嘉陵江流域降水变化及旱涝多时间尺度分析

依据嘉陵江流域1961-2012 年的气象数据,采用数理统计方法结合GIS空间分析技术,探讨了嘉陵江流域降水量时空变化和旱涝灾害特征。结果表明:近52 a 来全流域年平均降水量以13.69 mm/10 a 的速率减少,并在1984 年发生突变,随后降水量明显减少;从区域分析看,受季风和海拔高度等因素的影响,降水量东南多西北少;近52 a 来,除达县和沙坪坝两个站点降水量呈微弱增加外,其余地区降水量均呈减少趋势,略阳-广元-绵阳一带降水量减少速率最高。嘉陵江流域20 世纪60 年代偏涝,涝灾发生频率高;70 至80 年代旱涝灾害交替出现,整体偏涝;90 年代以来,该流域旱灾发生频率与程度均高于涝灾,整体偏旱;该流域由涝灾向旱灾转化的趋势明显。     

Uncertain sightings and the extinction of the Ivory-billed Woodpecker

The extinction of a species can be inferred from a record of its sightings. Existing methods for doing so assume that all sightings in the record are valid. Often, however, there are sightings of uncertain validity. To date, uncertain sightings have been treated in an ad hoc way, either excluding them from the record or including them as if they were certain. We developed a Bayesian method that formally accounts for such uncertain sightings. The method assumes that valid and invalid sightings follow independent Poisson processes and use noninformative prior distributions for the rate of valid sightings and for a measure of the quality of uncertain sightings. We applied the method to a recently published record of sightings of the Ivory-billed Woodpecker (Campephilus principalis). This record covers the period 1897-2010 and contains 39 sightings classified as certain and 29 classified as uncertain. The Bayes factor in favor of extinction was 4.03, which constitutes substantial support for extinction. The posterior distribution of the time of extinction has 3 main modes in 1944, 1952, and 1988. The method can be applied to sighting records of other purportedly extinct species.     

FLOOD DAMAGES IN CHANGING FLOOD PLAINS: A FORENSIC‐HYDROLOGIC CASE STUDY1

ABSTRACT: Hydraulic modification of flood plains by human activity is the primary cause of rising flood damages throughout the world. As flood‐plain hydraulic roughness increases, so does the water level for a fixed flow rate. This raises the flood damage associated with a flood of given return period, and thus, magnifies the flood risk. This article presents an approach that integrates climatic, hydrologic, and hydraulic principles and presents models to discern the probable causes of flood damage in a basin that undergoes flood‐plain development. The article documents key factors that govern flood damage and presents a case study that illustrates the principles of forensic hydrology in an impacted flood plain. The study demonstrates flood level rise caused by hydraulic alteration of a flood plain between 1969 and 1995 and apportioned the increased water level among agricultural and structural factors located in the study area.     

Estimating the extinction date of the thylacine with mixed certainty data

The thylacine (Thylacinus cynocephalus), one of Australia's most characteristic megafauna, was the largest marsupial carnivore until hunting, and potentially disease, drove it to extinction in 1936. Although thylacines were restricted to Tasmania for 2 millennia prior to their extinction, recent so‐called plausible sightings on the Cape York Peninsula in northern Queensland have emerged, leading some to speculate the species may have persisted undetected. We compiled a data set that included physical evidence, expert‐validated sightings, and unconfirmed sightings up to the present day and implemented a range of extinction models (focusing on a Bayesian approach that incorporates all 3 types of data by modeling valid and invalid sightings as independent processes) to evaluate the likelihood of the thylacine's persistence. Although the last captive individual died in September 1936, our results suggested that the most likely extinction date would be 1940. Our other extinction models estimated the thylacine's extinction date between 1936 and 1943, and the most optimistic scenario indicated that the species did not persist beyond 1956. The search for the thylacine, much like similar efforts to rediscover other recently extinct charismatic taxa, is likely to be fruitless, especially given that persistence on Tasmania would have been no guarantee the species could reappear in regions that had been unoccupied for millennia. The search for the thylacine may become a rallying point for conservation and wildlife biology and could indirectly help fund and support critical research in understudied areas such as Cape York. However, our results suggest that attempts to rediscover the thylacine will be unsuccessful and that the continued survival of the thylacine is entirely implausible based on most current mathematical theories of extinction.     

Floods in the Douala metropolis,Cameroon: attribution to changes in rainfall characteristics or planning failures?

With urban populations worldwide expected to witness substantial growth over the next decades, pressure on urban land and resources is projected to increase in response. For policy-makers to adequately meet the challenges brought about by changes in the dynamics of urban areas, it is important to clearly identify and communicate their causes. Floods in Douala (the most densely populated city in the central African sub-region), are being associated chiefly with changing rainfall patterns, resulting from climate change in major policy circles. We investigate this contention using statistical analysis of daily rainfall time-series data covering the period 1951–2008, and tools of geographic information systems. Using attributes such as rainfall anomalies, trends in the rainfall time series, daily rainfall maxima and rainfall intensity–duration–frequency, we find no explanation for the attribution of an increase in the occurrences and severity of floods to changing rainfall patterns. The culprit seems to be the massive increase in the population of Douala, in association with poor planning and investment in the city's infrastructure. These demographic changes and poor planning have occurred within a physical geography setting that is conducive for the inducement of floods. Failed urban planning in Cameroon since independence set the city up for a flood-prone land colonization. This today translates to a situation in which large portions of the city's surface area and the populations they harbor are vulnerable to the city's habitual annual floods. While climate change stands to render the city even more vulnerable to floods, there is no evidence that current floods can be attributed to the changes in patterns of rainfall being reported in policy and news domains.     

大连台地磁数字记录与模拟记录的对比分析

对正在运行的大连台地磁数字记录和模拟记录,从地磁相对记录的三种变化磁场的类型进行了逐一对比分析,结果表明,虽然数字记录的整体方面明显优于模拟记录,但二者又各有其特点,数字记录代替模拟记录应该还有一段过渡的过程。     

Occurrence of severe floods in the Salado River Basin,Buenos Aires province,Argentina

Floods in the Salado Riverbasin, Argentina, seriously affect bothhuman activities and the environment.Inadequate and improper water managementaggravates the effects of natural extremeevents. The damage caused by the extremeflood in 1993 cost US$507 million,affected 14,500 farmers and flooded6,500,000 ha within the basin. This paperanalyses natural trends within the rainfalland riverflow records, and considers thepossible effects of human interference. Theriver basin is mainly underlain byimpermeable soils with a high water table.The soil factor and the low topographicgradients often produce surface run-off withslow lateral drainage. Very often, heavyrainfall associated with high soil moisturecontent leads to flooding of the basin.Three major flood events that have occurredsince 1960 have been analysed. Floodoccurrences have been placed in the contextof precipitation variability and soil waterstorage. The precipitation records of twolong-term stations in the basin (Junin andDolores) show an increasing trend and thisis due to rainfall increases in the warmseason. However, none of the rain eventsreached the probable maximum precipitationof 100 year return period. The dischargerecords of the Salado River are comparedwith the pattern of the ElNiño/Southern Oscillation and it isfound that only the May discharge anomaliesare weakly related to the El Niñodriven climate variability. Results fromthis study are useful for the formulationof flood mitigation measures. The paperconcludes with a consideration of the floodmitigation policy developed in PlanMaestro.     

GENERALIZED LOW-FLOW FREQUENCY RELATIONSHIPS FOR UNGAGED SITES IN MASSACHUSETTS1

ABSTRACT: Regional hydrologic procedures such as generalized least squares regression and streamflow record augmentation have been advocated for obtaining estimates of both flood-flow and low-flow statistics at ungaged sites. While such procedures are extremely useful in regional flood-flow studies, no evaluation of their merit in regional low-flow estimation has been made using actual streamflow data. This study develops generalized regional regression equations for estimating the d-day, T-year low-flow discharge, Q_{d, t}, at ungaged sites in Massachusetts where d = 3, 7, 14, and 30 days. A two-parameter lognormal distribution is fit to sequences of annual minimum d-day low-flows and the estimated parameters of the lognormal distribution are then related to two drainage basin characteristics: drainage area and relief. The resulting models are general, simple to use, and about as precise as most previous models that only provide estimates of a single statistic such as Q_7,10. Comparisons are provided of the impact of using ordinary least squares regression, generalized least squares regression, and streamflow record augmentation procedures to fit regional low-flow frequency models in Massachusetts.     

HISTORICAL CHANGES IN UPPER MISSISSIPPI RIVER WATER AREAS AND ISLANDS1

ABSTRACT: Periodic surveys of the upper Mississippi River since 1866 and a discharge record of nearly equal length provided an opportunity to learn more about the magnitudes and rates of geomorphic processes at work in large stream systems. Furthermore, geomorphic and hydrologic adjustments could be evaluated in relation to watershed land use changes, small‐scale climate fluctuations, and considerable modifications to the channel and floodplain during the period of record. The present study uses GIS mapping to quantitatively compare historical changes in mapped land and water phenomena in the upper Mississippi River Pool 10, located along southwest Wisconsin's border. Modest channel widening and decreases in island area throughout the study reach during the last century are detectable. Flood magnitudes and frequencies also have varied during this time, and stages and low flow discharges have increased since the 1940s. The latter hydrologic change appears to be closely associated with the reach's geomorphic adjustments. Results are representative of a valley reach where a major tributary contributes a large sand bedload, forming an alluvial fan of considerable size in the floodplain.