Monthly and seasonal streamflow forecasting of large dryland catchments in Brazil

Streamflow forecasting in drylands is challenging.Data are scarce,catchments are highly humanmodified and streamflow exhibits strong nonlinear responses to rainfall.The goal of this study was to evaluate the monthly and seasonal streamflow forecasting in two large catchments in the Jaguaribe River Basin in the Brazilian semi-arid area.We adopted four different lead times:one month ahead for monthly scale and two,three and four months ahead for seasonal scale.The gaps of the historic streamflow series were filled up by using rainfall-runoff modelling.Then,time series model techniques were applied,i.e.,the locally constant,the locally averaged,the k-nearest-neighbours algorithm(k-NN)and the autoregressive(AR)model.The criterion of reliability of the validation results is that the forecast is more skillful than streamflow climatology.Our approach outperformed the streamflow climatology for all monthly streamflows.On average,the former was 25%better than the latter.The seasonal streamflow forecasting(SSF)was also reliable(on average,20%better than the climatology),failing slightly only for the high flow season of one catchment(6%worse than the climatology).Considering an uncertainty envelope(probabilistic forecasting),which was considerably narrower than the data standard deviation,the streamflow forecasting performance increased by about 50%at both scales.The forecast errors were mainly driven by the streamflow intra-seasonality at monthly scale,while they were by the forecast lead time at seasonal scale.The best-fit and worst-fit time series model were the k-NN approach and the AR model,respectively.The rainfall-runoff modelling outputs played an important role in improving streamflow forecasting for one streamgauge that showed 35%of data gaps.The developed data-driven approach is mathematical and computationally very simple,demands few resources to accomplish its operational implementation and is applicable to other dryland watersheds.Our findings may be part of drought forecasting systems and potentially help allocating water months in advance.Moreover,the developed strategy can serve as a baseline for more complex streamflow forecast systems.     

Rainfall interception and stem flow by eucalypt street trees – The impacts of canopy density and bark type

Understanding how trees influence water movement in an urban landscape is important because in an ‘engineered xeriscape’ small changes in rainfall frequency or magnitude have significant implications to plant water availability and mortality at one extreme, and stormwater runoff and flooding at the other. This study relates direct measures of tree canopy interception and discusses their implication for catchment hydrology in different urban landscape contexts. We measured canopy throughfall and stemflow under two eucalypt tree species in an urban street setting over a continuous five month period. Eucalyptus nicholii has a dense canopy and rough bark, whereas Eucalyptus saligna has a less-dense canopy and smooth bark. E. nicholii, with the greater plant area index, intercepted more of the smaller rainfall events, such that 44% of annual rainfall was intercepted as compared to 29% for the less dense E. saligna canopy (2010). Stemflow was less in amount and frequency for the rough barked E. nicholii as compared to the smooth barked E. saligna. However, annual estimates of stemflow to the ground surface for even the smooth barked E. saligna would only offset approximately 10 mm of the 200 mm intercepted by its canopy (2010).Tree canopy and bark characteristics should be considered when planting in pervious green space, or impervious streetscapes, because of their profound impact upon tree and surrounding water availability, soil water recharge or runoff. This study provides an evidence base for tree canopy impacts upon urban catchment hydrology, and suggests that rainfall and runoff reductions of up to 20% are quite possible in impervious streetscapes. Street tree canopies can function as a cost-effective compliment to water sensitive urban design for stormwater reduction benefits.     

福建近海若干个拟投放深水网箱海湾理化环境调查与评估

根据2000和2001年福建主要港湾调查所获得的海洋水文和海洋化学环境资料，对拟投放深水抗风浪网箱海域的海水理化因子作了较详细的分析研究，以评估该海域是否适合于投放深水网箱。结果表明，三都澳、官井洋、东吾洋、罗源湾、福清湾、兴化湾，湄州湾和东山湾水深在25m以上，湾外有岛屿屏障，环境隐蔽、水流稳定，水温、盐度和透明度有显著的季节变化，pH和DO符合国家渔业水质标准，COD一般符合一类海水水质标准，局部海域达到二类海水水质标准，IN、PO3-P一般符合二类海水水质标准，在秋季有些港湾达到三类海水水质标准。从理化环境的角度分析，上述海湾可作为投放深水网箱之场所。     

基于遥感技术的珠三角6类林分的蒸散比研究

对珠江三角洲六类主要林分(区域)的蒸散发比进行了研究,6类林分包括桉树林、果树林、针阔混交林、灌木林、针叶混交林、阔叶混交林.同时对基于Priestley-Taylor扩展模型的物理机制进行分析与推理,发现可以通过MODIS和TM热红外数据计算的地温值来评估较大区域上的蒸散发能力,并结合2008-2009年的晴空数据进行计算分析.结果表明珠三角6类林分(区域)的蒸散发作用相当,桉树林并非耗水量最大的林种.     

Estimating Drainage under Cotton with Chloride Mass Balance and an EM38

Methodologies that use electromagnetic induction and resistivity in soil profiles to estimate drainage across whole fields and catchments require complex models or measurement systems that are not easily available or difficult to apply at the farm level. The objective of the present study was to define a methodology that could use information easily available to agronomists and commercial cotton consultants to estimate drainage in irrigated Vertisols using a chloride (Cl^?) mass balance approach. A secondary objective of this study was to eliminate or minimize the expensive and tedious laboratory analyses for determining Cl^? concentration in soils. A model was developed using electromagnetic induction measurements taken with an EM38 instrument in the horizontal mode (EM_H) to estimate the chloride concentration in a saturated soil extract in the 0- to 1.2-m depth of irrigated Vertisols. A stepwise linear regression model where the independent variables were soil water storage, exchangeable sodium percentage, and EM_H predicted chloride concentration the best. The chloride concentrations thus estimated were similar to measured values only when measured chloride concentrations in the saturated extract were ≤10 meq L^?1 (355 mg L^?1 = 240 mg kg^?1). These values of chloride were then inserted into a chloride mass balance model to estimate deep drainage. In more saline soils, large differences occurred between measured and estimated chloride. Values of drainage based on estimated chloride concentrations in the range of 0–10 meq L^?1 were very similar to those based on measured chloride concentrations. There is potential to use an EM38 for quick assessment of deep drainage under irrigated conditions in the field.     

论水文生态学的建立及其历史使命

通过水文生态学的背景及过程,给出了水文生态的内涵和定义,水文生态学就是研究水文和生态相互关系及其形成各种水文生态系统的科学。对水文生态作了论述,认为水文生态实际上表现为水文生态系统,它是由水文系统和生态系统耦合而成。生态要素中必然包含着水,水文系统必然影响和伴随着相应的生态系统,生态系统的变化也必然影响水文系统,2个系统相互影响,相互依存,从而启示人们在认识和揭示生态问题时不应忘记水文作用,而在研究和揭示水文问题时也必须考虑相应的生态条件。以灌区、梯田和绿洲为例,进一步论述了不同水文和生态条件下的水文生态系统。水文生态学将以生态学、水文学、河流学、湖泊学、水文地质学、水工建筑学、农田水利学等为基础而获得发展,从而推动人类认识自然的新飞跃,推进水利建设和生态建设的新发展。     

海南岛橡胶林水分循环过程特征研究

为了研究橡胶林生态系统中降雨在林冠层、土壤层等不同界面层的水分转换机制及各项水因子量之间的关系,利用野外观测试验站,针对橡胶林水分循环动态变化过程中各项相关因子进行持续1年的观测。结果表明：穿透雨量、树干茎流量、林冠截留量分别占年降水量的71.63%、11.54%、16.30%;净降水中以地表径流、渗漏形式损耗的水分分别占年降雨量的4.71%、26.23%;橡胶林林冠和土壤以蒸散形式返回大气系统的水分分别占总降雨量的52.65%、16.30%。分析比较橡胶林水分循环过程中各水因子量的分配特征,从理论基础和量化指标的角度上阐明了橡胶林生态建设的水文效应评价问题。     

水文多变量相空间重构自记忆模型研究

【目的】针对单变量相空间重构自记忆模型存在的不足,研究多变量相空间重构自记忆模型在水文预报中的适用性。【方法】根据多变量相空间重构理论构造多维相空间,并在此基础上,结合自忆性原理,建立多变量相空间重构自记忆模型,最后利用新疆和田绿洲的实测月蒸发能力资料进行验证。【结果】和田绿洲月蒸发能力实测资料检验结果表明,建立多变量相空间重构模型是可行的,可以取得理想的效果。【结论】多变量相空间重构自记忆模型的建立使得相空间重构自记忆模型从一维拓展到了多维,也使得该模型更加符合生产实际。     

湿地种子库研究中的几个问题探讨

湿地种子库研究对于生物多样性保护、湿地恢复和管理具有重要意义。国内外开展了大量湿地种子库以及利用种子库进行湿地植被恢复的研究,但是也存在一些问题。在分析了国内外湿地种子库研究的基础上,指出无性繁殖在湿地生态系统中广泛存在,而且很多优势物种以无性繁殖为主要的繁殖方式,因此,在湿地种子库研究中,采用广义种子库的概念更为科学。此外,干扰因素,尤其是水文条件变化对湿地种子库的影响非常大。水位的高低,洪水的强度、持续时间和频率都会显著影响种子库的物种组成和种子萌发格局,进而对地表植物群落产生影响。研究事实证明,在利用种子库进行湿地恢复时,也必须考虑干扰等因素的影响,否则很难实现群落结构和物种多样性的恢复。     

湿地水文功能研究进展

湿地是流域水资源和水循环的重要组成部分,是自然界最富生物多样性的生态系统和人类最重要的生存环境之一,它不仅为人类的生产、生活提供多种资源,而且具有巨大的生态环境功能和效益。湿地的水文功能主要包括调蓄洪水、补充地下水、提供水源、保持或改善水质、调节气候、保护海岸带等功能,其独特的水文功能对维持流域生态系统的健康和改善区域生态环境具有十分重要的意义。因此,湿地水文功能的研究已引起国内外学者的关注。本文从湿地水文、水文功能两个方面综述了国内外研究的现状,并指出了目前研究中存在的主要问题及未来研究的发展趋势。