Individual Storm Events Research Articles

Bayesian inference of uncertainties in precipitation‐streamflow modeling in a snow affected catchment

Bayesian inference is used to study the effect of precipitation and model structural uncertainty on estimates of model parameters and confidence limits of predictive variables in a conceptual rainfall‐runoff model in the snow‐fed Rudbäck catchment (142 ha) in southern Finland. The IHACRES model is coupled with a simple degree day model to account for snow accumulation and melt. The posterior probability distribution of the model parameters is sampled by using the Differential Evolution Adaptive Metropolis (DREAM(ZS)) algorithm and the generalized likelihood function. Precipitation uncertainty is taken into account by introducing additional latent variables that were used as multipliers for individual storm events. Results suggest that occasional snow water equivalent (SWE) observations together with daily streamflow observations do not contain enough information to simultaneously identify model parameters, precipitation uncertainty and model structural uncertainty in the Rudbäck catchment. The addition of an autoregressive component to account for model structure error and latent variables having uniform priors to account for input uncertainty lead to dubious posterior distributions of model parameters. Thus our hypothesis that informative priors for latent variables could be replaced by additional SWE data could not be confirmed. The model was found to work adequately in 1‐day‐ahead simulation mode, but the results were poor in the simulation batch mode. This was caused by the interaction of parameters that were used to describe different sources of uncertainty. The findings may have lessons for other cases where parameterizations are similarly high in relation to available prior information.

Synoptic Scale Weather Patterns and Size-5 Avalanches on Mt. Shasta, California

Upper atmospheric synoptic scale patterns associated with size-5 avalanches, the largest and most destructive types of avalanches, occur on Mt. Shasta, California in the Southern Cascade mountain range. We identified and analyzed fifteen size-5 avalanches over nine individual storm events in the last 50 years using composite and anomaly plots of surface and upper-air data and relationships between: 250hPa wind field, 500 hPa geopotential height field, 700 hPa precipitable water, atmospheric thickness, and surface temperature. Results indicated a strong correlation between synoptic scale warm air advection, moisture advection, strong southwest winds, and low geopotential heights and the formation of large, size-5 slab avalanches. The identification and orientation of a jet streak adds to the growing body of synoptic ingredients used for avalanche forecasting on Mt. Shasta.

Sediment transport by runoff on debris‐mantled dryland hillslopes

Hillslopes supply sediment to river channels, and therefore impact drainage basin functioning and evolution. The relationship between hillslope attributes and sediment flux forms the basis of geomorphic transport laws used to model the long‐term topographic evolution of drainage basins, but their specific interactions during individual storm events are not well understood. Runoff‐driven erosion of coarse particles, prevalent in dryland environments, presents a particular set of conditions for sediment transport that is poorly resolved in current models. In order to address this gap, we developed a particle‐based, force‐balance model for sheetwash sediment transport on coarse, debris‐mantled hillslopes within a rainfall‐runoff model. We use the model to examine how the interplay between hillslope attributes (gradient, length and grain size distribution) and runoff characteristics affects sediment transport, grain‐size changes on the hillslope, and sediment supply to the slope base. The relationship between sediment flux and hillslope gradient was found to transition from linear above a threshold to sigmoidal depending on hillslope length, initial grain sizes, and runoff characteristics. Grain sizes supplied to the slope base vary in a complex manner with hillslope attributes but an overall coarsening of the hillslopes is found to occur with increasing gradient, corroborating previous findings from field measurements. Intense, short duration storms result in within‐hillslope sediment redistribution and equifinality in sediment supply for different hillslope characteristics, which explain the lack of field evidence for any systematic relationships. Our model findings provide insights into hillslope responses to climatic forcing and have theoretical implications for modeling hillslope evolution in dry lands.

Response of a modern cave system to large seasonal precipitation variability

Speleothems are capable of providing information on the response of middle and low-latitude terrestrial environments to global climate change during the Pleistocene and Holocene. Multiproxy speleothem studies, however, have demonstrated that complex interactions can occur in cave settings between processes that are directly and indirectly related to climate change. Thorough and extended monitoring of modern cave environments is necessary in order to fully understand how each cave responds to these processes on seasonal and interannual timescales, and how environmental signals are preserved in speleothem carbonate.Regular environmental monitoring began at Black Chasm Cavern in the Sierra Nevada foothills, California, during the winter of 2006–2007. Monthly measurements of cave air temperature, humidity, and pCO2 in Black Chasm demonstrate that the cave is ventilated in the winter months, when cold, dense surface air sinks into the cave. Cave drip-water flow nearly ceases during the late summer and autumn, increases substantially during the winter and spring, and responds within hours to storm events during the height of the rainy season. Rainwater and drip water δ18O and δ2H are controlled by variations in surface air temperature and moisture source. While rainfall source influences rainwater isotopes through individual storm events, it has less influence on drip water isotopic composition due to mixing of recharge waters delivered by different rainfall events in the epikarst. Variations in drip water chemistry (δ13C, Mg/Ca, and Sr/Ca) indicate that the greatest level of calcite precipitation upflow from the drip water collection site (prior calcite precipitation) occurs during the autumn (October–November) when drip rates are slow and cave air pCO2 is low. The least prior calcite precipitation occurs during the summer (July–August) when drip rates are slow but cave air pCO2 is at a maximum. While pCO2 is a primary control on prior calcite precipitation during all seasons, the predominant influence of drip rate variability on prior calcite precipitation is evident when considering only those seasons (winter, spring, and autumn) characterized by low cave air pCO2. Thus, drip rate variability, and in turn rainfall amount, should provide the primary control on trace element variations ultimately captured in speleothem calcite. The isotopic and chemical variability observed in Black Chasm drip waters supports previous interpretations of speleothem paleoclimate proxy records from a nearby cave where such monitoring is not feasible. Observations of the modern cave environment at Black Chasm provide a reference point for the interpretation of stalagmite proxy records from similar seasonal (Mediterranean) climates.

Moisture Measurements as Performance Criteria for Extensive Living Roof Substrates

AbstractExtensive living roof substrate design to promote storm-water management while balancing structural load and maintaining >60% nonirrigated plant cover is investigated through linked laboratory and field experiments in Auckland, New Zealand. Setting quantifiable goals for the 2002 FLL guidelines and agronomic testing methods resulted in successful design of multiple nonproprietary substrates. Particle size distribution and quality control in the materials’ supply chain are critical. Additional work is required to define a meaningful standard permeability test for living roofs. While the maximum water capacity guideline provides a conservative estimate for structural loading when a substrate is wet, it should not be used to predict storm-water retention. Agronomic measures of readily available water (10–100 kPa suction) plus plant stress water (100–1,500 kPa suction) provide a reasonable estimate for the maximum potential rainfall storage during individual storm events. Subject to Auckland’s frequen...

Correspondence between a plasma-based EMIC wave proxy and subauroral proton precipitation

[1] The loss of relativistic electrons from the Earth's radiation belts as a result of resonant interactions with electromagnetic ion cyclotron waves (EMIC) waves has yet to be fully quantified, in part, due to the lack of global measurements of the wave distribution during individual storm events. Recent work has focused on augmenting direct wave measurements with proxy wave indicators. Here we compare two different techniques for inferring the presence of EMIC waves: 1) a wave-growth proxy and amplitude estimate based on in situ plasma measurements of the cold and hot ion distributions, and 2) FUV observations of subauroral proton precipitation, which is thought to result from interactions with EMIC waves. For two event intervals, we show good correspondence between proxy predictions of wave growth, calculated using measurements from geostationary spacecraft, and precipitation observed at the northern hemisphere ionospheric footprint. Further, for times when the proxy is positive, we observe a moderate positive correlation (r = 0.56) between the predicted wave amplitude and the mean FUV brightness in a 300-km circle about the footprint. Further development and verification of these techniques will enhance our ability to infer the global distribution of EMIC waves when direct measurements are not available.

Drought sensitivity of patterned vegetation determined by rainfall-land surface feedbacks

[1] Vegetation pattern morphology is suggested as one indicator of system closeness to desertification. Using pattern morphology as an indicator requires understanding the timescales at which patterned vegetation systems respond to drought. Modeling these timescales requires accounting for rainfall intermittency and all the pathways controlling vegetation-precipitation feedbacks. In this paper, a model of rainfall initiation and intensity based on the dynamics of a single-column atmospheric boundary layer is coupled to a patterned vegetation model. The coupled climate-vegetation model, parameterized to represent a typical vegetation morphology in southwestern Niger, is used to investigate the timescales of desertification due to shifts in the total annual rainfall regime, and the effect of precipitation feedbacks on these timescales. Depending on the exact rainfall history, biomass and spatial morphology may not respond monotonically to a decrease in rainfall. The model results suggest changes in pattern morphology responding to shifts in annual rainfall require at least 4–5 years. Feedbacks acting through vegetation's influence on surface albedo and, to a lesser extent, surface evapotranspiration act to speed up the vegetation response to drought. Although the overall local-scale vegetation-precipitation feedback is positive, individual storm events may exhibit negative feedbacks, in which rainfall only occurs for low vegetation cover, depending on the free atmospheric conditions. Vegetation-precipitation feedbacks are sufficiently important to speed up changes in vegetation patterns, even in marginal drylands with low biomass levels.

Temporal clustering of tropical cyclones and its ecosystem impacts

Tropical cyclones have massive economic, social, and ecological impacts, and models of their occurrence influence many planning activities from setting insurance premiums to conservation planning. Most impact models allow for geographically varying cyclone rates but assume that individual storm events occur randomly with constant rate in time. This study analyzes the statistical properties of Atlantic tropical cyclones and shows that local cyclone counts vary in time, with periods of elevated activity followed by relative quiescence. Such temporal clustering is particularly strong in the Caribbean Sea, along the coasts of Belize, Honduras, Costa Rica, Jamaica, the southwest of Haiti, and in the main hurricane development region in the North Atlantic between Africa and the Caribbean. Failing to recognize this natural nonstationarity in cyclone rates can give inaccurate impact predictions. We demonstrate this by exploring cyclone impacts on coral reefs. For a given cyclone rate, we find that clustered events have a less detrimental impact than independent random events. Predictions using a standard random hurricane model were overly pessimistic, predicting reef degradation more than a decade earlier than that expected under clustered disturbance. The presence of clustering allows coral reefs more time to recover to healthier states, but the impacts of clustering will vary from one ecosystem to another.

Effect of High Flow Events on In-Stream Dissolved Organic Nitrogen Concentration

Dissolved organic nitrogen (DON) can comprise a large and biologically important fraction of total dissolved N in surface water. Biotic and abiotic processes result in heterogeneous DON concentrations and bioavailability in soils, and as hydrologic connectivity expands and flow paths change in watersheds, novel sources of DON can be mobilized and transported to surface water. Although the relationship between in-stream DOC concentration and stream discharge has previously been examined in the literature, up to now there has not been a synthesis examining how DON concentrations, loads, and composition change during transitions from base flow to pulse flow conditions. We present a meta-analysis examining the effect of high flow on DON concentration ([DON]). The ratio of mean pulse flow [DON] to mean base flow [DON] (P:B) was calculated for individual events and averaged (geometric) within and then across sites to generate an overall effect size. For 47 sites (78 events), mean P:B was 1.58, which was significantly different from unity. This moderate increase in DON concentration contributed to over a more than 10-fold average increase in the rate of DON yield from base flow to high flow. The response of [DON] to high flow was significant in catchments where individual storm events or snowmelt runoff events were responsible for elevated flows, whereas the response was not significant in catchments where high discharge resulted from a mixture of upstream snowmelt and rain events. Additionally, an examination of DOC:DON ratios during high flow indicates that multiple sources of DON may be mobilized during high flow. Finally, current models of annual DON export may be improved by including a positive relationship between discharge and DON.

HYDROLOGICAL CHARACTERISTICS THAT DETERMINE SUSPENDED SEDIMENT LOAD OF TROPICAL URBAN STORM EVENTS

Dwelling on the less investigated tropical urban river channels, this paper attempts to understand the hydrological characteristics that dominate and account for most of the suspended loads of individual events through intra-events SS concentrations-Discharge (Q) relationship. Individual storm event has a variable signature due to the differing hydrological characteristics. As such, suspended sediment (SS) loads transported during storm events are never equivalent. A total of 34 storm events were determined from four gauging stations in the Kallang subcatchment, of the Marina Barrage Catchment, Singapore. There is a need for authorities to understand the nature of storm dynamics for optimal management of water resources in the new reservoir’s catchment. Step-wise regression model was used to determine the dominating hydrological characteristics of the total loads during the storm events. Peak SS concentrations and the duration of high rainfall intensity (>60mm/h) are the main determinant of SS loads in the tropical urban waterways. Rapid rising and falling limbs of the storm hydrograph and short, intense storm events, typical of tropical, urban environment are explanations for the outcomes attained from the regression analysis. (Keywords: Tropical urban catchment, Suspended Sediment, Discharge, Regression modeling, Hydrological Characteristics ) INTRO

A seismic signature of river bedload transport during storm events

A seismic signature of river bedload transport during storm events

Runoff, Sediment Transport, and Effects of Feral Pig (Sus scrofa) Exclusion in a Forested Hawaiian Watershed

Browsing and trampling by nonnative feral pigs (Sus scrofa) negatively impact native flora and fauna in forested ecosystems and cause soil compaction. However, their impact on runoff and erosion is largely unknown. This study addressed this knowledge gap by investigating effects of feral pigs on runoff volume and total suspended solids (TSS) in runoff from the upper forested area of a Hawaiian watershed. Correlations between TSS, runoff, and other environmental variables were also examined. Runoff was collected monthly after 11 individual storm events from June 2008 to April 2009 at seven sites in the Mānoa watershed on the island of O'ahu. Each site consisted of paired runoff plots (5.04 m2) with one plot located inside a fenced pig exclosure (exclosures 1 yr old at study initiation) and the other located in an adjacent area open to feral pigs. Forest composition and structure (stem density, stand basal area, and seedling/ sapling counts) were quantified at each site. Soil moisture, throughfall, runoff volume, and TSS in runoff were sampled for each storm event. The seven sites varied considerably in terms of forest structure, with stem densities ranging from 1,500 to 9,000 stems ha-1 and basal areas ranging from 20 to 132 m2 ha-1. Vegetation at all sites was dominated by nonnative species. Runoff volumes from fenced and unfenced plots were highly variable, ranging from <1 to >128 liters. TSS levels in runoff ranged from <0.01 to 7.05 g liter-1. TSS levels were generally higher in wet-season months, but this pattern was not consistent across all sites. TSS in runoff was significantly correlated with throughfall, soil moisture, and coarse woody debris cover. Although pig exclusion did not reduce TSS, significant reductions in runoff volume from pig exclusion plots were observed at one site, and two other sites showed a similar trend. Longer-term studies may reveal stronger or more consistent impacts of feral pigs. Using paired fenced versus unfenced runoff plots to study erosion impacts of feral pigs is a novel approach, and results from this study will help forest managers better understand and manage runoff and erosion dynamics.

Runoff water quality and vegetative establishment for groundcovers on steep slopes

Construction sites can be a major source of sediment, a common pollutant in surface waters, because steep slopes are often bare during active construction. The use of mulch and polymers has been found to reduce erosion rates and improve runoff water quality on construction sites. Different erosion control methods on steep slopes (2:1) consisting of straw, straw plus 37 kg ha−1 (33 lb ac−1) linear anionic polyacrylamide (straw + PAM), and excelsior blankets were evaluated based on runoff water quality, vegetative establishment, or both at six construction sites. Plots (3 to 9 m [10 to 30 ft] wide by 9 m [29.5 ft] long) were established on cut slopes. Runoff was collected at four of six sites by installing plastic barriers to direct a portion of runoff into containers, later analyzed for turbidity and total suspended solids (TSS) in the laboratory. Large differences in water quality were often not statistically significant for individual storms due to high variability. However, when data were averaged across all storm events, the straw + PAM treatment reduced mean runoff turbidity at three of four sites and mean TSS at two of the four sites compared to straw alone. Maximum reductions in turbidity and TSS were 81% and 56%, respectively. Runoff from the excelsior plots had significantly lower turbidity and TSS than straw plots in one of three sites. Compared to straw + PAM, excelsior had significantly higher turbidity at two of three sites and higher TSS at one of three sites. All differences among treatments for individual storm events occurred within the first three events. Vegetative cover was determined in the field, and aboveground vegetation was harvested to determine biomass production. Neither vegetative cover nor biomass were affected by treatment, and average cover was 60% or less for five of the six sites. Rainfall patterns were largely responsible for vegetative growth, with heavier rainfall soon after seeding tending to reduce cover.

Using 137Cs and 210Pbex to assess soil redistribution on slopes at different temporal scales

Increasing risk of soil loss as a result of climate change, has generated a need for reliable information on erosion rates at different temporal scales. Use of the fallout radionuclides 137 Cs, 210 Pb ex and 7 Be as tracers of sediment mobilization and redistribution makes it possible to obtain estimates of soil redistribution rates within both undisturbed and cultivated landscapes over a range of timescales. Mediterranean landscapes are characterized by a great diversity of physiography and land use, and as a consequence erosion and deposition patterns are highly variable spatially. To document such spatial variability, a slope transect located in the subhumid Pre-Pyrenean mountains (NE Spain) was selected to use 137 Cs and 210 Pb ex to assess medium- and longer-term soil redistribution rates. A total of 23 sectioned soil cores spaced 50 m apart were collected along the slope transect, where 7 Be had been previously used to document soil redistribution resulting from an individual storm event. The inventories of both radionuclides varied markedly, between 409 and 6080 Bq m − 2 for 137 Cs, and between 0 and 6734 Bq m − 2 for 210 Pb ex . Estimates of soil redistribution, derived from the 137 Cs depth profiles, using appropriate conversion models, show that erosion rates along the transect vary between 2.6 and 31.9 Mg ha − 1 year − 1 , and that sedimentation rates vary between 0.2 and 24.5 Mg ha − 1 year − 1 . The highest soil losses occur in cultivated fields, within the midslope zone of the transect, while the highest deposition rates are found in tilled fields within the lower part of the transect. Erosion rates from 210 Pb ex varied widely between 0.1 and 83.7 Mg ha − 1 year − 1 on the lower slope, whereas sedimentation rates ranged between 0.8 and 110 Mg ha − 1 year − 1 also at the bottom slope. The spatial distribution of the radionuclides along the transect reflects the effects of different land use and slope gradient on water erosion. The results obtained confirm the potential for using 137 Cs and 210 Pb ex measurements for assessing soil redistribution on slopes in the Mediterranean environment over different temporal scales. ► 137 Cs and 210 Pb ex soil redistribution rates reflect different temporal sensitivity. ► Land use and slope gradient exert important controls on soil erosion. ► Dense forest protects the soil surface from erosion on steeper slopes. ► 137 Cs and 210 Pb ex provide evidences of the complex patterns of soil redistribution.

Throughfall characteristics in three non-native Hawaiian forest stands

The effect of non-native trees on hydrological processes in Hawaiian forests remains largely unquantified. In this study, throughfall was determined by stationary methods over 18–23-month study periods at three locations each dominated by one of three non-native tree species including Schinus terebinthifolius, Coffea arabica, and Psidium cattleianum. The lowest mean throughfall percentage of 44% occurred under a monotypic stand of P. cattleianum. Mean throughfall under canopies dominated by C. arabica and S. terebinthifolius were 59 and 60%, respectively. Annualized throughfall rates were computed as 62, 60, and 45% under canopies dominated by S. terebinthifolius, C. arabica, and P. cattleianum, respectively. The low mean throughfall at each location is likely due to high wet-canopy evaporation combined with frequent low-intensity/low magnitude rainfall. The exceptionally low throughfall under P. cattleianum may be the result of larger amounts of intercepted rainfall being diverted to stemflow and/or trunk storage. Observations suggest that stemflow is a substantial component of the canopy water balance in stands of P. cattleianum. Plant area index (PAI) was the lowest (3.66) under P. cattleianum and highest (4.64) under C. arabica. Mean direct throughfall coefficient p was computed from individual storm events at each location and ranged from a low of 0.16 under the canopy dominated by P. cattleianum to a high of 0.31 under the canopy dominated by S. terebinthifolius. A similarly computed mean canopy storage capacity S varied from 2.5 mm under primarily S. terebinthifolius to 4.0 mm at the location dominated by C. arabica.

Environmental controls on stable isotope precipitation values over Mali and Niger, West Africa

This study evaluated the effects of the environmental factors precipitation amount (P), temperature (T), and vapor pressure (V p) on the stable isotope composition (δ) of precipitation and the excess-deuterium (d) parameter in Mali and Niger, West Africa. At both locations, δ values were greatly affected by seasonal climatic conditions and a statistically significant negative correlation was observed between δ and P. In Mali, a statistically significant negative correlation was also observed between δ and V p. There was no statistically significant correlation between δ and T. Mean-weighting of δ values may be masking both dry-season and individual storm event precipitation phenomena, which are otherwise observed in arithmetically averaged δ values. Mean monthly d values for peak monsoonal months indicate that precipitation is first-fraction, gaining little recycled water on its journey inland from the Atlantic Ocean near the equator. Agreement between rainy-season precipitation and groundwater δ values, specifically peak monsoonal months, indicates that groundwater is being recharged by infiltration of current monsoonal rains and is not paleo-groundwater recharged under past climatic conditions. Similarity between rainy-season precipitation and groundwater d values provide another indication that monsoonal precipitation under current climatic conditions is the source of groundwater recharge. The knowledge that groundwater is recently recharged monsoonal rains, rather than paleo-groundwater, is important for evaluating groundwater sustainability and the effects that climate change will have on water resources. Understanding and predicting changes in precipitation amounts and intensities, which ultimately affect timing and amount of groundwater recharge, is critical for water resource management.

Analysis and Synthesis of Transmission Loss Hydrographs

Accounting for transmission losses properly is critical in hydrologic analyses in arid and semiarid climates. The objective of this research was to develop a model that could account for the spatial and temporal variations of transmission losses while routing the flow hydrograph through the channel reach. This model was based on Hortonian infiltration methods and hydrologic channel routing. While most transmission loss models predict flow volumes, the model developed herein uses hydrographs of individual storm events. A numerical optimization procedure was used to identify optimum parameter values for each of Horton’s parameters and the routing coefficient, which were then used in modeling transmission losses. Flow gauge data were obtained from the Walnut Gulch Experimental Watershed, which is located near Tucson, Ariz. Testing of this model indicates that it is able to account for transmission losses and predict downstreamflow with reasonable accuracy. To provide a measure of verification, the model was compared to predictions from Lane’s model, which is a commonly used method of accounting for transmission losses based on upstreamflow and downstreamflow volumes. Overall the two methods were found to agree fairly well though differing assumptions in the methods influence the results.

Comment on “Power law catchment‐scale recessions arising from heterogeneous linear small‐scale dynamics” by C. J. Harman, M. Sivapalan, and P. Kumar

Comment on “Power law catchment‐scale recessions arising from heterogeneous linear small‐scale dynamics” by C. J. Harman, M. Sivapalan, and P. Kumar

Using atmospheric chemistry and storm track information to explain the variation of nitrate stable isotopes in precipitation at a site in central Pennsylvania, USA

Stable isotopes of NO 3 − ( δ 15N–NO 3 − and δ 18O–NO 3 −) were monitored in precipitation at a central Pennsylvania site during six storm events in 2005 to determine whether information on atmospheric oxidants (e.g., O 3, NO 2, and NO x), and storm tracks (using the NOAA HYSPLIT model) were capable of explaining observed seasonal and within-storm isotopic variation. Results showed that δ 15N–NO 3 − and δ 18O–NO 3 − in precipitation varied significantly during individual storm events. Seasonally, δ 15N–NO 3 − and δ 18O–NO 3 − in precipitation followed a pattern of depletion during the summer months and enrichment during the winter months. NO 3 − precursor concentrations and atmospheric oxidants were useful for explaining the seasonal and within-storm variation of δ 15N–NO 3 − for all six storm events as evidenced by negative relationships with NO 2:NO x ratios and ozone (O 3). In comparison, δ 18O–NO 3 − was positively related to O 3 in three dormant season storms, which suggested that the O 3 oxidation pathway was important for producing the high δ 18O–NO 3 − observed in wintertime precipitation. Storm track information was especially useful for describing differences in δ 15N–NO 3 −. Cool-sector storms originating from the E/NE produced slightly negative δ 15N–NO 3 − values characteristic of automobile emissions, whereas warm-sector storms with tracks from the SW/S/SE produced slightly positive δ 15N–NO 3 − values characteristic of coal-fired emissions. Lightning also may have been an important source of atmospheric NO 3 − during two warm-sector thunderstorms. This study showed that (1) information about oxidant levels can be useful to predict the seasonal and within-storm variation of NO 3 − stable isotopes in precipitation, and (2) knowledge of storm tracks (warm-sector versus cool-sector) may be important for determining sources of NO 3 − in wet deposition.

Two‐dimensional physically based finite element runoff model for small agricultural watersheds: II. Model testing and field application

AbstractMathematical models are useful analysis tools to understand problems in watersheds associated with runoff, and to find solutions through land use changes and best management practices. However, before a model is applied in the field, it must be tested and checked to ensure that the model represents the real world adequately. In this paper, a two‐dimensional physically based finite element runoff model ROMO2D has been verified and validated by comparing the model output with analytic solution under simplified conditions, published data, and field measurements. Calibration of the model was done manually through a multi‐objective calibration procedure, using observed field data. Before going for field validation/application of ROMO2D, analysis was carried out to determine the optimum number of finite elements into which the watershed should be discretized and the size of the time step. A sensitivity analysis of the model was performed using the observed values of watershed parameters. The model was applied to a 1·45 ha agricultural watershed located in the Shiwalik foothills (India) to simulate runoff. The results demonstrated the potential of the model to simulate runoff from small agricultural watersheds for individual storm events with reasonable accuracy. Copyright © 2008 John Wiley &amp; Sons, Ltd.