Factors affecting connectivity and sediment yields following wildfire and post-fire salvage logging in California's Sierra Nevada

Sediment delivery following post-fire logging is a concern relative to water quality. While studies have assessed the effect of post-fire logging on sediment yields at different spatial scales, none have explicitly identified sediment sources. Our goal was to quantify post-fire and post-salvage logging sediment yields and use rill patterns to identify sediment sources. We measured the extent and type of logging disturbance, length of rills per unit area or “rill density”, ground cover, and sediment yields in nine logged and five control small catchments or “swales”, 0.09 to 0.81 ha, for 5 years after the 2013 Rim Fire in California's Sierra Nevada. The logged swales had a mean ground disturbance of 31%. After the first wet season following logging, there was no difference in either mean rill density (0.071 and 0.088 m m⁻², respectively) or mean transformed, normalized sediment yields between the control and logged swales. Untransformed mean sediment yields across three sites ranged from 0.11–11.8 and 1.1–3.2 Mg ha⁻¹ for the controls and salvage-logged swales, respectively. Rill density was strongly related to sediment yield and increased significantly with the amount of high-traffic skid trail disturbance in logged swales. Rill density was not significantly related to the amount of bare soil despite a significant relationship between sediment yields and bare soil. Rills usually initiated in bare soil and frequently connected high traffic skid trails to the drainage network after being diverted by waterbars. Rill connectivity and sediment yields decreased in control and logged swales where vegetation or other surface cover was high, suggesting this cover disconnected rills from the drainage network. Increasing ground cover on skid trails and between areas disturbed by post-fire logging and stream channels may reduce sediment yields as well as the hydrologic connectivity between hillslopes and the drainage network.     

Climatic changes and associated impacts in the Mediterranean resulting from a 2 °C global warming

Climatic changes over the Mediterranean basin in 2031–2060, when a 2 °C global warming is most likely to occur, are investigated with the HadCM3 global circulation model and their impacts on human activities and natural ecosystem are assessed. Precipitation and surface temperature changes are examined through mean and extreme values analysis, under the A2 and B2 emission scenarios. Confidence in results is obtained via bootstrapping. Over the land areas, the warming is larger than the global average. The rate of warming is found to be around 2 °C in spring and winter, while it reaches 4 °C in summer. An additional month of summer days is expected, along with 2–4 weeks of tropical nights. Increase in heatwave days and decrease in frost nights are expected to be a month inland. In the northern part of the basin the widespread drop in summer rainfall is partially compensated by a winter precipitation increase. One to 3 weeks of additional dry days lead to a dry season lengthened by a week and shifted toward spring in the south of France and inland Algeria, and autumn elsewhere. In central Mediterranean droughts are extended by a month, starting a week earlier and ending 3 weeks later. The impacts of these climatic changes on human activities such as agriculture, energy, tourism and natural ecosystems (forest fires) are also assessed. Regarding agriculture, crops whose growing cycle occurs mostly in autumn and winter show no changes or even an increase in yield. In contrast, summer crops show a remarkable decrease of yield. This different pattern is attributed to a lengthier drought period during summer and to an increased rainfall in winter and autumn. Regarding forest fire risk, an additional month of risk is expected over a great part of the basin. Energy demand levels are expected to fall significantly during a warmer winter period inland, whereas they seem to substantially increase nearly everywhere during summer. Extremely high summer temperatures in the Mediterranean, coupled with improved climate conditions in northern Europe, may lead to a gradual decrease in summer tourism in the Mediterranean, but an increase in spring and autumn.     

小波分析方法在水文学研究中的应用现状及展望

本文首先介绍了小波分析的基本方法,主要包括小波函数、小波变换和小波消噪等。然后从6个方面,即基于连续小波变换的水文序列多时间尺度变化特性分析、基于离散小波变换的水文序列分解和重构、水文过程复杂性定量描述、水文序列小波消噪、水文序列小波互相关分析和基于小波方法的水文序列模拟预报技术,综述了小波分析方法在水文学各领域的研究应用现状和主要不足,以及存在的关键和难点问题。最后,对小波分析方法在今后的水文学研究中的应用进行了展望,并就小波函数选择、小波阈值消噪、小波分解、小波互相关分析、水文序列小波预报等具体问题提出了建议。     

Thermal Remote Sensing of Near Surface Environmental Variables: Application Over the Oklahoma Mesonet

Many recent studies have applied satellite remote sensing data to large‐scale hydrologic and biospheric modeling. It is widely accepted that the thermal infrared observations from the Advanced Very High Resolution Radiometer (AVHRR) have the potential to estimate land surface conditions, such as surface temperature, near surface air temperature, and near surface water vapor. In this study, algorithms to estimate all three variables are presented and applied to an area covering the state of Oklahoma for a six day period in August, 1994. The results were validated using ground observations from the 111 station Oklahoma Mesonet. Validation of the remote sensing algorithms with Mesonet observations produced comparable results to previous validation studies. In addition, the validation process revealed inadequacies in thermal modeling that had not been detected in previous validation studies leading to the development of a new approach to estimate atmospheric water vapor.     

Research Status and Prospect of the Subsurface Hydrology and Ecological Effect in Arid Regions

Centering on the scientific problems faced by subsurface hydrology in arid regions and ecological effect, the urgency of national ecological civilization and the Belt and Road construction towards the research of groundwater discipline, this article analyzed the formation and evolution mechanisms of groundwater and studied the groundwater function of arid regions. Based on the analysis and research, this article discussed domestic and overseas research status, existing problems and developing trend from six aspects, raised key and scientific problems which urgently need to be addressed, aiming at the existing bottlenecks of subsurface hydrology and ecological effect in arid regions and national requirement, so as to make some contribution to the innovative development of China’s groundwater science and national economic construction.     

应用层次贝斯模型研究气候变化对威塔流域流量的影响(英文)

我们应用层次贝叶斯模型模拟大气二氧化碳浓度加倍可能对美国北卡罗来纳州西部威塔(Coweeta)流域水文的影响。这个模型整合了多重数据来源并且同时考虑了数据,参数和模型结构的不确定性。贝叶斯分析的预测分布显示流量和土壤含水量在秋季和夏季将明显下降,这将造成这两个季节更严重的干旱。同时我们用通用极值分布(Generalized Extreme Value distribution)和通用普拉托分布(Generalized Pareto distribution)分析预测流量,结果显示洪水频率也会增减。层次贝叶斯模型,和许多只能得到最佳参数估计的水文模型相比,能提供更丰富的信息,包括预测的不确定性。这将有助于可持续水资源管理的大前提下发展应对气候变化的措施。     

基于Copula函数的鄱阳湖流域极值流量遭遇频率及灾害风险

在以气温上升为主要特征的全球气候变化导致区域水循环加剧、极端气候水文事件频发的背景下,对极端水文事件,特别是水文极值遭遇频率的科学认识,对区域防洪抗旱具有重要意义.基于此,本文引入当前多变量分析中较常用的Copula函数.分析鄱阳湖流域主要支流赣江与抚河、乐安河与昌江的洪水、枯水流量联合概率特征,并对引起该流域水文极值...     

Suitability of North American Regional Reanalysis (NARR) output for hydrologic modelling and analysis in mountainous terrain

Meteorological observations at high elevations in mountainous regions are often lacking. One opportunity to fill this data gap is through the use of downscaled output from weather reanalysis models. In this study, we tested the accuracy of downscaled output from the North American Regional Reanalysis (NARR) against high‐elevation surface observations at four ridgetop locations in the southern Coast Mountains of British Columbia, Canada. NARR model output was downscaled to the surface observation locations through three‐dimensional interpolation for air temperature, vapour pressure and wind speed and two‐dimensional interpolation for radiation variables. Accuracy was tested at both the 3‐hourly and daily time scales. Air temperature displayed a high level of agreement, especially at the daily scale, with root mean square error (RMSE) values ranging from 0.98 to 1.21 °C across all sites. Vapour pressure downscaling accuracy was also quite high (RMSE of 0.06 to 0.11 hPa) but displayed some site specific bias. Although NARR overestimated wind speed, there were moderate to strong linear relations (r² from 0.38 to 0.84 for daily means), suggesting that the NARR output could be used as an index and bias‐corrected. NARR output reproduced the seasonal cycle for incoming short‐wave radiation, with Nash–Sutcliffe model efficiencies ranging from 0.78 to 0.87, but accuracy suffered on days with cloud cover, resulting in a positive bias and RMSE ranged from 42 to 46 Wm^{? 2}. Although fewer data were available, incoming long‐wave radiation from NARR had an RMSE of 19 Wm^{? 2} and outperformed common methods for estimating incoming long‐wave radiation. NARR air temperature showed potential to assist in hydrologic analysis and modelling during an atmospheric river storm event, which are characterized by warm and wet air masses with atypical vertical temperature gradients. The incorporation of a synthetic NARR air temperature station to better represent the higher freezing levels resulted in increased predicted peak flows, which better match the observed run‐off during the event. Copyright © 2016 John Wiley & Sons, Ltd.     

Trends in Temperature Extremes in Association with Weather-Intraseasonal Fluctuations in Eastern China

Trends in the frequencies of four temperature extremes (the occurrence of warm days, cold days, warm nights and cold nights) with respect to a modulated annual cycle (MAC), and those associated exclusively with weather-intraseasonal fluctuations (WIF) in eastern China were investigated based on an updated homogenized daily maximum and minimum temperature dataset for 1960–2008. The Ensemble Empirical Mode Decomposition (EEMD) method was used to isolate the WIF, MAC, and longer-term components from the temperature series. The annual, winter and summer occurrences of warm (cold) nights were found to have increased (decreased) significantly almost everywhere, while those of warm (cold) days have increased (decreased) in northern China (north of 40°N). However, the four temperature extremes associated exclusively with WIF for winter have decreased almost everywhere, while those for summer have decreased in the north but increased in the south. These characteristics agree with changes in the amplitude of WIF. In particular, winter WIF of maximum temperature tended to weaken almost everywhere, especially in eastern coastal areas (by 10%–20%); summer WIF tended to intensify in southern China by 10%–20%. It is notable that in northern China, the occurrence of warm days has increased, even where that associated with WIF has decreased significantly. This suggests that the recent increasing frequency of warm extremes is due to a considerable rise in the mean temperature level, which surpasses the effect of the weakening weather fluctuations in northern China.