Colorado Front Range Research Articles

Contrasting behavior of slow and fast photoreactive gases during the August 21, 2017, solar eclipse

The total solar eclipse on August 21, 2017, provided a rare opportunity to observe and test our understanding of atmospheric dynamics and photochemical dependency on solar irradiance. Here, we utilize observations from the continuous monitoring of both slow and fast photochemically reacting trace gases near Boulder, Colorado, for evaluating the unique dynamic and photochemical forcings on the eclipse day. The monitoring station saw a 93% solar obstruction during the peak of the eclipse. Eclipse day data are contrasted with the full month’s record from this site. The loss of irradiance caused cooling of the surface air by ~3°C, and weakened convective and turbulent mixing. This resulted in a buildup of slow photoreactive gases (methane, short-chain non-methane hydrocarbons), as well as total nitrogen oxides (the sum of nitric oxide (NO) + nitrogen dioxide (NO2)) in the surface layer. In contrast, ozone (O3) declined by ~15 ppb during the first phase of the eclipse compared to median August diurnal mixing ratios. Similar O3 signatures were observed at a series of network stations along the Northern Colorado Front Range. With the loss of irradiance, the initial ratio of NO/(NO + NO2) of ~0.2 dropped steadily, bottoming out at <0.01, but rebounded to approximately two times above August median levels for this time of day towards the end of the eclipse. Above average O3 enhancements were seen in the afternoon hours following the eclipse at this and a series of other nearby surface O3 monitoring sites. The contrasting behavior of these slow and fast photoreactive gases, and comparison with other published eclipse data, allow characterizing these responses as more typical for an urban/polluted environment.

Magnetotelluric investigation of the Colorado front range thrust fault between Castle Rock and Colorado Springs, Colorado

Magnetotelluric investigation of the Colorado front range thrust fault between Castle Rock and Colorado Springs, Colorado

Tall Tower Vertical Profiles and Diurnal Trends of Ammonia in the Colorado Front Range

AbstractAmmonia (NH3) mixing ratios were measured between the surface and 280 m aboveground level from a moveable carriage at the Boulder Atmospheric Observatory tower in summer 2014 as part of the Front Range Air Pollution and Photochemistry Éxperiment. The campaign median mixing ratio was 3.3 ppb, ranging from below detection limits to 192 ppb. Median vertical profiles show an overall increase in NH3 mixing ratios toward the surface of 6.7 ppb (89%) during the day and 3.9 ppb (141%) at night. In contrast to the overall increasing trend, some individual profiles show decreasing NH3 in the lowest 10 m. This suggests that the local surface is capable of acting as either a source or a sink, depending on the relative amounts of NH3 at the surface, and in advected air parcels. We further use this data set to investigate the variation in diurnal patterns of NH3 as a function of height above the surface. At higher altitudes (100 ± 5 and 280 ± 5 m), NH3 mixing ratios reach a gradual maximum during the day between 9:00 and 16:00 local time, likely driven by changes in source region. At lower altitudes (10 ± 5 m), the daytime maximum begins earlier at about 7:00 local time, followed by a sharper increase at 9:00 local time. At this height we also observe a peak in NH3 mixing ratios during the night, likely driven by the trapping of emitted NH3 within the shallower nocturnal boundary layer.

The effects of demographic, social, and environmental characteristics on pathogen prevalence in wild felids across a gradient of urbanization.

Transmission of pathogens among animals is influenced by demographic, social, and environmental factors. Anthropogenic alteration of landscapes can impact patterns of disease dynamics in wildlife populations, increasing the potential for spillover and spread of emerging infectious diseases in wildlife, human, and domestic animal populations. We evaluated the effects of multiple ecological mechanisms on patterns of pathogen exposure in animal populations. Specifically, we evaluated how ecological factors affected the prevalence of Toxoplasma gondii (Toxoplasma), Bartonella spp. (Bartonella), feline immunodeficiency virus (FIV), and feline calicivirus (FCV) in bobcat and puma populations across wildland-urban interface (WUI), low-density exurban development, and wildland habitat on the Western Slope (WS) and Front Range (FR) of Colorado during 2009–2011. Samples were collected from 37 bobcats and 29 pumas on the WS and FR. As predicted, age appeared to be positively related to the exposure to pathogens that are both environmentally transmitted (Toxoplasma) and directly transmitted between animals (FIV). In addition, WS bobcats appeared more likely to be exposed to Toxoplasma with increasing intraspecific space-use overlap. However, counter to our predictions, exposure to directly-transmitted pathogens (FCV and FIV) was more likely with decreasing space-use overlap (FCV: WS bobcats) and potential intraspecific contacts (FIV: FR pumas). Environmental factors, including urbanization and landscape covariates, were generally unsupported in our models. This study is an approximation of how pathogens can be evaluated in relation to demographic, social, and environmental factors to understand pathogen exposure in wild animal populations.

A Multialgorithm Approach to Land Surface Modeling of Suspended Sediment in the Colorado Front Range.

A new paradigm of simulating suspended sediment load (SSL) with a Land Surface Model (LSM) is presented here. Five erosion and SSL algorithms were applied within a common LSM framework to quantify uncertainties and evaluate predictability in two steep, forested catchments (>1,000 km2). The algorithms were chosen from among widely used sediment models, including empirically based: monovariate rating curve (MRC) and the Modified Universal Soil Loss Equation (MUSLE); stochastically based: the Load Estimator (LOADEST); conceptually based: the Hydrologic Simulation Program—Fortran (HSPF); and physically based: the Distributed Hydrology Soil Vegetation Model (DHSVM). The algorithms were driven by the hydrologic fluxes and meteorological inputs generated from the Variable Infiltration Capacity (VIC) LSM. A multiobjective calibration was applied to each algorithm and optimized parameter sets were validated over an excluded period, as well as in a transfer experiment to a nearby catchment to explore parameter robustness. Algorithm performance showed consistent decreases when parameter sets were applied to periods with greatly differing SSL variability relative to the calibration period. Of interest was a joint calibration of all sediment algorithm and streamflow parameters simultaneously, from which trade‐offs between streamflow performance and partitioning of runoff and base flow to optimize SSL timing were noted, decreasing the flexibility and robustness of the streamflow to adapt to different time periods. Parameter transferability to another catchment was most successful in more process‐oriented algorithms, the HSPF and the DHSVM. This first‐of‐its‐kind multialgorithm sediment scheme offers a unique capability to portray acute episodic loading while quantifying trade‐offs and uncertainties across a range of algorithm structures.

Using an integrated remote sensing approach for identification of bedrock and alluvium along the Front Range mountains, Colorado

The Colorado front range (CFR) mountains have a history of significant debris flows. For instance, flash floods in September 2013 triggered over 1138 debris flows in the CFR, leading to eight fatalities and causing damage to buildings, highways, railroads, and infrastructure. Following this event, the United States Geological Survey (USGS) studied these debris flows with the intention of modeling debris flow susceptibility in this region. They identified a problem that the preliminary susceptibility map, before correction, included areas of exposed bedrock as regions that were modeled to have high susceptibility, even though those regions should have been low susceptibility. The objective of this research is to develop and execute an integrated sequential land cover classification (iSLCC) remote sensing approach to discriminate bedrock outcrop from colluvium and, hence, constrain the USGS susceptibility modeling. The approach integrates multispectral, hyperspectral, and radar methods to discriminate colluvium from bedrock outcrops over a study area of nine 7½ min quadrangles. Calibrating against six smaller field study areas that span different geologic formations and ecoregions, a map of land cover, including exposed bedrock outcrops, was produced over a study area that encompasses portions of the St. Vrain and Big Thompson watersheds. The resulting map was compared with the results from traditional land cover classification methods. The iSLCC approach yielded the best overall results and the highest observed agreement (observed accuracy).

Higher measured than modeled ozone production at increased NO<sub><i>x</i></sub> levels in the Colorado Front Range

Abstract. Chemical models must correctly calculate the ozone formation rate, P(O3), to accurately predict ozone levels and to test mitigation strategies. However, air quality models can have large uncertainties in P(O3) calculations, which can create uncertainties in ozone forecasts, especially during the summertime when P(O3) is high. One way to test mechanisms is to compare modeled P(O3) to direct measurements. During summer 2014, the Measurement of Ozone Production Sensor (MOPS) directly measured net P(O3) in Golden, CO, approximately 25 km west of Denver along the Colorado Front Range. Net P(O3) was compared to rates calculated by a photochemical box model that was constrained by measurements of other chemical species and that used a lumped chemical mechanism and a more explicit one. Median observed P(O3) was up to a factor of 2 higher than that modeled during early morning hours when nitric oxide (NO) levels were high and was similar to modeled P(O3) for the rest of the day. While all interferences and offsets in this new method are not fully understood, simulations of these possible uncertainties cannot explain the observed P(O3) behavior. Modeled and measured P(O3) and peroxy radical (HO2 and RO2) discrepancies observed here are similar to those presented in prior studies. While a missing atmospheric organic peroxy radical source from volatile organic compounds co-emitted with NO could be one plausible solution to the P(O3) discrepancy, such a source has not been identified and does not fully explain the peroxy radical model–data mismatch. If the MOPS accurately depicts atmospheric P(O3), then these results would imply that P(O3) in Golden, CO, would be NOx-sensitive for more of the day than what is calculated by models, extending the NOx-sensitive P(O3) regime from the afternoon further into the morning. These results could affect ozone reduction strategies for the region surrounding Golden and possibly other areas that do not comply with national ozone regulations. Thus, it is important to continue the development of this direct ozone measurement technique to understand P(O3), especially under high-NOx regimes.

Changes in ozone and precursors during two aged wildfire smoke events in the Colorado Front Range in summer 2015

Abstract. The relative importance of wildfire smoke for air quality over the western US is expected to increase as the climate warms and anthropogenic emissions decline. We report on in situ measurements of ozone (O3), a suite of volatile organic compounds (VOCs), and reactive oxidized nitrogen species collected during summer 2015 at the Boulder Atmospheric Observatory (BAO) in Erie, CO. Aged wildfire smoke impacted BAO during two distinct time periods during summer 2015: 6–10 July and 16–30 August. The smoke was transported from the Pacific Northwest and Canada across much of the continental US. Carbon monoxide and particulate matter increased during the smoke-impacted periods, along with peroxyacyl nitrates and several VOCs that have atmospheric lifetimes longer than the transport timescale of the smoke. During the August smoke-impacted period, nitrogen dioxide was also elevated during the morning and evening compared to the smoke-free periods. There were nine empirically defined high-O3 days during our study period at BAO, and two of these days were smoke impacted. We examined the relationship between O3 and temperature at BAO and found that for a given temperature, O3 mixing ratios were greater (∼ 10 ppbv) during the smoke-impacted periods. Enhancements in O3 during the August smoke-impacted period were also observed at two long-term monitoring sites in Colorado: Rocky Mountain National Park and the Arapahoe National Wildlife Refuge near Walden, CO. Our data provide a new case study of how aged wildfire smoke can influence atmospheric composition at an urban site, and how smoke can contribute to increased O3 abundances across an urban–rural gradient.

Regional and National Scale Spatial Variability of Photovoltaic Cover Plate Soiling and Subsequent Solar Transmission Losses

Soiling can cause large reductions in solar energy system production. To study the spatial variability of soiling, transmission loss and mass accumulation of particulates on photovoltaic (PV) cover plates were measured at five sites across the continental United States. Three sites were in the Front Range of Colorado in rural, suburban, and urban areas representing a semi-arid environment. One site was in Cocoa Florida in a hot and humid environment, and the final site was in Albuquerque, New Mexico, in a hot and arid environment. Total suspended particulate concentrations (TSP) were measured simultaneously at each site. Comparisons between transmission loss and mass accumulation measurements are made. Both mass accumulation and ambient TSP are shown to have some predictive power for transmission loss. Mean deposition velocities of 1.5 cm/s were observed. For every g/m2 of PM deposited on the PV cover plate, a 2.8% reduction in transmission was observed independent of site. These results provide a method for estimating soiling rates at sites across the United States.

Effects of an Extreme Flood on Trace Elements in River Water-From Urban Stream to Major River Basin.

Major floods adversely affect water quality through surface runoff, groundwater discharge, and damage to municipal water infrastructure. Despite their importance, it can be difficult to assess the effects of floods on streamwater chemistry because of challenges collecting samples and the absence of baseline data. This study documents water quality during the September 2013 extreme flood in the South Platte River, Colorado, USA. Weekly time-series water samples were collected from 3 urban source waters (municipal tap water, streamwater, and wastewater treatment facility effluent) under normal-flow and flood conditions. In addition, water samples were collected during the flood at 5 locations along the South Platte River and from 7 tributaries along the Colorado Front Range. Samples were analyzed for 54 major and trace elements. Specific chemical tracers, representing different natural and anthropogenic sources and geochemical behaviors, were used to compare streamwater composition before and during the flood. The results differentiate hydrological processes that affected water quality: (1) in the upper watershed, runoff diluted most dissolved constituents, (2) in the urban corridor and lower watershed, runoff mobilized soluble constituents accumulated on the landscape and contributed to stream loading, and (3) flood-induced groundwater discharge mobilized soluble constituents stored in the vadose zone.

Dominant tree species of the Colorado Rockies have divergent physiological and morphological responses to warming

Increasing temperatures worldwide, as a primary manifestation of climate change, may cause substantial alterations in forests, presenting a major challenge to predicting responses in forest composition and function. Yet, recent empirical research on climate and forests has found patterns at odds with theoretical and modeling expectations. Indeed, the need for an improved mechanistic understanding of climate’s effects on forests is clear but controlled field studies that address this issue are lacking. Montane and subalpine systems may be particularly sensitive to changes in temperature yet quantifying temperature effects in real-world conditions can be challenging. We used three common gardens arrayed over a 1200m elevation and 6°C mean annual temperature gradient in the Front Range of Colorado to evaluate the temperature responses of seedlings of three widespread and dominant tree species in Colorado: lodgepole pine (Pinus contorta var. latifolia), ponderosa pine (Pinus ponderosa) and aspen (Populus tremuloides). Seedlings for the gardens were sourced from populations naturally occurring at the intermediate elevation on this gradient and were planted into identical soils in all three gardens. We focused on in situ photosynthetic performance of seedlings, plasticity in spring phenology, and adjustments in leaf morphology. We found no evidence for clear temperature sensitivities in photosynthetic rates of the two coniferous species, neither across a 6°C range in growing season temperatures between sites nor across manipulated leaf temperatures of 15–30°C within sites. Likewise, lodgepole pine exhibited uniform leaf size across the temperature gradient; however, ponderosa pine leaf size did increase significantly at the warmest site. In contrast, aspen displayed pronounced temperature sensitivity in photosynthesis and leaf morphology, with maximum observed values at intermediate temperatures which both declined at the colder or warmer temperatures. Relative to the conifers, aspen also showed reduced phenological responses to warming with ∼12% fewer growing days at the intermediate site, and 6% at the warmest site. These divergent responses suggest that warming temperatures can alter seedling success in a number of different ways, and taken together, are likely to alter forest composition of Colorado in favor of greater dominance by montane conifer species.

Reconstructing extreme post‐wildfire floods: a comparison of convective and mesoscale events

AbstractIn much of western United States destructive floods after wildfire are frequently caused by localized, short‐duration convective thunderstorms; however, little is known about post‐fire flooding from longer‐duration, low‐intensity mesoscale storms. In this study we estimate and compare peak flows from convective and mesoscale floods following the 2012 High Park Fire in the ungaged 15.5 km2 Skin Gulch basin in the northcentral Colorado Front Range. The convective storm on 6 July 2012 came just days after the wildfire was contained. Radar data indicated that the total rainfall was 20–47 mm, and the maximum rainfall intensities (upwards of 50 mm h−1) were concentrated over portions of the watershed that burned at high severity. The mesoscale storm on 9–15 September 2013 produced 220–240 mm of rain but had maximum 15‐min intensities of only 25–32 mm h−1.Peak flows for each flood were estimated using three independent techniques. Our best estimate using a 2D hydraulic model was 28 m3 s−1 km−2 for the flood following the convective storm, placing it among the largest rainfall‐runoff floods per unit area in the United States. In contrast, the flood associated with the mesoscale flood was only 6 m3 s−1 km−2, but the long‐duration flood caused extensive channel incision and widening, indicating that this storm was much more geomorphically effective. The peak flow estimates for the 2013 flood had a higher relative uncertainty and this stemmed from whether we used pre‐ or post‐flood channel topography. The results document the extent to which a high and moderate severity forest fire can greatly increase peak flows and alter channel morphology, illustrate how indirect peak flow estimates have larger errors than is generally assumed, and indicate that the magnitude of post‐fire floods and geomorphic change can be affected by the timing, magnitude, duration, and sequence of rainstorms. Copyright © 2017 John Wiley & Sons, Ltd.

Erratum to: Critical zone properties control the fate of nitrogen during experimental rainfall in montane forests of the Colorado Front Range

Erratum to: Critical zone properties control the fate of nitrogen during experimental rainfall in montane forests of the Colorado Front Range

Substantial soil organic carbon retention along floodplains of mountain streams

AbstractSmall, snowmelt‐dominated mountain streams have the potential to store substantial organic carbon in floodplain sediment because of high inputs of particulate organic matter, relatively lower temperatures compared with lowland regions, and potential for increased moisture conditions. This work (i) quantifies mean soil organic carbon (OC) content along 24 study reaches in the Colorado Rocky Mountains using 660 soil samples, (ii) identifies potential controls of OC content based on soil properties and spatial position with respect to the channel, and (iii) and examines soil properties and OC across various floodplain geomorphic features in the study area. Stepwise multiple linear regression (adjusted r2 = 0.48, p < 0.001) indicates that percentage of silt and clay, sample depth, percent sand, distance from the channel, and relative elevation from the channel are significant predictors of OC content in the study area. Principle component analysis indicates limited separation between geomorphic floodplain features based on predictors of OC content. A lack of significant differences among floodplain features suggests that the systematic random sampling employed in this study can capture the variability of OC across floodplains in the study area. Mean floodplain OC (6.3 ± 0.3%) is more variable but on average greater than values in uplands (1.5 ± 0.08% to 2.2 ± 0.14%) of the Colorado Front Range and higher than published values from floodplains in other regions, particularly those of larger rivers.

Erratum: “Species Richness, Diversity, and Ecology of Chironomidae (Diptera) in Fountain Creek: A Colorado Front Range Sandy-Bottom Watershed” (2016)

Erratum: “Species Richness, Diversity, and Ecology of Chironomidae (Diptera) in Fountain Creek: A Colorado Front Range Sandy-Bottom Watershed” (2016)

Dating of river terraces along Lefthand Creek, western High Plains, Colorado, reveals punctuated incision

The response of erosional landscapes to Quaternary climate oscillations is recorded in fluvial terraces whose quantitative interpretation requires numerical ages. We investigate gravel-capped strath terraces along the western edge of Colorado's High Plains to constrain the incision history of this shale-dominated landscape. We use 10Be and 26Al cosmogenic radionuclides (CRNs), optically stimulated luminescence (OSL), and thermally transferred OSL (TT-OSL) to date three strath terraces, all beveled in shale bedrock and then deposited upon by Lefthand Creek, which drains the crystalline core of the Front Range. Our study reveals: (i) a long history (hundreds of thousands of years) of fluvial occupation of the second highest terrace, T2 (Table Mountain), with fluvial abandonment at 92±3ka; (ii) a brief occupation of a narrow and spatially confined terrace, T3, at 98±7ka; and (iii) a 10–25 thousand year period of cutting and fluvial occupation of a lower terrace, T4, marked by the deposition of a lower alluvial unit between 59 and 68ka, followed by deposition of an upper alluvial package at 40±3ka. In conjunction with other recent CRN studies of strath terraces along the Colorado Front Range (Riihimaki et al., 2006; Dühnforth et al., 2012), our data reveal that long periods of lateral planation and fluvial occupation of strath terraces, sometimes lasting several glacial-interglacial cycles, are punctuated by brief episodes of rapid vertical bedrock incision. These data call into question what a singular terrace age represents, as the strath may be cut at one time (its cutting-age) and the terrace surface may be abandoned at a much later time (its abandonment age), and challenge models of strath terraces that appeal to simple pacing by the glacial-interglacial cycles.

Reductions in road sediment production and road-stream connectivity from two decommissioning treatments

Unpaved forest roads can be an important source of sediment to streams. Road decommissioning is an increasingly common technique to eliminate these impacts, but few pre- and post-treatment studies have rigorously assessed its effectiveness. The objectives of this study in the northern Colorado Front Range were to: (1) quantify the effects of key variables on road sediment production before decommissioning; (2) quantify the changes over time in segment-scale sediment production from two decommissioning treatments (ripping only, and ripping plus mulching) versus untreated controls; and (3) quantify the factors affecting road-stream connectivity and the changes in connectivity due to decommissioning 12.3km of roads. Median sediment production rate in the first year prior to decommissioning was 0.3kgm−2, but values varied from 0.0kgm−2 to 3.0kgm−2. Traffic, precipitation intensity, and road segment area had the greatest effects on road sediment production. In the first two years after decommissioning the median road sediment production was zero kgm−2, as the furrows created by ripping trapped nearly all of the eroded sediment. Decommissioning also reduced road-stream connectivity from 12% of the total length to only 2%, with most of the connected segments being immediately adjacent to a stream. While both decommissioning treatments were effective, the ripping plus mulching treatment had visibly less surface erosion and no segment generated any measurable sediment. These results can help guide the design and quantify the benefits of future road decommissioning projects.

The effect of entrainment through atmospheric boundary layer growth on observed and modeled surface ozone in the Colorado Front Range

AbstractOzone concentrations at the Earth's surface are controlled by meteorological and chemical processes and are a function of advection, entrainment, deposition, and net chemical production/loss. The relative contributions of these processes vary in time and space. Understanding the relative importance of these processes controlling surface ozone concentrations is an essential component for designing effective regulatory strategies. Here we focus on the diurnal cycle of entrainment through atmospheric boundary layer (ABL) growth in the Colorado Front Range. Aircraft soundings and surface observations collected in July/August 2014 during the DISCOVER‐AQ/FRAPPÉ (Deriving Information on Surface conditions from Column and Vertically Resolved Observations Relevant to Air Quality/Front Range Air Pollution and Photochemistry Éxperiment) campaigns and equivalent data simulated by a regional chemical transport model are analyzed. Entrainment through ABL growth is most important in the early morning, fumigating the surface at a rate of ~5 ppbv/h. The fumigation effect weakens near noon and changes sign to become a small dilution effect in the afternoon on the order of −1 ppbv/h. The chemical transport model WRF‐Chem (Weather Research and Forecasting Model with chemistry) underestimates ozone at all altitudes during this study on the order of 10–15 ppbv. The entrainment through ABL growth is overestimated by the model in the order of 0.6–0.8 ppbv/h. This results from differences in boundary layer growth in the morning and ozone concentration jump across the ABL top in the afternoon. This implicates stronger modeled fumigation in the morning and weaker modeled dilution after 11:00 LT.

Trapping the Walnut Twig Beetle to Determine Flight Patterns in Colorado

Abstract. The walnut twig beetle, Pityophthorus juglandis Blackman, and its fungal associate Geosmithia morbida Kolařik et al., produce thousand cankers disease, which has devastated black walnut (Juglans nigra L.) in several states of the western U.S.A. To better understand beetle flight dynamics and life history, flight times were documented in the urban corridor along the Colorado Front Range during 2 years -- in 2008 with yellow sticky card traps and in 2012 with baited multiple funnel traps. Walnut twig beetles were determined to be active throughout the trapping season from March through November, exhibited overlapping generations, and potentially a bivoltine life cycle. Most beetles were collected from traps between July and September, and the greatest trap density frequently occurred in August. The total number of beetles collected throughout the trapping season differed at each location. In 2008 the number of beetles collected ranged from 12 to 145, and from 60 to 12,909 in 2012. More beetles wer...

Estimates of Extreme Precipitation Frequency Derived from Spatially Dense Rain Gauge Observations: A Case Study of Two Urban Areas in the Colorado Front Range Region

Precipitation design values, which describe precipitation extremes expected within a specified time period, provide critical guidance for public policy and the design of hydrologic infrastructure. Unfortunately, conventional design value calculations are limited by a major assumption: They treat precipitation as a point-based phenomenon, measured at spatially isolated gauges. We argue that because precipitation occurs over areas, design value calculations should be based on an areal conception of precipitation. Using spatially dense Community Collaborative Rain, Hail and Snow (CoCoRaHS) Network data in two Colorado cities (Fort Collins and Boulder), we develop a “hyperlocal” design value calculation in which nearby observations within a representative precipitation region (RPR) “compete” to capture a single twenty-four-hour maximum. We find that design values for shorter return periods (one to fifty years) derived from just ten years of hyperlocal data, which we express as probabilistic distributions rather than single values, typically exceed those calculated using single-point records of 100 years or more. Hyperlocal design values for longer return periods (more than fifty years) are generally smaller than those calculated from the single-point data due to the temporally limited CoCoRaHS record. We also find that the dependence of design values on RPR size contrasts between Fort Collins and Boulder, as design values grow markedly larger as the RPR size increases in Fort Collins but not in Boulder. We attribute this behavior to the Boulder Global Historical Climatology Network station's location in a topographically favored area for precipitation and propose that future studies evaluate the hyperlocal design value method in a variety of geographic settings.