Derivation and verification of empirical catchment response time equations for medium to large catchments in South Africa

Despite uncertainties and errors in measurement, observed peak discharges are the best estimate of the true peak discharge from a catchment. However, in ungauged catchments, the catchment response time is a fundamental input to all methods of estimating peak discharges; hence, errors in estimated catchment response time directly impact on estimated peak discharges. In South Africa, this is particularly the case in ungauged medium to large catchments where practitioners are limited to use empirical methods that were calibrated on small catchments not located in South Africa. The time to peak (T_P), time of concentration (T_C) and lag time (T_L) are internationally the most frequently used catchment response time parameters and are normally estimated using either hydraulic or empirical methods. Almost 95% of all the time parameter estimation methods developed internationally are empirically based. This paper presents the derivation and verification of empirical T_P equations in a pilot scale study using 74 catchments located in four climatologically different regions of South Africa, with catchment areas ranging from 20 km² to 35 000 km². The objective is to develop unique relationships between observed T_P values and key climatological and geomorphological catchment predictor variables in order to estimate catchment T_P values at ungauged catchments. The results show that the derived empirical T_P equation(s) meet the requirement of consistency and ease of application. Independent verification tests confirmed the consistency, while the statistically significant independent predictor variables included in the regressions provide a good estimation of catchment response times and are also easy to determine by practitioners when required for future applications in ungauged catchments. It is recommended that the methodology used in this study should be expanded to other catchments to enable the development of a regional approach to improve estimation of time parameters on a national‐scale. However, such a national‐scale application would not only increase the confidence in using the suggested methodology and equation(s) in South Africa, but also highlights that a similar approach could be adopted internationally. Copyright © 2016 John Wiley & Sons, Ltd.     

Land snails from the last glacial maximum on Andikithira,southern Greece and their palaeoclimatic implications

An assemblage of land snails from an aeolianite deposit on the coast of the southern Greek island of Andikithira is shown to date to 16 000 yr BP and thus represents the period of the last glacial maximum (LGM; Oxygen Isotope Stage 2). The assemblage has no modern analogue. Five of the ten species are extinct on the island and some of these now live only at high elevations (> 950 m). Significantly cooler temperatures, some 5-8°C below present, and slightly drier moisture conditions (lower rainfall, partially offset by reduced evapotranspiration at the lower temperature) are inferred. The large temperature depression at the LGM, well documented in northern and central Europe, extended also to the Mediterranean climate of southern Europe. Late Quaternary climatic changes had a considerable impact on the fauna of this isolated island.     

Cosmic ray produced isotopes in terrestrial systems

Continuing improvements in the sensitivity of measurement of cosmic ray produced isotopes in environmental samples have progressively broadened the scope of their applications to characterise and quantify a wide variety of processes in earth and planetary sciences. In this article, I will concentrate on the new developments in the field of nuclear geophysics, based on isotopic changes produced by cosmic rays in the terrestrial systems. This field, which is best described as cosmic ray geophysics, caught roots with the discovery of cosmogenic¹⁴C on the Earth by Willard Libby in 1948, and grew rapidly at first, but slowed down during the ’60s and ’70s. In the ’80s, there was arenaissance in cosmic ray produced isotope studies, thanks mainly to the developments of the accelerator mass spectrometry technique capable of measuring minute amounts of radioactivity in terrestrial samples. This technological advance has considerably enhanced the applications of cosmic ray produced isotopes and today we find them being used to address diverse problems in earth and planetary sciences I discuss the present scope of the field of cosmic ray geophysics with an emphasis ongeomorphology. I must stress here that this is the decade in which this field, which has been studied passionately by geographers, geomorphologists and geochemists for more than five decades, has at its service nuclear methods to introduce numeric time controls in the range of centuries to millions of years.     

中原末次冰期间冰阶以来的古季风气候变迁

中原邙山黄土地层以巨厚的马兰黄土为特色。本文研究了末次冰期间冰阶以来邙山黄土－古土壤序列的粗颗粒含量和磁化率值曲线反映的冬夏季风变迁及其相互关系,发现在万年尺度上夏季风增强对应于冬季风减弱,冬季风增强对应于夏季风减弱,但在千年尺度上冬季风变化比夏季风强烈得多,而且末次间冰段开始时冬季风减弱明显早于夏季风增强。通过中原黄土记录与深海及冰芯Ｏ同位素记录的对比,发现短时间尺度气候变化阶段明显具有很大的区域性特征,它们不能简单地进行等时性全球对比,而应该通过各自独立的时间标尺来建立古气候变化的远距离联系。     

Geomorphology, tectonism and sedimentation in the Nal region, western India

The low lying Nal region in western India, linking the Gulf of Kachchh with the Gulf of Khambhat through the Little Rann and Nal Sarovar is barely 15 m above msl and lacks surface exposures. The evolutionary history of the Nal region using remote sensing data and sub-surface lithological correlation indicated that late Quaternary sedimentation in the Nal region was governed by changes in sea level and by tectonism in the region of Cambay Graben. The geomorphic evidence for changes in sea level was found in the form of inland palaeo-deltas and old mud flats. Abrupt changes in lithological data in the vicinity of Nal region pointed to the role of tectonism. Contrary to the earlier view, a shallow sea linked the Gulf of Kachchh to the Gulf of Khambhat only in a time period around Marine Isotope Stage 5. Our studies also suggest that the Nal region itself may not have witnessed any major uplift (beyond 10 m) during late Quaternary.     

Cryoplanation Terrace Orientation in Alaska

Exploratory analysis of the orientation of 303 cryoplanation terraces in interior and western Alaska lends tentative support to the hypothesis that these landforms develop through localized erosion related to spatial patterns of snow accumulation and ablation. Cryoplanation terraces exhibit orientation patterns similar to those of cirques in several regions of Alaska. In climatically continental east-central Alaska, cryoplanation terraces are developed preferentially on north-facing slopes and the frequency distribution of terrace orientation is similar to but less concentrated than that of glacial cirques. In south-central Alaska, both cirques and terraces have bimodal frequency distributions corresponding to generalized wind patterns that predominated during Pleistocene glaciations. In western Alaska, terraces and cirques have relatively diffuse patterns without preferred orientation. No clear relation is apparent between the orientation of cryoplanation terraces and their size or elevation, although this may be an artifact of the current inability to differentiate terraces by age. Data from the Eagle Summit/Mastodon Dome area in interior Alaska indicate a possible relation between snowline elevation and the concentration of terrace orientation.     

On the choice of timescale in glacial rebound modelling: mantle viscosity estimates and the radiocarbon timescale

Most glacial rebound studies have been carried out with respect to the radiocarbon timescale, whose departures from the calendar timescale are becoming increasingly well established. In consequence, it has sometimes been argued that the choice of the radiocarbon timescale may invalidate some of the conclusions drawn from rebound and sea-level analyses. The purpose of this note is to compare rebound model results based on both timescales, using the British Isles data for the test. The results indicate that the choice of timescale is unimportant provided that the time dimension of viscosity is appropriately defined. The results confirm that the radiocarbon viscosities are about 15 per cent less than the corresponding calendar-time viscosities. Also, provided that consistency of timescales is maintained in the analysis, and that the time-accuracy estimates of the radiocarbon data reflect the departures from a linear timescale, the use of the radiocarbon timescale does not impinge on inferences drawn about the timing of melting of ice sheets or eustatic sea-level change.     

中国季风气候地貌研究--以中国东部湿热季风区为例

通过分析气候地貌学的国际国内现状,给出了气候地貌学的定义,并主伙中国特色的气候地貌学是季风气候地貌学,最后从六个方面探讨了中国的湿热季风地貌。