Annual Peak Streamflow Research Articles

Effects of forest disturbance on water yield and peak flow in low‐relief glaciated catchments assessed with Bayesian parameter estimation

AbstractEmpirical assessment of how forest disturbance affects streamflow has been traditionally limited to small, experimental catchments. However, larger catchments where landscape management occurs have emergent drivers of streamflow at scale, and thus may exhibit novel responses to land cover disturbance. We used statistical models of water yield and annual maximum peak streamflow for multiple large (> 50 km2) forested catchments in the low‐relief glaciated region of central North America to investigate how forest disturbance and climatic variability affect water yield and peak flows in similar landscapes. We used linear models, linear mixed effects models, and probabilistic flood‐frequency analysis with Bayesian parameter estimation in two case studies. These included: (1) a wildfire that burned ~30% of the 650 km2 wilderness Upper Kawishiwi catchment, and (2) 11 catchments within the St. Louis River Basin ranging from 56 to 8880 km2 with a patchwork disturbance regime wherein ~0.25% to 1% of the catchment is harvested or converted to non‐forest land use each year. We also assessed the most likely hydrological recovery year after forest disturbance, and the relative importance of stationary and nonstationary drivers of streamflow. We found forest disturbance correlated with declines in water yield for low‐level disturbance regimes in some catchments, but that water yield increased in response to the large‐scale wildfire. Positive and negative associations of forest disturbance with peak flows were observed. Hydrologic recovery time ranged from 5 to 13 years for water yield and peak flows following disturbance. Despite these effects of forest disturbance on streamflow, effects of climatic variability and stationary catchment size factors were more prominent streamflow drivers. Basins larger than ~50 km2 in low‐relief glaciated regions can be impacted by forest cover change even on <30% of basin area, but climatic variability and catchment spatial scale has a larger effect than forest disturbance.

Science and the evolving management of environmental hazards at Yosemite National Park

US national park managers must address a complex portfolio of foreseen and unforeseen challenges that arise in part from a dual mandate to preserve nature and facilitate visitation. To deal with resource management challenges, managers can identify potential pathways toward a solution through the use of science to inform policy and guide actions. The way science has been applied has evolved over the course of the National Park Service’s history, in large part due to the prevailing societal context and ways of thinking about the environment, and relatedly as a necessity to mitigate the impact from development and anthropogenic climate change. Landscape-scale environmental hazards are a fitting proxy to recount the changing use of science and policy because biophysical processes become most hazardous at the interface of infrastructure and the natural environment, where people are most exposed. This paper synthesizes modern administrative and environmental histories of hazards in Yosemite National Park from the late19th century to the early 21st century through archival records and long-term data, including significant events and trends in wildland fire, tree mortality (falls), extreme floods, and rockfalls and slides. Findings confirm increased severity and extent of wildland fire, correlations between periods of drought and high rates of tree mortality, warmer precipitation events lead to earlier annual peak streamflow, and connections between periods of prolonged cold with rockfalls, and prolonged precipitation with slides. These hazards exist as an interconnected system in the context of high seasonal visitation, and while there are averages of seasonal conditions over time, there are no “normal” years.

Influence of warming and atmospheric circulation changes on multidecadal European flood variability

Abstract. European flood frequency and intensity change on a multidecadal scale. Floods were more frequent in the 19th (central Europe) and early 20th century (western Europe) than during the mid-20th century and again more frequent since the 1970s. The causes of this variability are not well understood and the relation to climate change is unclear. Palaeoclimate studies from the northern Alps suggest that past flood-rich periods coincided with cold periods. In contrast, some studies suggest that more floods might occur in a future, warming world. Here we address the contribution of atmospheric circulation and of warming to multidecadal flood variability. For this, we use long series of annual peak streamflow, daily weather data, reanalyses, and reconstructions. We show that both changes in atmospheric circulation and moisture content affected multidecadal changes of annual peak streamflow in central and western Europe over the past two centuries. We find that during the 19th and early 20th century, atmospheric circulation changes led to high peak values of moisture flux convergence. The circulation was more conducive to strong and long-lasting precipitation events than in the mid-20th century. These changes are also partly reflected in the seasonal mean circulation and reproduced in atmospheric model simulations, pointing to a possible role of oceanic variability. For the period after 1980, increasing moisture content in a warming atmosphere led to extremely high moisture flux convergence. Thus, the main atmospheric driver of flood variability changed from atmospheric circulation variability to water vapour increase.

Assessment and significance of the frequency domain for trends in annual peak streamflow

AbstractRisk management of nonstationary floods depends on an understanding of trends over a range of flood frequencies representing small (frequent) to large (infrequent) floods. Quantile regression is applied to the annual peak streamflow distributions at 2683 sites in the contiguous United States to test for trends in the 10th quantile (floods with a 0.9 annual exceedance probability), the 50th quantile (median annual flood), and 90th quantile (floods with a 0.1 annual exceedance probability). Trends are most common (36% of sites) for the median annual flood (50th quantile) and often coherent with trends in both frequent small floods (10th quantile) and infrequent large floods (90th quantile). Changes in the at‐site variance of annual peak streamflow, indicated by convergence (decreasing variance) or divergence (increasing variance) of the 10th and 90th quantiles over time, are primarily in response to reservoir operation or urban development rather than climate. An analysis of synthetic series generated from nonstationary distributions demonstrates that quantile regression and standard trend tests used in flood frequency analysis have limited power and high rates of false negatives (>70%) when a test has a significance of p = 0.05. Quantile regression and tests with lower significance complement standard trend testing to inform flood risk management.

Rainfall spatial-heterogeneity accelerates landscape evolution processes

Catchment hydro-morphological response is mainly conditioned on rainfall properties, such as rainfall intensity, storm duration and frequency, and the timing of these events. Rainfall spatial variability is likewise a major determinant affecting streamflow, erosion, and sediment transport, and is explored largely in the context of heavy rain triggering floods and fast morphological changes on hillslopes and in channels. In this study, we examine how the spatial structure of rainfall influences landscape evolution at the catchment scale over hundreds of years. To achieve this, multiple realizations of hourly rainfall fields, each differing only by their spatial distribution but identical in all other respects, were simulated using a weather generator. The impact of storm spatial-heterogeneity on the catchment morphology was then assessed with a landscape evolution model (CAESAR-Lisflood). A virtual “open-book” type catchment was used for this numerical experiment. The mean streamflow and low-flows remained the same while the magnitude of the annual peak streamflow increased by up to 12% in response to higher rainfall spatial heterogeneity. However, the erosion and deposition rates significantly increased (up to 50%) and the net erosion and deposition areas changed (increased by up to 9% and decreased by 13.5%, respectively) when the rain became less uniform in space. Furthermore, new gullies were found to be longer, deeper, and more branched in response to increased rainfall heterogeneity. The results suggest that heterogeneity in rainfall spatial patterns speeds up landscape development, even when rainfall volumes and temporal structures are the same. This implies that the spatial structure of rainfall may have more of an influence on catchment morphology at long time scales than previously thought.

Flood risk behaviors of United States riverine metropolitan areas are driven by local hydrology and shaped by race.

Flooding risk results from complex interactions between hydrological hazards (e.g., riverine inundation during periods of heavy rainfall), exposure, vulnerability (e.g., the potential for structural damage or loss of life), and resilience (how well we recover, learn from, and adapt to past floods). Building on recent coupled conceptualizations of these complex interactions, we characterize human-flood interactions (collective memory and risk-enduring attitude) at a more comprehensive scale than has been attempted to date across 50 US metropolitan statistical areas with a sociohydrologic (SH) model calibrated with accessible local data (historical records of annual peak streamflow, flood insurance loss claims, active insurance policy records, and population density). A cluster analysis on calibrated SH model parameter sets for metropolitan areas identified two dominant behaviors: 1) "risk-enduring" cities with lower flooding defenses and longer memory of past flood loss events and 2) "risk-averse" cities with higher flooding defenses and reduced memory of past flooding. These divergent behaviors correlated with differences in local stream flashiness indices (i.e., the frequency and rapidity of daily changes in streamflow), maximum dam heights, and the proportion of White to non-White residents in US metropolitan areas. Risk-averse cities tended to exist within regions characterized by flashier streamflow conditions, larger dams, and larger proportions of White residents. Our research supports the development of SH models in urban metropolitan areas and the design of risk management strategies that consider both demographically heterogeneous populations, changing flood defenses, and temporal changes in community risk perceptions and tolerance.

The Influence of Urban Development Patterns on Streamflow Characteristics in the Charlanta Megaregion

AbstractAlthough it is widely recognized that urbanization has a notable impact on streamflow characteristics, the relative influence of the extent, spatial configuration, and positioning of urban development on low, high, and peak flow regimes is still not fully understood. The overarching research objective of this study was to clarify these relationships by analyzing 119 watersheds throughout the Charlanta megaregion, which stretches from Charlotte, NC to Atlanta, GA. Spatial metrics were derived from land use/land cover data sets to quantify the urban development patterns of each watershed while the streamflow characteristics were evaluated using mean daily discharge and annual peak streamflow data. Analysis of variance tests, bivariate correlations, and multivariate regression models were used to identify intraregional variability and quantify the impact of urban development patterns on streamflow characteristics while controlling for the physical differences between watersheds. The statistical analysis revealed that increasing the extent of urban development enhanced high and low flow frequency as well as annual peak unit discharge. Therefore, urbanization within Charlanta generally produced a more extreme streamflow regime. In terms of the spatial configuration of urban development, the models indicated that more contiguous developed open space increased high and low flow frequency. Finally, the positional analysis suggested that clustering impervious surfaces in source areas distant from streams increased the frequency of high flows. The study highlights the overall importance of considering the extent, configuration, and positioning of urban development when devising land use policies aimed at minimizing streamflow alteration due to urbanization.

Examining controls on peak annual streamflow and floods in the Fraser River Basin of British Columbia

Abstract. The Fraser River Basin (FRB) of British Columbia is one of the largest and most important watersheds in western North America, and home to a rich diversity of biological species and economic assets that depend implicitly upon its extensive riverine habitats. The hydrology of the FRB is dominated by snow accumulation and melt processes, leading to a prominent annual peak streamflow invariably occurring in May–July. Nevertheless, while annual peak daily streamflow (APF) during the spring freshet in the FRB is historically well correlated with basin-averaged, 1 April snow water equivalent (SWE), there are numerous occurrences of anomalously large APF in below- or near-normal SWE years, some of which have resulted in damaging floods in the region. An imperfect understanding of which other climatic factors contribute to these anomalously large APFs hinders robust projections of their magnitude and frequency. We employ the Variable Infiltration Capacity (VIC) process-based hydrological model driven by gridded observations to investigate the key controlling factors of anomalous APF events in the FRB and four of its subbasins that contribute nearly 70 % of the annual flow at Fraser-Hope. The relative influence of a set of predictors characterizing the interannual variability of rainfall, snowfall, snowpack (characterized by the annual maximum value, SWEmax), soil moisture and temperature on simulated APF at Hope (the main outlet of the FRB) and at the subbasin outlets is examined within a regression framework. The influence of large-scale climate modes of variability (the Pacific Decadal Oscillation (PDO) and the El Niño–Southern Oscillation – ENSO) on APF magnitude is also assessed, and placed in context with these more localized controls. The results indicate that next to SWEmax (univariate Spearman correlation with APF of ρ^ = 0.64; 0.70 (observations; VIC simulation)), the snowmelt rate (ρ^ = 0.43 in VIC), the ENSO and PDO indices (ρ^ = −0.40; −0.41) and (ρ^ = −0.35; −0.38), respectively, and rate of warming subsequent to the date of SWEmax (ρ^ = 0.26; 0.38), are the most influential predictors of APF magnitude in the FRB and its subbasins. The identification of these controls on annual peak flows in the region may be of use in understanding seasonal predictions or future projected streamflow changes.

Hydrologic response to and recovery from differing silvicultural systems in a deciduous forest landscape with seasonal snow cover

Hydrological consequences of alternative harvesting strategies in deciduous forest landscapes with seasonal snow cover have received relatively little attention. Most forest harvesting experiments in landscapes with seasonal snow cover have focused on clearcutting in coniferous forests. Few have examined alternative strategies such as selection or shelterwood cutting in deciduous stands whose hydrologic responses to harvesting may differ from those of conifers. This study presents results from a 31-year examination of hydrological response to and recovery from alternative harvesting strategies in a deciduous forest landscape with seasonal snow cover in central Ontario, Canada. A quantitative means of assessing hydrologic recovery to harvesting is also developed. Clearcutting resulted in increased water year (WY) runoff. This was accompanied by increased runoff in all seasons, with greatest relative increases in Summer. Direct runoff and baseflow from treatment catchments generally increased following harvesting, although annual peak streamflow did not. Largest increases in WY runoff and seasonal runoff as well as direct runoff and baseflow generally occurred in the selection harvest catchment, likely as a result of interception of hillslope runoff by a forest access road and redirection to the stream channel. Hydrologic recovery appeared to begin towards the end of the experimental period for several streamflow metrics but was incomplete for all harvesting strategies 15 years after harvesting. Geochemical tracing indicated that harvesting enhanced the relative importance of surface and near-surface water pathways on catchment slopes for all treatments, with the clearcut catchment showing the most pronounced and prolonged response. Such insights into water partitioning between flow pathways may assist assessments of the ecological and biogeochemical consequences of forest disturbance.

Changes in seasonality and timing of peak streamflow in snow and semi‐arid climates of the north‐central United States, 1910–2012

AbstractChanges in the seasonality and timing of annual peak streamflow in the north‐central USA are likely because of changes in precipitation and temperature regimes. A source of long‐term information about flood events across the study area is the U.S. Geological Survey peak streamflow database. However, one challenge of answering climate‐related questions with this dataset is that even in snowmelt‐dominated areas, it is a mixed population of snowmelt/spring rain generated peaks and summer/fall rain generated peaks. Therefore, a process was developed to divide the annual peaks into two populations, or seasons, snowmelt/spring, and summer/fall. The two series were then tested for the hypotheses that because of changes in precipitation regimes, the odds of summer/fall peaks have increased and, because of temperature changes, snowmelt/spring peaks happen earlier. Over climatologically and geographically similar regions in the north‐central USA, logistic regression was used to model the odds of getting a summer/fall peak. When controlling for antecedent wet and dry conditions and geographical differences, the odds of summer/fall peaks occurring have increased across the study area. With respect to timing within the seasons, trend analysis showed that in northern portions of the study region, snowmelt/spring peaks are occurring earlier. The timing of snowmelt/spring peaks in three regions in the northern part of the study area is earlier by 8.7– 14.3 days. These changes have implications for water interests, such as potential changes in lead‐time for flood forecasting or changes in the operation of flood‐control dams. Copyright © 2015 John Wiley & Sons, Ltd.

Flood frequency under the influence of trends in the Pearl River basin, China: changing patterns, causes and implications

AbstractUsing a nonstationary flood frequency model, this study investigates the impact of trends on the estimation of flood frequencies and flood magnification factors. Analysis of annual peak streamflow data from 28 hydrological stations across the Pearl River basin, China, shows that: (1) northeast parts of the West and the North River basins are dominated by increasing annual peak streamflow, whereas decreasing trends of annual peak streamflow are prevailing in other regions of the Pearl River basin; (2) trends significantly impact the estimation of flood frequencies. The changing frequency of the same flood magnitude is related to the changing magnitude or significance/insignificance of trends, larger increasing frequency can be detected for stations with significant increasing trends of annual peak streamflow and vice versa, and smaller increasing magnitude for stations with not significant increasing annual peak streamflow, pointing to the critical impact of trends on estimation of flood frequencies; (3) larger‐than‐1 flood magnification factors are observed mainly in the northeast parts of the West River basin and in the North River basin, implying magnifying flood processes in these regions and a higher flood risk in comparison with design flood‐control standards; and (4) changes in hydrological extremes result from the integrated influence of human activities and climate change. Generally, magnifying flood regimes in the northeast Pearl River basin and in the North River basin are mainly the result of intensifying precipitation regime; smaller‐than‐1 flood magnification factors along the mainstream of the West River basin and also in the East River basin are the result of hydrological regulations of water reservoirs. Copyright © 2014 John Wiley & Sons, Ltd.

Potential impact of climate change on flooding in the Upper Great Miami River Watershed, Ohio, USA: a simulation-based approach

This study aims to assess the potential impact of climate change on flood risk for the city of Dayton, which lies at the outlet of the Upper Great Miami River Watershed, Ohio, USA. First the probability mapping method was used to downscale annual precipitation output from 14 global climate models (GCMs). We then built a statistical model based on regression and frequency analysis of random variables to simulate annual mean and peak streamflow from precipitation input. The model performed well in simulating quantile values for annual mean and peak streamflow for the 20th century. The correlation coefficients between simulated and observed quantile values for these variables exceed 0.99. Applying this model with the downscaled precipitation output from 14 GCMs, we project that the future 100-year flood for the study area is most likely to increase by 10–20%, with a mean increase of 13% from all 14 models. 79% of the models project increase in annual peak flow. Citation Wu, S.-Y. (2010) Potential impact of climate change on flooding in the Upper Great Miami River Watershed, Ohio, USA: a simulation-based approach. Hydrol. Sci. J. 55(8), 1251–1263.

Adjustment of Peak Streamflows of a Tropical River for Urbanization

Peak runoff from a catchment is influenced by many factors such as intensity and duration of rainfall, catchment topography, catchment shape, land use and other variables. For a particular catchment, landuse change and other human activities will alter the characteristic of catchment hydrograph. Problem statement: As a result of urbanization, the magnitude of floods occurring in a catchment increased. It was found that the land use change in the Langat River catchment has clear impact on annual peak streamflow record, particularly from 1983-2003 while, the change has no significant impact on streamflow record from 1960-1982. Spatial data confirms the heavy development occurred in river basin from 1983-2003. Thus, urbanization makes the historical record of Langat River non-homogenous and this makes the mathematical simulation for the record inappropriate due to poor expected output. Approach: In this study, historical record of Langat River, Selangor, Malaysia from 1960-2003 was used to study the impact of urbanization on the streamflow. The annual peak streamflow was selected for this purpose. The peak streamflow record was divided into two sets. Set one from 1960-1982 and set two from 1983-2003, which represent periods before and after urbanization, respectively. To adjust the set one data for urbanization, different adjustment factors were used to make the data homogeneous. Normal model was applied to find the best factor for model fitness. Results: The best adjustment factors were selected by trial and error technique based on 95% confidence level. To determine the optimum adjustment factors from the best ones, the point of intersection between the homogeneity and Normal model evaluation curves was located. This point represented the optimum adjustment factor and its value was found to be 1.9. Autorun model was used to validate the above finding and it was found that the model prediction is acceptable with reasonable accuracy. Conclusion/Recommendations: The proposed method can be recommended to be used for predicting the streamflow of Langat River considering the impact of urbanization on the streamflow. The method also, is applicable to adjust a flood record for which flood events had occurred on a watershed undergoing continuous changes in levels of urbanization to meet both homogeneity and best model fitness.

Estimating the Hydrological Influence of Maryland State Dams Using GIS and the HEC-1 Model

This study develops a quantitative relation defining the extent of influence that a dam imposes on annual peak streamflow, and employs the developed relation to retain the use of some USGS gauges in the state of Maryland for regional flood frequency analysis (FFA). Stage-storage–discharge curves for 34 dams in Maryland were provided by the Maryland Department of Environment Division of Dam Safety. Each watershed/dam system was analyzed using HEC-1. The results were used to form two linear equations that calculate the influence distance, or the downstream reach length affected by each dam, for a 5 and 10% level of regulation. The level of regulation is the measured amount, in percent, that the peak flow in a stream is influenced by the presence of the structure. When the influence distance predictor equations were applied throughout the state of Maryland at the 10% regulation level, we found that 32 of the 91 gauges that lie downstream of dams could be retained for use in regional FFA.

Estimation of Channel Bankfull Occurrence from Instantaneous Discharge Data

Bankfull discharge (Qbf) occurrence has predominantly been described with the annual maximum exceedance random variable, pa, however the wide availability of daily peak streamflow (DPS) data allows for the description of occurrence with two alternative random variables. The two alternative random variables are: (1) flow duration, pf, the probability that daily discharge is at, or exceeds, Qbf and (2) partial duration, pb, the probability that an independent daily discharge is at, or exceeds, Qbf. In this research, statistics for pf and pb use DPS data, whereas pa is estimated with four statistics using either DPS or annual peak streamflow (APS) data. Analyses of approximately 15years of DPS and 45years of APS at 46 bankfull surveyed gauges in Maryland, North Carolina, and New York were performed to illustrate differences between the four pa statistics and the three Qbf random variables, pa, pf, and pb. For the pa analysis, non-log Pearson type-III (non-LPT3) statistics generated median recurrence intervals (RI) for Qbf that were 9% longer than LPT3 statistics. Processing the DPS data with the partial duration estimator shows Qbf events arrive 1.5 times per year on average (RI=0.70years) and 8 times per year maximum (RI=0.12years). The flow duration estimator shows Qbf has durations of 2.1daysperyear on average and 13.2daysperyear maximum. Although the DPS record is approximately 30years shorter than the APS record, the DPS data capture the 1.4yearQbf frequency of the longer APS record. Statistics for pa, pf, and pb inform the river manager to the likelihood of three distinct Qbf phenomena: Annual maximum occurrence, daily duration of events, and daily time between events.

STREAM FLOW IN RELATION TO OHIA FOREST DECLINE ON THE ISLAND OF HAWAII1

ABSTRACT: Dieback of the ohia forest over a large part of the Hilo watershed and adjacent areas has resulted in a severe loss of the overstory crown component of the vegetation. The decline could cause serious damage to the watershed. To evaluate possible changes in conditions in the Hilo area since the decline began, stream flow, water quality, and precipitation data from 1929 to 1980 were collected and analyzed. The limited data available do not indicate that the ohia decline has resulted in a significant change in either annual stream flow or peak stream flow of a stream discharging from the ohia forest in the Hilo area. Suspended sediment production of two streams remains well within accepted levels as does the chemical makeup of components dissolved in the streams.