Watershed Response Research Articles

Evaluation of Hydrological Response of an Agricultural Watershed to Conservation Measures and Land Use Changes: A Case Study

An agricultural watershed falling in the catchment of Godavri basin was selected for the study. Paddy, Maize, Cotton, Red gram, and Vegetables are the major crops grown in the watershed. Severe soil erosion consequent degradation of land and lack of water resources for supplementary irrigation and high dependence on rainfed farming leading to poor crop yields were the major problems in the watershed. With a view to address the issues in rainfed farming compounded by increasing adverse effects of climate change, soil and water conservation measures including area and drainage line treatments from ridge to valley were implemented in the watershed from the year 2009 to 2015 with the active participation of local people with facilitation support by a local civil society organization. With the implementation of the conservation measures, visible impact in terms of increased water availability, change in the land use and increased area under cultivation were reported in the watershed. The present study aimed at assessing the hydrological response of the watershed to the conservation measures and land use changes. As the study watershed is an ungauged one, the hydrological response of watershed was simulated with commonly used SCS-CN model duly validated with additional surface storage capacity created in the watershed. The study revealed highly positive impact of conservation measures and land use changes on hydrological behaviour of watershed. The main observed change in hydrological response of watershed was the decrease in the monsoon seasonal runoff by 33% (from 15 % before taking up catchment management measures to 10 % of seasonal rainfall after the project). The conservation measures were found to facilitate storing excess runoff in the watershed itself contributing to improved soil moisture, groundwater recharge and availability of water. Further, the additional storage capacity of 336 cubic m per hectare as estimated from the present hydrological response study was found to be in very close agreement with actual storage capacity of 322 cubic m per hectare, created with different conservation works taken up in the watershed.

MODEL OF LAND USE CHANGE TO THE HYDROLOGY RESPONSE

This research intends to build a model of land use change to the watershed hydrology response and was conducted in the area of Indonesia’s new country capital (IKN Nusantara). The total area of IKN Nusantara (KIKN) is 56,181 ha that includes 7 watersheds that are Sanggai, Trunen, Semuntai, Baruangin, Sepaku, Semoi, and Pemaluan. However, this study will only focus on the flood model in the Government Centre Area (KIPP) with the area is about 6,671 ha and only includes 3 watersheds such as Sanggai, Trunen, and Semuntai. The methodology consists of collecting the hydrology data that are land use, watershed boundary, IKN Nusantara area boundary, soil type, spatial planning (RTRW), observed rainfall station, GPM satellite rainfall. After that, there is carried out the data evaluation to correct the satellite rainfall data to the observed data. There was carried out the analysis about ability to give the recommendation on the boundary of country capital area development based on the consideration of run-off hydrology response that is still suitable with the environmental carrying capacity. The simulation results of the land use model and the rainfall pattern change model are expected to become the boundary in the development design of a city, mainly in the relation to the environmental carrying capacity toward flood, especially to provide a recommendation of new country capital area boundary based on the recommendation of CN value as the run-off hydrology response mainly related to the zone regulation of built up and protected area.

Application of Hydrologic Engineering Centers Hydrologic Modeling System (HEC-HMS) Model for Modelling Flood in Sub Basin of Meenachil River, Kerala, India

Meenachil river basin, located in southern part of Kerala, is frequently liable to flood. It is an area predominant with agricultural land and falls under tropical humid zone. Hence, water resources planning and management and understanding of rainfall-runoff relationship along with its land characteristics, is necessary for irrigation scheduling, flood control and design of various engineering structures. HEC-HMS(Hydrologic Engineering Centers Hydrologic Modeling System) which is a widely used rainfall-runoff model was chosen for the simulation of watershed responses and generation of flood hydrographs. This research was done to establish the peak discharge rate of the river as well as calibrate and validate the HEC-HMS model for the Meenachil subbasin and obtain long-term flow data. The performance parameters NSE (Nash–Sutcliffe model efficiency) coefficient and R² (coefficient of determination) values were obtained above 0.7. The Error in Peak Flow and Volume were calculated below 20%. All these values indicated satisfactory performance of the model simulation both in the calibration (2013-2016) and validation (2017-2018) period. Curve number (61.46-79.93 mm), Initial abstraction(10.29-31.87 mm) and Lag time(208.27 min and 4456.2 min) were found to be the most sensitive parameters of the model. Simulated and observed stream flow values (viz. lowest peak flow of river was found during the year 2013 and it was predicted as 168.9 m³/s and observed as 158.5 m³/s) indicated that the model was able to predict and present credible results for the sub basin.

Significant regime shifts in historical water yield in the Upper Brahmaputra River basin

Abstract. Although evidence of the hydrological response of watersheds to climate change is abundant, reliable assessments of water yield (WY) over mountainous regions, such as the Upper Brahmaputra River (UBR) basin, remain unclear. Here, we examine long-term WY changes during 1982–2013 in the UBR basin, based on multi-station runoff observations. We find that there are significant shifts in hydrological regimes in the late 1990s; WY increases in the range of ∼10 % to ∼80 %, while the directions reverse from increasing to decreasing. Additionally, the double mass curve (DMC) technique is used to assess the effects of climate, vegetation, and cryosphere on WY changes. Results show that cryosphere and climate together contribute to over 80 % of the increase in WY across the entire UBR basin, while the role of vegetation is negligible. The combined effects, however, are either offsetting or additive, thus leading to slight or substantial magnitude increases, respectively. The downward WY trend has primarily been regulated by decreased precipitation in recent years. However, we find that meltwater may alleviate the resulting water shortage in some basins. Therefore, the combined effects of climate and cryosphere on WY should be considered in future water resources management over mountainous basins, particularly involving co-benefits between upstream and downstream regions.

Scalable deep learning for watershed model calibration

Watershed models such as the Soil and Water Assessment Tool (SWAT) consist of high-dimensional physical and empirical parameters. These parameters often need to be estimated/calibrated through inverse modeling to produce reliable predictions on hydrological fluxes and states. Existing parameter estimation methods can be time consuming, inefficient, and computationally expensive for high-dimensional problems. In this paper, we present an accurate and robust method to calibrate the SWAT model (i.e., 20 parameters) using scalable deep learning (DL). We developed inverse models based on convolutional neural networks (CNN) to assimilate observed streamflow data and estimate the SWAT model parameters. Scalable hyperparameter tuning is performed using high-performance computing resources to identify the top 50 optimal neural network architectures. We used ensemble SWAT simulations to train, validate, and test the CNN models. We estimated the parameters of the SWAT model using observed streamflow data and assessed the impact of measurement errors on SWAT model calibration. We tested and validated the proposed scalable DL methodology on the American River Watershed, located in the Pacific Northwest-based Yakima River basin. Our results show that the CNN-based calibration is better than two popular parameter estimation methods (i.e., the generalized likelihood uncertainty estimation [GLUE] and the dynamically dimensioned search [DDS], which is a global optimization algorithm). For the set of parameters that are sensitive to the observations, our proposed method yields narrower ranges than the GLUE method but broader ranges than values produced using the DDS method within the sampling range even under high relative observational errors. The SWAT model calibration performance using the CNNs, GLUE, and DDS methods are compared using R2 and a set of efficiency metrics, including Nash-Sutcliffe, logarithmic Nash-Sutcliffe, Kling-Gupta, modified Kling-Gupta, and non-parametric Kling-Gupta scores, computed on the observed and simulated watershed responses. The best CNN-based calibrated set has scores of 0.71, 0.75, 0.85, 0.85, 0.86, and 0.91. The best DDS-based calibrated set has scores of 0.62, 0.69, 0.8, 0.77, 0.79, and 0.82. The best GLUE-based calibrated set has scores of 0.56, 0.58, 0.71, 0.7, 0.71, and 0.8. The scores above show that the CNN-based calibration leads to more accurate low and high streamflow predictions than the GLUE and DDS sets. Our research demonstrates that the proposed method has high potential to improve our current practice in calibrating large-scale integrated hydrologic models.

Assessment of the Analytic and Hydrologic Methods in Separation of Watershed Response to Climate and Land Use Changes

Assessment of the Analytic and Hydrologic Methods in Separation of Watershed Response to Climate and Land Use Changes

Impacts of seasonally frozen ground on streamflow recession in the Red River of the North Basin

AbstractThe projected rising temperatures due to climate change can alter the frozen ground's duration and thickness in the cold regions of the Northern Hemisphere, leading to changes in surface and subsurface contributions to streamflow. The initial step in understanding the impacts of the changing climate on the hydrologic response of the cold climate watersheds is to investigate the effects of the cold climate processes (e.g., freeze–thaw processes) on watershed response. However, complexities associated with the spatiotemporal data collection of cold climate processes have limited the capabilities of hydrologic models in simulating cold climate watershed responses. This study aims to evaluate the impacts of seasonally frozen soil on the streamflow recession in the Red River of the North Basin (RRB). To the best of our knowledge, this study is one of the first attempts to quantify the impacts of frozen soil on the storage‐discharge relationship of the RRB. We define a set of hypotheses to evaluate how cold climate processes influence the surface and subsurface flow paths and affect the linearity/non‐linearity of the storage‐discharge relationship in spring and summer. The results confirmed that the cold climate processes control the recession behavior of the RRB. It was found that the streamflow discharge is linearly related to the storage during spring, whereas during summer, the relationship was less linear. Statistical analyses revealed that the antecedent winter soil temperature and snowpack control the seasonal dynamics of hydrograph recession. Particularly, results indicated a more linear storage‐discharge relationship for antecedent winters characterized by colder soil temperatures and larger snowpack. These findings highlight the importance of the cold climate hydrologic processes in cold climate basins such as the RRB.

In the shadow of the dam – Hydrology of the Little Conemaugh river and its South Fork, with insights about past and future flooding

The Little Conemaugh River watershed and its South Fork sub-basin figure prominently in historical flooding of Johnstown, Pennsylvania and nearby communities with catastrophic flooding in 1889, 1936, and 1977 (reviewed herein). Historical stream gage data and data from a new gage on the South Fork (established via a novel, portable cableway system) are used with Nexrad rainfall data to assess watershed response and provide novel analysis of flood hydrology in the Little Conemaugh basin and the sub-basin. Using unit hydrograph estimates for longer duration storms (>8 h) and different baseflow conditions, we probe possible effects of several design storms, including those stemming from a hurricane remnant scenario (Agnes in 1972) and 50-, 100-, and 500-year 12-hour precipitation depths. The unit hydrographs provided peak discharge (Qpeak) estimates for 1977 (the only flood event with available hourly rainfall data) that are in good agreement with empirical peak discharges.Significant channel improvements completed in 1943 were designed to carry the largest known natural flow on record at that time (1936 Qpeak). Preliminary results from design storm scenarios indicate the need for a careful evaluation of extreme discharges and their return periods (including snowmelt-related contributions), as future flood levels in Johnstown may occur more frequently than originally thought. The 1977 flood, which triggered 7 dam failures and eclipsed 1936 Qpeak, resulted from less than 40% the estimated probable maximum precipitation (PMP) for a 12-hour storm. Peak discharges of similar magnitude would have ensued in 1972 had remnants of Hurricane Agnes tracked slightly westward. Flooding and infrastructure problems could be compounded for storms of 24-hour or longer durations, similar to record flooding seen in central Pennsylvania and New York in 1972. Flood recurrence, emergency procedures, and dam safety (particularly, spillway capacity in the Little Conemaugh basin and surrounding region) should likely be reassessed and protective early-warning measures (ineffective in 1977) implemented for the people of Johnstown.

Analysis of Morphometric Parameters of the Drainage Network and Road Network of the Ribeirão Paraíso Watershed, Jataí - GO

Studies related to morphometric analysis are extremely important for hydrogemorphological knowledge in watersheds. However, most rural roads are not considered in these analyses. Therefore, the objective of this article was to verify if the relations between the drainage network, the relief parameters, and the road network indicate changes in the drainage dynamics of a watershed occupied by agricultural use. The sugarcane crop is an influencing factor in the increase in rural roads in the watershed and arrived in the region from 2009 onwards. Therefore, the time frame of 2005, 2010, 2015, and 2020 was chosen for the investigation. Bibliographic research and quantitative measurements were used as a methodology to extract information from the drainage network and road network through morphometric parameters. For this, ArcGIS® 10.6.1 and Excel 2019 software were used. As a result, it was identified that the watershed has a fourth-order river hierarchy; its area is 903.6 km², the drainage density is 0.45 km/km², and when rural roads were included in the analysis in 2005, 2010, 2015, and 2020, corresponding to 2.1, 2.2, 2.4, and 3.1 km/km², respectively. Thus, the average density of roads in the period was 84% higher when considering only natural drainage, increasing mainly after the insertion of sugarcane in the scenario. Therefore, it is concluded that the analysis of morphometric parameters is essential to generate new knowledge about the studied watershed. Rural roads should be included in the analysis since they influence the hydrogeomorphological aspects of the watersheds. In this case, the increase in drainage density is directly related to the increase in roads and sugarcane. With the inclusion of these in the morphometric analysis, the watershed increases its drainage capacity, significantly altering the hydrological response in hydrographic watersheds.

Decadal trends in solute concentrations, mass flux, and discharge reveal variable hydrologic and geochemical response to climate change in two alpine watersheds

High-alpine environments are particularly sensitive to changes driven by climate change and experience more dramatic shifts in vegetation, snowmelt timing, and the relative ratio of rain to snow compared to other lower-elevation environments. These shifts drive changes in stream discharge and solute concentrations, long-term records of which may be archived in publicly available databases. Here, we use three decades of discharge and water quality data from two alpine watersheds along the Continental Divide in the Rocky Mountains of Colorado, USA, to quantify temporal trends in solute concentration and solute mass flux, which serve as integrators of watershed processes and are used to identify controls on how these watersheds respond to climate change over decadal timescales. By analyzing both solute concentrations and mass flux we are able to remove the effects of seasonal changes in discharge and separate hydrologic and geochemical drivers of changes in solute export from these two watersheds. While we find that concentrations of calcium, bicarbonate, and sulfate increase through time in both watersheds, increasing solute mass flux is found in one watershed but not the other, despite similar watershed characteristics such as elevation, precipitation, average temperature, and bedrock geology. We identify different dominant weathering mechanisms as the cause for the differences in watershed response to climate change. In one watershed, sulfide oxidation was the dominant weathering mechanism at the beginning of the record and stayed dominant through the three-decade period of data. This consistency in weathering mechanism likely controls why the solute flux did not change significantly. In contrast, in the other watershed, solute flux increased and water chemistry shows that the dominant weathering mechanism shifted from dominantly CO2-driven to more influence from sulfide-oxidation driven weathering. This shift in weathering mechanism is accompanied by significantly increasing solute fluxes. This study demonstrates the importance of quantifying geological weathering in watershed response to climate change where two similar watersheds exhibit different responses--one hydrological and one combined hydrological and geochemical--that could not have been predicted from a simple analysis of the watershed characteristics. Such analyses are needed on a large scale to quantify the type and magnitude of watershed changes in water quality and quantity to climate change, and suggest that weathering mechanisms, in particular weathering driven by oxidation of trace sulfide minerals, plays an important role in the geochemical response of watersheds to climate change.

Influence of Climate and Land Cover/Use Change on Water Balance: An Approach to Individual and Combined Effects

Land use/cover change (LUCC) and climate change (CC) affect water resource availability as they alter important hydrological processes. Mentioned factors modify the magnitude of surface runoff, groundwater recharge, and river flow among other parameters. In the present work, changes that occurred in the recent decades at the Quino and Muco river watersheds in the south-central zone of Chile were evaluated to predict future cover/use changes considering a forest expansion scenario according to Chilean regulations. In this way an expansion by 42.3 km2 and 52.7 km2 at Quino and Muco watersheds, respectively, was predicted, reaching a watersheds’ occupation of 35.4% and 22.3% in 2051. Additionally, the local climatic model RegCM4-MPI-ESM-MR was used considering periods from 2020–2049 and 2050–2079, under the RCP 8.5 scenario. Finally, the SWAT model was applied to assess the hydrological response of both watersheds facing the considered forcing factors. Five scenarios were determined to evaluate the LUCC and CC individual and combined effects. The results depict a higher sensitivity of the watersheds to CC impacts, where an increase of evapotranspiration, with a lessening of percolation, surface flow, lateral flow, and groundwater flow, triggered a water yield (WYLD) decrease in all predicted scenarios. However, when both global changes act synergistically, the WYLD decreases considerably with reductions of 109.8 mm and 123.3 mm at the Quino and Muco watersheds, respectively, in the most extreme simulated scenario. This water scarcity context highlights the necessity to promote land use management strategies to counteract the imminent effects of CC in the watersheds.

Subaerial volcaniclastic deposits – influences of initiation mechanisms and transport behaviour on characteristics and distributions

Abstract Subaerial volcaniclastic deposits are produced principally by volcanic debris avalanches, pyroclastic density currents, lahars, and tephra falls. Those deposits have widely ranging geomorphic and sedimentologic characteristics; they can mantle, modify, or create new topography, and their emplacement and subsequent reworking can have an outsized impact on the geomorphic and sedimentologic responses of watersheds surrounding, and channels draining, volcanoes. Volcaniclastic deposits provide a wealth of information about eruptive histories, volcanic processes, and landscape responses to eruptions. The volcanic processes that produce these deposits, and consequently the character and sedimentary structures of the deposits themselves, are influenced by initiation mechanism. Deposit preservation is affected by deposit magnitude, texture, and composition, depositional environment, and climate regime. Innovative analyses of deposits from several modern eruptions and advancements in physical and numerical modelling have vastly improved our understanding of volcanic processes, interpretations of eruptive histories, and recognition of the hazards posed by volcanic eruptions. This contribution highlights and summarizes major advances that have occurred in the past few decades in understanding of volcaniclastic deposits and linkages with volcanic processes.

Demand for Ecosystem Services Drive Large-Scale Shifts in Land-Use in Tropical Mountainous Watersheds Prone to Landslides

An increasing frequency of extreme atmospheric events is challenging our basic knowledge about the resilience mechanisms that mediate the response of small mountainous watersheds (SMW) to landslides, including production of water-derived ecosystem services (WES). We hypothesized that the demand for WES increases the connectivity between lowland and upland regions, and decreases the heterogeneity of SMW. Focusing on four watersheds in the Central Andes of Colombia and combining “site-specific knowledge”, historic land cover maps (1970s and 1980s), and open, analysis-ready remotely sensed data (GLAD Landsat ARD; 1990–2000), we addressed three questions. Over roughly 120 years, the site-specific data revealed an increasing demand for diverse WES, as well as variation among the watersheds in the supply of WES. At watershed-scales, variation in the water balances—a surrogate for water-derived ES flows—exhibited complex relationships with forest cover. Fractional forest cover (pi) and forest aggregation (AIi) varied between the historic and current data sets, but in general showed non-linear relationships with elevation and slope. In the current data set (1990–2000), differences in the number of significant, linear models explaining variation in pi with time, suggest that slope may play a more important role than elevation in land cover change. We found ample evidence for a combined effect of slope and elevation on the two land cover metrics, which would be consistent with strategies directed to mitigate site-specific landslide-associated risks. Overall, our work shows strong feedbacks between lowland and upland areas, raising questions about the sustainable production of WES.

Hydrological response of a paired watershed to rainfall storm events in arid region: a study in Dehgin of Hormozgan province, Iran.

Influenced by global climate change, rainfall characteristics have changed in recent years, especially in arid regions. However, the actual response of the watersheds' hydrological indicators to erosive rainfalls has not been understood yet. Therefore, this study sought to investigate the changes in the watersheds' hydrological response due to the intra-rainfall indices of various events in the Dehgin paired watershed in Hormozgan, Iran, using the data collected from 2007 to 2019. To this end, first, all rainfall events which elicited the response of watersheds were identified concurrently based on the meteorological and flume data. Then, the qualitative and quantitative intra-storm variations associated with hydrological indicators (i.e., total runoff and discharge variables) were extracted for statistical analysis. The study's results revealed that (1) the increasing rates of the continuous discharge time of the control and treatment watershed's front position were about 2.25 and 4.76 times the rear position, respectively. (2) A strong linear relationship was found between total runoff volume and variables including precipitation of storm and time to storm peak in both control and treatment watersheds, with the R2 reported to be 67.7 and 63.6%, respectively. (3) It was also found that the watershed management operations reduced the variables' values including the maximum discharge, the discharge variation coefficient, continuity time of discharge, the peak of the time to discharge, the number of discharge peaks, and the total runoff volume by 3, 1.6, 2.25, 2.37, 2.42, and 3.27 times, respectively. Therefore, it could conceivably be argued that extreme rainfalls can be controlled by management practices in the watersheds.

Pattern of spatio-temporal variability of extreme precipitation and flood-waterlogging process in Hanjiang River basin

Based on the uniform distributed rainfall data in the Hanjiang River basin, the characteristics of spatio-temporal variability of extreme precipitation and flood-waterlogging process are diagnosed in terms of index definition and mathematical statistics. The study found that: (1) no significant trends of extreme rainfall for the entire basin were tested, but there was a jump variation in 1990s from abundance to dryness, accompanied by 20-year main periodic oscillation. Since 2000, the frequency of extremely heavy rain has increased significantly. (2) there is a spatial distribution pattern of lower in the northeast and higher in the southwest, and decreasing from upstream to downstream in the annual means of extreme precipitation. High-value centers are concentrated in the southwestern mountainous areas and the plains in the downstream, which are prone to form the distribution pattern of Central-North Radiation Type and Southeast-Northwest Type. (3) basin usually suffers 5–6 waterlogging processes per year, most of which were light or moderate grade, lasting 2–4 days. Since 2000, the flood-waterlogging process has shown evolution characteristics in increasing of the intensity, frequency, duration, and fluctuation, having strong continuity in the future. (4) affecting by climate and topography, spatial distribution of flood-waterlogging is uneven. Downstream and southwest of upstream are regularly the high-value centers, which are easy to form three kinds of distribution patterns, namely Northeast Radiation Type, Middle-lower Radiation Type and Middle-upper Radiation Type. Since the 21st century, the Hanzhong area and the watershed below Xiangyang both often encountered flood-waterlogging processes of high-intensity, long-duration, and high-frequency, which easy to induce flood disasters. Spatio-temporal variability of extreme precipitation and flood-waterlogging is a direct result of the rational development and utilization of water resources. We expect the results here to provide a deep insight into flood-waterlogging and serve as a reference for the watershed flood disaster response, rain-flood utilization, and optimal allocation of water resources.

The effects of spatial and temporal resolution of gridded meteorological forcing on watershed hydrological responses

Abstract. Meteorological forcing plays a critical role in accurately simulating the watershed hydrological cycle. With the advancement of high-performance computing and the development of integrated watershed models, simulating the watershed hydrological cycle at high temporal (hourly to daily) and spatial resolution (tens of meters) has become efficient and computationally affordable. These hyperresolution watershed models require high resolution of meteorological forcing as model input to ensure the fidelity and accuracy of simulated responses. In this study, we utilized the Advanced Terrestrial Simulator (ATS), an integrated watershed model, to simulate surface and subsurface flow and land surface processes using unstructured meshes at the Coal Creek Watershed near Crested Butte (Colorado). We compared simulated watershed hydrologic responses including streamflow and distributed variables such as evapotranspiration, snow water equivalent (SWE), and groundwater table driven by three publicly available, gridded meteorological forcings (GMFs) – Daily Surface Weather and Climatological Summaries (Daymet), the Parameter-elevation Regressions on Independent Slopes Model (PRISM), and the North American Land Data Assimilation System (NLDAS). By comparing various spatial resolutions (ranging from 400 m to 4 km) of PRISM, the simulated streamflow only becomes marginally worse when spatial resolution of meteorological forcing is coarsened to 4 km (or 30 % of the watershed area). However, the 4 km-resolution has much worse performance than finer resolution in spatially distributed variables such as SWE. Using the temporally disaggregated PRISM, we compared models forced by different temporal resolutions (hourly to daily), and sub-daily resolution preserves the dynamic watershed responses (e.g., diurnal fluctuation of streamflow) that are absent in results forced by daily resolution. Conversely, the simulated streamflow shows better performance using daily resolution compared to that using sub-daily resolution. Our findings suggest that the choice of GMF and its spatiotemporal resolution depends on the quantity of interest and its spatial and temporal scale, which may have important implications for model calibration and watershed management decisions.

2D hydrodynamic approach supporting evaluations of hydrological response in small watersheds: Implications for lag time estimation

The use of integrated flood models represents an approach of growing interest in the literature, being the hydrological and hydrodynamic flood processes described entirely within the two-dimensional (2D) hydrodynamic unsteady flow equations. Due to its ability in simulating complex spatial–temporal dependence of both the hydrodynamic and hydrologic responses of a catchment to rainfall events, this kind of approach paves the way to the development of novel lines of research in catchment hydrology. With particular reference to the lag time estimation, the paper focuses on three interrelated issues: 1) the use of the 2D-SWEs model to provide evidence on the variability of the lag time in small basins, 2) the description of the hydrologic response of small catchments based on characteristic times influencing the hydrodynamic response to rainfall events and 3) the representativeness of hydrodynamic-based rainfall-runoff scenarios in the description of the hydrologic response observed in real events. To that purpose, synthetic rainfall-runoff scenarios for different return periods are firstly generated to analyze the hydrologic response time in three ungauged basins. Then regressive formulas, based on ad hoc variables representing characteristic times, are introduced to interpret the variability shown by the computed lag time. Finally, the physical soundness of the proposed approach is tested against observed rainfall-runoff data in four additional basins. Despite all the simplifications introduced in the proposed approach, the regressive formulas provided a reasonably good agreement with the estimations of the lag time of the observed events, showing errors of the order of 30%. The comparison with the predictions of empirical literature formulas further confirms the potential of the proposed approach. This study represents the basis for future research on basin response to rainfall events through the use of a 2D integrated hydrodynamic-hydrologic modeling.

Surface parameters and bedrock properties covary across a mountainous watershed: Insights from machine learning and geophysics.

Bedrock property quantification is critical for predicting the hydrological response of watersheds to climate disturbances. Estimating bedrock hydraulic properties over watershed scales is inherently difficult, particularly in fracture-dominated regions. Our analysis tests the covariability of above- and belowground features on a watershed scale, by linking borehole geophysical data, near-surface geophysics, and remote sensing data. We use machine learning to quantify the relationships between bedrock geophysical/hydrological properties and geomorphological/vegetation indices and show that machine learning relationships can estimate most of their covariability. Although we can predict the electrical resistivity variation across the watershed, regions of lower variability in the input parameters are shown to provide better estimates, indicating a limitation of commonly applied geomorphological models. Our results emphasize that such an integrated approach can be used to derive detailed bedrock characteristics, allowing for identification of small-scale variations across an entire watershed that may be critical to assess the impact of disturbances on hydrological systems.

Predicting the potential impact of forest fires on runoff and sediment loads using a distributed hydrological modeling approach

Forest fires profoundly affect the nature of watershed responses to precipitation, increases in runoff rate and volume, and post-fire sediment discharge. A post-fire watershed assessment to identify potential trouble spots for soil erosion and flooding can help land managers for decision-making on deploy mitigation, remediation measures, and restoration action plans. Predicting the potential impact of fires on runoff and soil erosion requires distributed hydrological modeling methods. This study used the Soil and Water Assessment Tool (SWAT), a rainfall-runoff model, to investigate the hydrological consequences of forest fires and their impact on sediment load under different burnt scenarios. For the pre-fire (baseline) scenario, the watershed is calibrated by using the measured discharge and suspended sediment concentration data from the weather station during the time step to estimate post-fire changes at the sub-catchment scale. The total water and sediment yield for the selected sub-catchment in the post-fire scenario with the highest spatial distribution of forest fire, due to the excessive surface runoff (an increase of 14.5%) increased significantly, resulted in 6.5 times increase in sediment yield. The results obtained from the study indicate a significant increase in sediment transport into the stream in the post-fire scenario. A large volume of soil losses occurred during the time step. In contrast, due to removing trees and vegetation from the ground, less evapotranspiration and infiltration occurred in selected sub-catchment areas after forest fires. In terms of watershed management, understanding the consequences of forest fires on hydrological services will be an effective method for sediment budget control. Therefore, applying the rainfall-runoff and erosion models for the watershed with developing plausible forest fire scenarios can be a productive method to deal with the threats and hydrological risks such as soil erosion and sediment transfer to the downstream environment.

Implementation of subsurface transport processes in the low-dimensional integrated hydrological model NIHM

Solute transport models based on the resolution of the 3-D Advection-Dispersion (AD) equation are frequently plagued by several numerical problems, which add to the high computational cost. The hydrological model NIHM (Normally Integrated Hydrological Model) was recently proposed as a tool simulating the hydrological responses of watersheds with shallow saturated aquifers by coupling surface flow and a low-dimensional subsurface system, including the vadose zone. In this paper, we couple the low-dimensional flow model NIHM with a transport module solving the AD to propose an approach that enables to reduce the dimensionality of both the flow and transport problems. In NIHM, the low-dimensionality in the subsurface compartment results from an integration along the local direction normal to the bedrock of the aquifer. NIHM was previously evaluated and applied to actual hydrosystems—without addressing mass transfers—and it showed its ability to capture various hydrological responses even from complex systems. However, the relevance of a low-dimensional approach to transport is not proven yet as the model reduction could also render approximated velocity fields inappropriate to mass transfer problems. The accuracy and computational efficiency of the proposed model have been thoroughly examined through various synthetic test cases under different hydrodynamic conditions to assess the influence of the reduction of dimensionality on solute transport simulations. The findings of this study demonstrate that the reduction of dimension remains suited to predicting solute transport behaviors in shallow subsurface systems while providing an important gain in computation time. This might be promising for various applications dealing with groundwater quality.