Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
A Technique to Detect
Microclimatic
Inhomogeneities in
Historical Records of
Screen-Level Air
Temperature
K. E.
Runnels, and
T.R. Oke
Journal of
Climate
Volume 19,
Issue 6, March
2006, Pages
959-978
1
http://journals.ametsoc.or
g/doi/pdf/10.1175/JCLI3
663.1
ABSTRACT
A new method to detect errors or biases in screen-level air temperature records at
standard climate stations is developed and applied. It differs from other methods by being
able to detect microclimatic inhomogeneities in time series. Such effects, often quite
subtle, are due to alterations in the immediate environment of the station such as changes
of vegetation, development (buildings, paving), irrigation, cropping, and even in the
maintenance of the site and its instruments. In essence, the technique recognizes two
facts: differences of thermal microclimate are enhanced at night, and taking the ratio of
the nocturnal cooling at a pair of neighboring stations nullifies thermal changes that occur
at larger-than-microclimatic scales. Such ratios are shown to be relatively insensitive to
weather conditions. After transforming the time series using Hurst rescaling, which
identifies long-term persistence in geophysical phenomena, cooling ratio records show
distinct discontinuities, which, when compared against detailed station metadata records,
are found to correspond to even minor changes in the station environment. Effects
detected by this method are shown to escape detection by current generally accepted
techniques. The existence of these microclimatic effects are a source of uncertainty in
long-term temperature records, which is in addition to those presently recognized such as
local and mesoscale urban development, deforestation, and irrigation.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
2
The Effect of Irrigation on Lobell, David J. Climate, 21, http://journals.ametsoc.or
Regional Temperatures: A B., Céline
2063–2071.
g/doi/abs/10.1175/2007J
Spatial and Temporal
Bonfils, 2008
CLI1755.1
Analysis of Trends in
California, 1934–2002
ABSTRACT
The response of air temperatures to widespread irrigation may represent an important
component of past and/or future regional climate changes. The quantitative impact of
irrigation on daily minimum and maximum temperatures (Tmin and Tmax) in California
was estimated using historical time series of county irrigated areas from agricultural
censuses and daily climate observations from the U.S. Historical Climatology Network.
Regression analysis of temperature and irrigation changes for stations within irrigated
areas revealed a highly significant (p < 0.01) effect of irrigation on June–August average
Tmax, with no significant effects on Tmin (p > 0.3). The mean estimate for Tmax was a
substantial 5.0°C cooling for 100% irrigation cover, with a 95% confidence interval of
2.0°–7.9°C. As a result of small changes in Tmin compared to Tmax, the diurnal
temperature range (DTR) decreased significantly in both spring and summer months.
Effects on percentiles of Tmax within summer months were not statistically
distinguishable, suggesting that irrigation’s impact is similar on warm and cool days in
California. Finally, average trends for stations within irrigated areas were compared to
those from nonirrigated stations to evaluate the robustness of conclusions from previous
studies based on pairwise comparisons of irrigated and nonirrigated sites. Stronger
negative Tmax trends in irrigated sites were consistent with the inferred effects of
irrigation on Tmax. However, Tmin trends were significantly more positive for nonirrigated
sites despite the apparent lack of effects of irrigation on Tmin from the analysis within
irrigated sites. Together with evidence of increases in urban areas near nonirrigated sites,
this finding indicates an important effect of urbanization on Tmin in California that had
previously been attributed to irrigation. The results therefore demonstrate that simple
pairwise comparisons between stations in a complex region such as California can lead to
misinterpretation of historical climate trends and the effects of land use changes.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
The Influence of Land
Use/Land Cover on
Climatological Values of
the Diurnal Temperature
Range
Gallo, Kevin
P., David R.
Easterling,
Thomas C.
Peterson,
1996
J. Climate, 9,
2941–2944.
3
http://dx.doi.org/10.1175/
15200442(1996)009<2941:TI
OLUC>2.0.CO;2
ABSTRACT
The diurnal temperature range (DTR) at weather observation stations that make up the
U.S. Historical Climatology Network was evaluated with respect to the predominant land
use/land cover associated with the stations within three radii intervals (100, 1000, and 10
000 m) of the stations. Those stations that were associated with predominantly rural land
use/land cover (LULC) usually displayed the greatest observed DTR, whereas those
associated with urban related land use or land cover displayed the least observed DTR.
The results of this study suggest that significant differences in the climatological DTR
were observed and could be attributed to the predominant LULC associated with the
observation stations. The results also suggest that changes in the predominant LULC
conditions, within as great as a 10 000 m radius of an observation station, could
significantly influence the climatological DTR. Future changes in the predominant LULC
associated with observation sites should be monitored similar to the current practice of
monitoring changes in instruments or time of observation at the observations sites.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Land use/land cover
change effects on
temperature trends at U.S.
Climate Normals stations
Hale, Gallo,
et. al., 2006
Geophysical
Research
Letters
Volume 33,
Issue 11, June
2006
4
http://onlinelibrary.wiley.
com/doi/10.1029/2006GL
026358/abstract
ABSTRACT
Alterations in land use/land cover (LULC) in areas near meteorological observation
stations can influence the measurement of climatological variables such as temperature.
Urbanization near climate stations has been the focus of considerable research attention,
however conversions between non-urban LULC classes may also have an impact. In this
study, trends of minimum, maximum, and average temperature at 366 U.S. Climate
Normals stations are analyzed based on changes in LULC defined by the U.S. Land
Cover Trends Project. Results indicate relatively few significant temperature trends
before periods of greatest LULC change, and these are generally evenly divided between
warming and cooling trends. In contrast, after the period of greatest LULC change was
observed, 95% of the stations that exhibited significant trends (minimum, maximum, or
mean temperature) displayed warming trends.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Temperature Trends of the
U.S. Historical
Climatology Network
Based on SatelliteDesignated Land
Use/Land Cover
Gallo, Kevin
P., Timothy
W. Owen,
David R.
Easterling,
Paul F.
Jamason,
1999
J. Climate, 12,
1344–1348.
5
http://journals.ametsoc.or
g/doi/abs/10.1175/15200442%281999%29012%
3C1344%3ATTOTUS%3
E2.0.CO%3B2
ABSTRACT
The 1221 weather observation stations that compose the U.S. Historical Climatology
Network were designated as either urban, suburban, or rural based on data from the
Defense Meteorological Satellite Program Operational Linescan System (OLS). The
designations were based on local and regional samples of the OLS data around the
stations (OLS method). Trends in monthly maximum and minimum temperature and the
diurnal temperature range (DTR) were determined for the 1950–96 interval for each of
three land use/land cover (LULC) designations. The temperature trends for the OLSderived designations of LULC were compared to similarly designated LULC based on (i)
map- (Operational Navigation Charts) and population-based estimates of LULC (ONCP
method), and (ii) LULC designations that resulted from of a survey of the network station
operators. Although differences were not statistically significant, the DTR trends (degrees
Celsius per 100 years) did differ between the LULC classes defined by the OLS method,
from −0.41 for the rural stations to −0.86 for the urban stations. Trends also differed,
although not significantly, between the methods used to define an LULC class, such that
the trends in rural DTR varied from −0.41 for the OLS defined stations to −0.67 for the
ONCP defined stations. Although the trends between classes were not significantly
different, they do present some contrasts that might confound the interpretation of
temperature trends when the local and regional environments associated with the
analyzed stations are not considered. The general (urban, suburban, or rural) LULC
associated with surface observation stations appears to be one of the factors that can
influence the trends observed in temperatures and thus should be considered in the
analysis and interpretation of temperature trends.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Influences of specific land
use/land cover
conversions on
climatological normals of
near-surface temperature
Robert C.
Hale,
Kevin P.
Gallo,
Thomas R.
Loveland,
July 2008
Journal of
Geophysical
Research
Atmosphere,
Volume 113,
Issue D14
6
http://onlinelibrary.wiley.
com/doi/10.1029/2007JD
009548/abstract
ABSTRACT
Quantification of the effects of land use/land cover (LULC) changes on proximal
measurements of near-surface air temperature is crucial to a better understanding of
natural and anthropogenically induced climate change. In this study, data from stations
utilized in deriving U.S. climatological temperature normals were analyzed in
conjunction with NCEP-NCAR 50-Year Reanalysis (NNR) estimates and highly accurate
LULC change maps in order to isolate the effects of LULC change from other
climatological factors. While the “Normals” temperatures exhibited considerable
warming in both minima and maxima, the NNR data revealed that the majority of the
warming of maximum temperatures was not due to nearby LULC change. Warming of
minimum temperatures was roughly evenly split between the effects of LULC change
and other influences. Furthermore, the effects of LULC change varied considerably
depending upon the particular type of land cover conversion that occurred. Urbanization,
in particular, was found to result in warming of minima and maxima, while some LULC
conversions that might be expected to have significantly altered nearby temperatures
(e.g., clear-cutting of forests) did not.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Impacts of land use land
cover on temperature
trends over the continental
United States: assessment
using the North American
Regional Reanalysis
Fall, Niyogi,
et. al., 2009
7
International
http://onlinelibrary.wiley.
Journal of
com/doi/10.1002/joc.199
Climatology
6/full
Special Issue:
Impacts of land
use change on
climate
Volume 30,
Issue 13, pages
1980–1993, 15
November
2010
ABSTRACT
We investigate the sensitivity of surface temperature trends to land use land cover change
(LULC) over the conterminous United States (CONUS) using the observation minus
reanalysis (OMR) approach. We estimated the OMR trends for the 1979–2003 period
from the US Historical Climate Network (USHCN), and the NCEP-NCAR North
American Regional Reanalysis (NARR). We used a new mean square differences
(MSDs)-based assessment for the comparisons between temperature anomalies from
observations and interpolated reanalysis data. Trends of monthly mean temperature
anomalies show a strong agreement, especially between adjusted USHCN and NARR (r
= 0.9 on average) and demonstrate that NARR captures the climate variability at different
time scales. OMR trend results suggest that, unlike findings from studies based on the
global reanalysis (NCEP/NCAR reanalysis), NARR often has a larger warming trend
than adjusted observations (on average, 0.28 and 0.27 °C/decade respectively).
OMR trends were found to be sensitive to land cover types. We analyzed decadal OMR
trends as a function of land types using the Advanced Very High Resolution Radiometer
(AVHRR) and new National Land Cover Database (NLCD) 1992–2001 Retrofit Land
Cover Change. The magnitude of OMR trends obtained from the NLDC is larger than the
one derived from the ‘static’ AVHRR. Moreover, land use conversion often results in
more warming than cooling.
Overall, our results confirm the robustness of the OMR method for detecting nonclimatic changes at the station level, evaluating the impacts of adjustments performed on
raw observations, and most importantly, providing a quantitative estimate of additional
warming trends associated with LULC changes at local and regional scales. As most of
the warming trends that we identify can be explained on the basis of LULC changes, we
suggest that in addition to considering the greenhouse gases–driven radiative forcings,
multi-decadal and longer climate models simulations must further include LULC
changes.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Shading Instrument
Shelters
Flora, S.D.
January 1994
Monthly
Weather
Review
Volume 48,
Issue 5, 271272
8
http://dx.doi.org/10.11
75/15200493(1920)48<271:SIS
>2.0.CO;2
ABSTRACT
NONE
COMMENTS: Describes purpose of shading instrument shelters. Describes 2 shelters;
one over thick sod in the open, the other, under a large Box Elder tree. The latter box,
was moved to the west side of the tree with the same shading effects.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
On the reliability of the
U.S. surface temperature
record
Matthew J.
Menne,
Claude N.
Williams Jr.,
Michael A.
Palecki, June
2010
Journal of
Geophysical
Reasearch
Atmospheres
9
http://onlinelibrary.wiley.
com/doi/10.1029/2009JD
013094/abstract
ABSTRACT
Recent photographic documentation of poor siting conditions at stations in the U.S.
Historical Climatology Network (USHCN) has led to questions regarding the reliability
of surface temperature trends over the conterminous United States (CONUS). To evaluate
the potential impact of poor siting/instrument exposure on CONUS temperatures, trends
derived from poor and well sited USHCN stations were compared. Results indicate that
there is a mean bias associated with poor exposure sites relative to good exposure sites;
however, this bias is consistent with previously documented changes associated with the
widespread conversion to electronic sensors in the USHCN during the last 25 years.
Moreover, the sign of the bias is counterintuitive to photographic documentation of poor
exposure because associated instrument changes have led to an artificial negative
(“cool”) bias in maximum temperatures and only a slight positive (“warm”) bias in
minimum temperatures. These results underscore the need to consider all changes in
observation practice when determining the impacts of siting irregularities. Further, the
influence of nonstandard siting on temperature trends can only be quantified through an
analysis of the data. Adjustments applied to USHCN Version 2 data largely account for
the impact of instrument and siting changes, although a small overall residual negative
(“cool”) bias appears to remain in the adjusted maximum temperature series.
Nevertheless, the adjusted USHCN temperatures are extremely well aligned with recent
measurements from instruments whose exposure characteristics meet the highest
standards for climate monitoring. In summary, we find no evidence that the CONUS
average temperature trends are inflated due to poor station siting.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Assessment of Urban
Versus Rural In Situ
Surface Temperatures in
the Contiguous United
States: No Difference
Found
Peterson
Journal of
Climate
Volume 16
issue 18
Sept 2003
10
http://journals.ametsoc.or
g/doi/abs/10.1175/15200442(2003)016%3C2941
:AOUVRI%3E2.0.CO%3
B2
ABSTRACT
All analyses of the impact of urban heat islands (UHIs) on in situ temperature
observations suffer from inhomogeneities or biases in the data. These inhomogeneities
make urban heat island analyses difficult and can lead to erroneous conclusions. To
remove the biases caused by differences in elevation, latitude, time of observation,
instrumentation, and nonstandard siting, a variety of adjustments were applied to the data.
The resultant data were the most thoroughly homogenized and the homogeneity
adjustments were the most rigorously evaluated and thoroughly documented of any largescale UHI analysis to date. Using satellite night-lights–derived urban/rural metadata,
urban and rural temperatures from 289 stations in 40 clusters were compared using data
from 1989 to 1991. Contrary to generally accepted wisdom, no statistically significant
impact of urbanization could be found in annual temperatures. It is postulated that this is
due to micro- and local-scale impacts dominating over the mesoscale urban heat island.
Industrial sections of towns may well be significantly warmer than rural sites, but urban
meteorological observations are more likely to be made within park cool islands than
industrial regions.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
11
Microclimate Exposures
Davey,
Bull. Amer.
http://dx.doi.org/10.1175/
of Surface-Based Weather Christopher
Meteor. Soc.,
BAMS-86-4-497
Stations: Implications For A., Roger A.
86, 497–504
The Assessment of Long- Pielke, 2005
Term Temperature Trends
ABSTRACT
The U.S. Historical Climate Network is a subset of surface weather observation stations
selected from the National Weather Service cooperative station network. The criteria
used to select these stations do not sufficiently address station exposure characteristics. In
addition, the current metadata available for cooperative network stations generally do not
describe site exposure characteristics in sufficient detail. This paper focuses on site
exposures with respect to air temperature measurements. A total of 57 stations were
photographically surveyed in eastern Colorado, comparing existing exposures to the
standards endorsed by the World Meteorological Organization. The exposures of most
sites surveyed, including U.S. Historical Climate Network sites, were observed to fall
short of these standards. This raises a critical question about the use of many Historical
Climate Network sites in the development of long-term climate records and the detection
of climate trends. Some of these sites clearly have poor exposures and therefore should
be considered for removal from the Historical Climate Network. Candidate replacement
sites do exist and should be considered for addition into the network to replace the
removed sites. Documentation as performed for this study should be conducted
worldwide in order to determine the extent of spatially nonrepresentative exposures and
possible temperature biases.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Comments on
“Microclimate Exposures
of Surface-Based Weather
Stations”
Vose, Russell
S., Easterling,
David R.,
Karl, Thomas
R., and
Helfert,
Michael
Bulletin of the
American
Meteorological
Society
Volume 86,
Issue 4, 504506
12
http://dx.doi.org/10.11
75/BAMS-86-4-504
ABSTRACT
NONE
COMMENTS: Provide background on U.S. Historical Climatology Network and
discuss weakness in site-exposure documentation. Clarify logic behind application
of USHCN in climate change studies, emphasizing relative importance of station
exposures therein. Short discussion of how USHCN (which was developed to control
exposure problems) will increase confidence in future estimates. 1221 uniformly
distributed, chosen based on spatial coverage, record length data completeness and
historical stability (not moved or different instrumentation and observing practice).
Comments agreed on inappropriate exposures for monitoring climate.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Examination of Potential
Biases in Air Temperature
Caused by Poor Station
Locations
Peterson,
Thomas C.
April 2006
Bull. Amer.
Meteor. Soc.,
Volume 87,
Issue 8, 10731089
13
http://dx.doi.org/10.11
75/BAMS-87-8-1073
ABSTRACT
NONE
Comments: For stations exposed to cold air drainage, (poor) observing practices,
instrumentation, latitude and elevation. Evaluate any time-dependent aspect of
siting-induced biases.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
14
Documentation of
Pielke, Roger, Bull. Amer.
http://journals.ametsoc.or
Uncertainties and Biases
and
Meteor. Soc.,
g/doi/abs/10.1175/BAMS
Associated with Surface
Coauthors,
88, 913–928
-88-6-913
Temperature
2007
Measurement Sites for
Climate Change
Assessment
ABSTRACT
The objective of this research is to determine whether poorly sited long-term surface
temperature monitoring sites have been adjusted in order to provide spatially
representative independent data for use in regional and global surface temperature
analyses. We present detailed analyses that demonstrate the lack of independence of the
poorly sited data when they are adjusted using the homogenization procedures employed
in past studies, as well as discuss the uncertainties associated with undocumented station
moves. We use simulation and mathematics to determine the effect of trend on station
adjustments and the associated effect of trend in the reference series on the trend of the
adjusted station. We also compare data before and after adjustment to the reanalysis data,
and we discuss the effect of land use changes on the uncertainty of measurement.
A major conclusion of our analysis is that there are large uncertainties associated with the
surface temperature trends from the poorly sited stations. Moreover, rather than providing
additional independent information, the use of the data from poorly sited stations
provides a false sense of confidence in the robustness of the surface temperature trend
assessments.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Analysis of the impacts of
station exposure on the
U.S. Historical
Climatology Network
temperatures and
temperature trends
Fall, Watts,
et. al. , 2011
15
Journal of
http://pielkeclimatesci.fil
Geophysical
es.wordpress.com/2011/0
Research:
7/r-367.pdf
Atmospheres
(1984–2012)
Volume 116,
Issue D14, July
2011
ABSTRACT
The recently concluded Surface Stations Project surveyed 82.5% of the U.S. Historical
Climatology Network (USHCN) stations and provided a classification based on exposure
conditions of each surveyed station, using a rating system employed by the National
Oceanic and Atmospheric Administration to develop the U.S. Climate Reference
Network. The unique opportunity offered by this completed survey permits an
examination of the relationship between USHCN station siting characteristics and
temperature trends at national and regional scales and on differences between USHCN
temperatures and North American Regional Reanalysis (NARR) temperatures. This
initial study examines temperature differences among different levels of siting quality
without controlling for other factors such as instrument type. Temperature trend estimates
vary according to site classification, with poor siting leading to an overestimate of
minimum temperature trends and an underestimate of maximum temperature trends,
resulting in particular in a substantial difference in estimates of the diurnal temperature
range trends. The opposite-signed differences of maximum and minimum temperature
trends are similar in magnitude, so that the overall mean temperature trends are nearly
identical across site classifications. Homogeneity adjustments tend to reduce trend
differences, but statistically significant differences remain for all but average temperature
trends. Comparison of observed temperatures with NARR shows that the most poorly
sited stations are warmer compared to NARR than are other stations, and a major portion
of this bias is associated with the siting classification rather than the geographical
distribution of stations. According to the best-sited stations, the diurnal temperature range
in the lower 48 states has no century-scale trend.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Homogeneity assessment
of a station climate series
(1933–2005) in the
Metropolitan Area of São
Paulo: instruments change
and urbanization effects
Sugahara,
Porfirio da Ro
cha
Theoretical
and applied
climatology
16
http://link.springer.com/a
rticle/10.1007/s00704011-0485-x
February 2012,
Volume 107,
Issue 3-4, pp
361-374
ABSTRACT
This work assessed homogeneity of the Institute of Astronomy, Geophysics and
Atmospheric Sciences (IAG) weather station climate series, using various statistical
techniques. The record from this target station is one of the longest in Brazil, having
commenced in 1933 with observations of precipitation, and temperatures and other
variables later in 1936. Thus, it is one of the few stations in Brazil with enough data for
long-term climate variability and climate change studies. There is, however, a possibility
that its data may have been contaminated by some artifacts over time. Admittedly, there
was an intervention on the observations in 1958, with the replacement of instruments, for
which the size of impact has not been yet evaluated. The station transformed in the course
of time from rural to urban, and this may also have influenced homogeneity of the
observations and makes the station less representative for climate studies over larger
spatial scales. Homogeneity of the target station was assessed applying both absolute, or
single station tests, and tests relatively to regional climate, in annual scale, regarding
daily precipitation, relative humidity, maximum (TMax), minimum (TMin), and wet bulb
temperatures. Among these quantities, only precipitation does not exhibit any
inhomogeneity. A clear signal of change of instruments in 1958 was detected in the
TMax and relative humidity data, the latter certainly because of its strong dependence on
temperature. This signal is not very clear in TMin, but it presents non-climatic
discontinuities around 1953 and around 1970. A significant homogeneity break is found
around 1990 for TMax and wet bulb temperature. The discontinuities detected after 1958
may have been caused by urbanization, as the observed warming trend in the station is
considerably greater than that corresponding to regional climate.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Impact of urbanization
and land-use change on
climate
Cai, Ming
Nature
Volume 423
Issue 6939
528-531
17
http://adsabs.harvard.edu/
abs/2003Natur.423..528K
ABSTRACT
The most important anthropogenic influences on climate are the emission of greenhouse
gases and changes in land use, such as urbanization and agriculture. But it has been
difficult to separate these two influences because both tend to increase the daily mean
surface temperature. The impact of urbanization has been estimated by comparing
observations in cities with those in surrounding rural areas, but the results differ
significantly depending on whether population data or satellite measurements of night
light are used to classify urban and rural areas. Here we use the difference between trends
in observed surface temperatures in the continental United States and the corresponding
trends in a reconstruction of surface temperatures determined from a reanalysis of global
weather over the past 50 years, which is insensitive to surface observations, to estimate
the impact of land-use changes on surface warming. Our results suggest that half of the
observed decrease in diurnal temperature range is due to urban and other land-use
changes. Moreover, our estimate of 0.27°C mean surface warming per century due to
land-use changes is at least twice as high as previous estimates based on urbanization
alone.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Estimation of the impact
of land-surface forcings
on temperature trends in
eastern United States
Kalnay, Cai,
and Tobin,
2006
Journal of
Geophysical
Research:
Atmospheres
(1984–2012)
Volume 111,
Issue D6,
March 2006
18
http://onlinelibrary.wiley.
com/doi/10.1029/2005JD
006555/abstract
ABSTRACT
We use the “observation minus reanalysis” difference (OMR) method to estimate the
impact of land-use changes by computing the difference between the trends of the surface
temperature observations (which reflect all the sources of climate forcing, including
surface effects) and the NCEP-NCAR reanalysis surface temperatures (only influenced
by the assimilated atmospheric temperature trends). This includes not only urbanization
effects but also changes in agricultural practices, such as irrigation and deforestation, as
well as other near-surface forcings related to industrialization, such as aerosols. We
slightly correct previous results by including the year 1979 within the satellite decades
and by excluding stations in the West Coast of the United States. The OMR estimate for
surface impact on the mean temperature is similar to that obtained using satellite
observations of night light to discriminate between rural and urban stations, with regions
of large positive and negative trends, in contrast with the urban corrections based on
population density, which are uniformly positive and much smaller. The OMR seasonal
cycle results suggest that the impact of the greenhouse gases dominates in the winter,
whereas it appears that the impact of surface forcings dominates in the summer. The
impact of the USHCN adjustments for nonclimatic trends in the observations does not
affect the geographical distribution of the OMR trends. The effect of using a model with
constant CO2 in the reanalysis, the use of other reanalyses, and the possible use of the
reanalyses to correct for nonclimatic jumps in the observations are also discussed.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Unresolved issues with the
assessment of
multidecadal global land
surface temperature trends
Pielke,
Davey, and
Coauthors,
2007
Journal of
Geophysical
Research:
Atmospheres
(1984–2012)
19
http://onlinelibrary.wiley.
com/doi/10.1029/2006JD
008229/full
ABSTRACT
This paper documents various unresolved issues in using surface temperature trends as a
metric for assessing global and regional climate change. A series of examples ranging
from errors caused by temperature measurements at a monitoring station to the
undocumented biases in the regionally and globally averaged time series are provided.
The issues are poorly understood or documented and relate to micrometeorological
impacts due to warm bias in nighttime minimum temperatures, poor siting of the
instrumentation, effect of winds as well as surface atmospheric water vapor content on
temperature trends, the quantification of uncertainties in the homogenization of surface
temperature data, and the influence of land use/land cover (LULC) change on surface
temperature trends. Because of the issues presented in this paper related to the analysis of
multidecadal surface temperature we recommend that greater, more complete
documentation and quantification of these issues be required for all observation stations
that are intended to be used in such assessments. This is necessary for confidence in the
actual observations of surface temperature variability and long-term trends.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Reference Station
Networks for Monitoring
Climatic Change in the
Conterminous United
States
Vose, Russell
S. February
2005
Journal of
Climate
Volume 18,
Issue 24,
5390-5395
20
http://dx.doi.org/10.11
75/JCLI3600.1
ABSTRACT
Set cover models are used to develop two reference station networks that can serve
as near-term substitutes (as well as long-term backups) for the recently established
Climate Reference Network (CRN) in the United States. The first network contains
135 stations distributed in a relatively uniform fashion in order to match the
recommended spatial density for CRN. The second network contains 157 welldistributed stations that are generally not in urban areas in order to minimize the
impact of future changes in land use. Both networks accurately reproduce the
historical temperature and precipitation variations of the twentieth century.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
21
Evaluation of temperature Kevin P.
Journal of
http://journals.ametsoc.or
differences for paired
Gallo
climate
g/doi/full/10.1175/JCLI3
stations of the U.S.
Journal 18
358.1
Climate Reference
Issue 10 May
Network
2005
ABSTRACT
Adjustments to data observed at pairs of climate stations have been recommended to
remove the biases introduced by differences between the stations in time of observation,
temperature instrumentation, latitude, and elevation. A new network of climate stations,
located in rural settings, permits comparisons of temperatures for several pairs of stations
without two of the biases (time of observation and instrumentation). The daily, monthly,
and annual minimum, maximum, and mean temperatures were compared for five pairs of
stations included in the U.S. Climate Reference Network. Significant differences were
found between the paired stations in the annual minimum, maximum, and mean
temperatures for all five pairs of stations. Adjustments for latitude and elevation
differences contributed to greater differences in mean annual temperature for four of the
five stations. Lapse rates computed from the mean annual temperature differences
between station pairs differed from a constant value, whether or not latitude adjustments
were made to the data. The results suggest that microclimate influences on temperatures
observed at nearby (horizontally and vertically) stations are potentially much greater than
influences that might be due to latitude or elevation differences between the stations.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
A Step toward Improving
the Quality of Daily
Temperature Data
Produced by Climate
Observing Networks
Christopher
A. Fiebrich
and Kenneth
C. Crawford,
2009
Journal of
Atmospheric
and Oceanic
Technology
Volume 26,
Issue 7,
pages12461260, July
2009
22
http://journals.ametsoc.or
g/doi/abs/10.1175/2009J
TECHA1241.1
ABSTRACT
The research documented in this manuscript demonstrates that undeniable differences
exist between values of daily temperature recorded by the National Weather Service
Cooperative Observer Program network and data recorded by the Oklahoma Mesonet.
Because of this fact, a transition to automated observations would have the effect of
changing the climate record for Oklahoma. However, the change to automated
observations would produce an improvement in overall data quality.
A sampling of daily data from the two networks was compared for closely spaced station
pairs for the period 1 January 2003 through 31 December 2005. As a result, a host of
observer errors were discovered (including transcription errors, incorrectly resetting the
manual sensors, and delaying the observation time). These errors created large daily
differences that sometimes exceeded 5°C between the two datasets. More than 55% of the
paired observations were found to differ by more than 1°C.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
23
An Investigation into the
Oswald, Evan J. Appl.
http://journals.ametsoc.or
Spatial Variability of
M., Richard
Meteor.
g/doi/abs/10.1175/JAMC
Near-Surface Air
B. Rood, et.
Climatol., 51,
-D-11-0127.1
Temperatures in the
al, 2012
1290–1304.
Detroit, Michigan,
Metropolitan Region
ABSTRACT
On an annual basis, heat is the chief cause of weather-related deaths in the United States.
Therefore, understanding the temperature structure where people live is important for
reducing the health burden imposed by hot weather. This study focused on the air
temperatures in the Detroit, Michigan, metropolitan region during the summer of 2009.
An observational network was established that included 1) monitors sited in the
backyards of residential participants, 2) National Weather Service standard observations,
and 3) a network of monitors operated by the State of Michigan. Daily high and low
temperatures were analyzed for spatial pattern, magnitude of spatial variability, and
relationships with weather conditions. The existence of spatial variability was confirmed
specifically during weather that was considered to be dangerous to public health. The
relationships between temperature observations and distance to water, distance to city
center, and local percent of impervious surface were investigated. The spatial variability
during the daily low was typically stronger in magnitude and the spatial pattern was more
consistent than were those during the daily high. The largest correlation with land-cover
and location attributes was between values of percent of impervious surface and daily
low temperatures. Daily high temperatures were most correlated with distance to water.
Consistent with previous studies on spatial variability in urban environments, the results
suggest a need for sensitivity to the spatially variable nature of exposure to heat events in
both public health and urban planning. For example, these results showed that the
downtown area experienced elevated temperatures during nights and that the eastern
portions of Detroit experienced decreased temperatures during afternoons.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
24
Urban Influences on
Cayan, Daniel J. Climate
http://dx.doi.org/10.1175/
Surface Temperatures in
R., Arthur V. Appl. Meteor., 1520the Southwestern United
Douglas, 1984 23, 1520–
0450(1984)023<1520:UI
States during Recent
1530.
OSTI>2.0.CO;2
Decades
ABSTRACT
Trends of surface temperature at rapidly growing urban sites during the last three to five
decades are compared to those at non-urban sites, temperatures at 70 kPa, and sea surface
temperature at a coastal Pacific station. Significant urban heat island effects have
apparently taken hold, with urban-affected temperature increases of 1 to 2°C common
over this period. In contrast, the trend of the non-urban records has been distinctly
smaller over this period. The urban warming appears to be predominantly a nighttime
phenomenon, with minimum temperatures displaying considerably more increase than
maximum temperatures. No uniform seasonal preference for this increase emerged from
these stations. Because of this increase, the distribution of observed temperatures shows a
marked warm bias at several of the urban sites during recent years.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Impact of land use and
precipitation changes on
surface temperature trends
in Argentina
Nunez,
Ciapessoni,
et. al., 2008
Journal of
Geophysical
Research:
Atmospheres
(1984–2012)
Volume 113,
Issue D6,
March 2008
25
http://onlinelibrary.wiley.
com/doi/10.1029/2007JD
008638/abstract
ABSTRACT
The “observation minus reanalysis” (OMR) method has been used to estimate the impact
of changes in land use (including urbanization and agricultural practices such as
irrigation) by computing the difference between the trends of the surface observations
(which reflect all the sources of climate forcing, including surface effects) and the
NCEP/NCAR reanalysis (which only contains the forcings influencing the assimilated
atmospheric trends). In this paper we apply the OMR method to surface stations in
Argentina for the period 1961–2000. In contrast to most other land areas, over most of
Argentina there has been net cooling, not warming (about −0.04°C/decade). Observations
also show a very strong decrease in the diurnal temperature range north of 40°S. This is
associated with an observed strong reduction in the maximum temperature
(−0.12°C/decade) together with a weak warming trend in the minimum temperature
(0.05°C/decade). The OMR trends show a warming contribution to the mean temperature
(+0.07°C/decade) and a decrease in diurnal temperature range (−0.08°C/decade),
especially strong in the areas where the observed precipitation has increased the most and
where, as a consequence, there has been an exponential increase of soy production in the
last decade. The increase in precipitation is apparently associated with an increase in the
moisture transport from the Amazons to northern Argentina by the low-level jet.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Homogeneity adjustments
of in situ atmospheric
climate data: a review
Peterson,
Easterling, et.
al., 1998
International
Journal of
Climatology
Volume 18,
Issue 13, pages
1493–1517, 15
November
1998
26
http://onlinelibrary.wiley.
com/store/10.1002/(SICI)
10970088(19981115)18:13%3
C1493::AIDJOC329%3E3.0.CO;2T/asset/329_ftp.pdf?v=1
&t=hcp21rvi&s=19ed8c9
a7f177a3a2bbc37997f03
50990e4e948c
ABSTRACT
Long-term in situ observations are widely used in a variety of climate analyses.
Unfortunately, most decade- to century-scale time series of atmospheric data have been
adversely impacted by inhomogeneities caused by, for example, changes in
instrumentation, station moves, changes in the local environment such as urbanization, or
the introduction of different observing practices like a new formula for calculating mean
daily temperature or different observation times. If these inhomogeneities are not
accounted for properly, the results of climate analyses using these data can be erroneous.
Over the last decade, many climatologists have put a great deal of effort into developing
techniques to identify inhomogeneities and adjust climatic time series to compensate for
the biases produced by the inhomogeneities. It is important for users of homogeneityadjusted data to understand how the data were adjusted and what impacts these
adjustments are likely to make on their analyses. And it is important for developers of
homogeneity-adjusted data sets to compare readily the different techniques most
commonly used today. Therefore, this paper reviews the methods and techniques
developed for homogeneity adjustments and describes many different approaches and
philosophies involved in adjusting in situ climate data. © 1998 Royal Meteorological
Society.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
A closer look at United
States and global surface
temperature change
Hansen,
Easterling and
Imhoff(2001)
Journal of
Geophysical
Research:
Atmospheres
(1984–2012)
Volume 106,
Issue D20,
p.23947-2396
27
http://onlinelibrary.wi
ley.com/doi/10.1029/
2001JD000354/full
ABSTRACT
We compare the United States and global surface air temperature changes of the past
century using the current Goddard Institute for Space Studies (GISS) analysis and the
U.S. Historical Climatology Network (USHCN) record [Karl et al., 1990]. Changes in
the GISS analysis subsequent to the documentation by Hansen et al. [1999] are as
follows: (1) incorporation of corrections for time-of-observation bias and station history
adjustments in the United States based on Easterling et al. [1996a], (2) reclassification of
rural, small-town, and urban stations in the United States, southern Canada, and northern
Mexico based on satellite measurements of night light intensity [Imhoff et al., 1997], and
(3) a more flexible urban adjustment than that employed by Hansen et al. [1999],
including reliance on only unlit stations in the United States and rural stations in the rest
of the world for determining long-term trends. We find evidence of local human effects
(“urban warming”) even in suburban and small-town surface air temperature records, but
the effect is modest in magnitude and conceivably could be an artifact of inhomogeneities
in the station records. We suggest further studies, including more complete satellite night
light analyses, which may clarify the potential urban effect. There are inherent
uncertainties in the long-term temperature change at least of the order of 0.1°C for both
the U.S. mean and the global mean. Nevertheless, it is clear that the post-1930s cooling
was much larger in the United States than in the global mean. The U.S. mean temperature
has now reached a level comparable to that of the 1930s, while the global temperature is
now far above the levels earlier in the century. The successive periods of global warming
(1900–1940), cooling (1940–1965), and warming (1965–2000) in the 20th century show
distinctive patterns of temperature change suggestive of roles for both climate forcings
and dynamical variability. The U.S. was warm in 2000 but cooler than the warmest years
in the 1930s and 1990s. Global temperature was moderately high in 2000 despite a
lingering La Niña in the Pacific Ocean.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
The effects of land-use
and anthropogenic heating
on the surface temperature
in the Tokyo Metropolitan
area: A numerical
experiment
Kimura,
Takahashi,
1991
Atmospheric
Environment.p
art B. Urban
Atmosphere
Volume 25,
Issue 2, p.155164
28
http://www.sciencedirect.
com/science/article/pii/09
5712729190050O
ABSTRACT
In order to investigate the effects of land-use and anthropogenically produced heat on the
surface air temperature in the Tokyo Metropolitan area, numerical experiments were
carried out under typical summer synoptic conditions. The model is based on the threedimensional Boussinesq equations, taking into account the hydrostatic assumption. Since
land-use differs over every subdivision in Tokyo, the model includes a sub-grid
parametrization scheme which can calculate the total heat flux a grid surface composed
of different surfaces.
The diurnal variation of the simulated surface air temperature agrees well with the
observed value; an average over 36 days which represent typical summer days; i.e.
negligible gradient winds and almost clear skies. The model shows that the contribution
of anthropogenic heat is much larger at night, in spite of the lower energy consumption as
compared to daytime use. Due to the scarcity of green vegetated areas in the central part
of the city, the surface air temperature is enhanced in this region during daytime, however
this enhancement is small after midnight.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
The GeoProfile metadata,
exposure of instruments,
and measurement bias in
climatic record revisited
Rezaul
Mahmood*,
Stuart A.
Foster, David
Logan, 2006
International
Journal of
Climatology
Volume 26,
Issue 8, pages
1091–1124, 30
June 2006
29
http://onlinelibrary.wiley.
com/store/10.1002/joc.12
98/asset/1298_ftp.pdf?v=
1&t=hcp36l2h&s=9f6f04
c97edb0d60700a94f7363
63d53791d8287
ABSTRACT
Station metadata plays a critical role in the accurate assessment of climate data and
eventually of climatic change, climate variability, and climate prediction. However,
current procedures of metadata collection are insufficient for these purposes. This paper
introduces the GeoProfile as a model for documenting and visualizing enhanced spatial
metadata. In addition to traditional metadata archiving, GeoProfiles integrate meso-scale
topography, slope, aspect, and land-use data from the vicinity of climate observing
stations (http://kyclim.wku.edu/tmp/geoprofiles/geoprofiles main.html). We describe how
GeoProfiles are created using Geographical Information Systems (GIS) and demonstrate
how they may be used to help identify measurement bias in climate observations due to
undesired instrument exposures and the subsequent forcings of micro- and mesoenvironments. A study involving 12 COOP and US Historical Climate Network
(USHCN) stations finds that undesirable instrument exposures associated with both
anthropogenic and natural influences resulted in biased measurement of temperature.
Differences in average monthly maximum and minimum temperatures between
proximate stations are as large as 1.6 and 3.8 C, respectively. In addition, it is found that
the difference in average extreme monthly minimum temperatures can be as high as 3.6C
between nearby stations, largely owing to the differences in instrument exposures.
Likewise, the difference in monthly extreme maximum temperatures between
neighboring stations are as large as 2.4C. This investigation finds similar differences in
the diurnal temperature range (DTR). GeoProfiles helped us to identify meso-scale
forcing, e.g. instruments on a south-facing slope and topography, in addition to forcing of
micro-scale setting. Copyright 2006 Royal Meteorological Society.
Kathyrn Westerman, Oliver Smith, Enrique Hernandez, Megan Fowler
Correcting Wind Speed
Measurements for Site
Obstructions
Woflson,
Marilyn M.,
Fujita, T.
Theodore
Journal of
Atmospheric
and Oceanic
Technology,
Volume 6,
Issue 2, 343352
30
http://dx.doi.org/10.11
75/15200426(1989)006<0343:
CWSMFS>2.0.CO;2
ABSTRACT
The effects of obstructions on winds measured by the 30 station FLOWS (FAALincoln Laboratory Operational Weather Studies) mesonet and the 6 station FAA
LLWAS (Low Level Wind Shear Alèrt System) near Memphis, TN in 1985 are
analyzed. The slowing of surface winds by anemometer site obstructions is a
continuing problem for scientific and operational wind shear measurement system
This paper considers an improved version of the technique used by Fujita and
Wakimoto for compensating the obstruction effects by the use of mathematical
models relating the unobstructed wind speed to the measured wind speed and the
observed obstructions at each site. Over eight million wind speed measurements
gathered over 197 days (15 February–31 August) were used. The effects of
obstructions at a particular site were evidenced by a strong negative correlation
between the observed wind speed transmission factors and the obstruction angles
as measured from panoramic photographs taken of the horizon around each station.
The functional relationship between them was modeled as a decaying exponential
plus a constant, and an iterative least squares regression technique was used on
data from all of the stations at once in deriving the three parameters of the equation.
It was found that the first 8° of obstruction have the greatest blockage effects, and
that even a 2° or 3° high isolated clump of trees can have a pronounced effect on the
measured wind speeds from that direction. The possibility that the transmission
factors are scale dependent and time dependent is explored.