Contribution of Climate Change and Urbanization to the Variation of
Extreme Precipitation in the Urban
Agglomerations over the Loess Plateau
Na Wei1,2,
NinglianWang1*,
Yurong Zheng1
1Shaanxi Key Laboratory of Earth Surface System and
Environmental Carrying Capacity, Northwest University, Xi’an, Shaanxi
Province, China, 710027
2 Climate Centre of Shaanxi Province, Xi’an, China,
710049
Abstract: With global warming and rapid urbanization,
urban agglomerations over the
Loess Plateau (LP) are suffering from various urban disasters.
Urbanization has aggravated the decreasing trends of
extreme precipitation in Taiyuan
and Xi’an urban agglomerations (UAs) and enhanced the increasing trends
of extreme precipitation in Luoyang, Hohhot and Xining UAs during
1979–2018. Meanwhile, the number of light rain days decreases in almost
all the cities, indicating the sensitivity of light rain days to
urbanization. The climate change is a primary contributor to the change
of urban precipitation during 1980–2000. However, the urbanization
contribution has been increasing gradually since 2000, and the
urbanization further amplifies the trend of extreme precipitation caused
by the climate change. In terms of
the physical mechanisms, the rapid increasing surface temperature and
aerosol particles are closely related to the urban precipitation. Our
findings provide a systematic understanding of the urbanization effects
on the extreme precipitation over the LP and may play an important role
in the mitigation of urban disasters.
Key words: Urban Extreme Precipitation Climate Change Urban Heat Island
Introduction
Global warming and urbanization are both rapidly changing the urban
climate environment, causing a series of urban climate problems, such as
urban heat island (UHI), urban waterlogging and water shortage, and air
pollution (Della-Marta, Haylock et al. 2007, Han, Baik et al. 2014, Ma,
Li et al. 2018, Paul, Ghosh et al. 2018). The UHI has been a common
phenomenon resulted from the urbanization, but it demonstrates different
impacts on the precipitation under different climatic backgrounds (Wang,
Zhou et al. 2007, Daniel, Lemonsu et al. 2018, Ma, Li et al. 2018, Yan,
Chan et al. 2020, Yang 2020){Chrysanthou, 2014 #30;Mazdiyasni, 2015
#23}. Many studies revealed that the UHI can induce updrafts and
trigger moist convections, resulting in more frequent extreme
precipitation near the urban areas, such as Beijing and the Pearl River
Delta, than in the rural areas (Della-Marta, Haylock et al. 2007,
Drobinski, Silva et al. 2016). In the urban agglomerations (UAs) of the
Yangtze River Delta in East China, there is a prominent urban dry island
(UDI) effect, which is characterized by reduced humidity and increased
vapor pressure deficit in the urban core area (Du, Wang et al. 2019, Luo
and Lau 2019). Some researchers concluded that the urbanization tends to
augment the precipitation trends caused by the climate change at
national scale in China (Gu, Zhang et al. 2019). Moreover, the UHI
effects are enhanced more obviously in wet climates than in dry climates
(Zhao, Lee et al. 2014). It can be found that the urbanization impact on
temperature and precipitation may also be different under different
climatic backgrounds and terrain conditions (Liao, Liu et al. 2018).
Climate change is a dominant contributor for the urban precipitation
trends, but the urbanization has been exhibiting a relatively strong
influence since the reform and opening up in China. Assessing the
contributions of climate change and urbanization to the changes in urban
precipitation is important for the disaster risk management.
Previous studies mainly evaluated the urbanization effect by analyzing
the difference between urban and rural meteorological observation
stations (Zhao and Wu 2017, Luo and Lau 2018, Ma, Li et al. 2018).
Because of the urban expansion, the distance between urban and rural
stations and the number of urban and rural stations vary greatly, which
may cause uncertainty of the urbanization effect evaluation (Song, Zhang
et al. 2014). High-resolution gridded precipitation data and artificial
impervious area have been well applied in urban precipitation researches
(Su, Li et al. 2019). Most of these studies focused on individual UAs
such as Beijing, Shanghai and the Pearl River Delta. There are also a
few studies that give an overall landscape of the urbanization impact on
climate at the national scale in China (Gu, Zhang et al. 2019, Lin, Gao
et al. 2020). Therefore, it is very interesting to study the variation
characteristics of the precipitation in the UAs within a unique climate
zone.
The Loess Plateau (LP), located over the central-northern part of China
and covering seven provinces and the middle reaches of the Yellow River,
belongs to the wet-arid transition area and hence is sensitive to
climate change. In recent decades, it has suffered severe water and soil
losses and ecological environment changes, with decreasing trends of
precipitation extreme in the Fen-Wei River valley and increasing trends
of rainfall intensity and frequency in the northwestern LP, which exert
negative effects on the social and economic developments (Zhao, Li et
al. 2017, Zhang, Gao et al. 2020). Meanwhile, the LP has experienced
drastically rapid urbanization in the last 20 years, and six typical
UAs (Taiyuan, Xi’an, Hohhot,
Yinchuan, Xining-Lanzhou and Luoyang) home to 70 percent of the LP
population play an important role in the economic development and the
ecological security(MA BB 2019). Precipitation over the LP is
primarily affected by the complex terrain, the land-atmosphere
interaction and the monsoon. During July to September, the East Asian
summer monsoon has a dominant effect on the LP at a spatial scale far
beyond the urban areas, which may overwhelm the local urban impacts.
However, during April–June, the rainfall is much weaker and thus local
urban effects may be more evident.
In this study, we present the first analysis of the changes of urban
extreme precipitation over the LP in different climate zones based on a
set of high-resolution gridded precipitation data. We also evaluate the
contributions of climate change and urbanization to the urban
precipitation across several UAs over the LP during different periods by
using an effective attribution method.
The paper is structured as follows. Section 2 introduces the study area,
the data, the definition of extreme climate events and the methods used
in the study. Section 3 presents and discusses the analysis results.
Conclusions are made in Section 4.