Impact of Asian Megacity Development on Local to Global Climate Change

1, Background of This Project
Urbanization is a major driving force of economic growth in developing countries. According to the UN report (2008), by the year 2050 there will be 6.4 billion people living in cities, up from 3.3 billion now. By 2025 there will be 27 megacities (more than 10 million) in the world and 15 in Asia. Around 40 percent of China's population is in cities now, a figure that is expected to exceed 70 percent by 2050, when more than 1 billion people will be living in Chinese cities. There are 3 cities in China experienced dramatic expending in last 30 years, they are Beijing, Shanghai (Yangtze River Delta) and Guangzhou (Pearl River Delta). For example, the urban area of Beijing was 350 KM2 in 1980, 490 KM2 in 1999 and extends to 600 KM2 in 2009.

Economic development has depended, and will continue to depend for some time in the future, on fossil fuel energy sources. In Asia megacities are projected to account for ~40% of their country's GNP (gross national product) by 2030. In rapidly urbanizing regions in the developing parts of Asia, deteriorating air quality is a common phenomenon with serious consequences for public health and the environment. Apart from locally significant pollutants, aerosols, trace gases and greenhouse gas emissions may have important impacts regionally and globally. Because fossil fuels will provide much of this energy, emissions of greenhouse gases and air pollutants such as sulfur and nitrogen oxides and particulates could dramatically increase.


Globally many megacities represent atmospheric brown cloud hotspots; regions with large aerosol radiative forcing of the atmosphere and surface (dimming), with annual mean surface dimming in most tropical mega cities exceeding 20 Wm-2, equivalent to reducing solar irradiance at the top of the atmosphere by more than 10%. The increase in solar energy absorbed by aerosols over the atmosphere of some of these mega cities is comparable to the heat input by energy consumption. Thus in addition to contributing to regional and global climate change, the atmospheric forcing may also contribute to the urban heat island effect.

Asia is both a typical monsoon region around the world and an important part of the global climate system. However, whether and how the Asia monsoon can be affected by such regional high intensity human activities has become an important basic scientific problem which has caused great international academic dispute due to lack of long term and systematical research. One view is that the change of Asian monsoon and the associated conversion between drought and flood are mainly controlled by the natural variation while global warming cannot explain the weakened east Asian monsoon over the past 20 years based on observations. Another view is that although regional high intensity human activities cannot fundamentally change the dynamic system of monsoon based on the natural change, it can alter the intensity of monsoon and the phase of monsoon change. But what influence these have on the intensity of monsoon circulation, onset timing, number of rainy days and extreme events is still not well understood. Nor is it clear to what extent do urban form or the pathways of transformation through which regions urbanize have consequences for emissions and pollution problems above and beyond those effects directly attributable to economic growth.

United Nations Environmental Protection Plan (UNEP) published the scientific assessment report of Asian region in 2008 and inferred that the so called “Atmospheric brown clouds” (ABCs) induced by the urbanization of East Asia (China) and South Asia (India) could lead to the negative radiative forcing, which may be an important reason of the surface cooling in summer monsoon region and the weaker of the Asian monsoon. Based on a series of evidences of the potential effects of regional human activities (changes of land use or land cover and anthropogenic pollution emissions) on regional climate and East Asian monsoon system, scientists in China launched an international project “Monsoon Asian Integrated Research Study” (MAIRS, 2006) under the Earth System Study Partnership (ESSP) to understand the key scientific issues of interaction between regional human activities and Asian monsoon system. Scientists from many countries initiate and organize “Joint Aerosol-Monsoon Experiment” (JAMEX, 2008) in order to understand the relations among human activities in Asia Pacific and India regional, Asian monsoon and hydrological cycle. So, the climatic effect of large-scale urbanization in Asia especially in East China has become an important scientific problem to be solved.

2, The objectives of this Project
The fast growing urbanization in monsoon Asian region leads to expansion of land utilization, highly concentrated energy consumption and degrading air quality, bringing large pressure to economic and social development in China, and could has potential impacts on local/regional/global climate systems. However, due to the lack of study in this field, the mechanism and the extent of such impact are still less understood and of high uncertainty. Therefore, the impacts of the increasing urbanization in east Asia on regional climate has now become an important hot issue in the world which deserves further study.
The main objectives of this project are:
1, to quantify feedbacks between megacity emissions/air quality and local/regional/ global climate
2, to assess impacts of large scale land cover change of urbanization in Asian megacities on local precipitation pattern and regional climate.
3, to better understand the resilience of Asian monsoon system to urbanization and related transformations of land, water and air in mega-cities

3, Research Contents
3.1) comprehensive analyses of historical data in China and Japan on climate change, large scale land cover change and industrial emissions
The research targets are as follows:
(a) by using the long-term historical meteorological observation data (1951~current) as well as land cover and industrial emissions from Chinese and Japanese megacities and surrounding regions, the impacts of urbanization in the recent decades on the local/regional climate (e.g., temperature, precipitation, extreme events), as well as the heat/water balance will be made.
(b) By comparison with the observation in non-urbanized areas, the impacts of large scale urbanization on the local/regional heat and water balance and regional climate will be estimated,


3.2) Local/regional and large-scale climatic effects and feedbacks of the air pollution and aerosol emissions from Chinese megacities.
The research targets are as follows:
(a) Through comprehensive analyses of the temporal and spatial distribution of main air pollutants (e.g., oxidizing gases, and fine particles) and their radiative properties, the radiative forcing and their impacts on atmospheric energy cycle and climate will be estimated by using aerosol-atmospheric chemistry models.
(b) Through analyses of high-resolution outputs from a regional chemistry model experiment, the interaction between the air pollutants in urban agglomeration and atmospheric boundary layer will also be examined, including radiative transfer processes and influence on surface energy balances.


3.3) Interaction between the changes of land cover/use associated with large scale urbanization and regional hydro-climate.
The main research items are listed below:
(a) High-resolution analysis of land cover/use changes in Chinese megacities and urban agglomerations will be made based on ground-based and satellite-based data in the past few decades.
(b) High resolution simulation on impacts of land cover/use change and urban  canopy change on meso-scale hydro-climate conditions (precipitation, cloud systems) will be made using cloud-resolving regional models (e.g., CReSS).

4, Feasibility for Joint Research

  1. Monsoon Asian Integrated Regional Study (MAIRS) is being conducted by the IAP/CAS as a unique international research program in Asia under the framework of Earth System Science Partnership (ESSP). The objective of MAIRS is to better understand the relationships between human activities and Asian monsoon system. The research focused on the Asian megacities in this project is one of four most important topics in MAIRS research agenda. Prof. Fu, Chinese leader of this project, is a chairman of MAIRS. MAIRS megacities working group was set up in 2008, and Japanese scientists led by Prof. Yasunari, Japanese leader of this project, are the main members of this group. This MOST/JST collaborative project will further strengthen the collaboration and joint research between China and Japan on the megacity studies and sustainable urban development in monsoon Asia.
  2. Based on the concept of "general monsoon system", the regional integrated environment modeling system (RIEMS model) was developed by Chinese group.  It's fully coupled modeling system which contains climate, biosphere, hydrology, chemical and aerosol processes.
  3. The Japanese group has an excellent cloud-resolving storm simulator called “CReSS” developed at HyARC, Nagoya University, which can be used for assessing impacts of land surface change relevant to urbanization on cloud/precipitation system. This research proposal is based on these high performance of modeling by this group.
  4. Chinese group has strong research background and experiences in Atmospheric Boundary Layer, Pollution Meteorology, Atmospheric Chemistry, Regional and Global Climate models, Modeling of Regional Climate of East Asia, City Disaster Meteorology and City Environmental Planning.
  5. The Japanese group also has a high research performance on analysis of long-term surface climate change including energy and water budget changes, by using a sophisticated surface energy balance model.
  6. Sufficient global reanalysis data, ground and sounding meteorological observations (700 stations from 1951) in China,satellite retrieval technique and ground observation from (200 stations from 1951) Japan will be shared by both groups.  And also a number of enhanced observational data of major air pollutants in Beijing and Shanghai through field experiments will be used.
  7. Japanese group has a strong scientific background on conducting anthropogenic impacts (of greenhouse gas increases, aerosol forcing and land cover/use changes) on Asian monsoon climate, through the research project (for FY2006-2008) under the Ministry of Environment. The leader of this project is Prof. T. Yasunari. Through this project, they have developed a new-generation aerosol-chemistry-climate model (GCM) which can be used for assessing the impact of aerosol emission from megacities in east Asia on Asian monsoon and global climate.
  8. Chinese group is leading/involving in some of national key projects.  The researches on air pollution-climate are partly supported by National Basic Research Program of China (973 project) sponsored by Ministry of Science & Technology of China, namely “Trends of aridity and human adaptation over northern China” (2006/1 – 2010/12) and “Atmospheric aerosols and their climate impacts over China” (2007/1 – 2011/12) . The leader of this program is Prof. Fu Congbin.

College of Environmental Sciences and Engineering Peking University
No.5 Yiheyuan Road Haidian District Beijing, P.R.China 100871