High Streamflow Research Articles

Understanding the controls on sediment-P interactions and dynamics along a non-tidal river system in a rural–urban catchment: The River Nene

The release of Phosphorus (P) from river sediments has been identified as a contributing factor to waters failing the criteria for ‘Good Ecological Status’ under the EU Water Framework Directive (WFD). To identify the contribution of sediment-P to river systems, an understanding of the factors that influence its distribution within the entire non-tidal system is required. Thus the aims of this work were to examine the (i) total (PTotal) and labile (PLabile) concentrations in sediment, (ii) the sequestration processes and (iii) the interactions between sediment P and the river water in the six non-tidal water bodies of the River Nene, U.K. Collection of sediments followed a long period of flooding and high stream flow. In each water body, five cores were extracted and homogenised for analysis with an additional core being taken and sampled by depth increments. Comparing the distribution of sediment particle size and PTotal data with soil catchment geochemical survey data, large increases in PTotal were identified in sediments from water body 4–6, where median concentrations of PTotal in the sediment (3603 mg kg−1) were up to double those of the catchment soils. A large proportion of this increase may be related to in-stream sorption of P, particularly from sewage treatment facilities where the catchment becomes more urbanised after water body 3. A linear correlation (r = 0.8) between soluble reactive phosphate (SRP) and Boron in the sampled river waters was found suggesting increased STW input in water bodies 4–6.PLabile concentrations in homogenised cores were up to 100 mg kg−1 PO4–P (generally < 2% of PTotal) and showed a general increase with distance from the headwaters. A general increase in Equilibrium Phosphate Concentrations (EPC0) from an average of 0.9–∼1.7 μm L−1 was found between water bodies 1–3 and 4–6. Fixation within oxalate extractable phases (Al, Fe and Mn) accounted for ∼90% of P binding in water bodies 4–6, but only between 31 and 74% in water bodies 1–3. Statistical models predicting PTotal (R2 = 0.78), oxalate extractable P (R2 = 0.78) and Olsen P (R2 = 0.73) concentrations in river sediments identified Mn oxy-hydroxides (MnOx) as a strong predictive variable along with the location within the river system. It is suggested that MnOx within model predictions is identifying a pool of mixed Fe–Mn oxy-hydroxides (MnOx–FeOOH) or Fe oxy-hydroxide (FeOOH) from the wider FeOxalate pool that are particularly effective at sorbing and fixing P. The findings demonstrate how sediment and P may accumulate along a 100 km non-tidal river system, the extent to which a range of processes can fix P within mineral phases and how natural flooding processes may flush sediment from the river channel. The processes identified in this study are likely to be applicable to similar river systems over their non-tidal water bodies in eastern England.

Stream macroinvertebrate community responses to fire: are they the same in different fire-prone biogeographic regions?

AbstractDroughts, fires, and floods are natural disturbances influencing aquatic ecosystems. If drought is accompanied by fires, and if fires are closely followed by floods, teasing apart their distinctive and potentially interactive responses can be difficult. We compared the responses of macroinvertebrate communities to fire via comparisons of streams in burned and unburned catchments in 3 fire-prone biomes that differ biogeographically and climatically (northwestern Mediterranean, southeastern Australia, and northwestern intermountain USA). The responses of macroinvertebrate communities in streams in burned catchments were similar in all biogeographic regions, but the magnitude of these responses varied. Fire combined with high seasonal stream flows, flooding, or drought was associated with reduced measures of taxonomic richness and increased abundance, especially of r-strategist taxa. Differences between sites in burned and unburned catchments were consistently stronger in southeastern Australia than ...

Evaluating an unconfined aquifer by analysis of age‐dating tracers in stream water

AbstractThe mean transit time (MTT) is a fundamental property of a groundwater flow system that is strongly related to the ratio of recharge rate to storage volume. However, obtaining samples for estimating the MTT using environmental tracers is problematic as flow‐weighted samples over the full spectrum of transit times are needed. Samples collected from the base flow of a gaining stream in the North Carolina Coastal Plain (West Bear Creek) that were corrected for exchange with the atmosphere yielded environmental tracer concentrations (SF6 and CFC‐11) very similar to flow‐weighted values from nine or ten streambed piezometers that directly sampled groundwater during low streamflow. At higher streamflow on the falling limb of the hydrograph, stream tracer concentrations (after correction for gas exchange) were significantly higher than the flow‐weighted mean from piezometers, consistent with dominance of the stream tracer signal by transient influx of surface water and/or younger subsurface water. The apparent MTT derived from SF6 in low flow stream water samples was 26 years, suggesting a groundwater recharge rate of about 210 mm/yr, that is consistent with vertical profiles obtained by sampling nested piezometers in the aquifer. When sampled under low flow conditions when streamflow consists of a high component of groundwater discharge, West Bear Creek appears to act as a flow‐weighted integrator of transit times and, streamflow samples can provide fundamental information regarding groundwater recharge rate and MTT. Our study suggests that watershed‐scale evaluation of some groundwater flow systems is possible without utilizing monitoring wells.

Understanding runoff processes in a semi-arid environment through isotope and hydrochemical hydrograph separations

Abstract. The understanding of runoff generation mechanisms is crucial for the sustainable management of river basins such as the allocation of water resources or the prediction of floods and droughts. However, identifying the mechanisms of runoff generation has been a challenging task, even more so in arid and semi-arid areas where high rainfall and streamflow variability, high evaporation rates, and deep groundwater reservoirs may increase the complexity of hydrological process dynamics. Isotope and hydrochemical tracers have proven to be useful in identifying runoff components and their characteristics. Moreover, although widely used in humid temperate regions, isotope hydrograph separations have not been studied in detail in arid and semi-arid areas. Thus the purpose of this study is to determine whether isotope hydrograph separations are suitable for the quantification and characterization of runoff components in a semi-arid catchment considering the hydrological complexities of these regions. Through a hydrochemical characterization of the surface water and groundwater sources of the catchment and two- and three-component hydrograph separations, runoff components of the Kaap catchment in South Africa were quantified using both isotope and hydrochemical tracers. No major disadvantages while using isotope tracers over hydrochemical tracers were found. Hydrograph separation results showed that runoff in the Kaap catchment is mainly generated by groundwater sources. Two-component hydrograph separations revealed groundwater contributions of between 64 and 98 % of total runoff. By means of three-component hydrograph separations, runoff components were further separated into direct runoff, shallow and deep groundwater components. Direct runoff, defined as the direct precipitation on the stream channel and overland flow, contributed up to 41 % of total runoff during wet catchment conditions. Shallow groundwater defined as the soil water and near-surface water component (and potentially surface runoff) contributed up to 45 % of total runoff, and deep groundwater contributed up to 84 % of total runoff. A strong correlation for the four studied events was found between the antecedent precipitation conditions and direct runoff. These findings suggest that direct runoff is enhanced by wetter conditions in the catchment that trigger saturation excess overland flow as observed in the hydrograph separations.

Combining rainfall data from rain gauges and TRMM in hydrological modelling of Laotian data-sparse basins

At present, prediction of streamflow simulation in data-sparse basins of the South East Asia is a challenging task due to the absence of reliable ground-based rainfall information, while satellite-based rainfall estimates are immensely useful to improve our understanding of spatio-temporal variation of rainfall, particularly for data-sparse basins. In this study the TRMM 3B42 V7 and its bias-corrected data were, respectively, used to drive a physically based distributed hydrological model BTOPMC to perform daily streamflow simulations in Nam Khan River and Nam Like River basins during the years from 2000 to 2004 so as to investigate the potential use of the TRMM in complementing rain gauge data in hydrological modelling of data-sparse basins. The results show that although larger difference exists in the high streamflow process and the low streamflow process, the daily simulations fed with TRMM precipitation data could basically reflect the daily streamflow processes at the four stations and determine the time to peak. Furthermore, the calibrated parameters in the Nam Khan River basin are more suitable than that in the Nam Like River basin. By comparing the two precipitation data, it indicates that the integration of TRMM precipitation data and rain gauge data have a promising prospect on the hydrological process simulation in data-sparse basin.

Optimal ranking regime analysis of TreeFlow dendrohydrological reconstructions

Abstract. The optimal ranking regime (ORR) method was used to identify 6–100-year time windows containing significant ranking sequences in 55 western US streamflow reconstructions, and reconstructions of the level of the Great Salt Lake and San Francisco Bay salinity during 1500–2007. The method's ability to identify optimally significant and non-overlapping runs of low- and high-rankings allows it to re-express a reconstruction time series as a simplified sequence of regime segments marking intra- to multi-decadal (IMD) periods of low or high streamflow, lake level, and salinity. Those ORR sequences, referred to here as Z-lines, can be plotted to identify consistent regime patterns in the analysis of numerous reconstructions. The Z-lines for the 57 reconstructions evaluated here show a common pattern of IMD cycles of drought and pluvial periods during the late 16th and 17th centuries, a relatively dormant period during the 18th century, and the reappearance of alternating dry and wet IMD periods during the 19th and early 20th centuries. Although this pattern suggests the possibility of similarly active and inactive oceanic modes in the North Pacific and North Atlantic, such centennial-scale patterns are not evident in the ORR analyses of reconstructed Pacific Decadal Oscillation (PDO), El Niño–Southern Oscillation, and North Atlantic sea-surface temperature variation. However, given the inconsistency in the analyses of four PDO reconstructions, the possible role of centennial-scale oceanic mechanisms is uncertain. In future research the ORR method might be applied to climate reconstructions around the Pacific Basin to try to resolve this uncertainty. Given its ability to compare regime patterns in climate reconstructions derived using different methods and proxies, the method may also be used in future research to evaluate long-term regional temperature reconstructions.

Application of multivariate statistical analysis to incorporate physico-chemical surface water quality in low and high flow hydrology

Multivariate statistical methods, such as principal components analysis (PCA), discriminant analysis (DA) and general linear models (GLM) were applied to incorporate physico-chemical surface water quality in low and high flow hydrology in Northern Iran, based on analysis of the 7-day low flow index and existing water quality data. In view of this, 7-day low flows were calculated for 15 water years (1991–2006) at 15 monitoring stations. Eleven water quality parameters were extracted during the low flows from the water quality data and compared to water quality during high flows. Significant differences in water quality were noted for some monitoring stations and the pattern and magnitude of the statistically significant responses (t test, p < 0.05) varied among sites. PCA, was applied to the data sets of the two low and high flow periods, and resulted in three effective factors explaining 77.8 and 67.4 % of the total variance in surface water quality data sets of the two periods, respectively. The main factors obtained from PCA indicated that the parameters influencing surface water quality are mainly related to natural, point and non-point source pollution in the study area. DA provided an important data reduction as it used only three parameters, i.e. magnesium (Mg2+), calcium (Ca2+) and bicarbonate (HCO3 −) affording 60 % correct assignations, to discriminate between the two low and high stream flow periods. General regression models revealed that surface water quality parameters were explained by low and high flow and specific discharge. The results of this study can be useful for water managers for effective surface water quality management under climate change.

An independent and combined effect analysis of land use and climate change in the upper Rhone River watershed, Switzerland

Land use and climate change play a significant role in hydrological processes. This study assesses the impact of land use and climate change in a snow and glacier dominated high altitude watershed, located in the southwestern part of Switzerland. Climate projections until the middle of the 21st century were analyzed using a Regional Climate Model from the IPCC A1B scenario. Land use maps were created using Idrisi TAIGA land change modeler, based on historical changes over two time periods and transformed for future forecasting. Logistic regression was used to generate these maps containing the probability of change between two different land use categories. Subsequently, the allocation of the land use was based on a multi-objective land distribution. The semi-distributed hydrological model called the Soil and Water Assessment Tool (SWAT) was used for simulating streamflow. The analysis was done to assess the impact of streamflow in three time periods where 1981–2010 is considered as the observed period and the two other time periods from 2011 to 2025 and 2026–2050 are considered as the scenario periods. Flow Duration Curves (FDC) were generated to assess the impact of low and high streamflow periods. Our study shows a decrease in the summer peak flow and an early start of the melt driven peak flow. The major change observed in this study is the rising period of the hydrograph, i.e. in May and June an early shift is observed in the discharge. Independent analysis from land use change and climate change shows that the peak flow reduction occurs as a result of land use change, but the peak flow together with the timing of peak flow occurrence is also influenced by climatic change. The combined effect suggests a reduction of peak flow and early melt driven streamflow in the future. Information obtained from this study can be useful for water managers, especially for the hydropower based energy production sector in the Rhone watershed.

Temporal variations of streamflow in a mid-latitude Eurasian steppe watershed in the past half century

Previous studies either did not identify abrupt change or identified such change but did not exclude it from the detection of trend in streamflow. As a result, an overall downward trend might be erroneously detected as an upward trend because of abrupt increase, while an overall upward trend could be faked as a downward trend due to abrupt decrease. The objectives of this study were to: (1) present a methodology to analyze trend in streamflow in the presence of abrupt change; and (2) use this methodology to detect trend and extreme occurrence of streamflow in the Upper Balagaer River watershed, a mid-latitude nearly pristine precipitation-fed Eurasian steppe watershed in north China. The results indicate that streamflow abruptly decreased around 1994 and exhibited no significant trend from 1960 to 1993 but a significant decrease trend since 1994 (in particular after 1999). In addition, the occurrence of days with a low streamflow was greater after 1994, whereas the occurrence of days with a high streamflow was smaller. Further, the inclusion of the abrupt change in the analysis could compound the detection of the pre-1994 trends but had minimal influences on the detection of the post-1994 trends. These results can be representative across the Eurasian steppe region beyond the study watershed.

The promise and peril of intensive-site-based ecological research: insights from the Hubbard Brook ecosystem study.

Ecological research is increasingly concentrated at particular locations or sites. This trend reflects a variety of advantages of intensive, site-based research, but also raises important questions about the nature of such spatially delimited research: how well does site based research represent broader areas, and does it constrain scientific discovery? We provide an overview of these issues with a particular focus on one prominent intensive research site: the Hubbard Brook Experimental Forest (HBEF), New Hampshire, USA. Among the key features of intensive sites are: long-term, archived data sets that provide a context for new discoveries and the elucidation of ecological mechanisms; the capacity to constrain inputs and parameters, and to validate models of complex ecological processes; and the intellectual cross-fertilization among disciplines in ecological and environmental sciences. The feasibility of scaling up ecological observations from intensive sites depends upon both the phenomenon of interest and the characteristics of the site. An evaluation of deviation metrics for the HBEF illustrates that, in some respects, including sensitivity and recovery of streams and trees from acid deposition, this site is representative of the Northern Forest region, of which HBEF is a part. However, the mountainous terrain and lack of significant agricultural legacy make the HBEF among the least disturbed sites in the Northern Forest region. Its relatively cool, wet climate contributes to high stream flow compared to other sites. These similarities and differences between the HBEF and the region can profoundly influence ecological patterns and processes and potentially limit the generality of observations at this and other intensive sites. Indeed, the difficulty of scaling up may be greatest for ecological phenomena that are sensitive to historical disturbance and that exhibit the greatest spatiotemporal variation, such as denitrification in soils and the dynamics of bird communities. Our research shows that end member sites for some processes often provide important insights into the behavior of inherently heterogeneous ecological processes. In the current era of rapid environmental and biological change, key ecological responses at intensive sites will reflect both specific local drivers and regional trends.

Attribution of high resolution streamflow trends in Western Austria – an approach based on climate and discharge station data

Abstract. The results of streamflow trend studies are often characterized by mostly insignificant trends and inexplicable spatial patterns. In our study region, Western Austria, this applies especially for trends of annually averaged runoff. However, analysing the altitudinal aspect, we found that there is a trend gradient from higher-altitude to lower-altitude stations, i.e. a pattern of mostly positive annual trends at higher stations and negative ones at lower stations. At mid-altitudes, the trends are mostly insignificant. Here we hypothesize that the streamflow trends are caused by the following two main processes: on the one hand, melting glaciers produce excess runoff at higher-altitude watersheds. On the other hand, rising temperatures potentially alter hydrological conditions in terms of less snowfall, higher infiltration, enhanced evapotranspiration, etc., which in turn results in decreasing streamflow trends at lower-altitude watersheds. However, these patterns are masked at mid-altitudes because the resulting positive and negative trends balance each other. To support these hypotheses, we attempted to attribute the detected trends to specific causes. For this purpose, we analysed trends of filtered daily streamflow data, as the causes for these changes might be restricted to a smaller temporal scale than the annual one. This allowed for the explicit determination of the exact days of year (DOYs) when certain streamflow trends emerge, which were then linked with the corresponding DOYs of the trends and characteristic dates of other observed variables, e.g. the average DOY when temperature crosses the freezing point in spring. Based on these analyses, an empirical statistical model was derived that was able to simulate daily streamflow trends sufficiently well. Analyses of subdaily streamflow changes provided additional insights. Finally, the present study supports many modelling approaches in the literature which found out that the main drivers of alpine streamflow changes are increased glacial melt, earlier snowmelt and lower snow accumulation in wintertime.

Simulating low and high streamflow driven by snowmelt in an insufficiently gauged alpine basin

Snowmelt and water infiltration are two important processes of the hydrological cycle in alpine basins where snowmelt water is a main contributor of streamflow. In insufficiently gauged basins, hydrologic modeling is a useful approach to understand the runoff formation process and to simulate streamflow. In this study, an existing hydrologic model based on the principles of system dynamics was modified by using the effective cumulative temperature (>0 °C) to calculate snowmelt rate, and the soil temperature to adjust the influence of the soil’s physical state on water infiltration. This modified model was used to simulate streamflows in the Kaidu River basin from 1982 to 2002, including normal, high, and low flows categorized by the Z index. Sensitivity analyses, visual inspection, and statistical measures were employed to evaluate the capability of the model to simulate various components of the streamflow. Results showed that the modified model was robust, and able to simulate the three categories of flows well. The model’s ability to reproduce streamflow in low-flow and normal-flow years was better than that in high-flow years. The model was also able to simulate the baseflow. Further, its ability to simulate spring-peak flow was much better than its ability to simulate the summer-peak flow. This study could provide useful information for water managers in determining water allocations as well as in managing water resources.

The effects of flow and stream characteristics on the variation in freshwater mussel growth in a Southeast US river basin

Summary The evaluation of the age and growth of animal populations is essential for understanding and predicting how populations will respond to changes in environmental conditions and anthropogenic stressors. We used a novel, von Bertalanffy hierarchical modelling approach to quantify relationships between the growth of three freshwater mussel species and various site‐ and watershed‐level factors including seasonal discharge, land cover and stream size in the lower Flint River Basin, Georgia, U.S.A. Our modelling approach quantified the mussel‐to‐mussel variation in the von Bertalanffy parameters and accounted for biases associated with multiple measurements made on each mussel specimen, which are generally not accounted for as sources of bias in age and growth studies. Modelling results suggested that maximum shell size parameter and the Brody growth coefficient varied across species, on average, 19 and 33%, respectively, among individual mussels within sample sites. The variation was related to short‐term high streamflows during the spring season, stream size, channel geomorphology and land cover in the watershed. This study provides insight to the factors affecting the growth of stream‐dwelling freshwater mussels. Although hierarchical von Bertalanffy growth models are rarely used for freshwater mussel age and growth studies, this approach can provide important information regarding the ecology of freshwater mussels.

Impacts of land use changes on hydrological components and macroinvertebrate distributions in the Poyang lake area

AbstractLand use and land cover changes are important issues globally resulting in changing hydrological and ecological conditions. In addition to field sampling and measurements, we applied a model cascade comprising an ecohydrological model and a species distribution model. We developed five land use scenarios (three deforestation and two afforestation scenarios) for our Chinese study basin in the Poyang lake area. In detail, we assessed the impact of land use changes on the hydrologic regime and stream macroinvertebrate distributions for the most likely deforestation scenario.Simulated deforestation scenarios result in higher streamflow and surface runoff compared with the base model. The spatial distribution of stream macroinvertebrates, a group of organisms well known as water quality indicators, was modelled to describe the effect of the changing environmental conditions on the freshwater ecosystem. For the deforestation scenario, species richness was reduced, and the occurrence of the stonefly Togoperla sp. decreased considerably. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Streamflow rating uncertainty: Characterisation and impacts on model calibration and performance

Common streamflow gauging procedures require assumptions about the stage-discharge relationship (the ‘rating curve’) that can introduce considerable uncertainties in streamflow records. These rating uncertainties are not usually considered fully in hydrological model calibration and evaluation yet can have potentially important impacts. We analysed streamflow gauge data and conducted two modelling experiments to assess rating uncertainty in operational rating curves, its impacts on modelling and possible ways to reduce those impacts. We found clear evidence of variance heterogeneity (heteroscedasticity) in streamflow estimates, with higher residual values at higher stage values. In addition, we confirmed the occurrence of streamflow extrapolation beyond the highest or lowest stage measurement in many operational rating curves, even when these were previously flagged as not extrapolated. The first experiment investigated the impact on regional calibration/evaluation of: (i) using two streamflow data transformations (logarithmic and square-root), compared to using non-transformed streamflow data, in an attempt to reduce heteroscedasticity and; (ii) censoring the extrapolated flows, compared to no censoring. Results of calibration/evaluation showed that using a square-root transformed streamflow (thus, compromising weight on high and low streamflow) performed better than using non-transformed and log-transformed streamflow. Also, surprisingly, censoring extrapolated streamflow reduced rather than improved model performance. The second experiment investigated the impact of rating curve uncertainty on catchment calibration/evaluation and parameter estimation. A Monte-Carlo approach and the nonparametric Weighted Nadaraya-Watson (WNW) estimator were used to derive streamflow uncertainty bounds. These were later used in calibration/evaluation using a standard Nash-Sutcliffe Efficiency (NSE) objective function (OBJ) and a modified NSE OBJ that penalised uncertain flows. Using square-root transformed flows and the modified NSE OBJ considerably improved calibration and predictions, particularly for mid and low flows, and there was an overall reduction in parameter uncertainty.

Stream flow velocity alters submerged macrophyte morphology and cascading interactions among associated invertebrate and periphyton assemblages

Submerged macrophytes play a key role in the functioning of stream ecosystems since they strongly affect the biological and physical environment of the habitat. On the other hand, flow velocity may affect growth and establishment of submerged macrophytes in streams and rivers. However, little attention has been paid to the morphological responses of submerged macrophytes to different stream flows and in the present study we investigate the intraspecific difference in flow adaptation of a common submerged macrophyte, Myriophyllum spicatum L. We found no difference in length of main shoot or total length of lateral shoots of M. spicatum plants grown at high and low stream flow. However, shoot and root dry weight biomass, number of lateral shoots, degree of branching and stem diameter of the main shoot increased significantly with increasing water velocity. In contrast, the opposite trend was observed for leaf whorl area and distances between the internodes of the main shoot. The amount of periphytic algae also decreased with increased water velocity, whereas the macroinvertebrate abundances were nine fold higher at high than at low stream flow, suggesting that grazing may, besides higher stream flow, have been a process behind the lower periphyton growth at high flow. Hence, stream flow not only acts as a stress factor leading to morphological changes in submerged macrophytes, but also induces cascading trophic interactions among periphytic algae and invertebrate assemblages, thereby being a major force in shaping the organism communities of streams and rivers.

Sensitivity analysis of climate on streamflow in north China

The economics and crowded cities of north China play important roles in China’s overall economic development. Streamflow is a hot issue in ecohydrological studies, and research into changes in streamflow in north China is of great significance. In this study, the sensitivities of streamflow to the aridity index, precipitation, and potential evapotranspiration are evaluated to assess the impact of climatic variation in streamflow in north China. The results show that the average coefficient of sensitivity of streamflow to aridity index is −2.24, and streamflow would decrease by 22.4 % with a 10 % increase in the aridity index. The average coefficients of sensitivity of streamflow to precipitation and potential evapotranspiration are 3.21 and −2.21, respectively. A 10 % increase in precipitation or potential evapotranspiration would induce a 32.1 % increase or a 22.1 % decrease of streamflow, respectively. Basins with low streamflows would be more sensitive to climatic variation than basins with high streamflows.

A hydrogeologic framework for characterizing summer streamflow sensitivity to climate warming in the Pacific Northwest, USA

Abstract. Summer streamflows in the Pacific Northwest are largely derived from melting snow and groundwater discharge. As the climate warms, diminishing snowpack and earlier snowmelt will cause reductions in summer streamflow. Most regional-scale assessments of climate change impacts on streamflow use downscaled temperature and precipitation projections from general circulation models (GCMs) coupled with large-scale hydrologic models. Here we develop and apply an analytical hydrogeologic framework for characterizing summer streamflow sensitivity to a change in the timing and magnitude of recharge in a spatially explicit fashion. In particular, we incorporate the role of deep groundwater, which large-scale hydrologic models generally fail to capture, into streamflow sensitivity assessments. We validate our analytical streamflow sensitivities against two empirical measures of sensitivity derived using historical observations of temperature, precipitation, and streamflow from 217 watersheds. In general, empirically and analytically derived streamflow sensitivity values correspond. Although the selected watersheds cover a range of hydrologic regimes (e.g., rain-dominated, mixture of rain and snow, and snow-dominated), sensitivity validation was primarily driven by the snow-dominated watersheds, which are subjected to a wider range of change in recharge timing and magnitude as a result of increased temperature. Overall, two patterns emerge from this analysis: first, areas with high streamflow sensitivity also have higher summer streamflows as compared to low-sensitivity areas. Second, the level of sensitivity and spatial extent of highly sensitive areas diminishes over time as the summer progresses. Results of this analysis point to a robust, practical, and scalable approach that can help assess risk at the landscape scale, complement the downscaling approach, be applied to any climate scenario of interest, and provide a framework to assist land and water managers in adapting to an uncertain and potentially challenging future.

Biodiversity values of remnant freshwater floodplain lagoons in agricultural catchments: evidence for fish of the Wet Tropics bioregion, northern Australia

Abstract Tropical floodplain wetlands are among the world's most threatened and poorly documented freshwater ecosystems. This paper describes patterns of fish diversity in remnant freshwater lagoons in relation to natural environmental gradients and impacts of agriculture in the Tully–Murray catchment, Queensland Wet Tropics bioregion (QWT), in north‐eastern Australia. Floodplain lagoons supported 21 of 29 native fish species recorded from freshwater habitats of these rivers, including three species not typically found in main river channels or tributaries, and six that require access to saline areas for spawning or larval development. Eight species favoured lagoons during their early life history, highlighting the vital role of these water bodies in providing nursery habitat. Assemblage composition differed with distance from the coast, position on the floodplain, water quality and habitat. Aquatic vegetation discriminated lagoons and habitat patches within lagoons, and fish species richness was lower in patches of exotic ponded‐pasture grasses. Although the lagoons are surrounded by intensive agriculture, especially sugarcane plantations, they are in good ecological condition, largely because of retention of some riparian vegetation, and frequent flushing by high stream flows. They offer opportunities to conserve taxonomic and functional biodiversity that is at present poorly protected by terrestrial reserves focused mainly on forested uplands. Of the 21 native species recorded, only one has &gt;20% of its QWT distribution protected in IUCN category II protected areas (National Parks), and nine species have &lt;10% of their QWT distribution in protected areas. Opportunities to protect tropical freshwater fish diversity may be lost if threatening processes are not held in check through maintenance of natural flow regimes and floodplain connectivity, protection of riparian vegetation and aquatic habitat structure, continued application of best management farming practices and off‐reserve protection of freshwater habitats on public and private lands. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Numerical Investigation on Unsteady Flow Field of the Forward-Facing Cavity and Opposing Jet Combine Thermal Protection System

In this paper, the unsteady flow field formed by the hemisphere nose-tip with forward-facing cavity and opposing jet combined thermal protection system (TPS) under high speed free stream flow (Ma4.98) was investigated numerically. The periodic variation of the drag coefficient and the flow field of the nose-tip were obtained. The numerical results show that a suitable cooperation between the opposing jet stream condition and the physical dimension of the cavity is necessary.