Rural Stations Research Articles

Reassessment of urbanization effect on surface air temperature trends at an urban station of North China

Based on a homogenized data set of monthly mean temperature, minimum temperature, and maximum temperature at Shijiazhuang City Meteorological Station (Shijiazhuang station) and four rural meteorological stations selected applying a more sophisticated methodology, we reanalyzed the urbanization effects on annual, seasonal, and monthly mean surface air temperature (SAT) trends for updated time period 1960–2012 at the typical urban station in North China. The results showed that (1) urbanization effects on the long-term trends of annual mean SAT, minimum SAT, and diurnal temperature range (DTR) in the last 53 years reached 0.25, 0.47, and − 0.50 °C/decade, respectively, all statistically significant at the 0.001 confidence level, with the contributions from urbanization effects to the overall long-term trends reaching 67.8, 78.6, and 100%, respectively; (2) the urbanization effects on the trends of seasonal mean SAT, minimum SAT, and DTR were also large and statistically highly significant. Except for November and December, the urbanization effects on monthly mean SAT, minimum SAT, and DTR were also all statistically significant at the 0.05 confidence level; and (3) the annual, seasonal, and monthly mean maximum SAT series at the urban station registered a generally weaker and non-significant urbanization effect. The updated analysis evidenced that our previous work for this same urban station had underestimated the urbanization effect and its contribution to the overall changes in the SAT series. Many similar urban stations were being included in the current national and regional SAT data sets, and the results of this paper further indicated the importance and urgency for paying more attention to the urbanization bias in the monitoring and detection of global and regional SAT change based on the data sets.

Harmonic analysis of 130-year hourly air temperature in Hong Kong: detecting urban warming from the perspective of annual and daily cycles

The century-long search for the precise mechanisms responsible for urban heat islands continues, while urban warming worsens in many megacities. Most studies have focused on mean temperature, daily and annual temperature ranges and urban heat island intensity. We hypothesize that an analysis of the changes in the characteristics of the complete daily and annual temperature cycles, including not only the mean temperature and temperature ranges (amplitudes) but also the maximum and minimum temperatures and the phases, can provide more information on urban warming phenomena. Through a detailed analysis of long-term observations in Hong Kong, we found that the difference in the daily cycle between urban and rural stations is very distinct, whereas the annual cycles are much more similar, suggesting that the urban environment has a greater effect on the daily cycle than on the annual cycle. The daily phase has shifted a total of 1.77 h later over the last 130 years (1.36 h per century) in the urban area of Hong Kong according to the Hong Kong Observatory (HKO) data. The annual phase change at HKO reflects the globally observed phenomenon that the annual phase advances or seasons onset earlier.

Urban Heat Island and Urban Dry Island in Moscow and Their Centennial Changes

AbstractThe long-term dynamics of both urban heat island (UHI) and urban dry island (UDI) intensities over the city of Moscow, Russia, has been analyzed for the period from the end of the nineteenth century until recent years using data of the ground meteorological network. Besides traditional maximum heat/dry island intensity, an additional parameter—station-averaged intensity as a mean difference between the data of all urban and rural stations—has been used. The traditional maximum (mean annual) UHI intensity in Moscow was nearly 1.0°C at the end of the nineteenth century, 1.2°C one century ago, 1.5°–1.6°C both in the middle and at the end of the twentieth century, and 2.0°C in recent years. The station-averaged UHI intensity was equal to 0.7°–0.8°C in the second half of the twentieth century and increased up to 1.0°C in recent years. It is probable that stabilization of both parameters from the 1950s to the 1990s was connected with the extensive city growth at that time (mass resettlement of inhabitants from the overpopulated city center to the new urban periphery since the 1960s). The new increase of UHI intensities is the result of the new intensive city growth. The relative humidity in Moscow significantly decreased during the last 146 years (mostly because of warming), unlike water vapor pressure. The UDI is closely connected with the UHI; the absolute value (modulus) of its intensity is increasing in time from −4% at the end of the nineteenth century to −9% now. During the last two decades, the UDI as well as the UHI became much stronger than before.

Upper gastrointestinal tract endoscopic lesions in a rural African hospitalo: 252endoscopies at the Kara University Hospital, Togo.

To analyze the indications for upper gastrointestinal endoscopy (UGIE) and determine the frequency of the pathological findings observed in rural areas of Africa. This retrospective study includes 9 series of 5-day visits to perform these examinations. Patients were informed of the presence of the endoscopy team by a bulletin on a rural radio station and by general practitioners at the Kara University Hospital. Patients were recruited from the hospital clinics and from the general population of the Kara region. The study includes all UGIE reports from August, 2007, through September, 2014; these contain the indications for the procedure, the patients' sex and age, and the examination report. The study included 252 reports for 133 women and 119 men with a mean age of 42.44 years (range: 20 to 102 years). The most frequent indications were dyspeptic syndrome (79.76%) and diffuse abdominal pain (11.11%). In all, we observed 139 gastroduodenal lesions among the patients with dyspepsia, principally bile reflux (23.02%), gastroduodenal inflammatory lesions (18.71%) and gastroduodenal ulcers (17.99%). The most commonly observed lesions for diffuse abdominal pain were again, bile reflux (30.77%), followed by gastritis, esophageal mycoses, and tumors. This work made it possible to identify the various pathological lesions of the UGI tract seen on endoscopies in a rural hospital in Togo.

Corrosion Failure of the External Surface of Chlorinator’s Copper Pipes in a Water Disinfection Station

This work investigates the corrosion failure of the chlorinator’s copper pipes in a rural water disinfection station. For this purpose, some corroded samples were provided from the failed pipes and investigated using the X-ray diffraction (XRD) and the scanning electron microscope (SEM) equipped with the energy-dispersive X-ray spectroscopy (EDS). Also, an experimental setup was designed to study the role of the electrolyte formation on the copper pipes. This experimental setup demonstrated that the main factor of pipe failure was the formation of a corrosive electrolyte layer with varying chlorine (presented due to gas leakage) concentration during a day. The electrochemical impedance spectroscopy (EIS) confirmed that variations in the chlorine concentration had an unexpected effect on the corrosion rate. Furthermore, it was found that the main phase in the corrosion products was cupric chloride hydroxide (Cu2(OH)3Cl) with many porosities and cracks. These defects provide suitable places for the formation of the corrosive electrolyte and the following corrosion which ultimately led to the failure of the copper pipes.

Impact of tropical cyclone track change on regional air quality

There has been an increase in tropical cyclones (TCs) in the western North Pacific (WNP) that traverse with a northward recurving track towards East Asia and a decrease in TC tracks entering the South China Sea (SCS) in the past few decades. To investigate the potential impact of the prevailing TC track change on Hong Kong air quality, an analysis has been carried out based on historical data (1991 to 2010) of TC tracks and air quality. Compared to TCs in other regions, TCs in the vicinity of Taiwan (Region 2, R2) have the greatest impact on Hong Kong air quality due to regional transport of air pollutants from the highly industrialized Pearl River Delta (PRD). In the last twenty years, the number of days with TCs in R2 (May to October) has increased by 45% from 111days in the period 1991–2000 to 161days in 2001–2010, during which there was an increase in yearly TC-related pollution episodes of approximately 3 episodes per year in Hong Kong. The enhancement of mean O3 concentration due to TCs in R2 is reported as 82% (~50.8μg/m3 at a rural station) and 58% (~16.8μg/m3 at an urban station) higher than the summer averages. A similar enhancement is also observed for PM10 (called RSP) and SO2 with an average of 70% (i.e., 22.2μg/m3) and 100% (i.e., 15.2μg/m3) increases, respectively. Overall, the 20years of historical data show that the O3 concentrations on the TC-affected days are increasing at the estimated rates of 0.5μg/m3 and 2.6μg/m3 per year, respectively, in the urban and remote areas, which are significantly higher than the increase of 0.3μg/m3 and 0.4μg/m3 per year in the average summer concentrations.

Detecting the effect of urban land use on extreme precipitation in the Netherlands

A notable increase in heavy precipitation has been observed over the Netherlands in recent decades. The aim of this study was to assess the influences of urban land use on these extreme precipitation patterns. Significant differences between an earlier multi-decadal period and a recent period were found in the Netherlands between 1961 and 2014. The significant changes in different indices indicate that severe precipitation events were not distributed homogeneously across the study area. The precipitation probability and distribution were assessed using the block maxima approach by comparing observations from urban and rural areas at different timescales. The possible effects of land use on extreme precipitation were assessed by quantifying the differences between urban and rural rain gauge stations according to the spatial gridding method. This study shows that urban land use may have affected the extreme precipitation patterns across the Netherlands. The data from all the categorized stations show that urban areas receive more intense extreme precipitation than do rural areas. Relative to other areas in the Netherlands, the urban areas in the western populated regions of the country exhibit prominent urban land use influences on the extreme precipitation patterns.

River effects on the heat island of a small urban area

This study examined the urban heat island (UHI) of a small urban area divided by a river in central Pennsylvania. As more of the population resides in urban areas, the study of UHIs is imperative due to increased mortality during heat waves, elevated energy costs, and increased air pollution. Hourly temperatures were collected from 19 urban stations and one rural reference station. All stations were compared to one another to assess UHI intensity and intra-urban variability and were also assessed based on their distance to the bisecting river. Results indicate an average yearly UHI of 2.25°C that is strongest at night, in summer, in the most urbanized areas, and closer to the river. For every 1000m increase in distance from the river, the UHI decreased by 0.6°C to 0.3°C depending on season. In the summer, the distance to the river is more important that the urban score at a station for predicting the UHI. The river enhances the UHI due to its warmer temperatures during the nighttime and by increasing the local humidity levels. Assessment of the heat island of this area can assist in determining the best locations for mitigation efforts to reduce the heat island effect.

Effect of Urbanization on Land-Surface Temperature at an Urban Climate Station in North China

While the land-surface temperature (LST) observed at meteorological stations has significantly increased over the previous few decades, it is still unclear to what extent urbanization has affected these positive trends. Based on the LST data recorded at an urban station in Shijiazhuang in North China, and two rural meteorological stations, the effect of urbanization at the Shijiazhuang station for the period 1965–2012 is examined. We find, (1) a statistically-significant linear trend in annual mean urban–rural LST difference of $$0.27\,^{\circ }\hbox {C}$$ $$\hbox {(10 year)}^{-1}$$ , with an urbanization contribution of 100% indicating that the increase in the annual mean LST at the urban station is entirely caused by urbanization. The urbanization effects in spring, summer and autumn on the trends of mean LST are also significant; (2) the urbanization effect is small for time series of the annual mean minimum LST, and statistically marginal for the trend in annual mean maximum LST [ $$0.19\,^{\circ }\hbox {C}\,\hbox {(10 year)}^{-1}$$ ]; (3) the urbanization effect on the annual mean diurnal LST range ( $$\Delta {LST}$$ ) at the urban station is a strongly significant trend of $$0.23\,^{\circ }\hbox {C (10\,year)}^{-1}$$ , with an urbanization contribution of 21%. The urbanization effects on trends in the spring and autumn mean $$\Delta {LST}$$ are also larger and more significant than for the other seasons; (4) the urbanization effects on the long-term LST trends are remarkably different from those on the near-surface air temperature at the same urban station. Nonetheless, the significant warming of the urban boundary layer is expected to affect the urban environment and ecosystems. However, the problem of data representativeness at an urban station for the monitoring and investigation of large-scale climate change remains.

Prediction of size-resolved number concentration of cloud condensation nuclei and long-term measurements of their activation characteristics

Atmospheric aerosol particles acting as cloud condensation nuclei (CCN) are key elements in the hydrological cycle and climate. To improve our understanding of the activation characteristics of CCN and to obtain accurate predictions of their concentrations, a long-term field campaign was carried out in the Yangtze River Delta, China. The results indicated that the CCN were easier to activate in this relatively polluted rural station than in clean (e.g., the Amazon region) or dusty (e.g., Kanpur-spring) locations, but were harder to activate than in more polluted urban areas (e.g., Beijing). An improved method, using two additional parameters—the maximum activation fraction and the degree of heterogeneity, is proposed to predict the accurate, size-resolved concentration of CCN. The value ranges and prediction uncertainties of these parameters were evaluated. The CCN predicted using this improved method with size-resolved chemical compositions under an assumption that all particles were internally mixed showed the best agreement with the long-term field measurements.

Urbanization effect on trends in sunshine duration in China

Abstract. There is an ongoing debate on whether the observed decadal variations in surface solar radiation, known as dimming and brightening periods, are a large-scale or solely local phenomenon. We investigated this issue using long-term sunshine duration records from China, which experienced a rapid increase in urbanization during the past decades. Over the period 1960–2013, 172 pairs of urban and nearby rural stations were analyzed. Urban and rural sunshine duration trends show similar spatial patterns during a dimming phase (1960–1989) and a subsequent period during which trends were leveling off (1990–2013). This indicates that rather than local effects, the trends in sunshine duration are on more of a national or regional scale in China. Nevertheless, in the dimming phase, the declining rate of sunshine duration in rural areas is around two-thirds of that in urban areas. The ratio of rural to urban dimming generally increases from a minimum of 0.39 to a maximum of 0.87 with increasing indices of urbanization calculated based on the year 2013. It reaches a maximum when the urbanization level exceeds 50 %, the urban population exceeds 20 million, or the population density becomes higher than 250 person km−2. After the transition into the leveling-off period, sunshine duration trends are no longer significantly affected by urbanization. Meanwhile, the number of laws and regulations related to air pollution and investment in pollution treatment have been increasing in China.

Contribution of urbanization to the increase of extreme heat events in an urban agglomeration in east China

AbstractThe urban agglomeration of Yangtze River Delta (YRD) is emblematic of China's rapid urbanization during the past decades. Based on homogenized daily maximum and minimum temperature data, the contributions of urbanization to trends of summer extreme temperature indices (ETIs) in YRD are evaluated. Dynamically classifying the observational stations into urban and rural, this study presents unexplored changes in temperature extremes during the past four decades in YRD and quantifies the amplification of the positive trends in ETIs by the urban heat island effect. Overall, urbanization contributes to more than one third of the increase of intensity of extreme heat events in the region, which is comparable to the contribution of greenhouse gases. Compared to rural stations, more notable shifts to the right in the probability distribution of temperature and ETIs are found in urban stations. The rapid urbanization in YRD has resulted in large increases in the risk of heat extremes.

The Effects of Heat Advection on UK Weather and Climate Observations in the Vicinity of Small Urbanized Areas

Weather and climate networks traditionally follow rigorous siting guidelines, with individual stations located away from frost hollows, trees or urban areas. However, the diverse nature of the UK landscape suggests that the feasibility of siting stations that are truly representative of regional climate and free from distorting local effects is increasingly difficult. Whilst the urban heat island is a well-studied phenomenon and usually accounted for, the effect of warm urban air advected downwind is rarely considered, particularly at rural stations adjacent to urban areas. Until recently, urban heat advection (UHA) was viewed as an urban boundary-layer process through the formation of an urban plume that rises above the surface as it is advected. However, these dynamic UHA effects are shown to also have an impact on surface observations. Results show a significant difference in temperatures anomalies (p,< ,0.001) between observations taken downwind of urban and rural areas. For example, urban heat advection from small urbanized areas (sim 1,hbox {km}^{2}) under low cloud cover and wind speeds of 2–3,hbox {m},hbox {s}^{-1} is found to increase mean nocturnal air temperatures by 0.6,^{circ }hbox {C} at a horizontal distance of 0.5 km. Fundamentally, these UHA results highlight the importance of careful interpretation of long-term temperature data taken near small urban areas.

Assessing the urban heat island and its energy impact on residential buildings in Mediterranean climate: Barcelona case study

The Urban Heat Island (UHI) effect is particularly concerning in Mediterranean zone, as climate change and UHI scenarios foresee a fast growth of energy consumption for next years, due to the widespread of air conditioning systems and the increase of cooling demand. The UHI intensity is thus a key variable for the prediction of energy needs in urban areas.This study investigates the intensity of UHI in Barcelona (Spain), the densest Mediterranean coastal city, and its impact on cooling demand of residential buildings.The experimental analysis is based on temperature data from rural and urban Weather Stations and field measurements at street level. The maximum average UHI intensity is found to be 2.8°C in winter and 1.7°C in summer, reaching 4.3°C at street level. Simulations performed with EnergyPlus indicate that the UHI intensity increases the sensible cooling load of residential buildings by around 18%–28%, depending on UHI intensity, amount of solar gains and cooling set point.In the light of the results, the UHI intensity in Mediterranean context should be properly considered in performing energy evaluations for urban contexts, since standard meteorological data from airport weather stations are not found to be accurate enough.

Temporal and spatial characteristics of the urban heat island in Beijing and the impact on building design and energy performance

With the increased urbanization in most countries worldwide, the urban heat island (UHI) effect, referring to the phenomenon that an urban area has higher ambient temperature than the surrounding rural area, has gained much attention in recent years. Given that Beijing is developing rapidly both in urban population and economically, the UHI effect can be significant. A long-term measured weather dataset from 1961 to 2014 for ten rural stations and seven urban stations in Beijing, was analyzed in this study, to understand the detailed temporal and spatial characteristics of the UHI in Beijing. The UHI effect in Beijing is significant, with an urban-to-rural temperature difference of up to 8 °C during the winter nighttime. Furthermore, the impacts of UHIs on building design and energy performance were also investigated. The UHI in Beijing led to an approximately 11% increase in cooling load and 16% decrease in heating load in the urban area compared with the rural area, whereas the urban heating peak load decreased 9% and the cooling peak load increased 7% because of the UHI effect. This study provides insights into the UHI in Beijing and recommendations to improve building design and decision-making while considering the urban microclimate.

Carbonaceous aerosol source apportionment using the Aethalometer model – evaluation by radiocarbon and levoglucosan analysis at a rural background site in southern Sweden

Abstract. With the present demand on fast and inexpensive aerosol source apportionment methods, the Aethalometer model was evaluated for a full seasonal cycle (June 2014–June 2015) at a rural atmospheric measurement station in southern Sweden by using radiocarbon and levoglucosan measurements. By utilizing differences in absorption of UV and IR, the Aethalometer model apportions carbon mass into wood burning (WB) and fossil fuel combustion (FF) aerosol. In this study, a small modification in the model in conjunction with carbon measurements from thermal–optical analysis allowed apportioned non-light-absorbing biogenic aerosol to vary in time. The absorption differences between WB and FF can be quantified by the absorption Ångström exponent (AAE). In this study AAEWB was set to 1.81 and AAEFF to 1.0. Our observations show that the AAE was elevated during winter (1.36 ± 0.07) compared to summer (1.12 ± 0.07). Quantified WB aerosol showed good agreement with levoglucosan concentrations, both in terms of correlation (R2 = 0.70) and in comparison to reference emission inventories. WB aerosol showed strong seasonal variation with high concentrations during winter (0.65 µg m−3, 56 % of total carbon) and low concentrations during summer (0.07 µg m−3, 6 % of total carbon). FF aerosol showed less seasonal dependence; however, black carbon (BC) FF showed clear diurnal patterns corresponding to traffic rush hour peaks. The presumed non-light-absorbing biogenic carbonaceous aerosol concentration was high during summer (1.04 µg m−3, 72 % of total carbon) and low during winter (0.13 µg m−3, 8 % of total carbon). Aethalometer model results were further compared to radiocarbon and levoglucosan source apportionment results. The comparison showed good agreement for apportioned mass of WB and biogenic carbonaceous aerosol, but discrepancies were found for FF aerosol mass. The Aethalometer model overestimated FF aerosol mass by a factor of 1.3 compared to radiocarbon and levoglucosan source apportionment. A performed sensitivity analysis suggests that this discrepancy can be explained by interference of non-light-absorbing biogenic carbon during winter. In summary, the Aethalometer model offers a cost-effective yet robust high-time-resolution source apportionment at rural background stations compared to a radiocarbon and levoglucosan alternative.

Research on the Operation Management of Rural Power Network Distribution in Leshan Area

农网用电性质决定了农网配电变压器较多，因此农网配电变压器的运行管理是基层农电工作的重要组成部分，也是解决农网当前供电质量问题的关键所在。从乐山地区农网运行现状看，目前乐山地区农村电网整体供电质量不高，供电可靠性不好，线损较大，农村配变台区运行管理水平不高，缺乏成熟的管理体制。本文提出新的农电D类低电压配变运行精益管理体系，开发农网配变信息管理系统，能够集在线监控、数据信息汇集、理论线损计算、决策辅助与抢修指挥于一体的“可视化”控制体系，以增强电网供电的稳定性与可靠性，促进供电质量。 Rural electricity properties determined the more rural distribution transformer, so the management of rural distribution transformer is an important part of rural grass-roots work, and also the key to solve the current problem of power supply quality in rural power network. The current situations of rural power network in Leshan are as follows: The overall power supply quality of rural power network is not high, the reliability of power supply is not good, the line loss is large, the management level of rural transformer station area is not high, and there is lack of mature management mechanism. In this paper, a new lean management system applied in class D low voltage transformer operation of rural power network is presented. A rural power grid distribution and transformation information management system is developed which is a visual system integrating online monitoring, data collection, theoretical line loss calculation, decision assistance and emergency repair command.

Multiscale multifractal properties between ground-level ozone and its precursors in rural area in Hong Kong

In rural area, due to the reduction of NOx and CO emitted from vehicle exhausts, the ozone photochemical reaction exhibits relatively weak effect and ozone formation presents different pattern with its precursors in contrast to urban situation. Hence, in this study, we apply detrended cross-correlation analysis to investigate the multifractal properties between ozone and its precursors in a rural area in Hong Kong.The observed databases of ozone, NO2, NOx and CO levels during 2005–2014 are obtained from a rural monitoring station in Hong Kong. Based on the collected database, the cross-correlation analysis is carried out firstly to examine the cross-correlation patterns and the results indicate that close interactive relations exist between them. Then the detrended cross-correlation analysis is performed for further analysis. The multifractal characters occur between ozone and its precursors. The long-term cross-correlations behaviors in winter are verified to be stronger than that in other seasons. Additionally, the method is extended on daily averaged data to explore the multifractal property on various time scales. The long-term cross-correlation behavior of ozone vs NO2 and NOx on daily basis becomes weaker while that of ozone vs CO becomes stronger. The multifractal properties for all pairs in summer are found to be the strongest among the whole year. These findings successfully illustrate that the multifractal analysis is a useful tool for describing the temporal scaling behaviors of ozone trends in different time series in rural areas.

Spatiotemporal analysis of the atmospheric and surface urban heat islands of the Metropolitan Area of Toluca, Mexico

The dynamic of consolidation of urban areas in Latin America has allowed that almost 80% of the population concentrates in cities; this has produced changes in land covers and modified regional climate, propitiating the appearance of urban heat islands. The Metropolitan Area of Toluca, State of Mexico, Mexico, holds the fifth national place in population size and experiences this process, because of this, the objective is to analyze and compare the spatiotemporal characteristics of the atmospheric urban heat island obtained from data gathered from 12 urban and rural weather stations with the surface urban heat island obtained from the digital processing of four Landsat 8 images. Results show the year-round presence of night-time atmospheric urban heat islands, which reach a peak in autumn (up to 6 °C). Daytime atmospheric urban heat islands occur in summer and autumn with a maximum intensity of 4 °C. For their part, surface urban heat islands occur in spring, summer and autumn and reach maximums of 19 °C in intensity. A strong correlation was found between wetness and surface temperature (coefficient of determination, 0.8) in spring and winter. Soil wetness directly impacts the formation of weak urban heat islands in dry season, and intense ones in wet season, while the green areas and the winds affect the spatial distribution of the same.

Comparing the diurnal and seasonal variabilities of atmospheric and surface urban heat islands based on the Beijing urban meteorological network

AbstractThis study compared the diurnal and seasonal cycles of atmospheric and surface urban heat islands (UHIs) based on hourly air temperatures (Ta) collected at 65 out of 262 stations in Beijing and land surface temperature (Ts) derived from Moderate Resolution Imaging Spectroradiometer in the years 2013–2014. We found that the nighttime atmospheric and surface UHIs referenced to rural cropland stations exhibited significant seasonal cycles, with the highest in winter. However, the seasonal variations in the nighttime UHIs referenced to mountainous forest stations were negligible, because mountainous forests have a higher nighttime Ts in winter and a lower nighttime Ta in summer than rural croplands. Daytime surface UHIs showed strong seasonal cycles, with the highest in summer. The daytime atmospheric UHIs exhibited a similar but less seasonal cycle under clear‐sky conditions, which was not apparent under cloudy‐sky conditions. Atmospheric UHIs in urban parks were higher in daytime. Nighttime atmospheric UHIs are influenced by energy stored in urban materials during daytime and released during nighttime. The stronger anthropogenic heat release in winter causes atmospheric UHIs to increase with time during winter nights, but decrease with time during summer nights. The percentage of impervious surfaces is responsible for 49%–54% of the nighttime atmospheric UHI variability and 31%–38% of the daytime surface UHI variability. However, the nighttime surface UHI was nearly uncorrelated with the percentage of impervious surfaces around the urban stations.