ensemble(MME) prediction system.It is found that the summer rainfall variance in this basin is largely internal,which leads to lower rainfall predictability for most individual climate models.By dividing the 10 models into three categories according to their sea surface temperature(SST) boundary conditions including observed,predicted,and persistent SSTs,the MME deterministic predictive skill of summer rainfall over Huaihe River basin is investigated.It is shown that the MME is effective for increasing the current seasonal forecast skill.Further analysis shows that the MME averaged over predicted SST models has the highest rainfall prediction skill,which is closely related to model's capability in reproducing the observed dominant modes of the summer rainfall anomalies in Huaihe River basin.This result can be further ascribed to the fact that the predicted SST MME is the most effective model ensemble for capturing the relationship between the summer rainfall anomalies over Huaihe River basin and the SST anomalies(SSTAs) in equatorial oceans.

Assessment of the Performance of WEPP in Purple Soil Area with Simulated Rainfall Experiments

The water erosion prediction project （WEPP） model is a popular water erosion prediction tool developed on the basis of the physical processes of water erosion. Although WEPP has been widely used around the world, its application in China is still insufficient. In this study, the performance of WEPP used to estimate the runoff and soil loss on purple soil （Calcaric Regosols in FAO taxonomy） sloping cropland was assessed with the data from runoff plots under simulated rainfall conditions. Based on measured soil properties, runoff and erosion parameters, namely effective hydraulic conductivity, inter-rill erodibility, rill erodibility, and critical shear stress were determined to be 2.68 mm h-1, 5.54 x l0^6 kg s-1 m-4, 0.027 s m-1 and 3-5 Pa, respectively, by using the recommended equations in the WEPP user manual. The simulated results were not good due to the low Nash efficiency of 0.41 for runoff and negative Nash efficiency for soil loss. After the four parameters were calibrated, WEPP performed better for soil loss prediction with a Nash efficiency of 0.76. The different results indicated that the equations recommended by WEPP to calculate parameters such as erodiblity and critical shear stress are not suitable for the purple soil areas, Sichuan Province, China. Although the predicted results can be accepted by optimizing the runoff and erosion parameters, more research related to the determination of erodibility and critical sheer stress must be conducted to improve the application of WEPP in the purple soil areas.

An Assessment of Climate Change and Available Water Resources in the Lowveld Region, Swaziland

Long-term climatic data （maximum temperature, minimum temperature, rainfall and evaporation） for Big Bend in the Lowveld, a semi-arid region of Swaziland, were analysed for any changes or variations. Evaporation and rainfall data were analysed to assess water resources availability in the region. Analysis of the available data shows that there is no indication of decrease in rainfall with time, but the results show that there has been a steady increase in minimum temperatures over the last 25 years. The average effective water resources index, measured as the difference between mean annual rainfall and mean annual evaporation, for the region in the period from 1965 to 2001 was -1,500 mm. The large negative index implies low available water for the region, a situation that is likely to affect agricultural, hydropower and other water related development activities in the region. The negative effective water index implies deficits in the region＇s water resources which call for better management of the region＇s water resources. In the agriculture sector, this requires promoting technologies and practices that provide for water saving, improved water use performance and high water productivity. These include soil conservation tillage, wastewater reuse, runoff harvesting and soil fertility interventions through application of fertilizers, manures and mulches, and agronomic management. There is need for more analysis for the other regions in order to get a countrywide picture of the climate as well as water resources situations.

Assessment of Groundwater Recharge from Rainfall in the Plain of Cai Phan Rang, Vietnam

This paper presents the quantitative assessment results of rainwater supply to groundwater in Cai Phan Rang River basin, Ninh Thuan province, Vietnam. In order to obtain the results, the authors developed two experimental areas with 10 wells which were monitored in one year to assess the infiltration supply of rainwater to groundwater. The results of this research assessed the amount of rainwater infiltrates into groundwater varies from 307.16-314.98 tam·year^-1, average is 311 mm·year^-1. The findings are significant in terms of science which identify sources of groundwater storage from the infiltration supply of rainwater. The findings are also practical in suggesting measures to reserve groundwater for the purpose of socio-economic development in the study area.