Simulating the Impact of Urban Surface Evapotranspiration on the Urban Heat Island Effect Using the Modified RS-PM Model: A Case Study of Xuzhou, China

Abstract

As an important energy absorption process in the Earth's surface energy balance, evapotranspiration (ET) from vegetation and bare soil plays an important role in regulating the environmental temperatures. However, little research has been done to explore the cooling effect of ET on the urban heat island (UHI) due to the lack of appropriate remote-sensing-based estimation models for complex urban surface. Here, we apply the modified remote sensing Penman-Monteith (RS-PM) model (also known as the urban RS-PM model), which has provided a new regional ET estimation method with the better accuracy for the urban complex underlying surface. Focusing on the city of Xuzhou in China, ET and land surface temperature (LST) were inversed by using 10 Landsat 8 images during 2014-2018. The impact of ET on LST was then analyzed and quantified through statistical and spatial analyses. The results indicate that: (1) The alleviating effect of ET on the UHI was stronger during the warmest months of the year (May-October) but not during the colder months (November-March); (2) ET had the most significant alleviating effect on the UHI effect in those regions with the highest ET intensities; and (3) in regions with high ET intensities and their surrounding areas (within a radius of 150 m), variation in ET was a key factor for UHI regulation; a 10 W· m −2 increase in ET equated to 0.56 K decrease in LST. These findings provide a new perspective for the improvement of urban thermal comfort, which can be applied to urban management, planning, and natural design.As the UHI effect has a negative environmental impact in urban areas, several studies have explored the factors that mediate the UHI effect with a view to mitigating its effects [9][10][11]. One common conclusion of this previous research is that vegetation and water have cooling and humidifying functions, which are the main factors acting to alleviate the UHI effect [12][13][14]. In general, water bodies in cities are often isolated and tend to be located in urban parks. Therefore, vegetation arguably plays a more important role in alleviating the thermal environment and in improving proximate human thermal comfort [15]. Urban vegetation has various types and functions, including vegetation in recreational parks and gardens, allotments, and street vegetation. One approach to alleviate the heat island effect is to use vegetation as shading on construction land to prevent direct solar heating [3,14,16]. It has been proven, for example, that the area and density of vegetation [3,10,14] can be used as indices for the degree of UHI mitigation, as can other indices such as the normalized difference vegetation index (NDVI) [17][18][19], which have also shown significant negative correlations with the UHI intensity. In addition, a series of remote-sensing-based studies have demonstrated that vegetation characteristics including size [14,20], shape [21], species [22], and spatial patterning [23,24] have significant impacts on the urban cooling effect.Another important mechanism through whic...

Estimasi Dampak Urban Heat Island terhadap Laju Evapotranspirasi: Studi Kasus di Kota Palembang

“…Disisi lain dengan terjadinya peningkatan laju ET tidak hanya berdampak negatif terhadap kehilangan air namun juga memberikan dampak positif, dengan terjadinya peningkatan laju ET dapat membantu menurunkan suhu udara (Wang et al, 2020 C, maksimum 0,43 o C, dan ratarata harian 0,41 o C. Perbedaan suhu udara ini dapat merepresentasikan UHI di kota Palembang. Estimasi dampak perbedaan suhu udara juga berdampak terhadap laju ET dengan rata-rata ∆ET model Hargreaves dan Samani 0,05 mm/hari, model Blaney dan Criddle 0,05 mm/hari, model Linacre 0,06 mm/hari, dan model Kharuffa 0,14 mm/hari.…”

Modelling hourly evapotranspiration in urban environments with SCOPE using open remote sensing and meteorological data

“…Evapotranspiration (ET) is essential for understanding water cycle and energy balance, regulating precipitation, temperature and vegetation productivity (Wang et al, 2020;Zheng et al, 2020). In urban environments, ET is inversely proportional to the intensity of the urban heat island (UHI) effect (Wang et al, 2020). The UHI effect adversely affects the health and quality of life of urban residents (Kovats and Hajat, 2008;Scherer et al, 2013;Vulova et al, 2020).…”

“…lives in cities (United Nations, 2019) and climate change is expected to further increase the frequency and intensity of heat islands (Huang et al, 2019), actions to mitigate the UHI effect are essential. Optimising ET capacity in urban areas could reduce extreme events such as severe heat waves, drought or flooding (Wang et al, 2020;Ward and Grimmond, 2017).Although ET is undeniably important for planning more sustainable cities, ET studies in urban environments are rare due to the challenges of measuring and modelling it in a highly heterogeneous landscape (Nouri et al, 2015(Nouri et al, , 2020.ET is a measurement of mass (millimetres) or energy (watts or joules) of the movement of water from the land surface to the atmosphere (i.e. liquid to vapour) (Liang and Wang, 2020).…”

“…incoming radiation), air temperature and relative humidity (Foltýnová et al, 2020). In contrast, the volume of ET over the year depends greatly on the land surface and the water availability in the soil (Dwarakish et al, 2015;Wang et al, 2020;Zheng et al, 2020). In climatology, ET is often measured by the eddy covariance method, which is based on the turbulence flux and energy balance (Liang and Wang, 2020).…”

“…lives in cities (United Nations, 2019) and climate change is expected to further increase the frequency and intensity of heat islands (Huang et al, 2019), actions to mitigate the UHI effect are essential. Optimising ET capacity in urban areas could reduce extreme events such as severe heat waves, drought or flooding (Wang et al, 2020;Ward and Grimmond, 2017).…”