Runoff Production Research Articles

Future land cover and climate may drive decreases in snow wind‐scour and transpiration, increasing streamflow at a Colorado, USA headwater catchment

AbstractUnderstanding how land cover change will impact water resources in snow‐dominated regions is of critical importance as these locations produce disproportionate runoff relative to their land area. We coupled a land cover evolution model with a spatially explicit, physics‐based, watershed process model to simulate land cover change and its impact on the water balance in a 5.0 km2 headwater catchment spanning the alpine–subalpine transition on the Colorado Front Range. We simulated two potential futures both with greater air temperature (+4°C/century) and more precipitation (+15%/century, MP) or less precipitation (−15%/century, LP) from 2000 to 2100. Forest cover in the catchment increased from 72% in 2000 to 84% and 83% in 2050 and to 95% and 92% in 2100 for MP and LP, respectively. Surprisingly, increases in forest cover led to mean increases in annual streamflow production of 12 mm (6%) and 2 mm (1%) for MP and LP in 2050 with an annual control streamflow of 208 mm. In 2100, mean streamflow production increased by 91 mm (44%) and 61 mm (29%) for MP and LP. This result counters previous work as runoff production increased with forested area due to decreases in snow wind‐scour and increases in drifting leeward of vegetation, highlighting the need to better understand the impacts of forest expansion on the spatial pattern of snow scour, deposition and catchment effective precipitation. Identifying the hydrologic response of mountainous areas to climate warming induced land cover change is critically important due to the potential water resources impacts on downstream regions.

Darkening of the Svalbard Fjords Waters Observed With Satellite Ocean Color Imagery in 1997–2019

Global warming is not often discussed in the context of light availability within the water column. However, the light regimes in the Arctic Ocean are controlled by three factors that are influenced by climate changes which are the sea icealbedofeedback, glacial meltwater runoff and marine primary production. Based on a satellite data series acquired during time period 1997 – 2019, we inspected long-term changes of the three commonly used optical characteristicsChla,atot(443), andKd(490) within the Svalbard fjords and on the West Spitsbergen Shelf. We revealed evident positive trends in summer (July – September) in the Isfjorden, the Kongsfjorden, the Hornsund fjord, and the Bellsund. Moreover, between 1997 and 2019 at the majority of locations we observed a regime shift toward darker waters. We showed that light availability has changed in the Svalbard fjords since 1997, which may be a symptom of transformations in the environment that should be further investigated and monitored.

A simulated study of surface morphological evolution on coarse-textured soils under intermittent rainfall events

The evolution of slope surface morphology directly affects the hydrological process and forms a dynamic feedback loop with the runoff and sediment production. However, the unique erosion processes and feedback mechanism for the surface morphological changes of coarse-textured granite soils have been rarely studied previously. Here, a series of rainfall simulation experiments (intensity of 90 mm h−1) were conducted under continual intermittent rainfall conditions (duration of 20 h) on a 0.8 m by 3.0 m soil flume packed with the four coarse-textured granite soils (sieved soils from the counties of Tongcheng, Ganxian, Changting, and Wuhua, China, defined as TCA, GXA, CTA and WHA, respectively) to measure the surface roughness, coarse grain coverage, soil erosion rate, stream power and sediment sorting. The results showed: 1) the coarse grain coverage of the four soils gradually increased with rainfall duration, with the final maximum (74.89%) for CTA soil, which corresponded to the enrichment of fine particles in the sediments; 2) the mean soil erosion rate of the four soils ranged from 0.090 to 0.76 kg m−2 min−1 with the decrease of clay content from 24.19% to 13.60% in the original soils, coinciding with the surface roughness controlled by rill erosion around the coarse grains; 3) the coarse grain cover provided a protective layer to reduce further soil loss in inter-rill areas; 4) the model of soil clay content and stream power was shown to be suitable for soil erosion prediction of coarse-textured soils (R2 = 0.93). The results highlighted soil mechanical composition and coarse grain coverage on the surface as the key factors affecting the coarse-textured soil erosion. This study facilitates our understanding of the unique erosion processes and the erosion feedback mechanism of coarse-textured soils.

Method to identify composition and production phases of spring runoff in high-latitude mid-temperate regions: a case study in the Second Songhua River Basin, China

Abstract Simulation and forecasting of runoff play an important role in the early warning and prevention of drought and flood disasters. To improve the accuracy of spring runoff simulations, it is important to identify spring runoff production patterns under the combined effect of snow and frozen soil. Based on the theory of the hydrological cycle, three important parameters, which include surface and subsurface runoff, precipitation and temperature, were selected for this study. The trend analysis, statistical analysis and Eckhardt's recursive numerical filtering method were used to qualitatively identify the production patterns of spring runoff, the start and end dates and stage periods of the production patterns. Based on the qualitative identification results, the contribution of each production runoff to the total annual runoff and the total annual spring runoff is quantitatively assessed. The results of the study show that the spring runoff production patterns in the Second Songhua River Basin can be divided into snowmelt runoff, frozen soil conditions of snowmelt–rainfall runoff and rainfall runoff under frozen soil conditions; the snowmelt production is from 21 March, the frozen soil conditions production is from 21 April and the frozen soil ablation ended on 15 June; the shortest phases of each production pattern last 28, 20 and 18 days and the longest last 31, 26 and 24 days. This research provides the basis for improving the principles of production runoff calculation in spring runoff simulation methods.

Modeling Riverine N2O Sources, Fates, and Emission Factors in a Typical River Network of Eastern China.

Estimates of riverine N2O emission contain great uncertainty because of the lack of quantitative knowledge concerning riverine N2O sources and fates. Using a 3.5-year record of monthly N2O measurements from the Yongan River network of eastern China, we developed a mass-balance model to address the riverine N2O source and sink processes. We achieved reasonable model efficacies (R2 = 0.44-0.84, Nash-Sutcliffe coefficients = 0.40-0.80) across three tributaries and the entire river system. Estimated riverine N2O loads originated from groundwater (38-88%), surface runoff (3-26%), and in-stream production (4-48%). Estimated in-stream losses via atmospheric release + complete denitrification accounted for 76, 95, 25, and 89% of riverine N2O fate for the agricultural, residential, forest, and entire river system, respectively. Considering limited complete denitrification, the model estimated an upper-bound riverine N2O emission rate of 2.65 ton N2O-N km-2 year-1 for the entire river system. Riverine N2O emission estimates were of comparable magnitude to those estimated with a power-law scaling model. Riverine N2O emissions using the IPCC default emission factor (0.26%) overestimated emissions by 3-15 times, whereas the dissolved N2O concentration-based emission factor overestimated or underestimated emissions. This study highlights the importance of combining comprehensive information on N2O sources and fates to achieve accurate riverine N2O emission estimates.

Determination of the Most Important Soil Factors in Runoff Production in Different Land uses in Gachsaran Formation

Determination of the Most Important Soil Factors in Runoff Production in Different Land uses in Gachsaran Formation

The importance of incorporating rain intensity profiles in rainfall simulation studies of infiltration, runoff production, soil erosion, and related landsurface processes

The temporal sequence of fluctuating rainfall intensities during an event - the intensity profile or 'rainfall pattern' - is known to affect water partitioning at the ground surface and associated erosional processes. There can be large differences in runoff ratios and runoff rates between early-peak and late-peak events, and hence in the depth, speed, and sediment transport capacity of resulting overland flow. Whilst rainfall intensity may fluctuate continually during all IPs in natural rainfall, there is little information on the rates of such intensity fluctuations that can be used to guide the design of rainfall simulation experiments. This review analyses relevant data derived from published high-resolution rainfall records and also from new analyses of data from Australian ground observing stations. Both sources confirm the occurrence of rates of intensity change of greater than 500 mm h−1 min−1. It is suggested that the fluctuating intensities characteristic of natural rainfall need to be employed in rainfall simulation experiments in order to generate results applicable to natural landsurface processes like infiltration or soil removal. Constant-intensity rain, as commonly used in rainfall simulation experiments, lacks both the kinds of rapid intensity fluctuations seen in natural rainfall, as well as any representation of natural intensity profiles. These unrepresentative conditions can result in lower runoff rates and larger proportions of infiltration than when intensity fluctuations are present. There is thus a strong case for changing the design of rainfall simulation to reflect more closely natural intensity fluctuations and intensity profiles and their influence on key surface processes such as overland flow and soil erosion.

Developmental characteristics of biological soil crusts and their effects on soil water infiltration on karst slope

Biological soil crusts (BSCs), as a pioneer for vegetation restoration and crucial component of surface landscape, greatly affect land surface process. To explore the development of BSCs and its effects on soil water infiltration in karst region, we investigated the development of BSCs and analyzed the infiltration processes with different BSCs coverages (0, 28%, 40%, 70%, 97%) and rainfall intensities (42 and 132 mm·h-1) in simulating rainfall experiments on a typical karst slope. The results showed that there were significant differences in the development of BSCs for different land use types, whereas the spatial variation of BSCs development on the slope was not obvious under the same land use type. Compared to the bare plot, the presence of BSCs significantly increased surface roughness, the initial runoff generation time, and soil water infiltration. In the cases of light (42 mm·h-1) and intensive (132 mm·h-1) rainfall, the initial infiltration rate of BSCs covered plots were 1.7-1.9 times and 1.2-1.9 times as that of bare plot, while the average infiltration rate in BSCs covered plots were 2.5-3.0 times and 1.4-3.3 times as that of bare plot, respectively. The BSCs coverage was significantly positively correlated with the initial runoff production time. The critical values of facilitating infiltration of BSCs coverage were between 65% and 70% under the test rainfall intensities. For heavy rainfall events, the inhibiting effects of BSCs on surface runoff were weakened. Horton model was the most reliable one for describing the infiltration process on karst slope with BSCs, followed by Kostiakov model and Philip model. In conclusion, the spatial variability of BSCs development on the karst slope was higher. The presence of BSCs had a significant effect on soil permeability in karst region.

Modelling Infiltration Process, Overland Flow and Sewer System Interactions for Urban Flood Mitigation

Rainfall-runoff transformation on urban catchments involves physical processes governing runoff production in urban areas (e.g., interception, evaporation, depression, infiltration). Some previous 1D/2D coupled models do not include these processes. Adequate representation of rainfall–runoff–infiltration within a dual drainage model is still needed for practical applications. In this paper we propose a new modelling setup which includes the rainfall–runoff–infiltration process on overland flow and its interaction with a sewer network. We first investigated the performance of an outflow hydrograph generator in a 2D model domain. The effect of infiltration losses on the overland flow was evaluated through an infiltration algorithm added in a so-called Surf-2D model. Then, the surface flow from a surcharge sewer was also investigated by coupling the Surf-2D model with the SWMM 5.1 (Storm Water Management Model). An evaluation of two approaches for representing urban floods was carried out based on two 1D/2D model interactions. Two test cases were implemented to validate the model. In general, similar results in terms of peak discharge, water depths and infiltration losses against other 1D/2D models were observed. The results from two 1D/2D model interactions show significant differences in terms of flood extent, maximum flood depths and inundation volume.

Hydrological connectivity assessment of landscape ecological network to mitigate development impacts

To mitigate the negative effects of land use developments, the current study focused on the hydrological connectivity within the landscape ecological network of Gharesou watershed, Iran, using Graph theory. Thus, scenarios of the future land use arrangements were used for the objective assessment of the effects of patterns on the ecological structures and functions, the main target being runoff control. Hydrological connectivity was analyzed using runoff source network, stream network and its buffer zone. Also, functions like permeability and runoff production potential were analyzed for the future scenarios. Following the ranking of the connectivity significance of the hydrological graphs elements, the ecosystem services hotspots and incompatible land uses were demonstrated. Subsequent assessments of the elements of runoff source networks using Circuit Theory helped identify the future critical areas. Analyses of the hydrological graphs and the runoff source network represented the amount and location of critical areas in each development scenario as well as the imposed hydrological costs. The hydrological and ecological land use costs were used in the process of land use optimization through Simulating Annealing algorithm (SA). Using these costs in the land use planning process resulted in detecting areas which may experience disturbance later in future. Finally, the results of the optimization of scenarios showed how land use arrangements in each scenario can be optimized to simultaneously include the ecological suitability (vertical relationships) and the ecological network relationships (horizontal relationships).

Evaluation of the impacts of land use/cover changes on water balance of Bilate watershed, Rift valley basin, Ethiopia

Abstract Land use/cover change is one of the factors responsible for changing the water balance of the watershed by altering the magnitude of surface runoff, interflow, base flow, and evapotranspiration. This study was aimed at evaluating the impacts of land use/cover change on the water balance of Bilate watershed between 1989, 2002, and 2015. The water balance simulation model (WaSiM) was used to access the impacts of land use/cover change on water balance. The model was calibrated (1989–2003) and validated (2007–2015) using the streamflow of at Bilate Tena gauging station. The result of land-use dynamics showed land use/cover change has a significant impact on the water balance of the watershed: on runoff production, base flow, interflow, evapotranspiration, and total simulation flow. In the study watershed, the change in total simulated flow increased by 77.83%; surface runoff, interflow, and base flow increased by 80.23%, 75.69%, and 87.79% respectively; and evapotranspiration decreased by 6% throughout the study period (1989–2015). The results obtained from this study revealed that the watershed is under land/cover change that shows its impacts on hydrological processes and water balance. Thus, effective information regarding the environmental response of land use/cover change is important to hydrologists, land-use planners, watershed management, and decision-makers for sustainable water resource projects and ecosystem services. Therefore, the policy-makers, planners, and stakeholders should design strategies to ensure the sustainability of the watershed hydrology for the sake of protecting agricultural activities, and urban planning and management systems within the watershed area.

Identification of phosphorus index improvements through model comparisons across topographic regions in a small agricultural watershed in Vermont (USA)

AbstractMany U.S. states require farmers to evaluate the risk of P loss from farm fields using P site assessment tools, such as the Phosphorus Index (P‐Index). The simplicity of the P‐Index allows for users with various backgrounds to utilize the tool; however, the P‐Index may be limited in its ability to reliably predict P losses across variable farm terrain, for instance where saturation‐excess runoff generation dominates. The objective of this study was to identify potential improvements that could be made to the Vermont P‐Index (VT P‐Index) by comparing VT P‐Index predictions of P loss with those of a model that considers topographic controls on P transport. Scenarios with varying P management strategies were developed and modeled for corn (Zea mays L.) silage production fields in a small agricultural watershed (360 ha) located in Vermont using both the VT P‐Index and a modified version of the Soil and Water Assessment Tool (SWAT). Modeled outputs from both the VT P‐Index and SWAT were aggregated based on topographic index (TI) class and compared for the directional agreement of P risk assessments and relative annual average dissolved and particulate P losses. The P‐Index nutrient management recommendations gave higher P loss risk ratings than SWAT for 94% of the 120 unique scenario combinations simulated. Results from this study suggest that the VT P‐Index could improve its ability to support farm nutrient management planning by incorporating topographic controls on runoff production into its estimation of P transport.

Monitoring and modelling of hydrological processes in the semiarid region of Brazil: The Cariri experimental basins

AbstractCatchments have highly variable yields of runoff and soil erosion. The size, land use and the surface cover play a significant role and influence the catchment response and parameter values of simulation models. Two experimental basins—the Cariri basins—were equipped in a semi‐arid region of Brazil, for obtaining runoff and sediment yield at different catchment scales, as well as, to evaluate the influence of the land use and surface cover. In the first basin, located in the municipality of Sumé, the field studies were carried out at two different scales: four micro‐catchments with an area of around 0.5 ha and nine standard Wischmeier‐type erosion plots of 100 m2. The experimental units had varied vegetation and management. They were subjected only to natural rainfall events, and were monitored from 1982 to 1991. The total runoff and total sediment yield were determined for each of the events. The installations in the second basin, in the municipality of São João do Cariri, from 1999, include two erosion plots, three micro‐catchments, and two sub‐catchments of a small basin. These basins are still being monitored for runoff and sediment production. Among the micro‐catchments two are nested to detect any scale effect at the micro‐catchment level. Nearly 600 events of precipitation, that produced runoff in at least one of the experimental units, have been registered. These data have been used to evaluate the influence of various factors, including cultivation practices and to calibrate hydrological models for plots and micro‐catchments. Parameters have been tested by means of cross validations among micro‐catchments and sub‐catchments. The data sets are made available to all the catchment hydrology researchers and others at https://doi.org/10.5281/zenodo.4690886.

Spatiotemporal Patterns of Hillslope Erosion Investigated Based on Field Scouring Experiments and Terrestrial Laser Scanning

Hillslope erosion is an essential source of catchment sediment yield. However, the current understanding of the spatiotemporal patterns of field hillslope erosion processes is limited. In this study, fourteen runoff scouring experiments were undertaken on two plots (A and B) established on one field slope of the hilly and gully loess plateau in China. Terrestrial laser scanning (TLS) was employed to investigate soil erosion processes across the hillslopes of the plots. The results demonstrated that the TLS-derived cumulative sediment yields of the hillslopes were more accurate than the TLS-derived consecutive sediment yields (i.e., the sediment yields for individual experiments). The magnitudes of the mean absolute/relative errors for the TLS-derived cumulative sediment yield for slopes A and B were 0.87 kg/25.02% and 1.26 kg/56.82%, respectively, with the linear relation R2 between the calculated and measured values over 0.60 (p < 0.001). The sediment yields from the hillslopes fluctuated considerably even when the runoff production became stable, leading to a weak relationship between the sediment yield and runoff discharge (the R2 values for slopes A and B were 0.57 (p = 0.002) and 0.08 (p = 0.321) for inter-experiments, and 0.37 (p < 0.001) and 0.06 (p = 0.035) for intra-experiments, respectively). The development of hillslope erosion was found to experience three major stages, which included a rapid increase and widespread distribution, a sharp decrease, and a stable distribution of the area with erosion/deposition. The rill development impacted the cumulative erosion and sediment yield rather than the cumulative deposition, with the impacts of rill depth and rill width development being stronger than those of rill length. The peak sediment yield corresponded well with the evolution of rills, partly accounting for the weak relationship between runoff and sediment yield. Our results provide a useful reference for the development of process-based soil erosion models and the establishment of spatially targeted control of soil erosion.

Aplicação do modelo SWAT como ferramenta para análises hidrossedimentológicas na bacia hidrográfica do Rio Mutum Paraná – RO

O uso de modelos na previsão de produção de água e sedimento apresenta um grande potencial para serem utilizados no planejamento dos recursos hídricos, sendo que através desta ferramenta é possível estimar impactos causados pelas atividades antrópicas. Com base nessa premissa, utilizamos o modelo SWAT (Soil and Water Assessment Tools) em uma bacia rural (771,2 km²) localizada nos municípios de Porto Velho e Nova Mamoré, denominada Sub bacia Mutum Paraná. Sua área tem influência direta da usina hidrelétrica de Jirau, e seu exutório localiza-se à montante da barragem. Neste contexto, o monitoramento e a modelagem fornecem suporte ao manejo hidrossedimentológico de bacias hidrográficas. Os métodos aplicados foram monitoramento hidrológico, geração de dados matriciais e tabulares, delimitação de sub bacias, validação do modelo, análises estatísticas e avaliação espacial da produção de água e sediment. O modelo SWAT gerou dados simulados que representaram os processos observados em campo, como de produção de água e sedimento. A partir das simulações foi possível conhecer as sub bacias que produziram maior quantidade de água e sedimentos. Os valores de escoamento superficial e sedimento máximos respectivamente encontrados são de 96,7 (mm/ano) e 3,35(ton/ha/ano).

Intensification scenarios in projected precipitation using stochastic weather generators: a case study of central Oklahoma

Previous studies have investigated the character and distribution of intense precipitation events across the United States. Increasing trends in intense, daily precipitation events at heavy (90–< 95th percentile), very heavy (95–< 99th percentile), and extreme (≥ 99th percentile) thresholds have all been reported. However, no previous studies have investigated the potential application of stochastic weather generators in determining future, site-specific distributions of such intense precipitation occurrences. In this study, two scenarios of future changes in intense precipitation for Weatherford, Oklahoma were examined through the use of a specific weather generator, SYNTOR, and by examination of heavy, very heavy, and extreme precipitation categories. All precipitation events across the three categories were increased multiple times by eight different percentages ranging from 5% to 75%, while precipitation events within the three categories were simultaneously increased by 14%, 20%, and 30%, respectively. Projected changes in the occurrence and categorical thresholds of intense precipitation events, as well as total monthly and annual precipitation and wet-dry transition probabilities, were assessed. The findings of this study show that projected increases in intense precipitation ranging from 5% to 40% are plausible and within the margin of error, based on the application of the two intensification scenarios to the synthetically generated weather data. Overall, the precipitation intensification scenarios markedly impacted estimates of intense precipitation, as well as average annual and monthly precipitation totals, but did not markedly impact the temporal distribution of precipitation annually or across seasons, nor the transition probabilities of projected precipitation between wet and dry days. Precipitation intensification scenarios can ultimately benefit in simulating erosion, runoff, and crop productivity responses to future precipitation distributions in agricultural watersheds of the Southern Great Plains as well as other locations.

Planning London’s green spaces in an integrated water management approach to enhance future resilience in urban stormwater control

Vegetation, as a fundamental element of urban green infrastructure, plays a vital role in mitigating urban flooding. Green infrastructure performance in mitigating floods depends on plant responses to meteorological forcing. This puts urban green infrastructure in risk under a changing climate. In this study, the resilience and efficiency of London’s green infrastructure under climate change is evaluated. The coupled water and carbon dynamics were evaluated using a mechanistic ecohydrological model forced with the new generation of 2018 UK Climate Projections (UKCP18).It was found that despite overall reductions of runoff production in London under climate change in winter/autumn, current urban green infrastructure in London can lose its efficiency due to the elevated levels of plant water stress unless it operates in an integrated manner with the traditional grey infrastructure drainage system. Plant water stress induced mostly by changes in climate is expected to limit vegetation performance during the end of growing seasons. The negative effects of varying climatic factors on vegetation dynamics can only be partially alleviated by the positive effects of the elevated CO2 concentration level, and are highly uncertain due to the large uncertainty of climate projections.

Hydrological basis of the Devils Lake, North Dakota (USA), terminal lake flood disaster

Devils Lake, a terminal lake in northeast North Dakota (USA), has experienced catastrophic flooding since 1993. From January 31, 1993, to December 31, 2014, lake level rose from 433.62 to 442.44 m, lake area expanded from 179.9 to 653.5 km2, and lake volume increased from 0.70 to 3.80 km3. More than $1 billion ($USD) has been spent in government payments to mitigate direct, primary, tangible flood damages. This paper provides a case study of the hydrological basis of the Devils Lake flood disaster. The unique geomorphic setting, paleoclimatic record, and hydroclimatic conditions of the region are summarized, and a wide range of hydroclimatic data is examined to provide a broad understanding of the physical basis of the flood disaster. The primary cause of the disaster was a transition to a sustained wetter climate that resulted in a dramatic response in basin hydrological variables in 1993. The transition from a long-term dry period to a long-term wet period caused the lake water budget to begin to change from an atmosphere-controlled water budget dominated by precipitation input to an amplifier lake water budget dominated by surface runoff input to the lake. Other important hydrological factors include a nonlinear precipitation–runoff relationship following the long-term drought, fill-spill and fill-merge hydrological behavior that is characteristic of wetland complexes, an increase in the lake area-to-basin area ratio, and the critical role of frozen soils in controlling infiltration and runoff production of spring snowmelt. Engineering works to manage lake volume through two outlets have reduced, but not entirely eliminated, future flood risk.

Glacial melt disturbance shifts community metabolism of an Antarctic seafloor ecosystem from net autotrophy to heterotrophy

Climate change-induced glacial melt affects benthic ecosystems along the West Antarctic Peninsula, but current understanding of the effects on benthic primary production and respiration is limited. Here we demonstrate with a series of in situ community metabolism measurements that climate-related glacial melt disturbance shifts benthic communities from net autotrophy to heterotrophy. With little glacial melt disturbance (during cold El Niño spring 2015), clear waters enabled high benthic microalgal production, resulting in net autotrophic benthic communities. In contrast, water column turbidity caused by increased glacial melt run-off (summer 2015 and warm La Niña spring 2016) limited benthic microalgal production and turned the benthic communities net heterotrophic. Ongoing accelerations in glacial melt and run-off may steer shallow Antarctic seafloor ecosystems towards net heterotrophy, altering the metabolic balance of benthic communities and potentially impacting the carbon balance and food webs at the Antarctic seafloor.

Assessing the Feasibility of a Cloud-Based, Spatially Distributed Modeling Approach for Tracking Green Stormwater Infrastructure Runoff Reductions

Use of green stormwater infrastructure (GSI) to mitigate urban runoff impacts has grown substantially in recent decades, but municipalities often lack an integrated approach to prioritize areas for implementation, demonstrate compelling evidence of catchment-scale improvements, and communicate stormwater program effectiveness. We present a method for quantifying runoff reduction benefits associated with distributed GSI that is designed to align with the spatial scale of information required by urban stormwater implementation. The model was driven by a probabilistic representation of rainfall events to estimate annual runoff and reductions associated with distributed GSI for various design storm levels. Raster-based calculations provide estimates on a 30-m grid, preserving unique combinations of drainage factors that drive runoff production, hydrologic storage, and infiltration benefits of GSI. The model showed strong correspondence with aggregated continuous runoff data from a set of urbanized catchments in Salinas, California, USA, over a three-year monitoring period and output sensitivity to the storm drain network inputs. Because the model runs through a web browser and the parameterization is based on readily available spatial data, it is suitable for nonmodeling experts to rapidly update GSI features, compare alternative implementation scenarios, track progress toward urban runoff reduction goals, and demonstrate regulatory compliance.