The effects of climate change on historical and future extreme rainfall in Antalya,Turkey

Abstract

There is increasing concern that flood risk will be exacerbated in Antalya, Turkey as a result of global-warming-induced, more frequent and intensive, heavy rainfalls. In this paper, first, trends in extreme rainfall indices in the Antalya region were analysed using daily rainfall data. All stations in the study area showed statistically significant increasing trends for at least one extreme rainfall index. Extreme rainfall datasets for current (1970–1989) and future periods (2080–2099) were then constructed for frequency analysis using the peaks-over-threshold method. Frequency analysis of extreme rainfall data was performed using generalized Pareto distribution for current and future periods in order to estimate rainfall intensities for various return periods. Rainfall intensities for the future period were found to increase by up to 23% more than the current period. This study contributed to better understanding of climate change effects on extreme rainfalls in Antalya, Turkey.     

Activity of Mount Etna preceding the February 1999 fissure eruption: inferred mechanism from seismological and geochemical data

The February 1999 eruption of Mt. Etna took place through a fissure on the SSE flank of the cone of the summit SE Crater. This event was preceded by continuous activity since 1995, sometimes accompanied by violent outbursts from one or more of the three other summit craters (NE Crater, Voragine or Chasm, and Bocca Nuova), and finally by a series of 20 short-lived eruptions from the SE Crater between September 1998 and January 1999. These phenomena could be accounted for by invoking gradual invasion of a shallow small reservoir by more primitive, basic and gas-rich magma coming from depth. The shallow “chamber” is more likely to be a plexus of dikes, which had developed during the previous years (1995–1997), following variations of the local stress field owing to enhanced magma generation and accumulation at the top of the mantle. Magma injection and mixing is evidenced through geochemistry, whereas the state of stress of the volcanic pile and underlying crust is determined using earthquake distributions and focal mechanisms. The behaviour of the seismic tremor amplitude appears to be a good indicator of the state of unrest of the volcano, although not always directly linked to the relative energy of degassing phenomena.     

Observation and analysis of low-frequency crustal earthquakes in Lake Van and its vicinity,eastern Turkey

Lake Van is located in very intensely deformed tectonic settings in the eastern Turkey. The surrounding area of Lake Van has major tectonic structures; NE and NW trending active conjugate strike-slip faults, pull-apart basins along these faults, E-W trending active thrust faults, folds, compressional ramp basins, N-S trending folds, NE-SW aligned continental collision-related volcanoes and N-S trending tensional cracks functioned as magma conduits. Since the area is tectonically very active, the earthquake activity within the basin and the surrounding area of Lake Van is very high. In this study, we have analysed the records of VANB broadband station of Kandilli Observatory and Earthquake Research Institute's network for the seismic events (2000–2004) that occurred in the basin and in the vicinity of Lake Van. Based on the spectral analysis of earthquake data, we have mainly observed three types of seismic events; hybrid event, long period event and tremor. We have suggested that the observed hybrid, long period and tremor type of seismic events that occurred in the study area are related to the upward moving materials and stress loading in the mid and lower crust based on the geophysical data.     

Sequence and eruptive style of the 1783 eruption of Asama Volcano, central Japan: a case study of an andesitic explosive eruption generating fountain-fed lava flow, pumice fall, scoria flow and forming a cone

The 3-month long eruption of Asama volcano in 1783 produced andesitic pumice falls, pyroclastic flows, lava flows, and constructed a cone. It is divided into six episodes on the basis of waxing and waning inferred from records made during the eruption. Episodes 1 to 4 were intermittent Vulcanian or Plinian eruptions, which generated several pumice fall deposits. The frequency and intensity of the eruption increased dramatically in episode 5, which started on 2 August, and culminated in a final phase that began on the night of 4 August, lasting for 15 h. This climactic phase is further divided into two subphases. The first subphase is characterized by generation of a pumice fall, whereas the second one is characterized by abundant pyroclastic flows. Stratigraphic relationships suggest that rapid growth of a cone and the generation of lava flows occurred simultaneously with the generation of both pumice falls and pyroclastic flows. The volumes of the ejecta during the first and second subphases are 0.21 km³ (DRE) and 0.27 km³ (DRE), respectively. The proportions of the different eruptive products are lava: cone: pumice fall=84:11:5 in the first subphase and lava: cone: pyroclastic flow=42:2:56 in the second subphase. The lava flows in this eruption consist of three flow units (L1, L2, and L3) and they characteristically possess abundant broken phenocrysts, and show extensive "welding" texture. These features, as well as ghost pyroclastic textures on the surface, indicate that the lava was a fountain-fed clastogenic lava. A high discharge rate for the lava flow (up to 10⁶ kg/s) may also suggest that the lava was initially explosively ejected from the conduit. The petrology of the juvenile materials indicates binary mixing of an andesitic magma and a crystal-rich dacitic magma. The mixing ratio changed with time; the dacitic component is dominant in the pyroclasts of the first subphase of the climactic phase, while the proportion of the andesitic component increases in the pyroclasts of the second subphase. The compositions of the lava flows vary from one flow unit to another; L1 and L3 have almost identical compositions to those of pyroclasts of the first and second subphases, respectively, while L2 has an intermediate composition, suggesting that the pyroclasts of the first and second subphases were the source of the lava flows, and were partly homogenized during flow. The complex features of this eruption can be explained by rapid deposition of coarse pyroclasts near the vent and the subsequent flowage of clastogenic lavas which were accompanied by a high eruption plume generating pumice falls and/or pyroclastic flows.Editorial responsibility: T. Druitt     

Fractal dimensions of suspended solids in streams: comparison of sampling and analysis techniques

Fluvial suspended sediment typically consists of a variety of complex, composite particles referred to as flocs. Floc characteristics are determined by factors such as the source, size and geochemical properties of the primary particles, chemical and biological coagulation processes in the water column and shear stress and turbulence levels in the stream. Studies of floc morphology have used two contrasting methods of sampling and analysis. In the first method, particles settle on a microscope slide and are observed from below using an inverted microscope. The second method uses filtration at no or low vacuum and particles deposited on the filter are observed with a microscope. Floc morphology can be quantified using fractal dimensions. The aims of the present study were to examine the effect of the two sampling methods on the fractal dimensions of particle populations, and to evaluate for each method how well the fractal dimensions at the various sampling sites reflect basin conditions. Suspended solids were collected in triplicate on inverted microscope slides and on 0·45 μm Millipore HA filters in two southern Ontario streams with contrasting riparian zones during a minor runoff event resulting from the melt of a freshly fallen snowpack. An image analysis system was used to determine area, longest axis and perimeter of particles. The morphology of the particle population of each sample was characterized using four fractal dimensions (D, D₁, D₂ and D_K). Systematic differences in fractal dimensions obtained with the two methods were observed. For the settling method, outlines of larger particles were frequently blurred because of the distance between the focal plane (the top of the inverted microscope slides) and the plane of the particle outline. In this method, the blurring of large particles can cause an increase in the projected area and length of the particle. The effect on the particle perimeter is unpredictable because it depends on the amount of detail lost through blurring and its effect on the apparent increase in particle size. Because of blurring, D and D₁ tend to be systematically lower for the settling method, whereas the net effect on D₂ is unpredictable. Particle size distributions derived from settling are typically coarser because small, low density particles may remain in the water column and all particles may not deposit on the slides. This loss of fines results in systematically lower D_K values for the settling method compared with the filtration method. Fractal dimensions and particle size distributions obtained with the filtration method were sensitive to and clearly indicated differences between drainage basins and between sites within each basin. These differences were explained by basin characteristics and conditions. Fractal dimensions and particle size distributions obtained with the settling method were less sensitive to drainage basin characteristics and conditions, which limits their usefulness as process indicators. Copyright © 1999 John Wiley & Sons, Ltd.     

Hydrogeochemistry and environmental impact of geothermal waters from Yangyi of Tibet,China

The Yangyi geothermal field, located 72 km northwest to Lhasa City, capital of Tibet, has a high reservoir temperature up to at least 207.2 °C. The geothermal waters from both geothermal wells and hot springs belong to the HCO₃ (+CO₃)–Na type. Factor analysis of all the chemical constituents shows that they can be divided into two factors: F₁ factor receives the contributions of SO₄²⁻, Cl⁻, SiO₂, As, B, Na⁺, K⁺, and Li⁺; whereas F₂ factor is explained by HCO₃⁻, F⁻, CO₃²⁻, Ca²⁺, and Sr²⁺. The F₁ factor can be regarded as an indicator of the reservoir temperature distribution at Yangyi, but its variable correlation with the results of different geothermometers (Na–K, quartz and K–Mg) does not allow one to draw further inferences. Different from F₁, the F₂ factor is an indicator of a group of hydrogeochemical processes resulting from the CO₂ pressure decrease in geothermal water during its ascent from the deep underground, including transformation of HCO₃⁻ to CO₃²⁻, precipitation of Ca²⁺ and Sr²⁺, and release of F⁻ from some fluoride-bearing minerals of reservoir rocks. The plot of enthalpy vs. chloride, prepared on the basis of Na–K equilibrium temperatures, suggests that a parent geothermal liquid (PGL) with Cl⁻ concentration of 185 mg/L (that of sample YYT-8) and enthalpy of 1020 J/g (corresponding to a temperature of 236–237 °C, i.e., somewhat higher than that of sample YYT-6) is present in the geothermal reservoir of the Yangyi area, below both the Qialagai valley and the Bujiemu valley, although the samples less affected by mixing and cooling (YYT-6 and YYT-7) come from the second site. The discharge of geothermal waters with high contents of toxic elements such as B, As and F into the Luolang River, the only drinking water source for local residents, has caused slight pollution of the river water. Great care should therefore be taken in the geothermal water resource management at Yangyi.     

Chloride,hydrochemical and isotope methods of groundwater recharge estimation in eastern Mediterranean areas: a case study in Jordan

Jordan is classified as an arid to semi‐arid country with a population according to 1999 estimates of 4·8 millions inhabitants and a growth rate of 3·4%. Efficient use of Jordan's scarce water is becoming increasingly important as the urban population grows. This study was carried out within the framework of the joint European Research project ‘Groundwater recharge in the eastern Mediterranean’ and describes a combined methodology for groundwater recharge estimation in Jordan, the chloride method, as well as isotopic and hydrochemical approaches. Recharge estimations using the chloride method range from 14 mm year^?1 (mean annual precipitation of 500 mm) for a shallow and stony soil to values of 3·7 mm year^?1 for a thick desert soil (mean annual precipitation of 100 mm) and values of well below 1 mm year^?1 for thick alluvial deposits (mean annual rainfall of 250 mm). Isotopically, most of the groundwater in the Hammad basin, east Jordan, falls below the global meteoric water line and far away from the Mediterranean meteoric water line, suggesting that the waters are ancient and were recharged in a climate different than Mediterranean. Tritium levels in the groundwater of the Hammad basin are less than the detection limit (<1·3 TU). However, three samples in east Hammad, where the aquifer is unconfined, present tritium values between 1 and 4 TU. Copyright © 2007 John Wiley & Sons, Ltd.     

Towards realistic flow modelling. Creation and evaluation of two-dimensional simulated porous media: An image analysis approach

This work is part of an attempt to quantify the relationship between the permeability tensor (K) and the micro-structure of natural porous media. A brief account is first provided of popular theories used to relate the micro-structure toK. Reasons for the lack of predictive power and restricted generality of current models are discussed. An alternative is an empirically based implicit model whereinK is expressed as a consequence of a few pore-types arising from the dynamics of depositional processes. The analytical form of that implicit model arises from evidence of universal association between pore-type and throat size in sandstones and carbonates. An explicit model, relying on the local change of scale technique is then addressed. That explicit model allows, from knowledge of the three-dimensional micro-geometry to calculateK explicitly without having recourse to any constitutive assumptions. The predictive and general character of the explicit model is underlined. The relevance of the change of scale technique is recalled to be contingent on the availability of rock-like three-dimensional synthetic media. A random stationary ergodic process is developed, that allows us to generate three-dimensional synthetic media from a two-dimensional autocorrelation functionr( _x , _y ) and associated probability density function measured on a single binary image. The focus of this work is to ensure the rock-like character of those synthetic media. This is done first through a direct approach:n two-dimensional synthetic media, derived from single set ( ,r( _x , _y )) yieldn permeability tensorsK _i-1,n ⁱ (calculated by the local change of scale) of the same order. This is a necessary condition to ensure thatr( _x , _y ) and carry all structural information relevant toK. The limits of this direct approach, in terms of required Central Process Unit time and Memory is underlined, raising the need for an alternative. This is done by comparing the pore-type content of a sandstone sample andn synthetic media derived fromr( _x , _y ) and measured on that sandstone-sample. Achievement of a good match ensures that the synthetic media comprise the fundamental structural level of all natural sandstones, that is a domainal structure of well-packed clusters of grains bounded by loose-packed pores.     

Soil loss,water ponding and sediment deposition variations as a consequence of rainfall intensity and land use: a multi‐criteria analysis

Prediction of areas prone to land degradation in agricultural catchments is a complex task. This is due to the difficulties encountered in data gathering over wide regions and in the translation of existing scientific knowledge to a quantitative and spatially explicit risk assessment system. This paper incorporates the use of remotely sensed data, terrain analysis and a multi‐criteria mechanism for evaluating risks of soil loss, water ponding, and sediment deposition in a mid‐size agricultural Mediterranean catchment, under 80 years of intensive cultivation. The research uses simulations to study the effect of topographic attributes, soil characteristics, vegetation cover, rainfall intensity and human activities on the three above‐mentioned processes. The results show that, from the methodological point of view, the integration of knowledge from several experts yields better predictive results than relying on a single expert, even the one found to be most consistent. Also, the use of a simple weighted linear combination was more useful than the more sophisticated computerized programming technique. From the phenomenological point of view, the increase in rainfall intensity and land‐use transformation from orchard to field‐crops has led to a significant increase in soil loss and sediment yield, while extreme changes in tillage direction have only yielded minor changes in water ponding. The developed system's predictive capabilities also show that the outcomes can be used as a basis for decisions on catchment management in regions of high environmental sensitivity. Copyright © 2009 John Wiley & Sons, Ltd.     

Vent area and depositional mechanisms of the Upper Member of the Neapolitan Yellow Tuff (Campi Flegrei, Italy): new insights from directional fabric through image analysis

In order to provide new information about the source area and depositional mechanisms of the Upper Member of the Neapolitan Yellow Tuff (NYT), a prominent pyroclastic deposit of the Campi Flegrei Volcanic District (southern Italy), statistics on directional fabric, by means of computer-assisted image analysis on 32 rock samples, were compiled. Seventeen samples were collected along vertical direction on two selected exposures and fifteen were taken from outcrops widely distributed all around the Campi Flegrei Volcanic District. Fabric measurements within the investigated successions reveal a vertically homogeneous direction of the mean particle iso-orientation, with considerable variability in the strength of particle iso-orientation even at cm-scale. The existence of particle iso-orientation can be related to continuous sedimentation from a concentrated bedload region beneath suspension currents, producing massive or inversely graded beds by traction carpet sedimentation. The considerable vertical variability in the strength of iso-orientation is the result of very unstable flow regimes, up to the extreme condition of discrete depositional events, with a variable combination of traction carpet and/or direct suspension sedimentation. The vertical homogeneity in the mean orientation values, found in the investigated sections, may derive from the sequential deposition of laminae to thin beds, whose relatively flat upper surfaces were unable to significantly deflect the depositional system of the following currents. According to the observed homogeneous mean particle orientation values along the investigated vertical profiles, samples collected through areal distribution are considered representative of the local paleo-flow directions of the whole deposit. The mean directions of the samples collected areally show two different coherent patterns which point to the existence of two different source areas. The first, which includes all samples from the northern outcrops, appears to converge in a narrow area about 2 km NE of the town of Pozzuoli, largely in coincidence with the inferred area on the basis of the pumice fall distribution. The second, which includes samples from Capo Miseno and Posillipo areas, points to the central part of the Pozzuoli Bay, about 4 km offshore the town of Pozzuoli.