Eco-Livability Assessment of a Newly Emerging Urban Sub-center in Shanghai: A Climatic Perspective

—Global warming and rapid urbanization are changing the livability of cities. The eco-livability (EL) in Jiading, a newly emerging urban sub-center in the northwestern part of Shanghai megacity, is assessed from a climatic perspective, by composing an EL index consisting of meteorological hazards, human comfort, vegetation ecology, and air quality, based on multi-source observations. The results show that the EL in Jiading has improved with the restoration of green spaces and the reduction of air pollution. However, with the rising risk of weather extremes (e.g., heat waves, rainstorms) brought by the warming world, the EL in Jiading is being undermined. We should take preventive measures to improve our ability to resist climate risks.


Introduction
With cities becoming the most densely populated area, human settlements are undergoing great challenges [1] . In the past decades, China experienced rapid urbanization [2] . The seventh Chinese census shows that the urban population in China exceeded 900 million in 2020 [3] . As urban development enters a new phase of paying equal attention to speed and quality, how to improve urban livability has become an urgent issue [4] . Urban livability is subject to many factors, among which the ecological environment and climate play key roles [5] . The warming world exacerbates the instability of the climate system, with widespread, frequent, intense, and simultaneous occurrences of extreme weather/climate events in recent years [6][7] . Global warming and rapid urbanization disrupt the regional distribution of precipitation and temperature [8] , leading to an increase in the frequency and intensity of meteorological hazards, ultimately affecting the livability of urban ecosystems.
Shanghai is one of the most urbanized areas in China, with many sub-urban centers that appeared when urbanization intensified in recent years. Here we choose Jiading District, a newly emerging urban sub-center in the northwestern part of Shanghai, as the study area. After analyzing the climate and ecological characteristics in Jiading, a comprehensive eco-livability (EL) evaluation index is established from a climatic perspective, consisting of meteorological hazards, human comfort, vegetation quality, and air quality, which are commonly used in previous EL assessments [9][10] . According to this comprehensive evaluation index based on multi-source observations, the EL of Jiading is assessed, to provide scientific reference for better adapting to climate change.

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Data and methodology

Study Area
Jiading District (463.16 km 2 ) belongs to Shanghai and is located in its northwest. It is home to about 183 million registered residents [3] . Jiading is one of the "Five New Cities" that Shanghai strives to build as a sub-center of the metropolis. As residents' demand for a better living environment has increased, Jiading has recently listed "eco-livability" as one of the main directions for the new round of construction.

Observation Data
The meteorological datasets of 2m-air daily mean (T mean,2m ), maximum (T max,2m ), and minimum (T min,2m ) temperature, precipitation amount, relative humidity, and wind speed were obtained from Jiading National Basic Meteorological Observatory and 20 automatic meteorological stations in Jiading District, provided by Shanghai Meteorological Bureau. The air quality index (AQI) was obtained from Jiading National Environmental Monitoring Station, provided by Shanghai Ecological Environment Bureau. These data are quality controlled.

Statistical analysis methods
Meteorological hazards such as heat waves, rainstorms, and gales, which are vulnerable in Jiading, are included in the EL assessment. Referring to the meteorological standards issued by the State General Administration of China for Quality Supervision and Inspection and Quarantine (AQSIQ) and Standardization Administration of China (SAC) [11][12][13] , heat waves are estimated by hightemperature days (HTD) with daily T max,2m ≥35 o C. Rainstorms are measured by heavy rain days (RD) with a daily-accumulated precipitation amount ≥50 mm, and windy days (WD) are measured by the daily maximum wind speed ≥17m/s. Urban heat island (UHI) is usually depicted by UHI intensity (UHII): Where UHII is the UHII to the pixel on the image by remote sensing, and T is the surface temperature, n is the number of effective pixels in suburban farmland, and T is the surface temperature in suburban farmland. UHII is graded into three classes according to its value range [14] for seasonal time-scales: weak UHI (1. The Ecological quality index (EQI) of vegetation is determined for each year (y): Counted as 100 if EQI y >100. is the weighting coefficient of fraction of vegetation coverage (FVC), taken as 0.5. FVC is the FVC [15] . is the weighting coefficient of Net Primary Productivity (NPP), taken as 0.5.
is NPP [16] . is the maximum value of NPP during the period of 2001-2020, i.e. the productivity under the optimized local meteorological conditions, and in this work, =1400 gC/m 2 .

Eco-livability Index
Four sub-indicators are considered when evaluating EL from the perspective of climatology: Meteorological disaster days (MDD, including HTD, RD, and GD), EQI, AQI, and HCD. Considering the scale differences among these sub-indicators, each sub-indicator ( ) is normalized to a value ( ) between 0 and 1 by linear functions: when the higher X, the better EL Y when the lower X, the better EL Where X max and X min are the maximum and minimum X, respectively.
Normalized MDD n , HCD n , EQI n , and AQI n are obtained by Eqn. 3. Therefore, the EL index (ELI) is composed: ELI MDD HCD EQI AQI (4) Where w 1 , w 2 , w 3 , and w 4 are the weight coefficients of each sub-indicators respectively.

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Climate and eco-environment in Jiading

Thermal environment
In recent decades (1961-2021), the near-surface air temperature in Jiading has remarkably increased (Fig.1a). The HTD also keeps growing (Fig.1b), reaching a peak of 47 days in 2013. The heavier UHII are detected in the district center and built-up areas in the south (red in Fig.1c), with UHII of 3.9°C and 3.1°C in Zhenxin Street and Jiading Town respectively. With the intensified UHI (Fig.1d), the risk of high temperatures is rising.

Precipitation
In recent years, Jiading has seen a notable increase in annual-cumulative precipitation amount (Fig.2a) and RD (Fig.2c). The highest annual-cumulative precipitation in Jiading's historic record was 1738.8 mm in 2015, and the highest number of annual RD was 7 days in 2019. The risk of ponding is higher in southern towns (streets), where the precipitation and RD are heavier ( Fig.2b and  2d).

Human comfort
Human comfort days (HCD) act as a biometeorological indicator evaluating human comfort based on heat exchange between the human organism and the near-earth atmosphere, based on observations of air temperature, wind speed and relative humidity. During 2017-2021, the number of HCDs in Jiading is higher in the western and northern parts of the district and lower in the central and southern parts of the district.

Vegetation ecology
In the past two decades, the ecological evolution of vegetation in Jiading can be divided into two stages ( Fig.3a): the decline stage (2000-2011) and the recovery stage (2012-2021). In 2021, the vegetation EQI was the highest. The district center (Jiading Town, Juyuan) and the southern towns/streets (Jiangqiao, Zhenxin, Anting, Nanxiang) increased by more than 45% compared with the average (Fig.3b). With the vigorous construction of public green parks in recent years, the ecological quality of the vegetation has been significantly improved.

AIR QUALITY
Over the past five years, the number of days with excellent and good air quality in Jiading has increased, and the number of days with light and moderate air pollution has decreased (Table 1). There has been no severe polluted weather during 2017-2021 and no severe polluted weather in 2019-2021, mainly due to the effective control of air pollution in recent years.

Evaluation of eco-livability in Jiading
The EL of Jiading was evaluated by a combined index consisting of MDD, HCD, EQI, and AQI (Eqn.4 in section 2.3). Based on the monthly distribution of subindicators in Jiading, the weighting coefficients for each sub-indicator were determined.
The results assessed by the EL index shows that Jiading's EL is higher in spring and autumn ( Fig.4a and  4c), followed by summer (Fig.4b), and worse in winter (Fig.4d). The EL in the northern and central areas is high, while the EL in the southern areas needs further improvement.

Conclusions and discussion
The ecological quality of vegetation and air quality has improved appreciably with the construction of public green spaces such as country parks and the control of air pollution. However, with global warming, the risk of extreme weather has intensified, adversely affecting the eco-livability of Jiading. Some proposals are recommended to improve resilience to climate risks: (1) Strengthen ground-level blue and green infrastructure (water bodies, green spaces, etc.) in the district center and southern built-up areas to play an ecological cooling role.
(2) Strengthen the construction of drainage facilities and drainage systems in the district center and southern areas to improve the ability to prevent and respond to stormwater flooding.