Reflectivity‐rain rate relationships for convective rainshowers in Edmonton: Research note

Abstract

A reflectivity‐rainfall rate (Z‐R) relationship is derived from Carvel radar and Edmonton rain gauge measurements. Our analysis indicates that the traditional point‐by‐point comparison method is not accurate for Alberta summertime precipitation due to timing errors in fast moving convective storms. The Window Probability Matching Method (WPMM) was superior and provided a robust Z‐R relationship in the form of Z = 32.5 R^1.65.     

Impact of model free parameters and sea-level rise uncertainties on 20-years shoreline hindcast: the case of Truc Vert beach (SW France)

Shoreline change is driven by various complex processes interacting at a large range of temporal and spatial scales, making shoreline reconstructions and predictions challenging and uncertain. Despite recent progress in addressing uncertainties related to the physics of sea-level rise, very little effort is made towards understanding and reducing the uncertainties related to wave-driven shoreline response. To fill this gap, the uncertainties associated with the long-term modelling of shoreline change are analysed at a high-energy cross-shore transport dominated site. Using the state-of-the-art LX-Shore shoreline change model, we produce a probabilistic shoreline reconstruction, based on 3000 simulations over the past 20 years at Truc Vert beach, southwest France, whereby sea-level rise rate, depth of closure and three model free parameters are considered uncertain variables. We further address the relative impact of each source of uncertainty on the model results performing a Global Sensitivity Analysis. This analysis shows that the shoreline changes are mainly sensitive to the three parameters of the wave-driven model, but also that the sensitivity to each of these parameters is strongly modulated seasonally and interannually, in relation with wave energy variability, and depends on the time scale of interest. These results have strong implications on the model skill sensitivity to the calibration period as well as for the predictive skill of the model in a context of future climate change affecting wave climate and extremes. © 2020 John Wiley & Sons, Ltd.     

Long-term large wood load fluctuations in two low-order streams in Southern Chile

The eco-hydrogeomorphic significance of large wood (LW) and its potential for increasing downstream hazards during extreme floods have been widely recognized. We used LW data collected for a 10-year period from the two low-order streams of Pichún (Pi) and Vuelta de Zorra (VZ) in Southern Chile to (a) determine if the abundance and dimensions of individual LW pieces change with time, (b) quantify wood load fluctuations during the 10-year period, and (c) assess the role of LW recruitment from the riparian forests to explain wood load fluctuations during the study period. Nine years after the first survey, the number of LW pieces in Pi and VZ diminished by 60 and 40%, respectively. Despite the reduction in these numbers, in Pi, the LW dimensions did not change significantly during the study. In VZ, the dimensions exhibited statistically significant differences, despite being within the same class. In both catchments, the LW load fluctuated during a 10-year period, but the drivers of change differed. Although tree toppling was the recruitment mechanism responsible for LW in both stream cases, the high wood load measured in Pi at the beginning of the study suggested massive tree recruitments before the first survey, followed by wood exports which were higher than inputs in the subsequent 10-year period. In VZ, LW load decreased during the first 9 years (mean annual rate of ~9.2 m³ year⁻¹) and then increased by ~12.1 m³ year⁻¹ in year 10. At VZ, the inputs consisted of single trees that were recruited from the riparian area and by upstream flotation, while exports occurred by downstream fluvial transport. Wood inputs and exports occurred asynchronously and led to LW load fluctuations at decadal and annual intervals. Land management and tree species thus exert a major influence on wood inventory and budget in streams. © 2020 John Wiley & Sons, Ltd.     

前陆褶皱冲断带厚皮缩短盐构造运动的物理模拟

尺度物理实验用干石英砂和聚合硅树脂为实验材料,模拟了前陆褶皱冲断带厚皮缩短盐构造,并与薄皮缩短盐构造及无盐层的褶皱冲断带构造模型进行了对比。实验表明,由于塑性盐层的存在,厚皮缩短盐构造呈3层式结构模式。盐上层主要形成敞开褶皱、箱状褶皱、前冲和背冲断层以及冲垒构造,盐下层形成逆冲断层及冲垒构造,断层通常都终止于盐层中。尽管盐层局部变薄或增厚,但不形成刺穿型盐构造。褶皱冲断带不具构造指向特征,其楔形库仑锥剖面呈平台与斜坡两段式形态。模型对比表明,厚皮缩短与薄皮缩短所产生的盐上层构造形态相似,不易区分;但二者的库仑锥剖面有所不同。厚皮前陆褶皱冲断盐构造与无盐层的褶皱冲断构造无论是其几何形态、还是库仑锥剖面都有极大的差别,极易区分：实验结果对解释前陆褶皱冲断构造和寻找盐下油气圈闭都有着重要的指导意义。