Evaluating the contributions of urban surface expansion to regional warming in Shanghai using different methods to calculate the daily mean temperature

AbstractThe contribution of urban surface expansion to regional warming as detected from meteorological observational station data may vary with considerable uncertainty because of the spatial heterogeneity of such data—a situation that promotes a requirement for numerical model-based investigations. Satellite-based images from 1980 to 2016 that have fine resolution over three city clusters and that display the urban surface expansion in China from rapid economic development and anthropogenic activity were used to perform 37-yr nested dynamical downscaling using the Weather Research and Forecasting (WRF) Model. The urban surface areas in Beijing, China, expressed marked expansion in the last 37 years. The contribution of urban surface expansion to regional warming was approximately 22% of the overall warming in Beijing and was stronger in the plains areas of Beijing (42%). The contributions to land-use grids that changed from nonurban (in 1980) to urban (in 2016; N2U) were much stronger than those to grids that were classified as urban in both time periods (U2U), which were closer to the values of urban areas (including N2U and U2U) because of the intense increase in urban surface areas. Urban-related warming expressed marked annual variation and was greater in the warm seasons and smaller in the cold seasons. The greater increase in surface air temperature (SAT) minimum and the weaker SAT maximum accounted for the decreased diurnal temperature range.

Download Full-text

Modelling Daily Mean Surface Air Temperature Calculated from Different Methods and Its Impact on Urban-Related Warming Evaluations over Guangzhou and Shenzhen Using the WRF Model

Atmosphere ◽

10.3390/atmos10020048 ◽

2019 ◽

Vol 10 (2) ◽

pp. 48

Author(s):

Deming Zhao ◽

Jian Wu

Keyword(s):

Air Temperature ◽

Diurnal Cycle ◽

Climate Model ◽

Dynamical Downscaling ◽

Spatial Scales ◽

Wrf Model ◽

Surface Air Temperature ◽

Urban Surface ◽

Surface Expansion ◽

Urban Surface Expansion

The impacts of urban surface expansion, based on satellite-derived data displaying urban surface expansion in China at different spatial scales from 1980 to 2016, were investigated using nested dynamical downscaling methods with the Weather Research and Forecasting (WRF) regional climate model at a 3.3-km resolution over a city and city cluster scale. Urban-related warming, based on daily mean surface air temperature at 2 m (SAT), calculated from the averages of four time records each day (00, 06, 12, and 18 h UTC, T4) and averages of SAT maximum (Tmax) and minimum (Tmin) (Txn), was evaluated. Differences in urban-related warming contributions calculated using T4 and Txn were small, whereas annual mean SAT and trends calculated using Txn were respectively and significantly larger and smaller than those calculated using T4 over Guangzhou and Shenzhen, excluding the trends over middle-northern Shenzhen. The differences in annual mean SAT calculated using T4 and Txn are attributed to nonlinear or asymmetric variations with time for the diurnal cycle of SAT. Meanwhile, differences in trends between T4 and Txn are interpreted as a strong trend for Tmin and a weak one for Tmax, which mitigated the trend for Txn. The impacts on the evaluations of urban-related warming contributions calculated from different methods were the largest over the areas classified as urban surfaces in both time periods (U2U), especially during intense urban-surface-expansion periods between 2000 and 2016. The subregional performances in the changes in annual mean SAT, trends, and urban-related warming are attributed to urban-surface-expansion, which induced varied changes in the diurnal cycle due to asymmetric warming during the daytime and nighttime over different subregions.

Download Full-text

Changes in daily and cumulative volumetric rainfall at various intensity levels due to urban surface expansion over China

Tellus A Dynamic Meteorology and Oceanography ◽

10.1080/16000870.2020.1745532 ◽

2020 ◽

Vol 72 (1) ◽

pp. 1-21

Author(s):

Deming Zhao ◽

Jinlin Zha ◽

Jian Wu

Keyword(s):

Urban Surface ◽

Surface Expansion ◽

Urban Surface Expansion

Download Full-text

The Influence of Urban Surface Expansion in China on Regional Climate

Journal of Climate ◽

10.1175/jcli-d-15-0604.1 ◽

2017 ◽

Vol 30 (3) ◽

pp. 1061-1080 ◽

Cited By ~ 14

Author(s):

Deming Zhao ◽

Jian Wu

Keyword(s):

East Asia ◽

Eastern China ◽

Urban Land Use ◽

Radiation Budget ◽

Urban Surface ◽

Eastern Coast ◽

Total Cloud Amount ◽

Surface Expansion ◽

Urban Surface Expansion ◽

The Impact

Abstract Incorporating satellite-based urban surface data for the 1980s, 1990s, 2000s, and 2010s in China, contributions to regional warming, and changes in the precipitation due to urban surface expansion were explored using the nested Fifth-generation Pennsylvania State University–NCAR Mesoscale Model version 3.7 (MM5V3.7) with urban effects considered. The impact on surface air temperature at 2 m (SAT) due to urban surface expansion between the 1980s and the 2010s revealed that annual urban-related warming was lower over East Asia (0.031°C) and China (0.075°C) but higher in eastern China (0.14°C), which experienced dramatic urbanization. Greater warming could be detected over urban surface areas in the three city clusters [Beijing–Tianjin–Hebei (BTH) and the Yangtze and Pearl River deltas (YRD and PRD, respectively)], which reached 1.06°, 0.84°, and 0.92°C, respectively. Urban-related warming was not limited to a single city or city clusters but extended over a SAT-increased belt that covered the eastern coast of China. Further analysis showed that urban-surface-expansion-induced changes in albedo and the total cloud amount contributed to the changes in the radiation budget, which resulted in strong surface radiative forcings in the urban surface (14.5, 11.2, and 11.7 W m−2 for BTH, YRD, and PRD, respectively). However, significant differences could be detected for the transition from nonurban to urban land use compared to those that were classified as urban in both time periods because of the varied albedo changes. The urbanization-related warming, especially in the city cluster areas, also had a further effect on the large-scale circulation and precipitation. The precipitation was weakened in northeastern and northern China but intensified in eastern and southern China, which resulted in the strengthened precipitation over China (0.016 mm day−1, 0.65%) and East Asia (0.011 mm day−1, 0.28%). Therefore, subregional characteristics with marked seasonal, interannual, and decadal variations were detected for the influence of the urban surface expansion.

Download Full-text

Evidence of elevation-dependent warming from the Chinese Tian Shan

The Cryosphere ◽

10.5194/tc-15-5765-2021 ◽

2021 ◽

Vol 15 (12) ◽

pp. 5765-5783

Author(s):

Lu Gao ◽

Haijun Deng ◽

Xiangyong Lei ◽

Jianhui Wei ◽

Yaning Chen ◽

...

Keyword(s):

Air Temperature ◽

Minimum Temperature ◽

Swiss Alps ◽

Maximum Temperature ◽

Current Evidence ◽

High Mountain ◽

Regional Warming ◽

Mean Temperature ◽

Warming Rate ◽

Tian Shan

Abstract. The phenomenon in which the warming rate of air temperature is amplified with elevation is termed elevation-dependent warming (EDW). It has been clarified that EDW can accelerate the retreat of glaciers and melting of snow, which can have significant impacts on the regional ecological environment. Owing to the lack of high-density ground observations in high mountains, there is widespread controversy regarding the existence of EDW. Current evidence is mainly derived from typical high-mountain regions such as the Swiss Alps, the Colorado Rocky Mountains, the tropical Andes and the Tibetan Plateau–Himalayas. Rare evidence in other mountain ranges has been reported, especially in arid regions. In this study, EDW features (regional warming amplification and altitude warming amplification) in the Chinese Tian Shan (CTM) were detected using a unique high-resolution (1 km, 6-hourly) air temperature dataset (CTMD) from 1979 to 2016. The results showed that there were significant EDW signals at different altitudes on different timescales. The CTM showed significant regional warming amplification in spring, especially in March, and the warming trends were greater than those of continental China with respect to three temperatures (minimum temperature, mean temperature and maximum temperature). The significance values of EDW above different altitude thresholds are distinct for three temperatures in 12 months. The warming rate of the minimum temperature in winter showed a significant elevation dependence (p<0.01), especially above 3000 m. The greatest altitudinal gradient in the warming rate of the maximum temperature was found above 4000 m in April. For the mean temperature, the warming rates in June and August showed prominent altitude warming amplification but with different significance above 4500 m. Within the CTM, the Tolm Mountains, the eastern part of the Borokoonu Mountains, the Bogda Mountains and the Balikun Mountains are representative regions that showed significant altitude warming amplification on different timescales. This new evidence could partly explain the accelerated melting of snow in the CTM, although the mechanisms remain to be explored.

Download Full-text

Effects of Regional Warming due to Urbanization on Daytime Local Circulations in a Complex Basin of the Daegu Metropolitan Area, Korea

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc1504.1 ◽

2008 ◽

Vol 47 (5) ◽

pp. 1427-1441 ◽

Cited By ~ 12

Author(s):

Soon-Hwan Lee ◽

Hae-Dong Kim

Keyword(s):

Land Use ◽

Metropolitan Area ◽

Surface Wind ◽

Sensible Heat Flux ◽

Central Basin ◽

Local Circulation ◽

Critical Height ◽

Regional Warming ◽

Rapid Urbanization ◽

Mean Temperature

Abstract Numerical and observational analyses were conducted using realistic and historical three-set land-use data over 40 yr from 1963 to 2002 to evaluate regional warming in the Daegu metropolitan area due to dramatic land-use alterations in the basin area and to quantitatively estimate the influence of nonuniform regional warming on complex local circulation. The results are as follows: (a) The daily mean temperature in the Daegu metropolitan area increased by 1.5 K over 40 yr, and the increase was higher than that of the mean temperature on the Korean Peninsula. (b) A simulated surface wind pattern in 2002 agreed well with the observed data. The rapid urbanization of the Daegu metropolitan area has had a large influence on the local circulation outside of the area. (c) Because of the variation in heat and momentum transfer due to land-use alteration, the prevailing wind has also changed in the central basin in the Daegu metropolitan area. The spatial distribution of the temperature change is very similar to the changes in the wind. (d) The two-dimensional mixed-height theory was applied to local circulations. By this theory, regional warming that occurs as a result of land-use alteration determines a higher critical height, which serves as an index for estimating the mixing intensity induced by a surface sensible heat flux. According to the observational data, this index can be used to quantitatively estimate regional warming in complex terrain.

Download Full-text

Investigation of future climate characteristics over the Carpathian Region by “tuning” CORDEX temperature time series – a new perspective

10.5194/egusphere-egu21-570 ◽

2021 ◽

Author(s):

Csaba Zsolt Torma

Keyword(s):

Climate Change ◽

Climate Models ◽

Climate Model ◽

Standard Procedure ◽

Regional Climate ◽

Global Climate Models ◽

Climate Projections ◽

Global Changes ◽

Regional Warming ◽

Mean Temperature

<p>The answers to the following questions &#8216;What are the consequences of climate change (warming)&#8230;?&#8217; and &#8216;By when do we have to be prepared for that level of climate change (warming)?&#8217; must be given only with caution. On the one hand, regional or local changes can be inconsistent with global changes, as local processes might not accurately interpreted by global climate models (GCMs) due to their relative coarse resolution. On the other hand, climate model simulations&#8217; outputs are prone to biases compared to observations; furthermore, climate projections can be very different in modelling future temperature characteristics. In this context, while the magnitude of expected change described by a climate model may seem to be reasonable, but the projected temperature is not necessarily realistic (considering the model&#8217;s relative bias compared to observations). More specifically, the standard procedure of assessing climate change can be illustrated by taking the mean for a future period (e.g. 2070&#8211;2099) and compute the change relative to a reference period (e.g. 1976&#8722;2005). Keeping in mind the expected changes based on those projections might come with high degree of uncertainty as simulations might show different mean temperature values for the same assessed periods with even a range of few degrees of &#176;C. When regional climate change is assessed based on at a given regional warming level (WL, e.g. 1.5 &#176;C) added to the observed mean, then the aforementioned uncertainty range is reduced as the models (GCM or regional climate models) are assessed with respect to the same 30-year mean temperature value, but not for the same periods (noting that the WL is defined at regional and not at global scale). Thus the uncertainty of expected changes with regard to temperature can be significantly reduced. In this case an additional uncertainty factor might rise: time, as climate models can reach that WL at different times. Accordingly, we can give information on relative changes with a specific uncertainty as a metric based on the timing of reaching the assessed WL. Aim of the present work is to illustrate the feasibility of this concept for the region of the Carpathian Basin based on high-resolution EURO- and Med-CORDEX simulations.</p>

Download Full-text