Contrasting Lumped and Distributed Hydrology Models for Estimating Climate Change Impacts on California Watersheds1

Maurer, Edwin P., Levi D. Brekke, and Tom Pruitt, 2010. Contrasting Lumped and Distributed Hydrology Models for Estimating Climate Change Impacts on California Watersheds. Journal of the American Water Resources Association (JAWRA) 46(5):1024–1035. DOI: 10.1111/j.1752-1688.2010.00473.x Abstract: We compare the projected changes to streamflows for three Sierra Nevada rivers using statistically downscaled output from 22 global climate projections. The downscaled meteorological data are used to drive two hydrology models: the Sacramento Soil Moisture Accounting model and the variable infiltration capacity model. These two models differ in their spatial resolution, computational time step, and degree and objective of calibration, thus producing significantly different simulations of current and future streamflow. However, the projected percentage changes in monthly streamflows through mid-21st Century generally did not differ, with the exceptions of streamflow during low flow months, and extreme low flows. These findings suggest that for physically based hydrology models applied to snow-dominated basins in Mediterranean climate regimes like the Sierra Nevada, California, model formulation, resolution, and calibration are secondary factors for estimating projected changes in extreme flows (seasonal or daily). For low flows, hydrology model selection and calibration can be significant factors in assessing impacts of projected climate change.     

Hydrologic Modeling of an Extreme Flood in the Guadalupe River in Texas1

Sharif, Hatim O., Almoutaz A. Hassan, Sazzad Bin-Shafique, Hongjie Xie, and Jon Zeitler, 2010. Hydrologic Modeling of an Extreme Flood in the Guadalupe River in Texas. Journal of the American Water Resources Association (JAWRA) 1-11. DOI: 10.1111/j.1752-1688.2010.00459.x Abstract: Many of the storms creating the greatest rainfall depths in Texas, measured over durations ranging from one minute to 48 hours, have occurred in the Texas Hill Country area. The upstream portion of the Guadalupe River Basin, located in the Texas Hill Country, is susceptible to flooding and rapid runoff due to thin soils, exposed bedrock, and sparse vegetation, in addition to the Balcones Escarpment uplift contributing to precipitation enhancement. In November 2004, a moist air mass from the Gulf of Mexico combined with moist air from the Pacific Ocean resulted in the wettest November in Texas since 1895. Although the peak discharges were not the highest on record, the U.S. Geological Survey (USGS) stream gauge on the Guadalupe River at Gonzales, Texas reported a daily mean discharge of 2,304 m³/s on November 23, 2004 (average discharge is 53 m³/s). In this paper, we examine the meteorological conditions that led to this event and apply a two-dimensional, physically based, distributed-parameter hydrologic model to simulate the response of a portion of the basin during this event. The study results clearly demonstrate the ability of physically based, distributed-parameter simulations, driven by operational radar rainfall products, to adequately model the cumulative effect of two rainfall events and route inflows from three upstream watersheds without the need for significant calibration.     

Assessment of pollution in road runoff using a Bufo viridis biological assay

Road runoff is a major source of environmental pollution, significantly threatening nearby aquatic habitats. Chemical analyses indicate high pollutant concentrations in the road’s “first flush”, but bioassays are more advantageous for addressing the cumulative effects of the numerous pollutants within the runoff. We used Bufo viridis embryos and larvae to assess the toxicity of road runoff from two major highways in Israel. We show, for the first time, that exposure to midseason runoff not only has an adverse effect on growth and development rates of B. viridis larvae but can also lead to increased rates of morphological deformations. Seasonal first flushes, despite having higher metal concentrations, did not adversely affect the toad larvae, apparently due to a counter effect of organic matter that potentially served as a supplementary energy resource. Road runoff can be a major cause for a qualitative decrease in the quality of aquatic habitats threatening amphibians in Israel.     

Farmyards, an overlooked source for highly contaminated runoff

Summer sampling of storm runoff generated from areas of roofs and hardstanding situated on four dairy/beef farms has provided novel information regarding its microbiological and chemical quality. All farm hardstandings generated runoff that was contaminated with respect to those pollutants (faecal coliforms, FC, and faecal streptococci, FS, major nutrients, organic carbon) that are ubiquitously associated with faecal matter and urine. The separate analysis of roof runoff indicated that these can contribute significant concentrations of FS, phosphorus (P) and potentially toxic elements such as zinc (Zn), and suggests a level of 'background' contamination originating from wash-off of bird droppings and in the case of Zn galvanised surfaces. On average hardstanding runoff showed enhanced concentrations of >4 orders of magnitude for FC and 2-3 for major nutrients and carbon relative to roof runoff. Organic forms of nitrogen (N) and P contributed significantly (averaging >40%) to the total dissolved fraction in both roof and hardstanding runoff. Part of the substantial variability in composition of runoff samples could be attributed to differences between farms as well as the timing of sample collection during individual storms. Where situations allowed, a comparison of water upstream and downstream of the farmyard demonstrated they acted as a source of multiple contaminants not only during hydrologically active storm events but also during dry periods. Contamination pathways included a combination of both point (e.g., septic overflows) and non-point (e.g., seepage from livestock housing) sources. Farmyards situated within intensive livestock farming areas such as SW Scotland, would be expected to have significant local and accumulated downstream impacts on the aquatic environment. Localised impacts would be particularly important for headwaters and low order streams.     

Runoff Simulation of the Headwaters of the Yellow River Using The SWAT Model With Three Snowmelt Algorithms1

Abstract: The Soil and Water Assessment Tool (SWAT) model combined with different snowmelt algorithms was evaluated for runoff simulation of an 114,345 km² mountainous river basin (the headwaters of the Yellow River), where snowmelt is a significant process. The three snowmelt algorithms incorporated into SWAT were as follows: (1) the temperature‐index, (2) the temperature‐index plus elevation band, and (3) the energy budget based SNOW17. The SNOW17 is more complex than the temperature‐based snowmelt algorithms, and requires more detailed meteorological and topographical inputs. In order to apply the SNOW17 in the SWAT framework, SWAT was modified to operate at the pixel scale rather than the normal Hydrologic Response Unit scale. The three snowmelt algorithms were evaluated under two parameter scenarios, the default and the calibrated parameters scenarios. Under the default parameters scenario, the parameter values were determined based on a review of the current literature. The purpose of this type of evaluation was to assess the applicability of SWAT in ungauged basins, where there is little observed data available for calibration. Under the calibrated parameters scenario, the parameters were calibrated using an automatic calibration program, the Shuffled Complex Evolution (SCE‐UA). The purpose of this type of evaluation was to assess the applicability of SWAT in gauged basins. Two time periods (1975‐1985 and 1986‐1990) of monthly runoff data were used in this study to evaluate the performance of SWAT with different snowmelt algorithms. Under the default parameters scenario, the SWAT model with complex energy budget based SNOW17 performed the best for both time periods. Under the calibrated parameters scenario, the parameters were calibrated using monthly runoff from 1975‐1985 and validated using monthly runoff from 1986‐1990. After parameter calibration, the performance of SWAT with the three snowmelt algorithms was improved from the default parameters scenario. Further, the SWAT model with temperature‐index plus elevation band performed as well as the SWAT model with SNOW17. The SWAT model with temperature‐index algorithm performed the poorest for both time periods under both scenarios. Therefore, it is suggested that the SNOW17 model be used for modeling ungauged basins; however, for gauged basins, the SNOW17 and simple temperature‐index plus elevation band models could provide almost equally good runoff simulation results.     

Modeling the Effect of Summertime Heating on Urban Runoff Temperature1

Abstract: The summertime heating of runoff in urban areas is recognized as a common and consistent urban climatological phenomenon. In this study, a simple thermal urban runoff model (TURM) is presented for the net energy flux at the impervious surfaces of urban areas to account for the heat transferred to runoff. The first step in developing TURM consists of calculating the various factors that control how urban impervious areas absorb heat and transfer it to moving water on the surface. The runoff temperature is determined based on the interactions of the physical characteristics of the impervious areas, the weather, and the heat transfer between the moving film of runoff and the impervious surface common in urban areas. Key surface and weather factors that affect runoff temperature predictions are type of impervious surface, air temperature, humidity, solar radiation before and during rain, rainfall intensity, and rainfall temperature. Runoff from pervious areas is considered separately and estimated using the Green‐Ampt Mein‐Larson rainfall excess method. Pervious runoff temperature is estimated as the rainfall temperature. Field measurements indicate that wet bulb temperature can be used as a surrogate for rainfall temperature and that runoff temperatures from sod average just 2°C higher than rainfall temperatures. Differences between measured and predicted impervious runoff temperature average approximately 2°C, indicating that TURM is a useful tool for determining runoff temperatures for typical urban areas.     

Constructed wetlands treating highway runoff in the central Mediterranean region

Two free water surface (FWS) and two subsurface flow (SSF) pilot-size constructed wetlands treating highway runoff (HRO) were monitored over a period of two years (September 2005-August 2007). One FWS and one SSF were designed with a hydraulic retention time (HRT) of 12h, named FWS12 and SSF12, respectively, with each one capable of treating a maximum HRO of 12.6 m(3) d(-1). The other couple, named FWS24 and SSF24, respectively, was designed with an HRT of 24h, with each receiving a maximum HRO of 6.3 m(3) d(-1). The influent flowed from a highway section with a total surface 2752 m(2) on the island of Crete, Greece, in the heart of the South-Central Mediterranean region. Influent and effluent were monitored for COD, TSS, total N (TN), NO(3)(-) and total P (TP) concentrations. Furthermore, removal efficiencies were examined for heavy metals (Cu, Ni, Pb, Zn) for both years, while polycyclic aromatic compounds (PAHs) were examined for the period between September 2006 and August 2007. The influent had a two-year average COD value of 101 mg l(-1), whereas the mean values for TSS, TN, N-NO(3)(-) and TP were 203, 4.30, 1.25 and 4.17 mg l(-1), respectively. For Cu, Ni, Pb and Zn the respective two-year mean influent concentrations were 56, 114, 49 and 250 microg l(-1). Mean concentration of total PAHs in runoff (summation operator PAHs, 16 compounds) were 12.01 microg l(-1). The performance among the four beds was not significantly different according to ANOVA analysis followed by Tukey test (at p<0.05) for almost all the above physicochemical parameters, suggesting that all systems performed in a similar way. All studied systems, achieved a mean of two-year removal efficiencies of 47% for COD, 89% for TSS, 49% for TN, 58% for N-NO(3)(-), 60% for TP, 47% for Cu, 23% for Ni, 33% for Pb, 61% for Zn and 59% for summation operator PAHs (16 compounds).     

模拟装置研究绿地系统在暴雨径流污染控制中的作用

采用城市绿地和降雨系统模拟装置,研究绿地系统对实际暴雨径流污染的削减作用.历时60 min,降雨重现期为1 a、3 a、5 a时,绿地系统可以削减雨水径流量.1 a一遇时,绿地系统对雨水径流中COD、氮和磷总量的去除率分别为60.2%,49.2%和61.5%.以无植被裸土为对照,模拟绿地系统对径流雨水中COD、NH+4N及TP去除率较对照组分别提高7.1%,6.2%和4.4%.降雨期间污染物的去除主要依靠土壤和植物根系的截留、吸附和吸收作用;降雨后微生物开始降解吸附于土壤颗粒表面和植物根系上的污染物,降雨后第5～8 d,土壤中微生物数量达到最大值,第14～17 d微生物完成对吸附有机物等的降解,数量恢复到降雨前水平.研究表明, 模拟绿地对降雨地表径流量的削减、径流污染物浓度的削减和污染物总量的控制有较好作用.     

一种基于MMS的改进降水径流模型在中国西北地区黑河上游流域的应用

以黑河流域上游为研究对象,通过对山区自然产水区的产汇流机理的研究,基于分布式水文模型集成环境的开发思想,利用MMS(modular modeling system)模型库中与降水径流相关的模块,通过综合各种产流(包括超渗、蓄满产流)机理、并且根据寒区产汇流的特点对USGS开发的流域PRMS(precipitation-runoff models)模型进行了改进,增加了土壤水运动中降雨入渗补给的多层土壤滞后效应模块以及积雪融雪和冻土面积识别模型,建立了适合于寒区流域的分布式PRMS模型。利用该模型对黑河上游出山径流过程进行了模拟与预报,模型研究结果表明:利用MMS建立的黑河上游改进的PRMS模型不仅完全可以模拟和预测黑河上游的产汇流过程,在考虑了冻土的情况下,预测年出山径流量误差小于2.7%;而且模型可以对黑河上游径流组成成分进行分析计算,对黑河上游产汇流机理做进一步阐明。利用改进的PRMS模型,预测分析了黑河上游未来气候和土地覆盖变化情景下流域出山径流变化的趋势,为黑河流域水资源合理利用和管理提供科学依据。     

山地城市地表径流源区水质特征监测研究

2010年通过对山地城市重庆江北城区10个地表源区5次地表径流过程水样的采集与分析,研究城区地表径流水质特征及其影响因素,以期为地表径流污染源区控制提供科学依据.结果表明,山地城市重庆地表径流污染过程具有明显的初期冲刷效应,降雨强度影响地表径流水质的变化,地表径流水质的波动同雨强的变化呈同步趋势,雨强增加,污染物浓度下降,表现出水质变化的随机性.山地城市重庆地表径流COD、TP与TSS具有显著的正相关性.悬浮物是城市地表径流污染的主要污染物,而且是有机物质和磷素的载体.有机物质与磷素主要以颗粒态的形式存在,而氮素以溶解态的氨和硝酸盐为主.山地城市地表径流水质TSS、COD、TN、TP和NH4+-N在各个源区的差异显著,商业区和城市交通主干道TSS、COD和TP的浓度最高,其次为城市支路、居民区道路、停车场和屋顶.不透水地表功能、交通流量、人流量和卫生管理是影响地表径流水质的主要因素.城市商业区、交通干道和人流量高的居民区道路是城市地表径流污染的关键源区.