Climate Change Impacts on Urban Flooding

This paper estimates changes in thepotential damage of flood events caused by increasesof CO₂ concentration in the atmosphere. It ispresented in two parts: 1. the modelling of floodfrequency and magnitude under global warming andassociated rainfall intensities and 2. the use ofgreenhouse flood data to assess changes in thevulnerability of flood prone urban areas, expressingthese in terms of direct losses.Three case studies were selected: theHawkesbury–Nepean corridor, the Queanbeyan and UpperParramatta Rivers. All three catchments are located insoutheastern Australia, near Sydney and Canberra.These were chosen because each had detailed buildingdata bases available and the localities are situatedon rivers that vary in catchment size andcharacteristics. All fall within a region that willexperience similar climate change under the availablegreenhouse scenarios. The GCMs' slab model scenariosof climate change in 2030 and 2070 will cause onlyminor changes to urban flood damage but the doubleCO₂ scenarios estimated using the StochasticWeather Generator technique will lead to significantincreases in building damage.For all the case studies, the hydrological modellingindicates that there will be increases in themagnitude and frequency of flood events under thedouble CO₂ conditions although these vary fromplace to place. However, the overall pattern of changeis that for the Upper Parramatta River the 1 in 100-year flood under currentconditions becomes the 1 in44-year event, the 1 in 35-year flood for theHawkesbury–Nepean and the 1 in 10 for Queanbeyan andCanberra. This indicates the importance of usingrainfall-runoff modelling in order to estimate changesin flood frequencies in catchments with differentphysical characteristics.     

Sensitivity of the Earth’s radiation budget to interannual variations in cloud amount

 Using two pairs of coincident long-term satellite derived cloud and earth radiation budget data sets (Nimbus-7 ERB/Nimbus-7 Cloud Climatology and ERBE Scanner/ISCCP-C2), estimates are made of the sensitivity of the top of the atmosphere radiation budget to interannual variations in the total cloud amount. Both sets of analyses indicate that the largest net warming due to interannual cloud cover changes occurs over desert regions, while the largest net cooling occurs in areas of persistent marine stratiform cloud. There is generally a large amount of cancellation between the large shortwave cooling and longwave warming effects in tropical convection regions. However, the Nimbus-7 analysis identifies an area of net warming in the tropical eastern Pacific Ocean which is shown to be associated with the 1982–83 ENSO event. In the zonal mean the Nimbus-7 data sets indicate that interannual cloud cover changes lead to a net warming at low latitudes and net cooling polewards of 25° in both hemispheres. In contrast, the analysis of the ERBE and ISCCP data sets indicates net cooling everywhere except for the Northern Hemisphere equatorwards of 20 °N. For the spatial average between 60 °N and 60 °S the ratio of the shortwave and longwave effects is 0.94 in the Nimbus-7 analysis (i.e. clouds cause a small net warming) and 1.21 in the ERBE-ISCCP analysis (i.e. a net cooling). Given their improved spatial and temporal sampling the analysis using the ERBE and ISCCP data sets should be the more reliable. However, the large differences between the two analyses still raises some issues concerning the confidence with which the sign of the effect of clouds on the radiation budget at these time scales is currently known. Received: 24 October 1995 / Accepted: 8 August 1996     

Estimation of Surface-Layer Scaling Parameters in the Unstable Boundary Layer: Implications for Orographic Flow Speed-Up

A method is proposed for estimating the surface-layer depth \((z_s)\) and the friction velocity \((u_*)\) as a function of stability (here quantified by the Obukhov length, L) over the complete range of unstable flow regimes. This method extends that developed previously for stable conditions by Argaín et al. (Boundary-Layer Meteorol 130:15–28, 2009), but uses a qualitatively different approach. The method is specifically used to calculate the fractional speed-up \((\varDelta S)\) in flow over a ridge, although it is suitable for more general boundary-layer applications. The behaviour of \(z_s \left( L\right) \) and \(u_*\left( L\right) \) as a function of L is indirectly assessed via calculation of \(\varDelta S\left( L\right) \) using the linear model of Hunt et al. (Q J R Meteorol Soc 29:16–26, 1988) and its comparison with the field measurements reported in Coppin et al. (Boundary-Layer Meteorol 69:173–199, 1994) and with numerical simulations carried out using a non-linear numerical model, FLEX. The behaviour of \(\varDelta S\) estimated from the linear model is clearly improved when \(u_*\) is calculated using the method proposed here, confirming the importance of accounting for the dependences of \(z_s\left( L \right) \) and \(u_*\left( L \right) \) on L to better represent processes in the unstable boundary layer.     

The meteorological observations of Bento Sanches Dorta, Rio de Janeiro, Brazil: 1781–1788

Bento Sanches Dorta was an astronomer and geographer in the Portuguese colony of Rio de Janeiro in Brazil from 1781 to 1788. He recorded daily readings of meteorological and geomagnetic variables during that period. This dataset provides, to the best of our knowledge, the earliest known continuous 8-year-long instrumental meteorological observations for any South American site. His data show that the winters in this period were relatively cool, and that 1785 was the rainiest and hottest year, and 1787 the driest and coolest. The records display a distinct seasonal cycle and a variability that are comparable with the modern data.     

Principal Components Analysis of Rainfall and Associated Synoptic Models of the Southwest Monsoon over India

Summary  The summer monsoon circulation shows various spatial and temporal oscillations and often a combination of systems produces an integrated effect. In this study phases of the southwest (SW) monsoon have been identified in an objective manner with the help of T-mode principal component analysis (PCA) of weekly rainfall anomalies. Mean composite charts have been prepared utilising all available upper air data (1977–1986) for each category of the SW monsoon epochs identified by the PCA. These sets of charts have been constructed for both the strong and weak phases associated with the first four significant principal components (PCs). A well defined east-west oriented trough system, extending from about 28° N Latitude/65° E Longitude to 20° N Latitude/90° E Longitude, in the lower levels, has been the main feature associated with the strong phase of the monsoon corresponding to PC I. The trough in the lower levels is more marked in the eastern half compared to the western half in both the sets of charts associated with strong phases of the monsoon related to the PC II and PC III. With PC II, the position of the troughs in the lower levels is further north of its location in PC III. The east-west trough system associated with the strong phase of PC IV has a large southward tilt with height. The charts corresponding to the weak phases of these PCs have synoptic features, such as the position of the trough close to the foothills of the Himalayas, and the shifting of middle and upper tropospheric anticyclones to the south. The study suggests an objective method of interpretation of principal components by utilising synoptic data. In addition, synoptic models and data sets corresponding to different phases of the monsoon can also be prepared in an objective manner by such PCA. Received July 18, 1997 Revised April 30, 1999     

SEISMIC VIBRATOR MODELLING1

The wavefield in, and at the surface of, a homogeneous, isotropic, perfectly elastic half-space, excited by a traction distribution at the surface of the medium is investigated. The emitted wavefield is a spatial convolution of the surface tractions and the spatial impulse response. The properties of the wavefield in the far-field of the medium are derived and it is shown that the far-field particle velocity is essentially equal to a weighted sum of the time derivative of the integrated surface tractions, that is, of the components of the ‘ground force’. The theory is valid for an arbitrary geometry and orientation of the surface tractions, and is independent of the boundary conditions at the surface of the medium. The surface tractions are related to a source that consists of a mass distribution with an arbitrary force distribution imposed upon it. A boundary condition is introduced that accounts for the mass load and the forces applied to it but neglects vibrations within the mass. The boundary condition follows from the equation of motion of the surface mass load. The theory is applied to the Vibroseis configuration, using a P-wave vibrator model with a uniformly distributed force imposed on top of the baseplate, and assuming that horizontal surface traction components are absent. The distribution of displacement and stress directly underneath the baseplate of a single vibrator and an array of vibrators is investigated. Three different boundary conditions are used: (1) assuming uniform pressure, (2) assuming uniform displacement, (3) using the equation of motion of the baseplate as a boundary condition. The calculations of the distribution of stress and displacement over the plate for different elastic media and several frequencies of operation show that only the results obtained with the mixed boundary condition agree with measurements made in the field. The accuracy of three different phase-feedback signals is compared using synthetic data. Baseplate velocity phase-feedback leads to huge deviations in the determination of the far-field wavelet; reaction mass acceleration phase-feedback looks stable but neglects the differentiating earth filter; and phase-feedback to a weighted sum of baseplate and reaction mass accelerations becomes unstable with increasing frequency. The instability can be overcome using measurements over the whole baseplate. The model can be extended to a lossy layered earth.     

Changes in Global Monsoon Circulations Since 1950

We examined changes in several independent intensity indices of four majortropical monsoonal circulations for the period 1950–1998. Theseintensity indices included observed land surface precipitation andobserved ocean surface pressure in the monsoon regions aswell as upper-level divergence calculated at severalstandard levels from the NCAR/NCEP reanalysis. These values wereaveraged seasonally over appropriate regions of southeastern Asian, western Africa, eastern Africa and the Australia/Maritime continent and adjacent ocean areas. Asa consistency check we also examined two secondary indices: mean sea level pressure trends and low level convergence both from theNCEP reanalysis.We find that in each of the four regions examined, a consistentpicture emerges indicating significantly diminished monsoonalcirculations over the period of record, evidence of diminished spatialmaxima in the global hydrological cycle since 1950. Trends since 1979,the period of strongest reported surface warming, do not indicate any change inmonsoon circulations. When strong ENSO years are removed from each of the time series the trends still show a general, significant reduction of monsoon intensity indicating that ENSO variability is not the direct cause for the observed weakening.Most previously reported model simulations of theeffects of rising CO₂ show an increase in monsoonal activity withrising global surface temperature. We find no support in these datafor an increasing hydrological cycle or increasing extremes as hypothesized bygreenhouse warming scenarios.     

A 2D finite volume model for bebris flow and its application to events occurred in the Eastern Pyrenees

FLATModel is a 2D finite volume code that contains several original approaches to improve debris-flow simulation. Firstly, FLATModel incorporates a ＂stop-and-go＂ technique in each cell to allow continuous collapses and remobilizations of the debris-flow mass. Secondly, flow velocity and consequently yield stress is directly associated with the type of rheology to improve boundary accuracy. Thirdly, a simple approach for entrainment is also included in the model to analyse the effect of basal erosion of debris flows. FLATMODEL was tested at several events that occurred in the Eastern Pyrenees and simulation results indicated that the model can represent rather well the different characteristics observed in the field.     

Cenozoic stratigraphy and subsidence history of the South China Sea margin in the Taiwan region

Seismic reflection profiles and well data are used to determine the Cenozoic stratigraphic and tectonic development of the northern margin of the South China Sea. In the Taiwan region, this margin evolved from a Palaeogene rift to a latest Miocene–Recent foreland basin. This evolution is related to the opening of the South China Sea and its subsequent partial closure by the Taiwan orogeny. Seismic data, together with the subsidence analysis of deep wells, show that during rifting (～58–37 Ma), lithospheric extension occurred simultaneously in discrete rift belts. These belts form a >200 km wide rift zone and are associated with a stretching factor, β, in the range ～1.4–1.6. By ～37 Ma, the focus of rifting shifted to the present‐day continent–ocean boundary off southern Taiwan, which led to continental rupture and initial seafloor spreading of the South China Sea at ～30 Ma. Intense rifting during the rift–drift transition (～37–30 Ma) may have induced a transient, small‐scale mantle convection beneath the rift. The coeval crustal uplift (Oligocene uplift) of the previously rifted margin, which led to erosion and development of the breakup unconformity, was most likely caused by the induced convection. Oligocene uplift was followed by rapid, early post‐breakup subsidence (～30–18 Ma) possibly as the inferred induced convection abated following initial seafloor spreading. Rapid subsidence of the inner margin is interpreted as thermally controlled subsidence, whereas rapid subsidence in the outer shelf of the outer margin was accompanied by fault activity during the interval ～30–21 Ma. This extension in the outer margin (β～1.5) is manifested in the Tainan Basin, which formed on top of the deeply eroded Mesozoic basement. During the interval ～21–12.5 Ma, the entire margin experienced broad thermal subsidence. It was not until ～12.5 Ma that rifting resumed, being especially active in the Tainan Basin (β～1.1). Rifting ceased at ～6.5 Ma due to the orogeny caused by the overthrusting of the Luzon volcanic arc. The Taiwan orogeny created a foreland basin by loading and flexing the underlying rifted margin. The foreland flexure inherited the mechanical and thermal properties of the underlying rifted margin, thereby dividing the basin into north and south segments. The north segment developed on a lithosphere where the major rift/thermal event occurred ～58–30 Ma, and this segment shows minor normal faulting related to lithospheric flexure. In contrast, the south segment developed on a lithosphere, which experienced two more recent rift/thermal events during ～30–21 and ～12.5–6.5 Ma. The basal foreland surface of the south segment is highly faulted, especially along the previous northern rifted flank, thereby creating a deeper foreland flexure that trends obliquely to the strike of the orogen.     

Risk Assessment and Disaster Management for Natural and Anthropogenically Induced Geologic Hazards: Application to the Preolkhon Region,Western Lake Baikal,Siberia, Russia

In the Western Lake Baikal, recent Baikal Rift's tectonics control the topography, seismicity, climate, geomorphology, and economy. Scarps, facets, structural terraces, horsts and grabens, and trapezoid valleys can be clearly observed. They have been generated by the recent tectonic movements along the faults and represent a serious geologic hazard. The specific geological conditions predetermine a unique variety of landscapes. Thus, the main type of the economy is tourism. However, unorganized tourism leads to the degradation of the unique landscapes. It increases risk and requires disaster management. Three criteria has been used for risk assessment: (1) degree of geologic hazard; (2) degree of landscape degradation; and (3) degree of the economy's vitality. The high ecological significance and low stability to antropogeneous pressure are typical for landscapes of the Western Lake Baikal. Thus, some special activities of disaster management should be implemented based on our investigation.