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Presentation

2nd Revision

Introduction

 
In-depth Analyses
Precipitation, People, and Land in China, 1958 - 1988
China is not only a very mountainous country, it is also quite dry. Precipitation levels necessary for rain-fed agriculture can be only found in the south and southeast of the country. Most of the huge western and northern landmass of China has very little rainfall (see Map 1). While these climate conditions are well documented, much less is known about their interaction with demographic, social, or economic factors. Here we will discuss the following question: How many people live in each of China's precipitation zones?
We have used a time series of grid-based digital precipitation maps for China between 1958 and 1988 with an overlay of population by county (see population distribution maps in this application). Unfortunately, we only had access to the 1992 population figures in a fine geographical resolution, so we could not use each year of precipitation with the corresponding population distribution. Our results therefore show the distribution of the 1992 population by precipitation zone, according to the average annual precipitation between 1958 and 1988.
In dry years, about 30% of the Chinese population lives in areas with a critically low level of precipitation.
  Only a very small fraction of the Chinese population - typically about 1% - lives in areas with average precipitation of less than 200 mm per year (red section of the bars in Figure 1). Less than 5% of the Chinese population lives in areas with precipitation below 400 mm per year. The percentage of people living in areas with 400-600 mm of average annual precipitation is much larger, on average some 15%. However in very dry years (such as in 1966), up to 25% of the population lives in areas with only 400-600 mm of precipitation. If one considers 600 mm of precipitation a critical level for rain-fed agriculture, we can conclude that in dry years some 30% of China's population lives in such critical areas. The data also show that in average years about 80% of the Chinese population lives in areas where the precipitation was more than 600 mm. In fact, half of China's population lives in areas where average precipitation was more than 1,000 mm per year. This indicates that in average years a great majority of people in China live in areas with sufficient rainfall of 600 mm or more (see Table 1).
Two conclusions can be drawn from these results. First, a significant number of people in China (in the order of 100 million) live in areas of the country that usually have sufficient rainfall, but that can be quite dry in "bad" years. This population is most vulnerable to fluctuations in precipitation.
Second, in average years a great majority of the Chinese population live in areas where precipitation is sufficient for rain-fed agriculture. However, we must be careful not to jump to premature conclusions: while there may be enough rainfall at some time during the year, it may be at the wrong time. Rain-fed agriculture requires a certain precipitation profile.
Average Annual Precipitation in China
Map 1

Population by Precipitation, 1958 - 1988
Land Area by Precipitation, 1958 - 1988

Figure 1

About 60% of China's landmass does not have enough precipitation for rain-fed agriculture.
  For comparison, we have also calculated the distribution of land by precipitation from our GIS data. Typically, about 60% of the land in China has precipitation below 600 mm per year, which can be considered a critical threshold for agriculture. Only about 20% of the land in China has average precipitation of more than 800 mm per year (see Table 1). default_th.gif (2517 bytes)
Table 1
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Revision 2.0 (First revision published in 1999)  - Copyright 2011 by Gerhard K. Heilig. All rights reserved. (First revision: Copyright 1999 by IIASA.)