Baseflow Component Research Articles

Validation of a Locally Revised Topographic Index in Central New Jersey, USA

Saturation excess is a major runoff process in humid regions such as the US Northeast. Topographic index (TI) is used to simulate the pattern of runoff-contributing areas following a saturation excess runoff process. Although TI is useful to delineate saturated areas, i.e., hydrologically sensitive areas, for taking spatially distinctive actions in watersheds for improving water quality, local resource management practitioners often question its applicability to local conditions. This study introduces two methods to validate a locally revised TI in humid central New Jersey, USA. The revised TI uses soil moisture deficit instead of water table depth as the state variable in simulating the saturation excess runoff process. First, the calculated TI values were compared to the soil moisture measurements sampled in two sites in Tewksbury Township in the region to evaluate their correlations. Second, a watershed model Variable Source Load Function (VSLF) that incorporates TI was applied to the Neshanic River Watershed in the region and compared to another watershed model Soil and Water Assessment Tool (SWAT) to evaluate its capability in predicting the streamflow and its runoff and baseflow components. The positive correlations between soil moisture measurements and TI suggested TI is a good indicator of runoff-generating potential. VSLF achieves a modeling efficiency comparable to SWAT in simulating watershed hydrology. Such validation gives practitioners confidence to incorporate TI pattern into watershed management practices for improving their efficiency. The results are applicable to shallow, interflow-driven watersheds in humid regions.

Investigating relationships between rainfall and karst-spring discharge by higher-order partial correlation functions

Time series of rainfall and karst-spring discharge are influenced by various space–time-variant processes involved in the transfer of water in hydrological cycle. The effects of these processes can be exhibited in auto-correlation and cross-correlation functions. Consequently, ambiguities with respect to the effects encoded in the correlation functions exist. To solve this problem, a new statistical method for investigating relationships between rainfall and karst-spring discharge is proposed. The method is based on the determination and analysis of higher-order partial correlation functions and their spectral representations. The study area is the catchment of the Jadro Spring in Croatia. The analyzed daily time series are the air temperature, relative humidity, spring discharge, and rainfall at seven rain-gauges over a period of 19 years, from 1995 to 2013. The application results show that the effects of spatial and temporal variations of hydrological time series and the space–time-variant behaviours of the karst system can be separated from the correlation functions. Specifically, the effect of evapotranspiration can be separated to obtain the forms of correlation functions that represent the hydrogeological characteristics of the karst system. Using the proposed method, it is also possible to separate the effects of the process of groundwater recharge that occurs in neighbouring parts of a catchment to identify the specific contribution of each part of the catchment to the karst-spring discharge. The main quantitative results obtained for the Jadro Spring show that the quick-flow duration is 14 days, the intermediate-flow duration is 80 days, and the pure base flow starts after 80 days. The base flow consists of an inter-catchment groundwater flow. The system memory of the spring is 80 days. The presented results indicate the far-reaching applicability of the proposed method in the analyses of relationships between rainfall and karst-spring discharge; e.g., the method can be used for (1) the identification of effects of various time series on the quick-flow, intermediate-flow and base-flow components of the discharge, (2) the detection of the seasonal effect of inter-catchment groundwater flows in the discharge, and (3) the estimation of the karst system memory. Generally, the presented approach can be applied to the qualitative analyses of the relationships between two time series whenever appropriate control time series are available.

Neural network river forecasting through baseflow separation and binary-coded swarm optimization

Summary The inclusion of expert knowledge in data-driven streamflow modeling is expected to yield more accurate estimates of river quantities. Modular models (MMs) designed to work on different parts of the hydrograph are preferred ways to implement such approach. Previous studies have suggested that better predictions of total streamflow could be obtained via modular Artificial Neural Networks (ANNs) trained to perform an implicit baseflow separation. These MMs fit separately the baseflow and excess flow components as produced by a digital filter, and reconstruct the total flow by adding these two signals at the output. The optimization of the filter parameters and ANN architectures is carried out through global search techniques. Despite the favorable premises, the real effectiveness of such MMs has been tested only on a few case studies, and the quality of the baseflow separation they perform has never been thoroughly assessed. In this work, we compare the performance of MM against global models (GMs) for nine different gaging stations in the northern United States. Binary-coded swarm optimization is employed for the identification of filter parameters and model structure, while Extreme Learning Machines, instead of ANN, are used to drastically reduce the large computational times required to perform the experiments. The results show that there is no evidence that MM outperform global GM for predicting the total flow. In addition, the baseflow produced by the MM largely underestimates the actual baseflow component expected for most of the considered gages. This occurs because the values of the filter parameters maximizing overall accuracy do not reflect the geological characteristics of the river basins. The results indeed show that setting the filter parameters according to expert knowledge results in accurate baseflow separation but lower accuracy of total flow predictions, suggesting that these two objectives are intrinsically conflicting rather than compatible.

A comparison between karst development in two main zones of Iran: case study—Keyno anticline (Zagros Range) and Shotori anticline (Central Iran)

This study focuses on the karstic groundwater of two main zones of Iran: Keyno anticline (Zagros Range) and Shotori Mountains (Central Iran). Mean annual precipitation of these areas is 1100 and 150 mm, respectively. The major carbonate rocks of Shotori Mountains consist of the Permian Jamal formation limestones, the middle Triassic Shotori formation dolomites, and middle to upper Jurassic Esfandiar formation grey limestones. Results of isotope analysis demonstrated that samples do not show serious evaporation effect and rain directly infiltrates into aquifers. By analyzing the hydrographs of karst springs, it is revealed that the contribution of quick flow is less than 33 % in all of them. Relatively stable discharge and electrical conductivity, low recession coefficients, and high base flow component imply a diffuse system in related aquifers. According to these studies, it seems that there is no developed karst system in Shotori Mountains, and some large voids observed in well logs can be attributed to the paleoclimate. Because of the complexity in structure and very low precipitation, the Shotori Mountains have many differences compared to other karstic area of Iran, such as the Zagros belt. Geomorphology studies show obvious differences between karstic features in this area and typical karstic area. There are not any advanced morphological karst features such as poljes and sinkholes and other typical features (rill karren, runnel karren, etc.) replace with vespiary features, microspitz karren, and similar features. Purity of limestone in Shotori Mountains is the same as Zagros, and then the main reason for morphological differences can be attributed to the lower precipitation in Shotori area. On the other hand, the main controlling factor in valley generation in this area is tectonic (faults and rejuvenation); therefore, there are no real karstic valleys.

A reevaluation of the snowmelt and glacial melt in river flows within Upper Indus Basin and its significance in a changing climate

Summary The hydrograph separation method, previously proposed to quantify base flow, seasonal snowmelt, and glacial melt components in river flows within Upper Indus basin underestimates glacial melt component. This is particularly limiting for highly glacierized watersheds. The limitation has been corrected by a further refinement of the method. The results with the refined procedure are highly consistent with the physical characteristics such as hypsometry and glacier extents of the watershed even though the method itself is completely independent of the physical characteristics of the watershed where it is applied. Glacial melt far outweigh snowmelt in the rivers draining the Karakoram and Zanskar ranges. In the Karakoram, on an annualized basis, glacial melt proportion varies from 43% to 50% whereas snowmelt varies from 27% to 31%. On the other hand, snowmelt dominates over glacial melt in the rivers draining the western Greater Himalayas and the Hindu Kush. Here snowmelt percentage in river discharge varies from 31% to 53% whereas that of glacial melt ranges from 16% to 30%. In the main stem of Upper Indus River, snowmelt fraction in most cases is slightly greater than the glacial melt fraction. In the main stem, snowmelt percentage ranges from 35% to 44% whereas glacial melt percentage ranges from 25% to 36%. Upper Indus River just upstream of Tarbela Reservoir carries annual flows constituted of 70% melt water of which 26% is contributed by glacial melts and 44% by snowmelts. We also show that during the later part of twentieth century and continuing into the early part of twenty first century glacial melt contributions to river discharge has decreased compared to the previous decades. This phenomenon can be ascribed to either basin wide loss of glacial mass in the recent decades in the elevation range from where most of the glacial melt originates or glacier growth and stability due to either reduction in energy inputs or increase in precipitation or both at the high altitude bands wherefrom glacial melt water originates.

A new approach for continuous estimation of baseflow using discrete water quality data: Method description and comparison with baseflow estimates from two existing approaches

Understanding how watershed characteristics and climate influence the baseflow component of stream discharge is a topic of interest to both the scientific and water management communities. Therefore, the development of baseflow estimation methods is a topic of active research. Previous studies have demonstrated that graphical hydrograph separation (GHS) and conductivity mass balance (CMB) methods can be applied to stream discharge data to estimate daily baseflow. While CMB is generally considered to be a more objective approach than GHS, its application across broad spatial scales is limited by a lack of high frequency specific conductance (SC) data. We propose a new method that uses discrete SC data, which are widely available, to estimate baseflow at a daily time step using the CMB method. The proposed approach involves the development of regression models that relate discrete SC concentrations to stream discharge and time. Regression-derived CMB baseflow estimates were more similar to baseflow estimates obtained using a CMB approach with measured high frequency SC data than were the GHS baseflow estimates at twelve snowmelt dominated streams and rivers. There was a near perfect fit between the regression-derived and measured CMB baseflow estimates at sites where the regression models were able to accurately predict daily SC concentrations. We propose that the regression-derived approach could be applied to estimate baseflow at large numbers of sites, thereby enabling future investigations of watershed and climatic characteristics that influence the baseflow component of stream discharge across large spatial scales.

Dual Forcing and State Correction via Soil Moisture Assimilation for Improved Rainfall–Runoff Modeling

AbstractUncertainties in precipitation forcing and prestorm soil moisture states represent important sources of error in streamflow predictions obtained from a hydrologic model. An earlier synthetic twin experiment has demonstrated that error in both antecedent soil moisture states and rainfall forcing can be filtered by assimilating remotely sensed surface soil moisture retrievals. This opens up the possibility of applying satellite soil moisture estimates to address both key sources of error in hydrologic model predictions. Here, in an attempt to extend the synthetic analysis into a real-data environment, two satellite-based surface soil moisture products—based on both passive and active microwave remote sensing—are assimilated using the same dual forcing/state correction approach. A bias correction scheme is implemented to remove bias in background forecasts caused by synthetic perturbations in the ensemble filtering routines, and a triple collocation–based technique is adopted to derive rescaled observations and observation error variances. Results are largely in agreement with the earlier synthetic analysis. That is, the correction of satellite-derived rainfall forcing is able to improve streamflow prediction, especially during relatively high-flow periods. In contrast, prestorm soil moisture state correction is more efficient in improving the base flow component of streamflow. When rainfall and soil moisture state corrections are combined, the RMSE of both the high- and low-flow components of streamflow can be reduced by ~40% and ~30%, respectively. However, an unresolved issue is that soil moisture data assimilation also leads to underprediction of very intense precipitation/high-flow events.

Hydrologically Based Environmental Flow Methods Applied to Rivers in the Maritime Provinces (Canada)

AbstractThe demand for water withdrawal continues to increase worldwide. These water withdrawals from rivers can affect fish habitat and aquatic life. As such, environmental flow assessment methods are used in order to protect rivers against excessive water withdrawals. The concept of environmental flow relates to the quantity of water required in rivers to sustain an acceptable level of living conditions for aquatic biota at various phases of their development. For many agencies, environmental flow methods are essential in environmental impact assessments and in the protection of important fisheries resources. The present study deals with the evaluation of hydrologically based environmental flow methods within the Maritime Province of Canada. In total, six hydrologically based environmental flow methods were compared using data from 52 hydrometric stations across the region. Some methods provided adequate environmental flow protection (e.g. 25% mean annual flow and Q50 flow duration method); however, other methods did not provide adequate flow protection (e.g. Q90 flow duration method and 7Q10 and 7Q2 low‐flow frequency). The 70% Q50 method provided adequate flow protection only under good baseflow conditions and should be applied with extreme caution. The present study shows the importance of the hydrologic flow regime, particularly as it pertains to the baseflow component, as a significant determinant in the level of instream flow protection. © 2014 Her Majesty the Queen in Right of Canada. River Research and Applications © 2014 John Wiley & Sons, Ltd.

Analyzing streamflow changes: irrigation-enhanced interaction between aquifer and streamflow in the Republican River basin

Abstract. Groundwater-fed irrigation has altered surface and groundwater interactions in the Republic River basin (RRB) in the midwestern United States, where agriculture heavily depends on irrigation. The decreasing flow trend recorded at the RRB gauging station since the 1950s reflects the synthetical effect of dynamic interactions between surface water and groundwater systems, which has been enhanced by groundwater pumping and irrigation return flow. This study uses a systematic modeling approach to analyze the conjunctive effects of pumping and return flow on streamflow. A watershed management model, the Soil and Water Assessment Tool (SWAT), is modified and established for the Frenchman Creek basin (FCB), a subbasin of RRB, to examine the causes of streamflow changes. The baseflow component in SWAT is linked to aquifer storage so that the model can simulate the combined effects of groundwater pumping and irrigation return flow on natural streamflow. Results show that irrigation has not only depleted streamflow but also changed the flow pattern and seasonal variability. The changes can be decomposed into decrease in the slow component (baseflow) and increase in the fast components (surface and subsurface flow). Since the fast components are subject to higher variability than the slow component, the annual streamflow variability is amplified. Agricultural water use in this region also has changed the groundwater storage seasonal regime from the pattern of "summer recharge and winter discharge" in the past to "summer discharge and winter recharge" at present. This challenges the existing groundwater modeling, which usually assumes fixed recharge pattern and rates.

Significance of scale and lower boundary condition in the 3D simulation of hydrological processes and soil moisture variability in a forested headwater catchment

• 3D-simulation of hydrology and soil moisture at two spatial and temporal resolutions. • Topsoil soil moisture dynamics and patterns well captured by all model versions. • Influence of bedrock aquifer on hydrological processes and soil moisture dynamics. • Role of bedrock for water balance is larger than that of spatio-temporal resolution. The measurement and simulation of soil moisture patterns and their spatio-temporal variability are current challenges in hydrology. This study investigated the capability of the three-dimensional model HydroGeoSphere to simulate hydrological processes, soil moisture dynamics and patterns at 25 and 100 m resolutions with daily and hourly time steps in a forested headwater catchment. All simulations reproduced discharge dynamics well, calculated a dominance of the baseflow component but missed macropore driven discharge peaks in the summer and slightly overestimated the discharge. A comparison of discharge and water balance results between daily and hourly time steps revealed considerable scaling issues of saturated conductivity values and in the model’s interception module. Temporally and spatially highly resolved soil moisture measurements were used to calibrate residual saturations and porosities at daily time steps. Therefore, all model setups simulated the long-term temporal soil moisture dynamics well, but short-term soil moisture dynamics were poorly simulated because the simulation did not take into account the effect of macropore flow. The spatial soil moisture patterns of the topsoil were well reproduced except for certain parts in the western part of the catchment. A correlation analysis revealed that the influence of the topography was overestimated in the simulated soil moisture pattern. The spatial scale dependency of all aforementioned results was small due to independent calibration. The consideration of bedrock damped discharge peaks, increased low flow and slightly improved temporal soil moisture simulation.

Increasing river flood preparedness by real-time warning based on wetness state conditions

Summary High wetness state levels can be considered as a primary indicator for potential river flooding. Therefore it is advisable to visualise real-time soil moisture information in flood forecasting or warning systems. Monitoring of soil moisture, however, is not an easy task due to its variable nature in time, space and depth. This paper presents and compares methods to assess the severity of the soil moisture state of hydrological catchments considered in a typical operational flood forecasting system. The severity of the relative soil moisture state is obtained and mapped by comparing the actual simulation result with the historical simulation results of a lumped conceptual hydrological model, directly by making use of the soil moisture component of the model or indirectly considering the baseflow component. Another approach uses rainfall, evapotranspiration and river flow observations. By applying a baseflow filter to the river flow observations and an advanced method for empirical catchment water balance computation, two indirect soil moisture indicators were defined, namely the filtered baseflow and the water balance based relative soil moisture content. It is shown that each of the methods allows to obtain useful estimates of the soil moisture state of a catchment in real time. The severity level of the soil moisture state is computed after comparison with long term statistics derived from a long term simulation. The severity level moreover is used to calculate the probability of exceedance of a predefined riverflow threshold, e.g. flood threshold, at the outlet or a given location in the catchment. This is done by means of a logit relation of the river flow probability of exceedance with the soil moisture indicator. The different soil moisture indicators are compared in their predicting capabilities by calculating and comparing the Brier score. Interestingly, the application of the logit relation or the use of a simple water balance computation for the catchment, based on real-time rainfall, evapotranspiration and river flow observations, leads to more reliable probability of exceedance estimates than the common direct use of total runoff results from a state-of-the art rainfall–runoff model. Mapping the probability of exceedance for the different hydrological catchments together with the width of the confidence interval on this probability is proposed as a useful tool to increase the preparedness for potential floods.

Modifying WEPP to Improve Streamflow Simulation in a Pacific Northwest Watershed

Abstract. The assessment of water yield from hillslopes into streams is critical in managing water supply and aquatic habitat. Streamflow is typically composed of surface runoff, subsurface lateral flow, and groundwater baseflow; baseflow sustains the stream during the dry season. The Water Erosion Prediction Project (WEPP) model simulates surface runoff, subsurface lateral flow, soil water, and deep percolation. However, to adequately simulate hydrologic conditions with significant quantities of groundwater flow into streams, a baseflow component for WEPP is needed. The objectives of this study were (1) to simulate streamflow in the Priest River Experimental Forest in the U.S. Pacific Northwest using the WEPP model and a baseflow routine, and (2) to compare the performance of the WEPP model with and without including the baseflow using observed streamflow data. The baseflow was determined using a linear reservoir model. The WEPP-simulated and observed streamflows were in reasonable agreement when baseflow was considered, with an overall Nash-Sutcliffe efficiency (NSE) of 0.67 and deviation of runoff volume (D v ) of 7%. In contrast, the WEPP simulations without including baseflow resulted in an overall NSE of 0.57 and D v of 47%. On average, the simulated baseflow accounted for 43% of the streamflow and 12% of precipitation annually. Integration of WEPP with a baseflow routine improved the model’s applicability to watersheds where groundwater contributes to streamflow.

An Exact Navier‐Stokes Solution for Three‐Dimensional, Spanwise‐Homogeneous Boundary Layers

AbstractThe plane stagnation flow onto (Hiemenz boundary layer, HBL) and the asymptotic suction boundary layer flow over a flat wall (ASBL) are two boundary layer flows for which the incompressible Navier‐Stokes equations are amenable to exact similarity solutions. The Hiemenz solution has been extended to swept Hiemenz flows by superposition of a third, spanwise‐homogeneous sweep velocity. This solution becomes singular as the chordwise, tangential base flow component vanishes. In this limit, the homogeneous ASBL solution is valid, which however cannot describe the swept Hiemenz flow, because it does not contain any chordwise velocity. This work presents a generalized three‐dimensional similarity solution which describes three‐dimensional spanwise homogeneously impinging boundary layers at arbitrary wall‐normal suction velocities, using a rescaled similarity coordinate. The HBL and the ASBL are shown to be two limits of this solution. Further extensions consist of oblique impingement or different boundary suction directions, such as slip or stretching walls. (© 2012 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Characterization of Storm Flow Dynamics of Headwater Streams in the South Carolina Lower Coastal Plain1

Epps, Thomas H., Daniel R. Hitchcock, Anand D. Jayakaran, Drake R. Loflin, Thomas M. Williams, and Devendra M. Amatya, 2012. Characterization of Storm Flow Dynamics of Headwater Streams in the South Carolina Lower Coastal Plain. Journal of the American Water Resources Association (JAWRA) 1‐14. DOI: 10.1111/jawr.12000Abstract: Hydrologic monitoring was conducted in two first‐order lower coastal plain watersheds in South Carolina, United States, a region with increasing growth and land use change. Storm events over a three‐year period were analyzed for direct runoff coefficients (ROC) and the total storm response (TSR) as percent rainfall. ROC calculations utilized an empirical hydrograph separation method that partitioned total streamflow into sustained base flow and direct runoff components. ROC ratios ranged from 0 to 0.32 on the Upper Debidue Creek (UDC) watershed and 0 to 0.57 on Watershed 80 (WS80); TSR results ranged from 0 to 0.93 at UDC and 0.01 to 0.74 at WS80. Variability in event runoff generation was attributed to seasonal trends in water table elevation fluctuation as regulated by evapotranspiration. Groundwater elevation breakpoints for each watershed were identified based on antecedent water table elevation, streamflow, ROCs, and TSRs. These thresholds represent the groundwater elevation above which event runoff generation increased sharply in response to rainfall. For effective coastal land use decision making, baseline watershed hydrology must be understood to serve as a benchmark for management goals, based on both seasonal and event‐based surface and groundwater interactions.

Baseflow separation in a small watershed in New Brunswick, Canada, using a recursive digital filter calibrated with the conductivity mass balance method

AbstractBaseflow separation is important for obtaining critical parameters for hydrological models. As measuring the baseflow component directly is difficult, various analytical and empirical baseflow separation methods have been developed and tested. The recursive digital filter (RDF) method is commonly used for baseflow separation due to its simplicity and low data requirement. However, parameters used in the RDF method are often determined arbitrarily, resulting in high uncertainty of the estimated baseflow rate. A more accurate method is the conductivity mass balance (CMB) method, which is established based on the differences in physical processes between baseflow and surface runoff. In this research, the output of the CMB method was used to calibrate the parameters of an RDF model, and the calibrated RDF model was used to estimate monthly, seasonal and annual baseflow rate and baseflow index for the past 19 years using streamflow discharge records. The characteristics of the baseflow hydrographs were found to be consistent with the hydrological and hydrogeological conditions of the research area. Research results indicated that the accuracy of the RDF model has been greatly enhanced after being calibrated with the CMB method so that the RDF model can provide more reliable baseflow separation results for a long‐term study. Copyright © 2012 John Wiley & Sons, Ltd.

Long-term streamflow relations with riparian gallery forest expansion into tallgrass prairie in the Southern Great Plains, USA

Though the effects of forests on water yields have been studied since the early 20th century, considerable uncertainty remains regarding streamflow relations in landscapes where forestation of degraded grassland is accompanied by recovery of soil hydrological function. This uncertainty arises because trees may reduce subsurface flow by transpiring water inaccessible to shallow-rooted grasses, but forestation of degraded grassland may also improve soil infiltration capacity, thereby increasing soil water recharge, a prerequisite for baseflow. To determine how riparian gallery forest expansion affected streamflow, we classified a chronosequence of historical aerial photography covering a 78 km 2 watershed equipped with a streamflow gauge. Here we show that in the Council Creek watershed in north-central Oklahoma, the baseflow component of streamflow increased from 1938 to 1992 during which time tree cover increased from 5% to 18% of the watershed area. During this period there were significant increasing trends in precipitation and evapotranspiration, but no significant trends in total streamflow. Stepwise regression indicated that relative to increases in precipitation, increases in forest cover were a better predictor of the observed baseflow increase. Baseflow increases over time were not distributed uniformly throughout the year, but rather occurred only from October through May, during most of which time the primarily deciduous riparian gallery forest species and the herbaceous species that they replaced would have been dormant. Due to confounding factors including elevated precipitation from 1980 to 1992, changing precipitation characteristics, and changing land-use, it was impossible to determine to what extent riparian gallery forest expansion caused the associated baseflow increases. Nonetheless, the method used in the study—relating an historical aerial photography chronosequence to existing long-term stream gauge data—proved to be an inexpensive, efficient, and effective in disproving our hypothesis that riparian gallery forest expansion would reduce baseflows. Further research is needed to better predict how long-term changes in forest cover, the position of forest cover within a watershed, and associated changes in soil and floodplain hydrology will affect streamflow in large mixed land-use watersheds.

Baseflow Separation of the Bribin River Upstream in Gilap Cave Flowage, Sewu Mountain Karst, Gunung Kidul, Yogyakarta

DOI: 10.17014/ijog.v6i3.124Baseflow of karst underground river is a dependable flow to recharge the underground flow within dry seasons. This research was conducted in Gilap Cave, located in the upper course of Bribin River. This location has a premeditated point for sustainable karst water along the Bribin River. The main objective of this study was to separate the components of Gilap underground river flow, with the intention on defining the proportion of baseflow component during the period of measurements. A water level data logger was installed during the period between 1 May 2006 and 31 March 2007 to determine the variation of water level during the dry season, rainy season, and when the prevalence of flood events. Subsequently, several times of discharge measurements at the time of high, medium, and low water level were carried out to define stage-discharge rating curve. Then, baseflow separation was conducted using automated baseflow separation by a digital filtering method. A digital filter value was obtained from a constant recession analysis of flood events all over the year, correlated with Maximum Baseflow Indices Value (BFImax) within karst aquifers. The result shows that during one year, 41 flood events occured in the Gilap Cave with digital filtering value of 0.996. In addition, the calculation of baseflow percentage performs that the overall value of the ratio is close to a number of around 80%. Meanwhile, the percentages within flood events vary between the range of 45-75%. From these figures, it generally confirms that flow from small fracture is still dominant to recharge dependable flow within the upper stream of Bribin River, especially in the dry season.

Historical summer base flow and stormflow trends for New England rivers

River base flow is important to aquatic ecosystems, particularly because of its influence on summer water temperatures. Summer (June through September) daily mean streamflows were separated into base flow and stormflow components by use of an automated method at 25 stations in the New England region of the United States that drain predominantly natural basins. Summer monthly mean base flows increased from 1950–2006 at most stations in western New England with many large increases (>20%) and some very large increases (>50%) in and near New Hampshire and Vermont. The same was true for increases in summer 7 day low base flows in and near New Hampshire and Vermont during this same period; in contrast, there were small and large decreases in 7 day low base flows in northern and coastal areas of Maine. Summer stormflows increased from 1950–2006 by more than 50% at many stations in New England, particularly in and near New Hampshire and Vermont. The increases in base flows and stormflows at many stations in and near New Hampshire and Vermont were likely driven by the large increases in summer precipitation recorded at weather stations in this area. Summer rainfall increased at most weather stations in New England from 1950–2006 with many increases of more than 20% in western New England. Summer air temperature increased on average by 1.1°C from 1950–2006 in New England and may have played a role in the decreased base flows in northern and coastal Maine through increased evapotranspiration. Many variables increased less from 1930–2006 than from 1950–2006.

Development, sensitivity and uncertainty analysis of LASH model

Many hydrologic models have been developed to help manage natural resources all over the world. Nevertheless, most models have presented a high complexity regarding data base requirements, as well as, many calibration parameters. This has brought serious difficulties for applying them in watersheds where there is scarcity of data. The development of the Lavras Simulation of Hydrology (LASH) in a GIS framework is described in this study, which focuses on its main components, parameters, and capabilities. Coupled with LASH, sensitivity analysis, parameter range reduction, and uncertainty analysis were performed prior to the calibration effort by using specific techniques (Morris method, Monte Carlo simulation and a Generalized Likelihood Uncertainty Estimation -GLUE) with a data base from a Brazilian Tropical Experimental Watershed (32 km²), in order to predict streamflow on a daily basis. LASH is a simple deterministic and spatially distributed model using long-term data sets, and a few maps to predict streamflow at a watershed outlet. We were able to identify the most sensitive parameters which are associated with the base flow and surface runoff components, using a reference watershed. Using a conservative threshold, two parameters had their range of values reduced, thus resulting in outputs closer to measured values and facilitating automatic calibration of the model with less required iterations. GLUE was found to be an efficient method to analyze uncertainties related to the prediction of mean daily streamflow in the watershed.

Assessment of climate change impacts at the catchment scale with a detailed hydrological model of surface‐subsurface interactions and comparison with a land surface model

A process‐based model that incorporates hydrodynamic feedbacks between the land surface, soil, and groundwater zones is used to assess the sensitivity of the hydrological response (river discharge, aquifer recharge, and soil water storage) to future climate conditions. The analysis is based on the Intergovernmental Panel on Climate Change Special Report on Emissions Scenario A2 and the des Anglais catchment in southwestern Quebec (Canada). Application of the coupled hydrological model (CATHY) to the study basin revealed significant spatiotemporal variations in the river discharge response to climate change owing to a different partitioning between the overland runoff and base flow components of the hydrograph, with the latter alleviating the marked decrease in discharge during the summer period. A spatial analysis of recharge patterns shows that the greatest variations are expected to occur, throughout the year, in the southern portion of the catchment, where the elevations are highest. Compared to river discharge and aquifer recharge, the soil water storage volumes are less sensitive to climate changes. From a spatial analysis of soil moisture variations it was possible to observe organizational patterns that follow the topographic and pedologic characteristics of the catchment. In addition to these analyses, we also compare predictions obtained with the land surface scheme (CLASS) that is coupled to the regional climate model (CRCM) to those from the detailed catchment model for past and future climate change projections. An examination of the runoff revealed that CLASS produces higher estimates than CATHY of surface and subsurface runoff throughout the annual cycle for both past and future projections. For soil water storage, the two models are in general agreement in terms of the intra‐annual variability of moisture content at shallower soil layers, whereas a larger difference is found for the deepest layer, with CATHY predicting wetter soil conditions over the entire simulation period and moisture fluctuations of much smaller amplitude.