Article Database

An investigation of warm-season spatial rainfall variability in Oklahoma City: Possible linkages to urbanization and prevailing wind

Abstract:

This study used 9 yr (1998–2006) of warm-season (June–September) mean daily cumulative rainfall data
from both the Tropical Rainfall Measuring Mission (TRMM) Multisatellite Precipitation Analysis and rain
gauge stations to examine spatial variability in warm-season rainfall events around Oklahoma City (OKC). It
was hypothesized that with warm-season rainfall variability, under weakly forced conditions, a rainfall
anomaly would be present in climatological downwind areas of OKC. Results from both satellite and gaugebased analyses revealed that the north-northeastern (NNE) regions of the metropolitan OKC area were
statistically wetter than other regions. Climatological sounding and reanalysis data revealed that, on average,
the NNE area of OKC was the climatologically downwind region, confirming that precipitation modification
by the urban environment may be more dominant than agricultural/topographic influences on weakly forced
days. The study also established that satellite precipitation estimates capture spatial rainfall variability as well
as traditional ground-based resources do. TRMM products slightly underestimate the precipitation recorded
by gauges, but the correlation R improves dramatically when the analysis is restricted to mean daily rainfall
estimates from OKC urban grid cells containing multiple gauge stations (R2 5 0.878). It was also quantitatively confirmed, using a relatively new concentration factor analysis, that prevailing wind–rainfall yields
were consistent with the overall framework of an urban rainfall effect. Overall, the study establishes a
prototype method for utilizing satellite-based rainfall estimates to examine rainfall modification by urbanization on global scales and in parts of the world that are not well instrumented with rain gauge or radar
networks.

The influence of large dams on surrounding climate and precipitation patterns

Abstract:

The spatial configuration of cities can affect how urban environments alter local energy balances. Previous studies have reached the paradoxical conclusions that both sprawling and high-density urban development can amplify urban heat island intensities, which has prevented consensus on how best to mitigate the urban heat island effect via urban planning. To investigate this apparent dichotomy, we estimated the urban heat island intensities of the 50 most populous cities in the United States using gridded minimum temperature datasets and quantified each city’s urban morphology with spatial metrics. The results indicated that the spatial contiguity of urban development, regardless of its density or degree of sprawl, was a critical factor that influenced the magnitude of the urban heat island effect. A ten percentage point increase in urban spatial contiguity was predicted to enhance the minimum temperature annual average urban heat island intensity by between 0.3 and 0.4 °C. Therefore, city contiguity should be considered when devising strategies for urban heat island mitigation, with more discontiguous development likely to ameliorate the urban heat island effect. Unraveling how urban morphology influences urban heat island intensity is paramount given the human health consequences associated with the continued growth of urban populations in the future.

The impact of urbanization on current and future coastal precipitation: a case study for Houston

Abstract:

The approach of this study was to determine, theoretically, what impact current and future
urban land use in the coastal city of Houston, Texas has on the space and time evolution of
precipitation on a `typical’ summer day. Regional model simulations of a case study for 25 July 2001
were applied to investigate possible effects of urban land cover on precipitation development.
Simulations in which Houston urban land cover was included resolved rain cells associated with
the sea breeze front and a possible urban circulation on the northwest fringe of the city. Simulations
without urban land cover did not capture the initiation and full intensity of the `hypothesized’
urban-induced rain cell. The response is given the terminology the `urban rainfall effect’ or URE.
An urban growth model (UrbanSim) was used to project the urban land-cover growth of Houston,
Texas from 1992 to 2025. A regional atmospheric-land surface model was then run with the 2025
urban land-cover scenario. Though we used a somewhat theoretical treatment, our results show the
sensitivity of the atmosphere to urban land cover and illustrate how atmosphere ^ land interactions
can affect cloud and precipitation processes. Two urban-induced features, convergence zones along
the inner fringe of the city and an urban low-pressure perturbation, appear to be important factors
that lead to enhanced rain clouds independently or in conjunction with the sea breeze. Simulations
without the city (NOURBAN) produced less cumulative rainfall in the west-northwest Houston area
than simulations with the city represented (URBAN). Future urban land-cover growth projected by
UrbanSim (URBAN2025) led to a more expansive area of rainfall, owing to the extended urban
boundary and increased secondary outflow activity. This suggests that the future urban land cover
might lead to temporal and spatial precipitation variability in coastal urban microclimates. It was
beyond the scope of the analysis to conduct an extensive sensitivity analysis of cause ^ effect relationships, though the experiments provide some clues as to why the rainfall evolution differs. This
research demonstrates a novel application of urban planning and weather ^ climate models. It also
raises viable questions concerning future planning strategies in urban environments in consideration
of hydroclimate changes.

The urban heat island effect and city contiguity

Abstract:

The spatial configuration of cities can affect how urban environments alter local energy balances. Previous studies have reached the paradoxical conclusions that both sprawling and high-density urban development can amplify urban heat island intensities, which has prevented consensus on how best to mitigate the urban heat island effect via urban planning. To investigate this apparent dichotomy, we estimated the urban heat island intensities of the 50 most populous cities in the United States using gridded minimum temperature datasets and quantified each city’s urban morphology with spatial metrics. The results indicated that the spatial contiguity of urban development, regardless of its density or degree of sprawl, was a critical factor that influenced the magnitude of the urban heat island effect. A ten percentage point increase in urban spatial contiguity was predicted to enhance the minimum temperature annual average urban heat island intensity by between 0.3 and 0.4 °C. Therefore, city contiguity should be considered when devising strategies for urban heat island mitigation, with more discontiguous development likely to ameliorate the urban heat island effect. Unraveling how urban morphology influences urban heat island intensity is paramount given the human health consequences associated with the continued growth of urban populations in the future.

Radar signatures of the urban effect on precipitation distribution: A case study for Atlanta, Georgia

Abstract:

Ground-based weather radar from Peachtree City, GA,
is used to examine the distribution of summer precipitation
in northern Georgia, including metropolitan Atlanta, during
June –August of 2002 – 2006. The study included 194
‘‘synoptically benign’’ days with a maritime tropical air
mass type. Areas in eastern metropolitan Atlanta are shown
to have 30% more rainfall during these days than areas west
of the city. Both precipitation amount and frequency were
enhanced up to 80 km to the east of the urban core of
Atlanta. A precipitation maxima northeast of Atlanta occurs
near a precipitation anomaly and lightning flash density
anomaly identified in previous studies. An hourly analysis
of precipitation data demonstrates that the enhanced
precipitation on the periphery of the urban core is most
evident from 00– 05 UTC (19-00 LST). This study is the
first to use ground-based radar precipitation estimates in an
attempt to quantify the impact of urbanization on
precipitation

Atlanta’s urban heat island under extreme heat conditions and potential mitigation strategies

Abstract:

t The urban heat island (UHI), together with summertime heat waves, foster’s
biophysical hazards such as heat stress, air pollution, and associated public health problems.
Mitigation strategies such as increased vegetative cover and higher albedo surface materials
have been proposed. Atlanta, Georgia, is often affected by extreme heat, and has recently
been investigated to better understand its heat island and related weather modifications. The
objectives of this research were to (1) characterize temporal variations in the magnitude of
UHI around Metro Atlanta area, (2) identify climatological attributes of the UHI under
extremely high temperature conditions during Atlanta’s summer (June, July, and August)
period, and (3) conduct theoretical numerical simulations to quantify the first-order effects
of proposed mitigation strategies. Over the period 1984–2007, the climatological mean UHI
magnitude for Atlanta-Athens and Athens-Monticello was 1.31 and 1.71C, respectively.
There were statistically significant minimum temperature trends of 0.70C per decade at
Athens and -1.79C per decade at Monticello while Atlanta’s minimum temperature
remained unchanged. The largest (smallest) UHI magnitudes were in spring (summer) and
may be coupled to cloud-radiative cycles. Heat waves in Atlanta occurred during 50% of the
years spanning 1984–2007 and were exclusively summertime phenomena. The mean
number of heat wave events in Atlanta during a given heat wave year was 1.83. On average,
Atlanta heat waves lasted 14.18 days, although there was quite a bit of variability (standard
deviation of 9.89). The mean maximum temperature during Atlanta’s heat waves was
35.85C. The Atlanta-Athens UHI was not statistically larger during a heat wave although the Atlanta-Monticello UHI was. Model simulations captured daytime and nocturnal UHIs
under heat wave conditions. Sensitivity results suggested that a 100% increase in Atlanta’s
surface vegetation or a tripling of its albedo effectively reduced UHI surface temperature.
However, from a mitigation and technological standpoint, there is low feasibility of tripling albedo in the foreseeable future. Increased vegetation seems to be a more likely choice for mitigating surface temperature.

Urban aerosols and their variations with clouds and rainfall: A case study for New York and Houston

Abstract:

[1] Diurnal, weekly, seasonal, and interannual variations of urban aerosols were analyzed with an emphasis on summer months using 4 years of the NASA Earth Observing System (EOS) Moderate Resolution Imaging Spectroradiometer (MODIS) observations, in situ Aerosol Robotic Network (AERONET) observations, and in situ U.S. Environmental Protection Agency (EPA) PM2.5 data for one midlatitude city (New York) and one subtropical city (Houston). Seasonality is evident in aerosol optical thickness measurements, with a minimum in January and a maximum in April to July. The diurnal variations of aerosols, however, are detectable but largely affected by local and regional weather conditions, such as surface and upper‐level winds. On calm clear days, aerosols peak during the two rush hours in the morning and evening. Furthermore, the anthropogenic‐induced weekly cycles of aerosols and clouds are analyzed, which by themselves are weak, as the anthropogenic signal is mixed with noise of natural weather variability. In addition, corresponding cloud properties observed from MODIS demonstrate an opposite phase to the seasonality of aerosols. Nevertheless, no clear relationship was observed between monthly mean aerosols and rainfall measurements from NASA’s Tropical Rainfall Measuring Mission (TRMM), implying that in the summer the aerosol impact may not be the primary reason for the change of urban rainfall amount.

Analyzing Challenges to Library Materials: An Incomplete Picture

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Social Responsibility, Librarianship, and the ALA: The 2015 Banned Books Week Poster Controversy

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Society, Institutions, and Common Sense: Themes in the Discourse of Book Challengers in 21st Century United States

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