Urbanization Effect on Precipitation Over the Pearl River Delta Based on CMORPH Data

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Advances in Climate Change Research xx (2015) 1e7 www.keaipublishing.com/en/journals/accr/

Urbanization effect on precipitation over the Pearl River Delta based on CMORPH data

CHEN Shenga,*, LI Wei-Biaoa, DU Yao-Dongb, MAO Cheng-Yanc, ZHANG Land

a Department of Atmospheric Sciences, Sun Yat-sen University, Guangzhou 510275, China b Guangdong Provincal Meteorological Service, Guangzhou 511430, China c Jiangshan Meteorological Bureau, Quzhou 324100, China d Guangzhou Meteorological Information Network Center, Guangzhou 511430, China

Received 7 March 2015; revised 31 May 2015; accepted 25 August 2015

Abstract

Based on the satellite data from the Climate Prediction Center morphing (CMORPH) at very high spatial and temporal resolution, the effects of urbanization on precipitation were assessed over the Pearl River Delta (PRD) metropolitan regions of China. CMORPH data has an accurate estimate of the precipitation features over the PRD. Compared to the surrounding rural areas, the PRD urban areas experience fewer and shorter precipitation events with a lower precipitation frequency (ratio of rainy hours, about 3 days per year less); however, short-duration heavy rain events play a more signiﬁcant role over the PRD urban areas. Afternoon precipitation is much more pronounced over the PRD urban areas than the surrounding rural areas, which is probably because of the increase in short-duration heavy rain over urban areas.

Keywords: CMORPH; Urbanization effects; Pearl River Delta

1. Introduction changes in the weather, local weather, and climate. A well- recognized phenomenon of the urban climate is the urban heat With rapid economic growth, China is undergoing rapid ur- island, in which there is a temperature contrast between a city banization. On December 31, 2013, the urban area was 8.58 and the surrounding rural areas (Collier, 2006). Zhou et al. million hm2. Urbanization is one of the very extreme cases of (2004) presented evidence for a significant urbanization effect land-use change. Compared with the surrounding rural areas, the on climate based on analysis of land-use changes and surface energy and water budgets in urban areas are altered owing to temperature in Southeast China, which experienced rapid ur- changes in the structure of the planetary boundary layer and banization. The warming of urbanization effect nearly reaches radiation process, because of the heterogeneous surface prop- 0.05 C per decade. Ren and Zhou (2014) and Ren et al. (2012, erties, high-rise buildings, and anthropogenic aerosols. These 2008) evaluated the urbanization effects on trends of extreme changes then affect local airflow and circulation, resulting in temperature in China mainland, by applying a homogenized daily temperature dataset of the national reference climate stations and basic meteorological stations, and a rural station * Corresponding author. network previously developed. It is pointed out that urbanization E-mail address: [email protected] (CHEN S.). Peer review under responsibility of National Climate Center (China effects are statistically significant for daily minimum tempera- Meteorological Administration). ture, maximum temperature, and declining diurnal temperature range. Besides urbanization effects on the summer days, tropical nights, and frost days are significant. An insignificant urbani- Production and Hosting by Elsevier on behalf of KeAi zation effect is detected for icing days. http://dx.doi.org/10.1016/j.accre.2015.08.002 1674-9278/Copyright © 2015, National Climate Center (China Meteorological Administration). Production and hosting by Elsevier B.V. on behalf of KeAi. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

However, the influence of urbanization on local precipita- Kaufmann (2009) further indicated that the precipitation tion is still a matter of debate. In general, results from the reduction induced by urban land cover change over the PRD metropolitan meteorological experiment have shown that occurs mainly during the winter months. However, some during the summer months, urban effects lead to increased recent studies reported an increase in precipitation and severe precipitation at distance of 30e75 km away from the city thunderstorms over the PRD (Meng et al., 2007; Li et al., center. This finding has been confirmed in many previous 2009; Zhang et al., 2009; Li et al., 2011; Liao et al., 2011). studies (Landsberg, 1970; Sanderson and Gorski, 1978; Although these results provide evidence that convection and Bornstein and Lin, 2000; Shepherd et al., 2002; Shepherd, precipitation can be enhanced or initiated by urban regions, the 2005; Shepherd, 2006; Mote et al., 2007; Hand and urbanization effects over the PRD on local precipitation are Shepherd, 2009; Halfon et al., 2009). However, using satel- still unclear. But it is very significant for us to understand the lite data that reveals plumes of reduced cloud particle size and clear effects of urbanization on precipitation. This can help to suppressed precipitation, Rosenfeld (2000) demonstrated that improve the weather prediction and climate diagnostics over urban and industrial air pollution can prevent precipitation in the PRD region. So in this study, we use satellite data with urban areas. This finding differs from previous results con- high spatial and temporal resolution to discuss the urbaniza- cerning the enhancement of precipitation by urbanization. tion effect on precipitation over the PRD. Measurements obtained by the Tropical Rainfall Measuring Mission satellite have demonstrated that both cloud droplet 2. Data coalescence and ice precipitation formation are inhibited in polluted clouds. However, precipitation is a very important Climate Prediction Center morphing (CMORPH) technique process in the global water and energy cycles. Thus, under- produces global precipitation analyses at very high spatial standing the effects of urbanization on precipitation is very (0.07277 lat/lon, about 8 km at the equator) and temporal important for ongoing climate diagnostics and prediction. (30 min) resolution. This technique uses precipitation esti- Our study region is the Pearl River Delta (PRD), which is mates that have been exclusively derived from low orbiter located in the southern Chinese province of Guangdong, and satellite microwave observations (Joyce et al., 2004). The experienced rapid urbanization. In this paper, the PRD is features of precipitation estimates are transported via spatial anchored by the cities of Guangzhou, Foshan, Jiangmen, propagation information that is obtained entirely from geo- Zhaoqing, Dongguan, Huizhou, Zhongshan, Zhuhai, Macao, stationary satellite IR data. Specifically, CMORPH uses mo- Shenzhen, and Hong Kong (Fig. 1). On the basis of observa- tion vectors derived from half-hourly interval geostationary tions in 1988e1996, Kaufmann et al. (2007) suggested that satellite IR imagery to propagate the relatively high-quality urbanization in the PRD has reduced local precipitation precipitation estimates derived from passive microwave data. because of the changes in the surface hydrology. Seto and In addition, the shape and intensity of the precipitation

Fig. 1. The location of the Pearl River Delta.

Fig. 2. Spatial distribution of annual precipitation over Guangdong province for 1998e2010 mean, (a) CMORPH data, (b) rain gauge data (unit: mm). The green regions denote the locations of the PRD metropolitan regions.

Fig. 3. Spatial distribution of annual precipitation events over Guangdong province (1998e2013 mean).

Fig. 4. Spatial distribution of the mean duration of precipitation event over Guangdong province (1998e2013 mean, unit: h). annual precipitation events over Guangdong province for We defined precipitation frequency as the ratio of the rainy 1998e2013 mean. Notably, the annual precipitation events hours in CMORPH data to the total hours. Fig. 5 shows the over the PRD are low, especially in Foshan, Guangzhou, and spatial distribution of precipitation frequency over Guangdong Dongguan, central areas of the PRD. This finding indicates province for 1998e2013. The PRD has lower precipitation that the PRD experiences fewer precipitation events. frequency compared to the surrounding rural areas, nearly one Fig. 4 shows the spatial distribution of the mean duration of percent less, about three days per year. This means that the precipitation event over Guangdong province for 1998e2013. It urban area has more time with no rain. This finding can be is obvious that the precipitation duration over the PRD is shorter explained by Rosenfeld (2000). Cloud droplet coalescence and in comparison with the surrounding rural areas. Figs. 3 and 4 ice precipitation formation are inhibited in urban areas by the suggest that urbanization remarkably influences precipitation polluted air (Rosenfeld, 1999; Rosenfeld et al., 2008). This is over the PRD, causing fewer and shorter precipitation events. not a favorable result for environmental protection because

Fig. 5. Spatial distribution of precipitation frequency over Guangdong province (1998e2013, unit: %).

Fig. 6. Spatial distribution of short-duration heavy rain amount relative to total precipitation over Guangdong province for 1998e2013 (unit: %). precipitation is very important for the wet deposition of distribution of the percentage of short-duration heavy rain polluted air to eliminate aerosols. amount to total precipitation over Guangdong province for Short-duration heavy rain is a type of severe convective 1998e2013. There are high value centers in this figure. The weather and can cause large losses of both property and life. first one is in the Yangjiang and Maoming region, located at We defined short-duration heavy rain as precipitation amount the southwest to the PRD. The second one is in the Haifeng exceeding 20 mm in an hour. Fig. 6 shows the spatial and Lufeng region. These two regions are the well-known

Fig. 7. Diurnal variations of precipitation along the center latitude (23.5N) of the PRD during 1998e2013 based on CMOPRH data (Regions between the two solid lines illustrates the PRD metropolitan regions. Unit: mm hÀ1).

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