Peak Streamflow Research Articles

Elevated Streamflows Increase Dam Passage by Juvenile Coho Salmon during Winter: Implications of Climate Change in the Pacific Northwest

AbstractA 4‐year evaluation was conducted to determine the proportion of juvenile coho salmon Oncorhynchus kisutch passing Cowlitz Falls Dam, on the Cowlitz River, Washington, during winter. River and reservoir populations of coho salmon parr were monitored using radiotelemetry to determine if streamflow increases resulted in increased downstream movement and dam passage. This was of interest because fish that pass downstream of Cowlitz Falls Dam become landlocked in Riffe Lake and are lost to the anadromous population. Higher proportions of reservoir‐released fish (0.391–0.480) passed Cowlitz Falls Dam than did river‐released fish (0.037–0.119). Event‐time analyses demonstrated that streamflow increases were important predictors of dam passage rates during the study. The estimated effect of increasing streamflows on the risk of dam passage varied annually and ranged from 9% to 75% for every 28.3 m3/s increase in streamflow. These results have current management implications because they demonstrate the significance of dam passage by juvenile coho salmon during winter months when juvenile fish collection facilities are typically not operating. The results also have future management implications because climate change predictions suggest that peak streamflow timing for many watersheds in the Pacific Northwest will shift from late spring and early summer to winter. Increased occurrence of intense winter flood events is also expected. Our results demonstrate that juvenile coho salmon respond readily to streamflow increases and initiate downstream movements during winter months, which could result in increased passage at dams during these periods if climate change predictions are realized in the coming decades.Received February 7, 2012; accepted July 31, 2012

Modelling the impact of subcatchment and regional scale drainage in the Blackwood Basin, Western Australia

This study assesses the impacts of several subcatchment and regional scale artificial drainage on on-site groundwater levels and salinity, and off-site streamflows, salt loads and lake discharge rates using a hydrological model LASCAM. The model is applied to the 21,147km2 Blackwood Basin in southwestern Australia, much of which has been experiencing long-term rises in groundwater levels in response to large-scale clearing of native vegetation over the past 160 years. These rises in groundwater levels have led to substantial increases in stream salinity, waterlogging and land salinisation.The model predicts that under the baseline scenario (that is, without artificial drainage or any other salinity management strategy) most of the subcatchments of the Blackwood Basin are likely to experience rises in both future average groundwater levels and groundwater salinity, but at a slower rate than is currently occurring. Streamflows and stream salinity are also projected to increase over time under the baseline scenario. Artificial drainage is likely to lower both the groundwater levels and groundwater salinities. Mean annual and peak streamflows are expected to be considerably larger under the drainage scenarios than under the baseline scenario. All strategies assessed for the management of artificial drainage water are projected to further degrade the lower Blackwood River from higher salinity levels than are expected under the baseline scenario, with the exception of one strategy where drainage discharge is managed via subcatchment scale evaporation basins.

How does afforestation affect the hydrology of a blanket peatland? A modelling study

AbstractOver the last century, afforestation in Ireland has increased from 1% of the land area to 10%, with most plantations on upland drained blanket peatlands. This land use change is considered to have altered the hydrological response and water balance of upland catchments with implications for water resources. Because of the difficulty of observing these long‐term changes in the field, the aim of this study was to utilize a hydrological model to simulate the rainfall runoff processes of an existing pristine blanket peatland and then to simulate the hydrology of the peatland if it were drained and afforested. The hydrological rainfall runoff model (GEOtop) was calibrated and validated for an existing small (76 ha) pristine blanket peatland in the southwest of Ireland for the 2‐year period, 2007–2008. The current hydrological response of the pristine blanket peatland catchment with regard to streamflow and water table (WT) levels was captured well in the simulations. Two land use change scenarios of afforestation were also examined, (A) a young 10‐year‐old and (B) a semi‐mature 15‐year‐old Sitka Spruce forest. Scenario A produced similar streamflow dynamics to the pristine peatland, whereas total annual streamflow from Scenario B was 20% lower. For Scenarios A and B, on an annual average basis, the WT was drawn down by 16 and 20 cm below that observed in the pristine peatland, respectively. The maximum WT draw down in Scenario B was 61 cm and occurred in the summer months, resulting in a significant decrease in summer streamflow. Occasionally in the winter (following rainfall), the WT for Scenario B was just 2 cm lower than the pristine peatland, which when coupled with the drainage networks associated with afforestation led to higher peak streamflows. Copyright © 2012 John Wiley & Sons, Ltd.

Floods in Central Texas, September 7–14, 2010

Severe flooding occurred near the Austin metropolitan area in central Texas September 7–14, 2010, because of heavy rainfall associated with Tropical Storm Hermine. The U.S. Geological Survey, in cooperation with the Upper Brushy Creek Water Control and Improvement District, determined rainfall amounts and annual exceedance probabilities for rainfall resulting in flooding in Bell, Williamson, and Travis counties in central Texas during September 2010. We documented peak streamflows and the annual exceedance probabilities for peak streamflows recorded at several streamflow-gaging stations in the study area. The 24-hour rainfall total exceeded 12 inches at some locations, with one report of 14.57 inches at Lake Georgetown. Rainfall probabilities were estimated using previously published depth-duration frequency maps for Texas. At 4 sites in Williamson County, the 24-hour rainfall had an annual exceedance probability of 0.002. Streamflow measurement data and flood-peak data from U.S. Geological Survey surface-water monitoring stations (streamflow and reservoir gaging stations) are presented, along with a comparison of September 2010 flood peaks to previous known maximums in the periods of record. Annual exceedance probabilities for peak streamflow were computed for 20 streamflow-gaging stations based on an analysis of streamflow-gaging station records. The annual exceedance probability was 0.03 for the September 2010 peak streamflow at the Geological Survey’s streamflow-gaging stations 08104700 North Fork San Gabriel River near Georgetown, Texas, and 08154700 Bull Creek at Loop 360 near Austin, Texas. The annual exceedance probability was 0.02 for the peak streamflow for Geological Survey´s streamflow-gaging station 08104500 Little River near Little River, Texas. The lack of similarity in the annual exceedance probabilities computed for precipitation and streamflow might be attributed to the small areal extent of the heaviest rainfall over these and the other gaged watersheds. Citation: Winters KE. 2012. Floods in Central Texas, September 7–14, 2010. Texas Water Journal. 3(1):14-25. Available from: https://doi.org/10.21423/twj.v3i1.3292.

Sensitivity of snowmelt hydrology in Marmot Creek, Alberta, to forest cover disturbance

AbstractA model including slope effects on snow redistribution, interception and energetics was developed using the Cold Regions Hydrological Model platform, parameterized with minimal calibration and manipulated to simulate the impacts of forest disturbance on mountain hydrology. A total of 40 forest disturbance scenarios were compared with the current land cover for four simulation years. Disturbance scenarios ranged from the impact of pine beetle kill of lodgepole pine to clear‐cutting of north‐ or south‐facing slopes, forest fire and salvage logging. Pine beetle impacts were small in all cases with increases in snowmelt volume of less than 10% and streamflow volume of less than 2%. This small impact is attributed to the low and relatively dry elevations of lodgepole pine forests in the basin. Forest disturbances due to fire and clear‐cutting affected much larger areas and higher elevations of the basin and were generally more than twice as effective as pine beetle in increasing snowmelt or streamflow. For complete forest cover removal by burning and salvage logging, a 45% increase in snowmelt volume was simulated; however, this only translated into a 5% increase in spring and summer streamflow volume. Forest burning with the retention of standing burned trunks was the most effective forest cover treatment for increasing streamflow (up to 8%) because of its minimizing of winter snow sublimation losses from interception and blowing snow. However, increases in streamflow volumes were almost entirely due to reductions in intercepted snow sublimation with decreasing canopy coverage. Peak daily streamflow discharges responded more strongly to forest cover disturbance than did seasonal streamflow volumes, with increases of almost 25% in peak streamflow from the removal of forest canopy by fire and the retention of standing burned trunks. Peak flow was most effectively increased by forest removal on south‐facing slopes and level sites. Copyright © 2012 John Wiley & Sons, Ltd.

Section 404 Permitting in Coastal Texas: A Longitudinal Analysis of the Relationship Between Peak Streamflow and Wetland Alteration

As early as the passage of the 1972 Federal Water Pollution Control Act the U.S. government has sought to protect the nation's water resources through regulatory tools. While there has been a large amount of research on wetlands and wetland mitigation, very little is known about the impact of Section 404 permitting on water quantity. This research examines the impact of Section 404 permit types on peak annual streamflow in Coastal Texas from 1996 to 2003. Results of cross-sectional time-series regression analyses indicate that all four permit types have positive and significant effects on peak streamflow. These effects also vary by permit type, with Individual permits having the highest per-permit impact on peak annual flow.

Spatial variation in transient water table responses: differences between an upper and lower hillslope zone

AbstractTo better understand storage‐runoff dynamics, transient groundwater responses were examined in one of the steep watersheds in British Columbia's coastal mountains. Streamflow and piezometric data were collected for 1 year to determine the spatial and temporal relations between transient groundwater levels and discharge. Correlations between piezometer responses and lag‐time analysis were used to identify and better understand runoff generation mechanisms in this watershed. Results showed a large spatial and temporal variation in transient water table dynamics and indicated that two distinct zones existed: a lower hillslope zone and an upslope zone. Each zone was characterized by very different water table responses. The upper hillslope was disconnected from the stream for the majority of time, suggesting that during most events, it does not directly contribute to streamflow. Piezometers in the lower hillslope zone showed hydrologically limited responses, suggesting rapid subsurface flow, likely through the many macropores and soil pipes. The lag time between peak streamflow and peak groundwater level decreased with increasing antecedent moisture conditions and was more variable for piezometers further away from the stream than for piezometers close to the stream. The study results indicate that a single storage‐runoff model is not appropriate for this steep watershed and that a two‐ or three‐compartment model would be more suitable. Copyright © 2011 John Wiley & Sons, Ltd.

Stationarity of Streamflow Records and Their Influence on Bankfull Regional Curves1

Haucke, Jessica and Katherine A. Clancy, 2011. Stationarity of Streamflow Records and Their Influence on Bankfull Regional Curves. Journal of the American Water Resources Association (JAWRA) 47(6):1338–1347. DOI: 10.1111/j.1752-1688.2011.00590.x Abstract: Bankfull regional curves, which are curves that establish relationships among channel morphology, discharge, drainage area, are used extensively for stream restoration. These curves are developed upon the assumption that streamflows maintain stationarity over the entire record. We examined this assumption in the Driftless Area of southwestern Wisconsin where agricultural soil retention practices have changed, and precipitation has increased since the 1970s. We developed a bankfull regional curve for this area using field surveys of bankfull channel performed during 2008-2009 and annual series of peak streamflows for 10 rivers with streamflow records ranging from the 1930s to 2009. We found bankfull flows to correlate to a 1.1 return period. To evaluate gage data statistics, we used the sign test to compare our channel morphology to historic 1.5 return period discharge (Q1.5) for five time periods: 1959-1972, 1973-1992, 1993-2008, 1999-2008, and the 1959-2008 period of record. Analysis of the historic gage data indicated that there has been a more than 30% decline in Q1.5 since 1959. Our research suggests that land conservation practices may have a larger impact on gaging station stationarity than annual precipitation changes do. Additionally, historic peak flow data from gages, which have records that span land conservation changes, may need to be truncated to represent current flow regimes.

Impacts of Land-Use Change on Streamflows in the Damansara Watershed, Malaysia

Land-use change has significant impacts on hydrologic processes at the watershed level. In this study, hydrologic models and spatial data were used to assess the effects of land-use changes and predict the effects of two future land-use scenarios on the flood regime of the Damansara Watershed. Due to urban growth, the Damansara Watershed has seen increasing streamflows and experienced occasional flooding. The hydrology was modeled using the Hydrologic Engineering Center-Hydrologic Modeling System (HEC-HMS) model, and land-use changes were quantified with land-use maps. Actual storms were used to calibrate and validate HEC-HMS rainfall-runoff model. The calibrated HEC-HMS model was used to simulate future streamflows and to forecast the impact of land-use changes on downstream peak streamflow. The model also estimated the contribution of individual sub-basins to downstream peak streamflows of the entire watershed. The model predicts that changes in land-use will increase the peak streamflow, and the increase is directly proportional to the rate of urbanization. It was found that the sensitivity of the hydrologic response to land-use change increases as the recurrence interval of rainfall events decreases, and that those impacts are more pronounced in different sub-basins. The results of this study provide support for land-use planning and the management of watersheds.

Seasonal versus transient snow and the elevation dependence of climate sensitivity in maritime mountainous regions

[1] In maritime mountainous regions, the phase of winter precipitation is elevation dependent, and in watersheds receiving both rain and snow, hydrologic impacts of climate change are less straightforward than in snowmelt-dominated systems. Here, 29 Pacific Northwest watersheds illustrate how distribution of seasonal snow, transient snow, and winter rain mediates sensitivity to 20th century warming. Watersheds with >50% of their area in the seasonal snow zone had significant (α ≤ 0.1) trends towards greater winter and lower summer discharge, while lower elevations had no consistent trends. In seasonal snow-dominated watersheds, runoff occurs 22–27 days earlier and minimum flows are 5–9% lower than in 1962, based on Sen's slope over the period. Trends in peak streamflow depend on whether watershed area susceptible to rain-on-snow events is increasing or decreasing. Delineation of elevation-dependent snow zones identifies climate sensitivity of maritime mountainous watersheds and enables planning for water and ecosystem impacts of climate change.

Statistical relations of precipitation and stream runoff for El Niño and La Niña periods, Texas Hill Country

The Texas Hill Country is threatened by devastating long-duration droughts and short-duration floods, either of which can occur at any time. In Central Texas, El Niño and La Niña conditions each occur about one-quarter of the time. Long-term precipitation data for the area reveal that greater rainfall generally occurs during La Niña periods for summer months but greater rainfall typically occurs during El Niño periods for other months. Annual streamflow peaks cannot be attributed to El Niño or La Niña conditions, but typically occur during the hurricane season (June through November), especially for the largest peaks. Additionally, El Niño period runoff volumes exceed those during La Niña at all runoff-gaged streams in the area. For the streams in the northern part of the Hill Country, El Niño period runoff only slightly exceeds La Niña period runoff. However, for the streams in the southern part of the area, El Niño period runoff greatly exceeds La Niña period runoff. Citation: RM Slade, TE Chow. 2011. Statistical relations of precipitation and stream runoff for El Niño and La Niña periods, Texas Hill Country. Texas Water Journal. 2(1):1-22. Available from: https://doi.org/10.21423/twj.v2i1.3665.

Streamflow response to headwater reforestation in the Ganaraska River basin, southern Ontario, Canada

AbstractIncreased attention is being paid to the role of reforestation in strategies for sustainable forest management, landscape restoration and carbon sequestration. Reforestation of drainage basins is generally assumed to reduce annual streamflow as well as peak and low flows. However, most studies of reforestation effects on streamflow have been conducted on small experimental basins, and the applicability of their results to larger basins is unclear. This study revisits an earlier examination of streamflow response to headwater reforestation in a 267 km2 basin (Ganaraska River) in southern Ontario, Canada for 1945–2007. Forest cover in the basin headwaters increased from 13 km2 in 1945 to 31 km2 by 1990, with most of this change between 1950 and 1965. Streamflow metrics from the reforested basin and two headwater sub‐basins were compared to those from a nearby basin and sub‐basin of similar size and physiography to the Ganaraska basins but without extensive headwater reforestation. No temporal trends were found for inter‐basin differences in annual runoff or runoff ratios for the entire Ganaraska basin or its largest sub‐basin; however, reforestation appears to have reduced several metrics of peak streamflow at the basin and sub‐basin scale. Relationships between high flows classified according to generating event type and the associated precipitation depth suggest that expansion of forest cover in the Ganaraska River basin (GRB) and associated changes in microclimatic conditions have reduced the potential for frozen soil to generate surface runoff and high flows in response to rain‐on‐snow during spring snowmelt. This was accompanied by increased low flows from the GRB and its sub‐basins from 1960 to 2007 relative to the control basin, suggesting that the expanded forest cover has enhanced groundwater recharge by prolonging spring snowmelt and promoting infiltration of rainfall and snowmelt inputs relative to non‐forested areas. Some discrepancies between these results and those of other studies of streamflow response to reforestation may be attributed to the relatively large size of the GRB and the limited extent of reforestation. Nevertheless, the results highlight the importance of considering how reforestation may affect key hydrologic processes in a given landscape when predicting the resulting streamflow response. Copyright © 2011 John Wiley & Sons, Ltd.

Simulating the hydrological impacts of climate change in the upper North Saskatchewan River basin, Alberta, Canada

Summary The ACRU agro-hydrological modeling system provided the framework, containing code to simulate all major hydrological processes, including actual evapotranspiration estimates, to simulate the impacts of climate change in the Cline River watershed, Alberta, Canada, under historical (1961–1990) and a range of future climate conditions (2010–2039, 2040–2069, and 2070–2099). Whilst uncertainties in the estimation of many hydrological variables were inevitable, verification analyses carried out for the historical baseline period resulted in good to very good simulations of a range of hydrological processes, including daily air temperature, snow water equivalent and streamflow. Five climate change scenarios were selected to cover the range of possible future climate conditions. In order to generate future climate time series, the 30-year baseline time series was perturbed according to predicted changes in air temperature and precipitation. Projected increases in air temperature and precipitation resulted in mean annual increases in potential and actual evapotranspiration, groundwater recharge, soil moisture, and streamflow in the Cline River watershed. Increases in both high and low flow magnitudes and frequencies, and large increases to winter and spring streamflow are predicted for all climate scenarios. Spring runoff and peak streamflow were simulated to occur up to 4 weeks earlier than in the 1961–1990 baseline period. Predicted changes were simulated to progressively increase into the future. A clear shift in the future hydrological regime is predicted, with significantly higher streamflow between October and June, and lower streamflow in July–September.

모자이크기법을 이용한 지표유출모형의 조도계수 리샘플링

Physically-based resampling scheme for roughness coefficient of surface runoff considering the spatial landuse distribution was suggested for the purpose of effective operational application of recent grid-based distributed rainfall runoff model. Generally grid scale(mother scale) of hydrologic modeling can be greater than the scale (child scale) of original GIS thematic digital map when the objective basin is wide or topographically simple, so the modeler uses large grid scale. The resampled roughness coefficient was estimated and compared using 3 different schemes of Predominant, Composite and Mosaic approaches and total runoff volume and peak streamflow were computed through distributed rainfall-runoff model. For quantitative assessment of biases between computational simulation and observation, runoff responses for the roughness estimated using the 3 different schemes were evaluated using MAPE(Mean Areal Percentage Error), RMSE(Root-Mean Squared Error), and COE(Coefficient of Efficiency). As a result, in the case of 500m scale Mosaic resampling for the natural and urban basin, the distribution of surface runoff roughness coefficient shows biggest difference from that of original scale but surface runoff simulation shows smallest, especially in peakflow rather than total runoff volume.

The role of sediment supply in channel instability and stream restoration

This paper examines the interaction between sediment supply and channel instability and implications of system-wide instability for stream restoration. Using examples from southwest Ohio, we show that recent channel instability is largely a consequence of reduced sediment supply over several past decades. The widths of the studied channels narrowed by a factor of three to four between the 1930s and 2000s, and channel beds have incised into glacial sediments. Lateral migration of these channels decreased after 1960, signaling the onset of channel incision. Soil loss rates in 2005 were 4 to 20 times lower than in the 1920s, mainly as a result of the shift from conventional to conservation tillage. The construction of impoundments has further reduced sediment delivery downstream, and climate change may exacerbate this imbalance by increasing sediment transport capacity, including peak flows. Thus the decrease in sediment supply occurred during a time when peak stream flows have been increasing, resulting in an imbalance between sediment supply and sediment transporting power in the stream systems. Because sediment supply and transport are governed by watershed-scale conditions, channel instability will persist in this region for some time to come. Reach-scale restoration will neither improve water quality nor prevent continued system-wide channel instability. We advocate an approach that uses setbacks/buffers that allow streams to develop new, dynamic floodplains with which to reestablish connections while selectively protecting significant sites with stabilization measures.

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.

Improvement of springtime streamflow simulations in a boreal environment by incorporating snow-covered area derived from remote sensing data

Summary Snow estimation is the major source of errors for spring streamflow simulations in Quebec, Canada. The objective of the study is to improve melting discharge estimation computed with the operational MOHYSE hydrological model by integrating remote sensing snow-cover area in its snow module (SPH-AV). The satellite-derived snow-cover area (SCA) (MODIS & IMS) is first compared with in situ snow depth data measurements and simulated snow-cover area. Results show that the remote sensing products underestimate the snow-cover area on the mainly forested study region. A direct-insertion method of daily satellite SCA images is developed based on an empirical snow water equivalent threshold compensating, on a pixel-by-pixel basis, for the small amount of snow that satellite sensors can not identify during the melting period. This approach improves the streamflow simulation for spring periods (25th March to 25th of May) over 4 years (2004–2007) with a Nash–Sutcliffe coefficient enhancement of 0.11 and a root mean square error (RMSE) improvement of 21% on the Du Nord watershed, for which the threshold was optimized. The threshold found on the Du Nord basin was then directly applied on another watershed ( Aux Ecorces basin) for validation. The simulated streamflow is significantly improved as compared to the observed streamflow for these 4 years (mean Nash increase from 0.72 to 0.85 and RMSE decrease by 22%). The method improves streamflow peaks identification as much as 36% on the Du Nord watershed and 19% on the Aux Ecorces watershed.

The Hydrological Effects of Lateral Preferential Flow Paths in a Glaciated Watershed in the Northeastern USA

Despite observational evidence of lateral preferential flow paths in northeastern U.S. watersheds, their effects on the sources of runoff remain unclear. An intense field survey was undertaken during the 2007 growing season to determine the sources of stream runoff from a 2.51 km2 watershed in the Catskill Mountains, New York State. Lateral preferential flow paths are caused by groundwater springs and soil piping in this region. A two‐component hydrograph separation using δ18O showed that event water (rain water) was a significant source of runoff during nine rainfall events (from July to October). With these rainfall events, 14 to 37% of the volume and 18 to 49% of the peak streamflow was attributable to event water. Further, end‐member mixing analysis (EMMA), using δ18O, Si, and dissolved organic carbon (DOC), showed that saturated areas accounted for 2 to 24% of the total volume and 4 to 59% of peak streamflow but that groundwater was the dominant source of runoff volume during all events. Field surveys of saturated areas also suggested that near‐stream areas were insufficient to generate the observed stream chemistry during rainfall events larger than 8 mm. A connection with the hillside saturated areas was therefore required to explain the results of the hydrograph separations, which were corroborated by the timing of the transient (perched) groundwater and overland flow. The hydrometric measurements confirmed that hillside lateral preferential flow paths rapidly transported water to near‐stream saturation areas during runoff events under relatively dry antecedent conditions. A qualitative comparison with conventional techniques for distributing variable saturation areas (VSA) using surface topography and soil transmissivity (i.e., topographic index and soil topographic index), which do not consider the effects of lateral preferential flow paths, demonstrated that typical parameterizations (on the order of <10−1 m) would not have the spatial resolution to represent the measured lateral preferential flow paths (on the order of <10−3 m). Overall, the results suggest that the lateral redistribution of water from hillside areas reduces the influence of surface topography and channel topology on the sources of stream runoff, a finding that is consistent with recent ones from other landscapes where glacial soils have coevolved with the terrestrial hydrology.

The relationship between morphoclimatic characteristics and peak flows: A case study of the southern Alborz Basins, Iran

Ideally, flood estimation in hydrological studies and applications requires recorded data, but this is missing or insufficient in many cases for a variety of reasons. Approaches to modelling the hydrologic response of ungauged basins may use physical characteristics of watersheds either to directly infer values for the parameters of hydrologic models or to establish regression relationships between watershed structure and model parameters. Most studies, however, are concentrated in humid hydroclimatic zones. In this study, a regional frequency analysis of annual peak maximum series of flood flows from rivers of the arid southern Alborz basins, Iran, was conducted, including identification of suitable regional flood frequency distributions. The peak stream flow for different data periods was estimated based on physiographic as well as climatic parameters. Because of the close relationship between elevation, stream flow regime and hydrological features, the development of a water response model first involved delimiting homogenous hydrological regions by using two-step cluster analysis. Equations were established for each region relating peak flow of different return periods and the basin parameters. The study results also revealed that the regional regression models developed in this study could be applied reasonably well at relatively similar ungauged sites, which is of potential interest in other water-stressed areas of the world, particularly given expected scenarios of population growth, development and climatic change.

Is the forest conversion to pasture affecting the hydrological response of Amazonian catchments? Signals in the Ji‐Paraná Basin

AbstractIt is well known that land use and land‐cover changes (LUCC), particularly deforestation, have the potential to modify the hydrological response. Although those signals are relatively well documented in worldwide microcatchment studies, conflicting results reported in literature indicate that those signals can be sometimes difficult to detect and isolate in basins at larger scales.In order to detect signals in the hydrological response potentially, related to LUCC, streamflow records from Ji‐Paraná Basin located in SW Amazonia are analysed in conjunction with deforestation maps derived from remote sensors. The basin has a drainage area greater than 30 000 km2 and has been through severe LUCC in the last decades.Statistical descriptors of daily streamflow series were correlated with landscape indices using non‐parametric methodologies. To take into account scale effects, statistical analyses were repeated in different sub‐basins.Results showed that the impact of LUCC on the hydrological response is time lagged at larger scales. The flow paths are clearly affected, depending on basin characteristics such as topography. In general, LUCC impacts lead to higher peak streamflows, the reduction of minimal values and the increment of stormflow. In agreement with previous studies, the detection of signals associated with LUCC was clearly detected at the smallest basin, but proved to be difficult at larger scales, suggesting the existence of non‐linear effects, which aggregate across scale compensating small scale effects. Such behaviour indicates a challenge for mathematical models, which are usually developed to represent immediate hydrological response to basin wide LUCC. Copyright © 2010 John Wiley & Sons, Ltd.