Large Spatial Areas Research Articles

Spatial analysis and simulation of extreme coastal flooding scenarios for national-scale emergency planning

The UK has a long history of coastal flooding, driven by large-scale low-pressure weather systems which can result in flooding over large spatial areas. Traditional coastal flood risk analysis is, however, often undertaken at local scales and hence does not consider the likelihood of simultaneous flooding over larger areas. The flooding within the UK over the Winter of 2013/2014 was notable both for its long duration, lasting over two months, and its spatial extent, affecting many different areas of England and Wales. It is thus apparent that to plan and prepare for these types of extreme event it is necessary to consider the likelihood of flood events arising at different locations simultaneously (i.e. to consider the spatial dependence of extreme flood events). This paper describes the application of a state-of-the-art multivariate extreme value methodology to extreme sea levels and wave conditions around the coast of England and Wales. The output of the analysis comprises a synthetic set of extreme but plausible events that explicitly captures the dependence between sea conditions at different spatial locations around the coast. These simulated extreme events can be used for emergency management and advanced flood risk analysis.

Experimental Evidence of the Feeding of the Free Troposphere with Aerosol Particles from the Mixing Layer

ABSTRACTAerosol particles emitted by both natural and anthropogenic sources have direct and indirect radiative impacts. Within the planetary mixing layer (ML), these particles are subjected to a large number of removal processes, e.g., rain, sedimentation, coagulation, and thus have a relatively short lifetime. Once aerosols are transported into the free troposphere (FT), their atmospheric lifetime increases significantly and they tend to be representative of large spatial areas. The work presented here shows evidence of anthropogenic emissions being transported from the ML to the FT during a cold period in February 2012. Using a wide range of in-situ measurements of aerosol chemical and physical properties at the Puy de Dome (PUY) station, as well as LIDAR measurements (at the Cezeaux site) of atmospheric back scattering we studied the exchange between the ML and the FT. Criteria used to identify when the PUY station was sampling in the ML or in the FT included mixing layer height estimates from LIDAR measurements, trace gas measurements, and air mass trajectories. Within the FT, we observed a gradual change in aerosol physical properties with increases in aerosol mass concentrations of up to 2 times the starting concentration, as well as increases in the number of larger particles (particle diameter >150 nm). Aerosol chemical properties showed increases in organic and nitrate particles. A series of linear fits were made through the data providing information on how different parameters change as a function of time. The impact of these changing aerosol properties are discussed in relation to the potential influence on aerosol direct and indirect effects. This work presents a unique combination of observations, and provide valuable data for future model validation.

Stability of ENSO and its tropical Pacific teleconnections over the Last Millennium

Abstract. Determining past changes in the amplitude, frequency and teleconnections of the El Niño-Southern Oscillation (ENSO) is important for understanding its potential sensitivity to future anthropogenic climate change. Palaeo-reconstructions from proxy records can provide long-term information of ENSO interactions with the background climatic state through time. However, it remains unclear how ENSO characteristics have changed on long timescales, and precisely which signals proxies record. Proxy interpretations are typically underpinned by the assumption of stationarity in relationships between local and remote climates, and often utilise archives from single locations located in the Pacific Ocean to reconstruct ENSO histories. Here, we investigate the long-term characteristics of ENSO and its teleconnections using the Last Millennium experiment of CMIP5 (Coupled Model Intercomparison Project phase 5; Taylor et al., 2012). We show that the relationship between ENSO conditions (NINO3.4) and local climates across the Pacific basin differs significantly for 100-year epochs defining the Last Millennium and the historical period 1906–2005. Furthermore, models demonstrate decadal- to centennial-scale modulation of ENSO behaviour during the Last Millennium. Overall, results suggest that the stability of teleconnections may be regionally dependent and that proxy climate records may reveal complex changes in teleconnected patterns, rather than large-scale changes in base ENSO characteristics. As such, proxy insights into ENSO may require evidence to be considered over large spatial areas in order to deconvolve changes occurring in the NINO3.4 region from those relating to local climatic variables. To obtain robust histories of the ENSO and its remote impacts, we recommend interpretations of proxy records should be considered in conjunction with palaeo-reconstructions from within the central Pacific.

Modeling Variability and Uncertainty of Photovoltaic Generation: A Hidden State Spatial Statistical Approach

In this paper, we construct, fit, and validate a hidden Markov model for predicting variability and uncertainty in generation from distributed (PV) systems. The model is unique in that it: 1) predicts metrics that are directly related to operational reserves, 2) accounts for the effects of stochastic volatility and geographic autocorrelation, and 3) conditions on latent variables referred to as “volatility states.” We fit and validate the model using 1-min resolution generation data from approximately 100 PV systems in the California Central Valley or the Los Angeles coastal area, and condition the volatility state of each system at each time on 15-min resolution generation data from nearby PV systems (which are available from over 6000 PV systems in our data set). We find that PV variability distributions are roughly Gaussian after conditioning on hidden states. We also propose a method for simulating hidden states that results in a very good upper bound for the probability of extreme events. Therefore, the model can be used as a tool for planning additional reserve capacity requirements to balance solar variability over large and small spatial areas.

Comparison of measured and predicted statistical measures in military jet noise propagation

Crackle, an annoying component of jet noise, has been associated with acoustic shocks that form as a waveform experiences nonlinear steepening. The skewness of the first time derivative of the pressure waveform, or derivative skewness, is a metric that is sensitive to acoustic shocks, and has shown that shocks, and therefore crackle, are found in the far field of full-scale military jets. Recent extensive measurements on F-35 aircraft enable a comparison of linear and nonlinear predictions and measured waveforms over a large spatial area. Waveforms measured at 76.2 m from the aircraft are numerically propagated using linear and nonlinear methods to several distances up to 305 m, and the derivative skewness calculations from these numerically propagated waveforms are compared with those of measured signals. Comparisons are made for both the A and B variants of the F-35, in changing meteorological conditions, and with engine conditions ranging from intermediate power to full afterburner. [Work supported by USAFRL through ORISE.]

Stream temperature prediction in ungauged basins: review of recent approaches and description of a new physics-derived statistical model

Abstract. The development of stream temperature regression models at regional scales has regained some popularity over the past years. These models are used to predict stream temperature in ungauged catchments to assess the impact of human activities or climate change on riverine fauna over large spatial areas. A comprehensive literature review presented in this study shows that the temperature metrics predicted by the majority of models correspond to yearly aggregates, such as the popular annual maximum weekly mean temperature (MWMT). As a consequence, current models are often unable to predict the annual cycle of stream temperature, nor can the majority of them forecast the inter-annual variation of stream temperature. This study presents a new statistical model to estimate the monthly mean stream temperature of ungauged rivers over multiple years in an Alpine country (Switzerland). Contrary to similar models developed to date, which are mostly based on standard regression approaches, this one attempts to incorporate physical aspects into its structure. It is based on the analytical solution to a simplified version of the energy-balance equation over an entire stream network. Some terms of this solution cannot be readily evaluated at the regional scale due to the lack of appropriate data, and are therefore approximated using classical statistical techniques. This physics-inspired approach presents some advantages: (1) the main model structure is directly obtained from first principles, (2) the spatial extent over which the predictor variables are averaged naturally arises during model development, and (3) most of the regression coefficients can be interpreted from a physical point of view – their values can therefore be constrained to remain within plausible bounds. The evaluation of the model over a new freely available data set shows that the monthly mean stream temperature curve can be reproduced with a root-mean-square error (RMSE) of ±1.3 °C, which is similar in precision to the predictions obtained with a multi-linear regression model. We illustrate through a simple example how the physical aspects contained in the model structure can be used to gain more insight into the stream temperature dynamics at regional scales.

Simulation of the phenological development of wheat and maize at the global scale

AbstractAimTo derive location‐specific parameters that reflect the geographic differences among cultivars in vernalization requirements, sensitivity to day length (photoperiod) and temperature, which can be used to simulate the phenological development of wheat and maize at the global scale.LocationGlobal.MethodsBased on crop calendar observations and literature describing the large‐scale patterns of phenological characteristics of cultivars, we developed algorithms to compute location‐specific parameters to represent this large‐scale pattern. Vernalization requirements were related to the duration and coldness of winter, sensitivity to day length was assumed to be represented by the minimum and maximum day lengths occurring at a location, and sensitivity to temperature was related to temperature conditions during the vegetative development phase of the crop.ResultsApplication of the derived location‐specific parameters resulted in high agreement between simulated and observed lengths of the cropping period. Agreement was especially high for wheat, with mean absolute errors of less than 3 weeks. In the main maize cropping regions, cropping periods were over‐ and underestimated by 0.5–1.5 months. We also found that interannual variability in simulated wheat harvest dates was more realistic when accounting for photoperiod effects.Main conclusionsThe methodology presented here provides a good basis for modelling the phenological characteristics of cultivars at the global scale. We show that current global patterns of growing season length as described in cropping calendars can be largely reproduced by phenology models if location‐specific parameters are derived from temperature and day length indicators. Growing seasons can be modelled more accurately for wheat than for maize, especially in warm regions. Our method for computing parameters for phenology models from temperature and day length offers opportunities to improve the simulation of crop productivity by crop simulation models developed for large spatial areas and for long‐term climate impact projections that account for adaptation in the selection of varieties.

Patterns of Mass Mortality among Rocky Shore Invertebrates across 100 km of Northeastern Pacific Coastline.

Mass mortalities in natural populations, particularly those that leave few survivors over large spatial areas, may cause long-term ecological perturbations. Yet mass mortalities may remain undocumented or poorly described due to challenges in responding rapidly to unforeseen events, scarcity of baseline data, and difficulties in quantifying rare or patchily distributed species, especially in remote or marine systems. Better chronicling the geographic pattern and intensity of mass mortalities is especially critical in the face of global changes predicted to alter regional disturbance regimes. Here, we couple replicated post-mortality surveys with preceding long-term surveys and historical data to describe a rapid and severe mass mortality of rocky shore invertebrates along the north-central California coast of the northeastern Pacific Ocean. In late August 2011, formerly abundant intertidal populations of the purple sea urchin (Strongylocentrotus purpuratus, a well-known ecosystem engineer), and the predatory six-armed sea star (Leptasterias sp.) were functionally extirpated from ~100 km of coastline. Other invertebrates, including the gumboot chiton (Cryptochiton stelleri) the ochre sea star (Pisaster ochraceus), and subtidal populations of purple sea urchins also exhibited elevated mortality. The pattern and extent of mortality suggest the potential for long-term population, community, and ecosystem consequences, recovery from which may depend on the different dispersal abilities of the affected species.

Connecting Point-Level and Gridded Moments in the Analysis of Climate Data*

Abstract The need to draw climate-related inferences from historical data makes understanding the biases and errors in these data critical. While climate data are collected at point-level monitoring sites, they are often postprocessed by averaging sites within a geographic area to align the data to a grid, easing analysis and visualization. Although this aggregation generally provides reasonable estimates of the mean, its use can be problematic for characterizing the full distribution of climate measures. Specifically, the process of averaging point-level data up to grid level can lead to inconsistencies, particularly when the grid box is heterogeneous and extremes are of interest. Point-level data are measured at individual points, while gridded data are the averaged product of many measurements within a larger spatial area. Because of this aggregation, point-level and grid-level distributions differ in many fundamental properties, such as their shape, skew, and tail behavior. This paper highlights these differences and their effects on analyses pertaining to current climatological questions. Mathematical relationships are derived to link the distributions of grid-level climate measures to the distributions of point-level climate measures using the notion of effective sample size. Then, these relationships are leveraged to propose a correction factor to use when modeling higher moments and extreme events.

An integrated approach for monitoring efficiency and investments of activated sludge-based wastewater treatment plants at large spatial scale

WISE, the Water Information System for Europe, is the web-portal of the European Commission (EU) that disseminates the quality state of the receiving water bodies and the efficiency of the municipal wastewater treatment plants (WWTPs) in order to monitor advances in the application of both the Water Framework Directive (WFD) as well as the Urban Wastewater Treatment Directive (UWWTD). With the intention to develop WISE applications, the aim of the work was to define and apply an integrated approach capable of monitoring the efficiency and investments of activated sludge-based WWTPs located in a large spatial area, providing the following outcomes useful to the decision-makers: (i) the identification of critical facilities and their critical processes by means of a Performance Assessment System (PAS), (ii) the choice of the most suitable upgrading actions, through a scenario analysis. (iii) the assessment of the investment costs to upgrade the critical WWTPs and (iv) the prioritization of the critical facilities by means of a multi-criteria approach which includes the stakeholders involvement, along with the integration of some technical, environmental, economic and health aspects. The implementation of the proposed approach to a high number of municipal WWTPs highlighted how the PAS developed was able to identify critical processes with a particular effectiveness in identifying the critical nutrient removal ones. In addition, a simplified approach that considers the cost related to a basic-configuration and those for the WWTP integration, allowed to link the critical processes identified and the investment costs. Finally, the questionnaire for the acquisition of data such as that provided by the Italian Institute of Statistics, the PAS defined and the database on the costs, if properly adapted, may allow for the extension of the integrated approach on an EU-scale by providing useful information to water utilities as well as institutions.

The Social Construction of a Gentrifying Neighborhood

This study draws upon cognitive maps and interviews with 56 residents living in a gentrifying area to examine how residents socially construct neighborhoods. Most minority respondents, regardless of socioeconomic status and years of residency, defined their neighborhood as a large and inclusive spatial area, using a single name and conventional boundaries, invoking the area’s Black cultural history, and often directly responding to the alternative way residents defined their neighborhoods. Both long-term and newer White respondents defined their neighborhood as smaller spatial areas and used a variety of names and unconventional boundaries that excluded areas that they perceived to have lower socioeconomic status and more crime. The large and inclusive socially constructed neighborhood was eventually displaced. These findings shed light on how the internal narratives of neighborhood identity and boundaries are meaningfully tied to a broader structure of inequality and shape how neighborhood identities and boundaries change or remain.

MAX-DOAS tropospheric nitrogen dioxide column measurements compared with the Lotos-Euros air quality model

Abstract. A 14-month data set of MAX-DOAS (Multi-Axis Differential Optical Absorption Spectroscopy) tropospheric NO2 column observations in De Bilt, the Netherlands, has been compared with the regional air quality model Lotos-Euros. The model was run on a 7×7 km2 grid, the same resolution as the emission inventory used. A study was performed to assess the effect of clouds on the retrieval accuracy of the MAX-DOAS observations. Good agreement was found between modeled and measured tropospheric NO2 columns, with an average difference of less than 1% of the average tropospheric column (14.5 · 1015 molec cm−2). The comparisons show little cloud cover dependence after cloud corrections for which ceilometer data were used. Hourly differences between observations and model show a Gaussian behavior with a standard deviation (σ) of 5.5 · 1015 molec cm−2. For daily averages of tropospheric NO2 columns, a correlation of 0.72 was found for all observations, and 0.79 for cloud free conditions. The measured and modeled tropospheric NO2 columns have an almost identical distribution over the wind direction. A significant difference between model and measurements was found for the average weekly cycle, which shows a much stronger decrease during the weekend for the observations; for the diurnal cycle, the observed range is about twice as large as the modeled range. The results of the comparison demonstrate that averaged over a long time period, the tropospheric NO2 column observations are representative for a large spatial area despite the fact that they were obtained in an urban region. This makes the MAX-DOAS technique especially suitable for validation of satellite observations and air quality models in urban regions.

Daily forecast of dengue fever incidents for urban villages in a city.

BackgroundInstead of traditional statistical models for large spatial areas and weekly or monthly temporal units, what public health workers urgently need is a timely risk prediction method for small areas. This risk prediction would provide information for early warning, target surveillance and intervention.MethodsDaily dengue cases in the 457 urban villages of Kaohsiung City, Taiwan from 2009 to 2012 were used for model development and evaluation. There were in total 2,997 confirmed dengue cases during this period. A logistic regression model was fitted to the daily incidents occurring in the villages for the past 30 days. The fitted model was then used to predict the incidence probabilities of dengue outbreak for the villages the next day. A percentile of the 457*30 fitted incidence probabilities was chosen to determine a cut-point for issuing the alerts. The covariates included three different levels of spatial effect, and with four lag time periods. The population density and the meteorological conditions were also included for the prediction.ResultsThe performance of the prediction models was evaluated on 122 consecutive days from September 1 to December 31, 2012. With the 80th percentile threshold, the median sensitivity was 83% and the median false positive rate was 23%. We found that most of the coefficients of the predictors of having cases at the same village in the previous 14 days were positive and significant for the 122 daily updated models. The estimated coefficients of population density were significant during the peak of the epidemic in 2012.ConclusionsThe proposed method can provide near real-time dengue risk prediction for a small area. This can serve as a useful decision making tool for front-line public health workers to control dengue epidemics. The precision of the spatial and temporal units can be easily adjusted to different settings for different cities.

Impacts of the local environment on recruitment: a comparative study of North Sea and Baltic Sea fish stocks

Abstract While the impact of environmental forcing on recruitment variability in marine populations remains largely elusive, studies spanning large spatial areas and many stocks are able to identify patterns common to different regions and species. In this study, we investigate the effects of the environment on the residuals of a Ricker stock–recruitment (SR) model, used as a proxy of prerecruits' survival, of 18 assessed stocks in the Baltic and North Seas. A probabilistic principal components (PCs) analysis permits the identification of groups of stocks with shared variability in the prerecruits' survival, most notably a group of pelagics in the Baltic Sea and a group composed of gadoids and herring in the North Sea. The first two PCs generally grouped the stocks according to their localizations: the North Sea, the Kattegat–Western Baltic, and the Baltic Sea. This suggests the importance of the local environmental variability on the recruitment strength. Hence, the prerecruits' survival variability is studied according to geographically disaggregated and potentially impacting abiotic or biotic variables. Time series (1990–2009) of nine environmental variables consistent with the spawning locations and season for each stock were extracted from a physical–biogeochemical model to evaluate their ability to explain the survival of prerecruits. Environmental variables explained >70% of the survival variability for eight stocks. The variables water current, salinity, temperature, and biomass of other fish stocks are regularly significant in the models. This study shows the importance of the local environment on the dynamics of SR. The results provide evidence of the necessity of including environmental variables in stock assessment for a realistic and efficient management of fisheries.

The application of the Intermittent SBAS (ISBAS) InSAR method to the South Wales Coalfield, UK

Satellite radar interferometry is a well-documented technique for the characterisation of ground motions over large spatial areas. However, the measurement density is often constrained by the land use, with best results obtained over urban and semi urban areas. We use an implementation of the Small Baseline Subset (SBAS) methodology, whereby areas exhibiting intermittent coherence are considered alongside those displaying full coherence, in the final result, to characterise the ground motion over the South Wales Coalfield, United Kingdom. 55 ERS-1/2 Synthetic Aperture Radar (SAR) C-band images for the period between 1992 and 1999 are processed using the ISBAS (Intermittent Small BAseline Subset) technique, which provides 3.4 times more targets, with associated measurements than a standard SBAS implementation. The dominant feature of the observed motions is a relatively large spatial area of uplift. Uplift rates are as much as 1cm/yr. and are centred on the part of the coalfield which was most recently exploited. Geological interpretation reveals that this uplift is most likely a result of mine water rebound. Collieries in this part of the coalfield required a ground water to be pumped to enable safe coal extraction; following their closure pumping activity ceased allowing the water levels to return to equilibrium. The ISBAS technique offers significant improvements in measurement density ensuring an increase in detection of surface motions and enabling easier interpretation.

Rediscovering nature as commons in environmental planning: new understandings through dialogue

A core challenge in environmental planning is the gap between a strong participatory ethos and top-down defined nature protection policies. Nature protection policies for large areas are concerned with securing ecological biodiversity and wildlife habitats against increasing societal claims. Such planning objectives also affect the socio-economic and cultural relations between the local community and the area they live in, and raise conflicts between local and national protection objectives and steering levels. Despite attempts to facilitate participatory planning approaches as a means of reducing conflict, nature protection continues to be contested in local communities. This paper explores the different understandings of nature at play between citizens and planning authorities throughout a habitat protection planning process in Norway. The paper discusses whether environmental planning of large spatial areas could develop communication arenas designed to deliberate different understandings of an area as a matter of commons between institutional planning perspectives of nature protection and (local) understandings of the area as part of everyday life. The paper sheds light on how large spatial areas are understood at different government levels and from everyday life orientations, and how these could be used to develop mutual understandings of the area as a common.

Rediscovering nature as commons in environmental planning: new understandings through dialogue

A core challenge in environmental planning is the gap between a strong participatory ethos and top-down defined nature protection policies. Nature protection policies for large areas are concerned with securing ecological biodiversity and wildlife habitats against increasing societal claims. Such planning objectives also affect the socio-economic and cultural relations between the local community and the area they live in, and raise conflicts between local and national protection objectives and steering levels. Despite attempts to facilitate participatory planning approaches as a means of reducing conflict, nature protection continues to be contested in local communities. This paper explores the different understandings of nature at play between citizens and planning authorities throughout a habitat protection planning process in Norway. The paper discusses whether environmental planning of large spatial areas could develop communication arenas designed to deliberate different understandings of an area as a matter of commons between institutional planning perspectives of nature protection and (local) understandings of the area as part of everyday life. The paper sheds light on how large spatial areas are understood at different government levels and from everyday life orientations, and how these could be used to develop mutual understandings of the area as a common.

Effects of a spatial closure on highly mobile fish species: an assessment using pelagic stereo-BRUVs

The effects of a spatial area closure on pelagic fish assemblages within the Houtman Abrolhos Islands were assessed using mid-water pelagic stereo-BRUVs. The spatial area closure within the Easter group of the Houtman Abrolhos Islands was found to have no significant effect on the species composition and relative abundance of pelagic fish assemblages. The most abundant demersal target species recorded was pink snapper (Chrysophrys auratus) and, individuals measured within the spatial closure were significantly larger than those sampled in the area open to fishing. This spatial area closure is of moderate size (22.3km2), but the spatial management of highly mobile species may require larger area closures than those for reef-associated species. The monitoring of pelagic species both in large and small spatial area closures is required in order to better understand how mobile species respond to this management strategy. Some species were only recorded in relatively low numbers using pelagic stereo-BRUVs. Moreover, some of the highly mobile pelagic fish species, such as tunas, mackerel and some shark species have proven difficult to measure, as these species were observed furthest from the camera systems. While pelagic stereo-BRUVs are an effective fishery-independent approach to monitor spatial fishing closures, improving the power of replicates by pooling individual deployments, and increasing the attraction rate of pelagic fish to the stereo-cameras, will enhance their performance in future studies.

Does Wave Height Matter for Effective Surface Dispersant Application?

ABSTRACTThe Deepwater Horizon (DWH) crude oil release provided an occasion to test the delivery and effectiveness of dispersants on surface oil slicks to reduce the potential exposure of shoreline habitats and marine wildlife to spilled oil. In the beginning of the DWH response, there was concern that the calm sea conditions did not provide sufficient wave energy for dispersant action to occur. At one point a minimum 3-foot wave height requirement for dispersant application was set in an attempt to ensure sufficient mixing energy for dispersant activation was present at the time of application. Because of the ability of aerial dispersant application to rapidly treat large spatial areas and quantities of oil, there was a contrasting concern that a 3-foot (0.91 m) minimum wave height requirement was overly restricting dispersant operations; thereby, increasing environmental exposures.To evaluate the wave heights that effectively dispersed the Macondo crude oil, the SMART (Special Monitoring of Applied Response Technologies) Tier II/III monitoring data of dispersant applications performed in low wave conditions, i.e., < 3 ft (0.91m) were analyzed. Of the 27 SMART Tier II/III monitoring operations conducted in significant wave heights (SWHs) of < 3 feet (0.91 m), 21 were reported as “effective,” 4 were reported as “inconclusive,” and only 2 were reported as “no observed dispersion.” These results demonstrate dispersants were effective in low wave conditions and on weathered Macondo crude oil as a function of distance from the spill site.The paper then estimates the impact that setting wave height restrictions has on dispersant operations showing that a > 3 feet requirement could reduce surface dispersant operational days by as much as 67%. With the dispersant assets available during the DWH response, this could have resulted in leaving up to 700,000 gallons of oil per day on the water,a thus exposing shoreline habitat and offshore wildlife to an increased risk of oiling.The paper concludes thatWave height should not be used as a criterion for approving or conducting surface dispersant application operations, becausewave heights as low as 0.5–1.0 feet were effective in immediately dispersing fresh and weathered Macondo crude oil, and may be sufficient to disperse other oils, andResearch on dispersant application in calm sea conditions has shown that oils would rapidly and almost totally disperse when exposed to breaking waves after being left on a calm water surface for prolonged periods.The paper recommends that government and response organizations should review and consider revising their guidance and operational procedures for dispersant application approval in light of the analysis presented in this paper.

Combined Effects of Reservoir Operations and Climate Warming on the Flow Regime of Hydropower Bypass Reaches of California's Sierra Nevada

AbstractAlterations to flow regimes from regulation and climatic change both affect the biophysical functioning of rivers over long time periods and large spatial areas. Historically, however, the effects of these flow alteration drivers have been studied separately. In this study, results from unregulated and regulated river management models were assessed to understand how flow regime alterations from river regulation differ under future climate conditions in the Sierra Nevada of California, USA. Four representative flow alteration metrics—mean annual flow, low flow duration, centroid timing and mean weekly rate of decrease—were calculated and statistically characterized under historical and future unregulated and regulated conditions over a 20‐year period at each of the eight regulated river locations below dams across the Sierra Nevada. Future climatic conditions were represented by assuming an increase in air temperature of 6 °C above historical (1981–2000) air temperatures, with no change in other meteorological conditions. Results indicate that climate warming will measurably alter some aspects of the flow regime. By comparison, however, river regulation with business‐as‐usual operations will alter flow regimes much more than climate warming. Existing reservoirs can possibly be used to dampen the anticipated effects of climate warming through improved operations, though additional research is needed to identify the full suite of such possibilities. Copyright © 2014 John Wiley & Sons, Ltd.