Turbulence in an almond orchard: Vertical variations in turbulent statistics

Three-dimensional wind velocity components were measured above and within a uniform almond orchard. Turbulent statistics associated with the turbulent flow inside the canopy are examined in detail. Turbulence in an almond orchard is characterized by relatively high turbulent intensities and large skewness and kurtosis values. These results indicate that the frequency distribution of wind velocity components is non-Gaussian. Conditional sampling of the turbulent measurements show that large, infrequent sweeps provide the predominant mechanism for tangential momentum stress in the canopy crown. Deep inside the canopy, a secondary wind maximum and small, but positive, tangential momentum stresses are observed.     

Climate change impacts on water management in the Puget Sound region, Washington State, USA

Climate change is projected to result, on average, in earlier snowmelt and reduced summer flows in the Pacific Northwest, patterns not well represented in historical observations used in water planning. We evaluate the sensitivities of water supply systems in the Puget Sound basin cities of Everett, Seattle, and Tacoma to historical and projected future streamflow variability and water demands. We simulate streamflow for the 2020s, 2040s, and 2080s using the distributed hydrology–soil–vegetation model (DHSVM), driven by downscaled ensembles of climate simulations archived from the 2007 IPCC Fourth Assessment Report. We use these streamflow predictions as inputs to reservoir system models for the three water supply systems. Over the next century, under average conditions all systems are projected to experience declines and eventual disappearance of the springtime snowmelt peak. How these shifts affect management depends on physical characteristics, operating objectives, and the adaptive capacity of each system. Without adaptations, average seasonal drawdown of reservoir storage is projected to increase in all three systems throughout the 21st century. Reliability of all systems in the absence of demand increases is robust through the 2020s however, and remains above 98% for Seattle and Everett in the 2040s and 2080s. With demand increases, however, reliability of the systems in their current configurations and with current operating policies progressively declines through the century.     

Global river discharge and water temperature under climate change

Climate change will affect hydrologic and thermal regimes of rivers, having a direct impact on freshwater ecosystems and human water use. Here we assess the impact of climate change on global river flows and river water temperatures, and identify regions that might become more critical for freshwater ecosystems and water use sectors. We used a global physically based hydrological-water temperature modelling framework forced with an ensemble of bias-corrected general circulation model (GCM) output for both the SRES A2 and B1 emissions scenario. This resulted in global projections of daily river discharge and water temperature under future climate. Our results show an increase in the seasonality of river discharge (both increase in high flow and decrease in low flow) for about one-third of the global land surface area for 2071–2100 relative to 1971–2000. Global mean and high (95th percentile) river water temperatures are projected to increase on average by 0.8–1.6 (1.0–2.2) °C for the SRES B1–A2 scenario for 2071–2100 relative to 1971–2000. The largest water temperature increases are projected for the United States, Europe, eastern China, and parts of southern Africa and Australia. In these regions, the sensitivities are exacerbated by projected decreases in low flows (resulting in a reduced thermal capacity). For strongly seasonal rivers with highest water temperatures during the low flow period, up to 26% of the increases in high (95th percentile) water temperature can be attributed indirectly to low flow changes, and the largest fraction is attributable directly to increased atmospheric energy input. A combination of large increases in river temperature and decreases in low flows are projected for the southeastern United States, Europe, eastern China, southern Africa and southern Australia. These regions could potentially be affected by increased deterioration of water quality and freshwater habitats, and reduced water available for human uses such as thermoelectric power and drinking water production.     

The Weather of the European Atlantic Seaboard During October 1805: An Exercise in Historical Climatology

Several thousand ships' logbooks havesurvived from the eighteenth and nineteenth centuries.They provide a valuable source of climaticinformation. This paper takes the Battle of Trafalgaras an example of how this source can be used toprovide a better knowledge and understanding ofweather and climate from those distant times. Thereliability of the non-instrumental climatic recordsof the logbooks is confirmed and a simple statisticalmeasure is used to quantify their degree ofconsistency. Reconstructions of daily weather patternsare made and a zonal index is calculated to representthe circulation patterns of the region. The movementsof pressure systems are plotted and indicate that thezonal index was negative (air pressure increasing fromsouth to north) for most of the month. The storm thatfollowed the battle is identified as one of notableseverity. This extreme behaviour is interpreted withinthe context of longer-term aspects of the contemporaryclimate.     

Behavior and Fate of PFOA and PFOS in Sandy Aquifer Sediment

Microcosms were constructed with sediment from beneath a landfill that received waste containing PFOA (perfluorooctanoic acid) and PFOS (perfluorooctane sulfonate). The microcosms were amended with PFOA and PFOS, and sampled after 91, 210, 343, 463, 574, and 740 d of incubation. After 740 d, selected microcosms were extracted to determine the mass of PFOA and PFOS remaining. There was no evidence for degradation of PFOA or PFOS. Over time, the aqueous concentrations of PFOA and PFOS increased in the microcosms, indicating that PFOA and PFOS that had originally sorbed to the sediment was desorbing. At the beginning of the experiment, the adsorption coefficient, K_d, averaged 0.27 L/kg for PFOA and 1.2 L/kg for PFOS. After 740 d of incubation, sorption of PFOA was not detectable and the K_d of PFOS was undetectable in two microcosms and was 0.08 L/kg in a third microcosm. During incubation, the pH of the pore water in the microcosms increased from pH 7.2 to pH ranging from 8.1 to 8.8. The zeta potential of the sediment decreased with increasing pH. These observations suggest that the sorption of PFOA and PFOS at near neutral pH was controlled by the electrostatic sorption on ferric oxide minerals, and not by the sorption to organic carbon. Accurate predictions of PFOA and PFOS mobility in ground water should be based on empirical estimates of sorption using affected aquifer sediment.     

Effects of nitrate and phosphate on growth and C2 toxin productivity of Alexandrium tamarense CI01 in culture

Growth and C2 toxin productivity of a marine dinoflagellate, Alexandrium tamarense CI01 (ATCI01) which predominantly produces C2 toxin, were studied in unialgal batch cultures to optimize the concentrations of nitrate and phosphate for a maximal toxin yield. A range of start concentrations of the two major nutrients was determined in which algal growth was proportional to the nutrient concentrations used. The highest concentrations of nitrate and phosphate in this growth-enhancing range were 264 and 20 μM, respectively. In this concentration range, the C2 toxin yield (μg/l) and cellular toxin content (Qt, fmole per cell) reached a maximum at the lowest end of phosphate (5 μM) and the highest end of nitrate (264 μM). Further increase in the supply of nitrate continued to enhance the toxin yield. Our results indicated that the growth and toxin productivity of this algal strain in batch cultures had distinctly different optimal ranges of nitrate and phosphate concentrations. For a maximum toxin yield, a judicious use of phosphate under a nitrate-replete condition is called for.     

A simple algorithm for generating streamflow networks for grid‐based,macroscale hydrological models

A simple algorithm for generating streamflow networks for macroscale hydrological models (MHMs) from digital elevation models (DEMs) is presented. Typically these hydrological models are grid based, with the simulated runoff produced within each cell routed through a stream network which connects the centers of cells in the direction of the major streams. Construction of such stream networks is a time consuming task, which has generally been done by hand with the aid of maps. Results indicate that the algorithm works satisfactorily in areas of both high and low relief, and for a wide range of model cell resolutions, although some manual adjustments may be necessary. Copyright © 1999 John Wiley & Sons, Ltd.     

Impact of number of realizations on the suitability of simulated weather data for hydrologic and environmental applications

Stochastic weather generators are widely used in hydrological, environmental, and agricultural applications to simulate weather time series. However, such stochastic models produce random outputs hence the question on how representative the generated data are if obtained from only one simulation run (realization) as is common practice. In this study, the impact of different numbers of realizations (1, 25, 50, and 100) on the suitability of generated weather data was investigated. Specifically, 50 years of daily precipitation, and maximum and minimum temperatures were generated for three weather stations in the Western Lake Erie Basin (WLEB), using three widely used weather generators, CLIGEN, LARSWG and WeaGETS. Generated results were compared with 50 years of observed data. For all three generators, the analyses showed that one realization of data for 50 years of daily precipitation, and maximum and minimum temperatures may not be representative enough to capture essential statistical characteristics of the climate. Results from the three generators captured the essential statistical characteristics of the climate when the number of realizations was increased from 1 to 25, 50 or 100. Performance did not improve substantially when realizations were increased above 25. Results suggest the need for more than a single realization when generating weather data and subsequently utilizing in other models, to obtain suitable representations of climate.