A comparison between the Mediterranean climates of Eurasia and the Americas

On the 19th and 20th September 1981 heavy rain fell throughout Scotland. Almost 140mm was recorded for the 24 hours up to 9.00 am on the 20th at Dundonnell in Wester Ross, an event with a recurrence interval of approximately 120 years. The storm generated a peak discharge of c.60m³ s‐¹ on the Ardessie Burn which drains a 13.3km² catchment on the northwestern slopes of An Teallach. The resulting flood caused severe localised bank erosion and partially destroyed a fish farm. The total volume of measured flood deposits exceeded 1800 tonnes, approximately equal to 14 years normal average annual non‐dissolved sediment output. The identification of specific sediment source areas and deposition sites allows an assessment of geomorphic work in terms of direct landscape adjustment in response to extreme rainfall. The flood stresses the importance of rare events in the landscape evolution of upland environments and the influence of antecedent catchment conditions.     

Natural flood management: small-scale progress and larger-scale challenges

ABSTRACT

Management of fluvial flood risk in the UK is undergoing a paradigm shift, with a change in emphasis from solely working with structural defences to considering catchment-based measures which attenuate flood runoff. Natural Flood Management (NFM) is promoted as a method that can reduce flood risk through the alteration, restoration or use of landscape features. Here we highlight the potential to manage runoff locally in the rural landscape using NFM by targeting flow pathways and utilising floodplains and riparian zones. Using two case study examples from the UK, we show that by accumulating dispersed small-scale storage in small catchment areas (<10 km²) can assist in attenuating flood runoff. However, there is currently a lack of evidence of measure effectiveness at larger catchment scales and for managing extreme flood events. Nevertheless, there is a strong evidence base to suggest many of these measures deliver a range of different ecosystem services if installed in the correct location in the landscape.     

Antarctic history: A reply to professor W. H. Hobbs

On July 25th 1983 a severe thunderstorm brought torrential rain and flooding to a small valley near Newcastleton in Roxburghshire. At one site within the valley, around 65 mm of rainfall was recorded in 75 minutes, though this was probably 2 km from the centre of the storm. The resulting peak flow was estimated at almost 170 m³s^‐1 from a drainage area of 36.9 km². Lightning killed some livestock whilst many more were drowned. The storm triggered peat slides on several hillsides and caused extensive erosion of river banks and damage to buildings and bridges. The associated high sediment load killed fish stocks in the receiving waters. The flood was a significant event in terms of its human disruption and its impact on the natural environment.     

Rugged Plateaus and Extensive Floodplains — Modelling Landform Evolution in a Northern Australian Catchment

Medium to large natural catchments are often more spatially heterogeneous than small catchments or single landforms. Attempting to model landform evolution of large areas is consequently more complex. This paper demonstrates that modelling landform evolution in medium to large catchments can be improved by calibrating the model to smaller, more geomorphologically homogenous sub‐catchments. The paper investigates landform evolution in the Ngarradj catchment in the Northern Territory of Australia (a medium scale catchment of approximately 67 km²). The catchment is complex and contains two distinct landform regions; an upland plateau region with highly dissected sandstone and shallow, sandy soils, and a lowlands region with gentle, wooded slopes and floodplains with deep, sandy soils. The SIBERIA landform evolution model is calibrated and applied to the Ngarradj catchment. The complexity of the Ngarradj catchment is incorporated into the modelling by dividing the catchment into three sub‐catchments (Swift Creek (SC), Upper Main (UM) and East Tributary (ET)) which are relatively homogeneous and for which hydrology and sediment transport data are available. A discharge‐area relationship and long‐term, sediment loss rates for the catchment are derived based on an annual series flood frequency analysis of a 20 year runoff record predicted in a previous study. Sediment transport modelling incorporates both suspended and bedload sediment loss. The denudation rates derived using these data are 37, 63 and 77 mm kyr^?1 for the SC, UM and ET sub‐catchments, respectively. Model predictions indicate that the UM sub‐catchment will have the greatest mean erosion. This is balanced by the large amount of deposition that will occur in the upper Ngarradj valley of the UM sub‐catchment. Further deposition occurs on the floodplain of Ngarradj, with the area between the SC and ET/UM (up‐stream) sub‐catchments experiencing a small net accretion of sediment (15 mm kyr^?1).     

敦煌莫高窟降雨分布及入渗特征研究

敦煌莫高窟文物具有唯一性和脆弱性,干燥环境是壁画和塑像长久保存的保障,降雨是病害发生诱因。为了弄清降雨对文物的损害机制,本研究通过气象监测数据分析和野外人工降雨模拟试验,分析莫高窟降雨分布特征和窟顶戈壁降雨入渗和产流规律,为开展洞窟内壁画病害发育机理分析和实施莫高窟洪水风险预控提供理论依据。25年气象监测数据分析表明,莫高窟区域多年平均降水量39mm,集中在5~8月,降雨类型主要为微雨和小雨,频现大于76%,大雨及暴雨均为突发性强降雨,频现仅为1.5%,常常伴随区域洪水的发生。降雨模拟试验结果表明,当平均降雨强度0.75mm/min,降雨历时160min时,入渗湿润锋迁移至深度80cm左右即趋于平衡。但是,高密度电阻率探测表明洞窟地层2~3m处,水分饱和度可达60%左右,极易带动可溶盐向壁画地仗层富集,致使病害发生发展。经计算,窟顶戈壁径流系数0.016,产流能力非常低。区域洪水主要来源于莫高窟周边戈壁及野马山地带降雨汇流。     

Rainfall,floods and river channel changes in the upper Hunter

Since 1946, there has been a significant increase in annual rainfall in the Hunter Valley, especially for stations in the western sector. Contemporaneous increases in rainfall intensities of frequent storms and flood peaks have also been recorded. From analyses of the data, together with a review of recent environmental changes in the Hunter Valley, it is concluded that human disturbance of the catchment has played no significant part in the increase in flood magnitude. Instead, the change in floods may be completely attributed to the variation in rainfall regime. The altered hydrologic regime combined with a decrease in sediment yield from extra-channel sources appears to be the primary cause of recent river channel changes.     

An Area‐Based Approach for Estimating Extreme Precipitation Probability

Accurate estimates of heavy rainfall probabilities reduce loss of life, property, and infrastructure failure resulting from flooding. NOAA's Atlas‐14 provides point‐based precipitation exceedance probability estimates for a range of durations and recurrence intervals. While it has been used as an engineering reference, Atlas‐14 does not provide direct estimates of areal rainfall totals which provide a better predictor of flooding that leads to infrastructure failure, and more relevant input for storm water or hydrologic modeling. This study produces heavy precipitation exceedance probability estimates based on basin‐level precipitation totals. We adapted a Generalized Extreme Value distribution to estimate Intensity‐Duration‐Frequency curves from annual maximum totals. The method exploits a high‐resolution precipitation data set and uses a bootstrapping approach to borrow spatially across homogeneous regions, substituting space in lieu of long‐time series. We compared area‐based estimates of 1‐, 2‐, and 4‐day annual maximum total probabilities against point‐based estimates at rain gauges within watersheds impacted by five recent extraordinary precipitation and flooding events. We found considerable differences between point‐based and area‐based estimates. It suggests that caveats are needed when using pointed‐based estimates to represent areal estimates as model inputs for the purpose of storm water management and flood risk assessment.     

Storm Drains as Assemblages: The Political Ecology of Flood Risk in Post‐Colonial Bangalore

Cities around the world are increasingly prone to unequal flood risk. In this paper, I “materialize” the political ecology of urban flood risk by casting stormwater drains—a key artifact implicated in flooding—as recombinant socionatural assemblages. I examine the production of flood risk in the city of Bangalore, India, focusing on the city's informal outskirts where wetlands and circulations of global capital intermingle. Staging a conversation between Marxian and Deleuzian positions, I argue, first, that the dialectics of “flow” and “fixity” are useful in historicizing the relational politics of storm drains from the colonial to the neoliberal era. Second, flood risk has been heightened in the contemporary moment because of an intensified alignment between the flow/fixity of capital and storm drains. Storm drains—and the larger wetlands that they traverse—possess a force‐giving materiality that fuels urban capitalism's risky “becoming‐being”. This argument raises the need for supplementing political‐economic critiques of the city with sociomaterialist understandings of capitalism and risk in the post‐colonial city. The paper concludes with reflections on how assemblage thinking opens up a more distributed notion of agency and a more relational urban political ecology.     

The deserts of the Kashmir‐Tibetan frontier

Abstract

Semi-arid landscapes are vulnerable to cultivation, overgrazing and climate variability, although it is difficult to identify the relative significance of these three factors. In the South African Karoo, the ‘desertification debate' seeks to explain a change to more shrubby vegetation in heavily grazed areas. We examine these issues in catchments where farm reservoirs provide sediment stores with 137Cs, 210Pb, geochemical and mineral magnetic signatures. Rainfall data and stocking numbers are reported and current erosion rates are estimated. Sediment accumulation in the reservoirs increases between 1935 and 1940, probably due to rises in the frequency of rainfall events of >25mm day. Significant increases in sedimentation rates (×8) occur during rain-fed wheat cultivation. In an uncultivated catchment, sediment yields remain relatively high and reflect increases in erosion from hillslopes, colluvial storage, and cultivated land sources. Gully systems have acted as transport routes rather than sediment sources over the last ～70 years. Badland erosion rates average ca. 50t ha^?1 yr^?1. At Ganora, their development in the 1920s strongly influences peak sedimentation between 1970 and 1980. Any delay between badland initiation and increased sediment yield appears to be a function of landscape connectivity. Recovery following disturbance is occurring slowly and is likely to take >100 years. De-stocking and better management systems are reducing erosion rates but may be offset by increases in rainfall intensity.     

Policy Change and Learning in Response to Extreme Flood Events in Hungary: An Advocacy Coalition Approach

In an analysis of the 200‐year history of flood management in Hungary, I use the advocacy coalition framework and the focusing event literature to examine what policy change occurs and what is learned as a result of experiencing extreme and damaging flood events. By analyzing the policy response to a series of extreme floods (1998–2001) in this newly democratizing nation, I attempt to identify the factors that influenced the occurrence of policy change and policy‐oriented learning. In 2003, Hungary enacted a comprehensive flood management program that included economic development and environmental protection goals, a distinct departure from Hungary's historical structural approach to flood management. However, it is less clear that long‐lasting changes in belief systems about how floods should be managed have occurred. In this analysis, I argue that processes external to the flood policy subsystem (e.g., process of democratization and Hungary's accession to the European Union), along with the occurrence of the extreme flood events, enabled a coalition of individuals and organizations to press for policy change.     

An Examination of Vertical Accretion of Floodplain Sediments in the Labasa River Sugarcane Belt of Northern Fiji: Rates,Influences and Contributing Processes

The ¹³⁷Cs (caesium‐137) method was used to investigate medium‐term rates of sediment deposition on the floodplain of the Labasa River, on Vanua Levu island in northern Fiji. The Labasa basin is commercially important for sugarcane farming, which provides much revenue and sustains the economy in the greater Labasa area. Alluvium was sampled at three riverbank sites in vertical increments of 30 mm. Measured net vertical accretion rates, based on analysis of depth‐profiles of ¹³⁷Cs activity, ranged from 10 mm yr^?1 at a low‐lying site near a tributary confluence with the main river, to 60 mm yr^?1 on a levée that was elevated slightly above the adjacent floodplain. These rates of accretion are high, but in general agreement with rates recorded using similar methods in other tropical Pacific island river systems. Soil erosion under sugarcane on hilly parts of the lower Labasa basin is an important factor in rapid floodplain development. Observations made during Cyclone Ami, which traversed Vanua Levu island in early 2003, illustrate the major contribution of severe storm events to floodplain sediment supply, by triggering numerous landslides on catchment slopes and in‐channel debris floods, and by generating large‐magnitude overbank floods.     

Ecohydrology and Environmental Change to Lake Albacutya and Wyperfeld Park in North‐Western Victoria,Australia

Lake Albacutya is a well‐known intermittent lake in north‐western Victoria. The lake is near the termination of the Wimmera River. From time‐to‐time the lake fills and flow passes down Outlet Creek into Wyperfeld National Park. The wetlands associated with the lake have a high biodiversity value and are named in international treaties. This paper examines the hydrologic factors associated with lake filling and flow into Wyperfeld. The lake has filled approximately six times since 1880 and has partially filled on other occasions. Examination of rainfall data from 1875 at Horsham gave no indication of long term rainfall decline, and showed that rainfall at Horsham can be viewed as representative of rainfall in the Wimmera River catchment. However a double‐mass analysis showed that the relationship between the Wimmera River flow and rainfall has varied from 1890 to the present. Examination of data associated with six fillings of Lake Albacutya suggested that filling is a two‐year event requiring at least 550 GL of flow passing Horsham over the two years immediately associated with the flood. A simple model based on rainfall and this threshold reproduced observed characteristics of the data reasonably well. This suggested that the flooding frequency of Lake Albacutya has dropped from about one in 25 years in the natural state to a substantially lower frequency under current river conditions. The results also suggested that because of changes in the Wimmera River the last filling and flood into Wyperfeld in 1976 was far smaller than it would otherwise have been. This is consistent with field mapping of the flood in relation to River Red Gum (Eucalyptus camaldulensis Dehnh.) stands. Analysis of the health of these stands showed major dieback with the severity of this being roughly proportional to the distance from the 1976 flood boundaries. An examination of values associated with the lake and adjoining Wyperfeld National Park suggested that biodiversity and economic values are and will be compromised by the reduction in flooding. In particular, an internationally‐known provenance of Red Gum is at risk, and bird‐breeding opportunities have diminished.     

Estimation of Soil Erosion Using Field and Modelling Approaches in an Undisturbed Arnhem Land Catchment,Northern Territory,Australia

An assessment of slope erosion at Tin Camp Creek catchment, Arnhem Land, Northern Territory, Australia, was carried out using the fallout environmental radioisotope caesium‐137 (¹³⁷Cs) as an indicator of soil erosion status, two numerical models (SIBERIA and the Revised Universal Soil Loss Equation (RUSLE)) and erosion pins. This undisturbed drainage basin is situated in the seasonally wet‐dry tropics, with high energy storms and a mean annual rainfall of 1389 mm. Tin Camp Creek catchment is unaffected by European agriculture or pastoral activities, but often experiences fire during the dry season. Two transects were sampled for ¹³⁷Cs in 2002 and 2004, and two models were used to convert ¹³⁷Cs measurements into soil loss estimates. Two methods using the theoretical Profile Distribution Model (PDM) gave net soil redistribution rates between +2.72 and –22.19 t ha^?1 yr^?1 and +2.95 and –24.06 t ha^?1 yr^?1, respectively, while an Australian empirical model (AEM) for uncultivated soils produced estimates between +1.84 and –7.00 t ha^?1 yr^?1 (negative values indicate soil erosion, positive, deposition). The RUSLE gave estimated soil losses for the two transects of approximately 10 t ha^?1 yr^?1, while the SIBERIA model produced values between 0.5 and 2 t ha^?1 yr^?1 for the transects and between 3.5 and 11 t ha^?1 yr^?1 for the total catchment. Average net soil losses of 14 and 15 t ha^?1 yr^?1 for the total catchment and slopes, respectively, were measured by erosion pins. The soil losses in the catchment are similar to those for some other transects in the Northern Territory and the Kimberley region of Western Australia (measured by the ¹³⁷Cs AEM), even though these areas are affected by pastoral activities. This may be at least partly explained by erosion in Tin Camp Creek catchment during high intensity rainstorms at the commencement of the wet season, especially if the slopes have been affected by fire during the previous dry season.     

Establishing Stage‐Discharge Relationships in Multiple‐Channelled,Ephemeral Rivers: a Case Study of the Diamantina River,Australia

The method for deriving a stage‐discharge relationship has a significant impact on the shape of the river's rating curve. We compare rating curves for a single gauging station on a mutiple‐channelled river in Australia compiled using three different methods – the Urban Runoff and Basin Systems (URBS) rainfall‐runoff model, an empirically‐based velocity‐area method, and the predictive Hydrologic Engineering Centre‐River Analysis System (HEC‐RAS) computer model. The rainfall‐runoff model was found to predict lower discharges for stage heights over 3.5 m than both the empirically‐based velocity‐area method and the HEC‐RAS model. The empirically‐based velocity‐area model predicts similar discharges to the rainfall‐runoff model for stage heights less than 3 m but much higher discharges for larger flood events. The HEC‐RAS model predicts higher discharges than both other rating curves at all stage heights probably due to under‐estimation of the impact of surface roughness on flow velocity. The three models are discussed with particular reference to their use on multiple‐channelled rivers.     

唐代长安、洛阳作为都城和陪都的气候原因

本文从气候角度探讨唐代以长安为都城、以洛阳为陪都的缘由。唐代由于气候温暖湿润,降水量增大,水灾增多。洛阳因为经度地带性作用、降雨季节分配不均及洛阳河流的特殊情况。使得水灾情况比长安更严重：一是降水量大、水灾次数多,二是水势大、灾情重。尽管唐政府注意治水修堤坝,但中桥被冲毁、雨水断路乃至宫城被淹之事仍屡屡发生。长安虽然旱灾较洛阳严重,但水灾对都城的危害更直接、更严重,灭顶之灾的威胁使洛阳不宜作都城,所以建都长安。     

Temporal Patterns and Effects of Surface‐Water Diversions on Daily Flows and Aquatic Habitats: Bega‐Bemboka River,New South Wales,Australia

An understanding of the nature and magnitude of hydrological, physical habitat and physico‐chemical effects resulting from surface‐water diversions in river systems is essential for effective management of water resources. For most coastal‐draining rivers in New South Wales, however, there are few data available on irrigation diversions, their hydrological impacts and environmental effects. This paper therefore presents an analysis of mean daily surface‐water diversions for pasture irrigation from approximately three years of metered data and the resultant effects on daily flows and aquatic habitats in the Bega‐Bemboka River. The period of analysis of the hydrological effects of irrigation diversions is extended to the full length of record (approximately five years) for gauging stations most affected by irrigation diversions, using Maintenance of Variance Extension Type 1 (MOVE.1) modelling techniques. The annual mean, median and peak daily rates of water diversion by metered surface‐water licences used to irrigate 925 ha of dairy pasture are 10.5 Ml d^?1, 7.3 Ml d^?1 and 41.5 Ml d^?1, respectively. Diversion effects on flow duration statistics are such that the measured 90th and 95th daily flow duration percentiles at the gauging station most affected by upstream irrigation diversions are equivalent to the 97th and 99th flow duration percentiles, respectively, under MOVE.1 modelled natural flow conditions. While diversions for irrigation over the three‐year data period account for only 6.6% of total flow volumes, diversions as a proportion of daily surface‐water inflows increase exponentially under decreasing flow rates. Median and maximum daily diversion rates attain 91% and 118%, respectively, of total surface‐water inflows to the diversion‐affected reach when upstream inflows range from 15 to 20 Ml d^?1. This exponentially‐increasing relationship between daily diversion rates and declining surface‐water inflows suggests that ‘rule of thumb’ guidelines on sustainable diversion limits based on mean or median annual percentage diversion volumes need to be applied cautiously to river systems with no or limited capacity to manipulate flows to meet downstream consumptive demands.     

REGIONAL ASPECTS OF DUST STORMS IN STEPPE REGIONS OF THE EAST EUROPEAN AND WEST SIBERIAN PLAINS

Two broad regions of the USSR most susceptible to dust storms, the southern East European Plain in the European USSR and the West Siberian Plain and adjacent areas of northern Kazakhstan, are contrasted according to a number of indicators of dust storm frequency and intensity. More specifically, the two regions, although roughly similar according to overall frequency of dust storms, were found to differ in terms of their interannual variability, years of peak activity, prevailing winds associated with dust storms, seasonal frequency, duration and erosive force of individual storms, and synoptic processes contributing to dust storm formation (translated by Jay K. Mitchell, PlanEcon, Inc., Washington, DC 20005).     

Stable nitrogen isotope values in arid‐land kangaroos correlated with mean annual rainfall: potential as a palaeoclimatic indicator

Bone collagen stable nitrogen isotope values are reported for modern kangaroos (Macropus spp.) from eight field sites along a 1160 km south–north transect from temperate coastal to arid interior South Australia, in order to investigate δ¹⁵N tissue variability in relation to rainfall and relative humidity. Mean annual rainfall along the transect ranges from 775 mm at Mount Gambier in the southeastern coast to 176 mm at Innamincka in the arid northern interior, while 3pm relative humidity ranges from 73% at coastal Flinders Chase to 36% at Innamincka. In arid habitats (176–238 mm rainfall), the δ¹⁵N values of kangaroo bone collagen become more positive in relation to decreasing mean annual rainfall (r² = 0.98), while there is only a weak correlation with relative humidity (r² = 0.67). In contrast, in temperate and semi‐arid coastal habitats (350–775 mm), there is no correlation between kangaroo bone collagen δ¹⁵N values and rainfall (r² = 0.0011) or between δ¹⁵N values and relative humidity (r² = 0.0035). Thus, in South Australia, kangaroo bone collagen δ¹⁵N values do not show a simple linear correlation with either rainfall or relative humidity across all habitats. These results suggest that stable nitrogen isotope analyses of herbivore bones obtained from archaeological and palaeontological sites may provide a reliable proxy for past rainfall values in arid‐land ecosystems. Copyright © 2007 John Wiley & Sons, Ltd.     

Screening Climatic and Non‐Climatic Risks to Australian Catchments

Emerging and future climatic change across the Australian continent has been identified as a significant threat to the successful sustainable management of the nation's water resources. However, the impacts of climate change must be viewed within the context of past, present and future climatic variability and human agency. A qualitative screening‐level risk assessment was undertaken for Australia's 325 surface water management areas by aggregating a suite of six relevant risk indicators. Four indicators addressed the antecedent conditions upon which future climate change will act. These included 50‐year trends in rainfall, the status of surface and groundwater development, and catchment condition. Two indicators addressed future drivers of supply and demand; specifically, projected changes in runoff and population. The results indicate that the management challenges currently experienced in Australia's population centres and key agricultural areas such as the Murray‐Darling Basin are likely to increase in future decades. Furthermore, the geographic distribution of net risk, inclusive of multiple biophysical and socioeconomic drivers, is more extensive than is suggested by consideration of surface water development and availability alone. Comparison of at‐risk catchments with the spatial distribution of various social and environmental assets identified a high degree of overlap among catchment risk and human populations, water storages, irrigated agricultural land, and wetlands of international significance. This suggests that the catchments of the greatest value are also those judged to be at greatest risk. Though considerable work remains in evaluating the security of Australia's water resources to climatic and other stressors, this study provides a first‐order scheme for prioritising the risks to which catchments are exposed and an assessment of how some key drivers are likely to interact to drive risk.     

Recent Hydrological Changes in the Avoca River Catchment,Victoria

Since the early 1970s the Avoca River catchment has experienced a marked increase in all discharges, particularly high magnitude ones. This results from a change in the rainfall/runoff relationship, which is probably due to rising groundwater tables. Since 1973 the frequency of flooding in the lower Avoca, Loddon and Avon-Richardson catchments has increased markedly, placing pressure on downstream flood mitigation and irrigation works, as well as contributing to the degradation of environmentally sensitive wetlands. It also has the potential to exacerbate rising groundwater/salinity problems of the lower catchments. Human interference and changes in the rainfall regime are assessed to explain the nature of the apparent change in streamflows of the Avoca River catchment.