Storm rainfall conditions for floods and debris flows from recently burned areas in southwestern Colorado and southern California   总被引：9，自引：1，他引：8  

Susan H. Cannon  Joseph E. Gartner  Raymond C. Wilson  James C. Bowers  Jayme L. Laber 《Geomorphology》2008,96(3-4):250

Debris flows generated during rain storms on recently burned areas have destroyed lives and property throughout the Western U.S. Field evidence indicate that unlike landslide-triggered debris flows, these events have no identifiable initiation source and can occur with little or no antecedent moisture. Using rain gage and response data from five fires in Colorado and southern California, we document the rainfall conditions that have triggered post-fire debris flows and develop empirical rainfall intensity–duration thresholds for the occurrence of debris flows and floods following wildfires in these settings. This information can provide guidance for warning systems and planning for emergency response in similar settings.Debris flows were produced from 25 recently burned basins in Colorado in response to 13 short-duration, high-intensity convective storms. Debris flows were triggered after as little as six to 10 min of storm rainfall. About 80% of the storms that generated debris flows lasted less than 3 h, with most of the rain falling in less than 1 h. The storms triggering debris flows ranged in average intensity between 1.0 and 32.0 mm/h, and had recurrence intervals of two years or less. Threshold rainfall conditions for floods and debris flows sufficiently large to pose threats to life and property from recently burned areas in south-central, and southwestern, Colorado are defined by: I = 6.5D^− 0.7 and I = 9.5D^− 0.7, respectively, where I = rainfall intensity (in mm/h) and D = duration (in hours).Debris flows were generated from 68 recently burned areas in southern California in response to long-duration frontal storms. The flows occurred after as little as two hours, and up to 16 h, of low-intensity (2–10 mm/h) rainfall. The storms lasted between 5.5 and 33 h, with average intensities between 1.3 and 20.4 mm/h, and had recurrence intervals of two years or less. Threshold rainfall conditions for life- and property-threatening floods and debris flows during the first winter season following fires in Ventura County, and in the San Bernardino, San Gabriel and San Jacinto Mountains of southern California are defined by I = 12.5D^−0.4, and I = 7.2D^−0.4, respectively. A threshold defined for flood and debris-flow conditions following a year of vegetative recovery and sediment removal for the San Bernardino, San Gabriel and San Jacinto Mountains of I = 14.0D^−0.5 is approximately 25 mm/h higher than that developed for the first year following fires.The thresholds defined here are significantly lower than most identified for unburned settings, perhaps because of the difference between extremely rapid, runoff-dominated processes acting in burned areas and longer-term, infiltration-dominated processes on unburned hillslopes.  相似文献   

RAINFALL AND TEMPERATURE ATTRIBUTES ON THE LESOTHO–DRAKENSBERG ESCARPMENT EDGE, SOUTHERN AFRICA     

WERNER NEL  PAUL SUMNER 《Geografiska Annaler: Series A, Physical Geography》2008,90(1):97-108

Located near the southeastern limit of Africa, the Lesotho‐Drakensberg and associated escarpment is the highest range of African mountains south of the massifs in Tanzania. At the escarpment summit and on the adjacent high peaks, the climate is generally interpreted as marginal periglacial yet few data, specifically rainfall and temperature, exist on record at these altitudes. Climatic data from two temporary field stations on the escarpment edge, one of which is the highest rainfall station yet on record in southern Africa, provide contemporary surface‐climate conditions. Mean annual rainfall recorded between 2001 and 2005 averages 767.8 mm at Sani Pass summit (three complete years), and 753.2 mm on Sentinel Peak (two complete years); these values are less than those recorded for the same period in the mountain foothills. Even though rainfall is slightly below long‐term rainfall averages for the area due to a marginally dry spell, the data show that earlier estimates of between 1000 mm and 2000 mm rainfall per annum on the escarpment are too high. A measured mean air temperature of 5.8°C at Sani Pass, however, falls within the range estimated for the escarpment summit. Frost cycles in air and at the soil surface are frequent in winter, but absent in soil for summer, and no long‐duration surface‐soil freeze was measured. Temperatures thus confirm the marginal periglacial nature as postulated for previously, but precipitation data indicate a dryer environment than anticipated. Palaeoenvironmental scenarios, notably arguments for former glaciation based on extrapolations from somewhat exaggerated contemporary precipitation values, thus require re‐consideration.  相似文献   

嘉山台地电阻率与降雨关系探究     

张伟峰  王远  潘洁  孙亮亮  肖攀  李露露 《华南地震》2015,35(1):84-89

地电阻率观测系统由于技术及环境变化等原因,在观测资料中常常会出现与地震孕育及地壳区域应力状态无关的变化,其中降雨就是比较显著的影响因素,根据嘉山台2000—2013年的数字化资料分析降雨与地电阻率之间的关系,结果表明:降雨与地电阻率的季节性变化之间存在较好的相关关系,并尝试通过数字方法剔除资料中的降雨影响。  相似文献   

Uncertainty of rainfall-induced landslides considering spatial variability of parameters     

《Computers and Geotechnics》2017

A cross-correlation analysis is conducted to determine the impacts of the heterogeneity of hydraulic conductivity K_s, soil cohesion c′ and soil friction angle (tan φ′) on the uncertainty of slope stability in time and space during rainfall. We find the relative importance of tan φ′ and c′ depends on the effective stress. While the sensitivity of the stability to the variability of K_s is small, the large coefficient of variation of K_s may exacerbate the variability of pore-water pressure. Therefore, characterizing the heterogeneity of hydraulic properties and pore-water distribution in the field is critical to the stability analysis.  相似文献   

A point based Eulerian definition of rain event based on statistical properties of inter drop time intervals: An application to Chilbolton data     

Massimiliano Ignaccolo  Carlo De Michele 《Advances in water resources》2010

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Response of the soil water content of mobile dunes to precipitation patterns in Inner Mongolia,northern China     

《Journal of Arid Environments》2013

We analyzed the relationship between soil water content (SWC) dynamics in mobile dunes to a depth of 100 cm and precipitation patterns from June to July 2010 in the Horqin Sand Land. The precipitation was dominated by small events of 0.1–3.0 mm, which accounted for 52% of the total events. Precipitation >20 mm had the highest intensity, accounting for 50% of the total precipitation. SWC differed significantly among the soil layers: mean SWC was greatest from 80 to 100 cm and lowest from 40 to 60 cm. SWC from 0 to 100 cm was significantly affected by relative humidity, water barometric pressure and minimum temperature, and the SWC of 0–40 cm was obviously influenced by precipitation amount and wind velocity. Precipitation <5 mm did not replenish SWC, precipitation between 5 and 20 mm provided some replenishment to SWC from 0 to 40 cm, and precipitation >20 mm increased significantly SWC from 0 to 100 cm. In addition, precipitation intensity significantly affected the infiltration rate, with higher intensity leading to deeper and faster infiltration. At longer intervals between precipitation events, SWC in each soil layer decreased continuously over time; however, SWC from 0 to 80 cm changed little within the first 3 days, and SWC from 0 to 100 cm started to decrease greatly after 5 days.  相似文献   

淮北平原降雨入渗补给系数随地下水埋深变化特征   总被引：1，自引：0，他引：1  

谢永玉 《地下水》2012,(1):9-11

水文地质参数对地下水资源评价起着至关重要的作用。其中,降雨入渗补给系数是影响浅层地下水水量、水质的重要参数。它对研究区域水量转化和水量平衡也十分重要。但是由于受降雨量、土壤类型、植被、地下水埋深等诸多因素的影响,准确判断降雨入渗补给系数存在很大困难。如果没有考虑这些因素的影响,尤其是降雨量和地下水埋深的影响,所推求的降雨入渗补给系数就会存在较大误差。结合安徽省淮北平原区五道沟水文实验站观测的降雨量、地下水补给量、地下水水位资料,利用两种不同的方法推求了不同降雨量等级的次降雨入渗补给系数。根据统计学理论研究了不同降雨量条件下,次降雨入渗补给系数随地下水埋深变化的分布规律,建立了次降雨入渗补给系数与地下水埋深的回归模型,并进行了相应的检验。研究表明,在控制地下水埋深的条件下,次降雨入渗补给系数随地下水埋深的变化符合指数分布;在地下水位自由变动的条件下符合伽玛分布。  相似文献   

Identification of trends in rainfall,rainy days and 24 h maximum rainfall over subtropical Assam in Northeast India     

Deepak Jhajharia  Brijesh K. Yadav  Sunil Maske  Surajit Chattopadhyay  Anil K. Kar 《Comptes Rendus Geoscience》2012,344(1):1-13

Trends in rainfall, rainy days and 24 h maximum rainfall are investigated using the Mann-Kendall non-parametric test at twenty-four sites of subtropical Assam located in the northeastern region of India. The trends are statistically confirmed by both the parametric and non-parametric methods and the magnitudes of significant trends are obtained through the linear regression test. In Assam, the average monsoon rainfall (rainy days) during the monsoon months of June to September is about 1606 mm (70), which accounts for about 70% (64%) of the annual rainfall (rainy days). On monthly time scales, sixteen and seventeen sites (twenty-one sites each) witnessed decreasing trends in the total rainfall (rainy days), out of which one and three trends (seven trends each) were found to be statistically significant in June and July, respectively. On the other hand, seventeen sites witnessed increasing trends in rainfall in the month of September, but none were statistically significant. In December (February), eighteen (twenty-two) sites witnessed decreasing (increasing) trends in total rainfall, out of which five (three) trends were statistically significant. For the rainy days during the months of November to January, twenty-two or more sites witnessed decreasing trends in Assam, but for nine (November), twelve (January) and eighteen (December) sites, these trends were statistically significant. These observed changes in rainfall, although most time series are not convincing as they show predominantly no significance, along with the well-reported climatic warming in monsoon and post-monsoon seasons may have implications for human health and water resources management over bio-diversity rich Northeast India.  相似文献   

Can a 25-year trend in Soudano-Sahelian vegetation dynamics be interpreted in terms of land use change? A remote sensing approach   总被引：3，自引：0，他引：3  

Agnès Bégué  Elodie VintrouDenis Ruelland  Maxime Claden 《Global Environmental Change》2011,21(2):413-420

This study is based on the premise that, in the Sahel/Sudanian belt of Africa, the main determinants of interannual variation in vegetation dynamics are rainfall and land cover type. We analyzed the spatio-temporal sensitivity of the NOAA-AVHRR 8 km-resolution vegetation index (NDVI) to (i) annual rainfall variability (0.5° × 0.5° resolution) acquired over a 25-year period (1982-2006); and (ii) land use changes in the different eco-climatic regions of the Bani catchment in Mali (130 000 km²). During the period 1982-2006, there was no clear trend in rainfall over the catchment, whereas there was a strong positive trend in the NDVI, both when the NDVI values were corrected using annual rainfall variability and when they were not. We divided the catchment into three eco-climatic regions based on the relationship between the annual NDVI and rainfall. In each region, we analyzed the observed greening in relation to changes in land use after correcting for the effect of annual rainfall on the NDVI. Results show that there is a mixed level of agreement between the land cover changes at the grid cell scale and the spatial pattern of the NDVI trend. Increased cropping does not explain the increase in the annual NDVI, except in the Sahelian part of the catchment. We hypothesize that the natural vegetation dynamics related to the non-linear rainfall patterns during the 25-year study period were responsible for these results.  相似文献   

六合体应变干扰因素与地震短临异常特征研究   总被引：1，自引：0，他引：1       下载免费PDF全文

郑江蓉  徐徐  王俊  江昊琳 《地震工程学报》2011,33(1):84-90

利用江苏省南京市六合地震台钻孔体应变2003年1月1日至2008年12月31日的数字化观测资料,对气压和降雨这二种主要干扰因素的基本变化规律进行分析,讨论了发生在该台预报效能范围内的3次中强地震的短临异常特征.结果表明:气压变化在各个季节对观测值均有较大的影响,以短周期的正相关干扰影响为主,在时间上往往表现为准同步,相关系数能达到0.6～0.7以上;降雨对体应变的影响与降雨过程、降雨量及降雨时间等有密切的关系,持续降雨只有积累到一定程度才能促成固体潮畸变,这一过程虽较复杂,但仍有一定的规律可循.六合体应变对区域内中强地震有1～2月的突出短临异常变化.  相似文献