Checking Global Warming through Monitoring of Agricultural Ecosystems

Background and Objectives

If global warming progresses at the pace presently forecasted, the world�fs agricultural ecosystem is expected to suffer many impacts already by the end of this century through changes in meteorological elements, ground temperature and other factors affecting the physical environment. Conversely, the agricultural ecosystem, along with forest and grassland ecosystems, is involved in the process of global warming by absorbing and releasing carbon dioxide and other greenhouse gases. Better understanding of such inter-relationship between global warming and agricultural ecosystem is important for the assessment of future global warming and its impact. NIAES, therefore, has set up monitoring stations in various parts of Asia (Fig. 1) to conduct long-term monitoring of the physical environment and gas flux of the agricultural ecosystem in cooperation with universities and research institutes in and out of Japan.

Project Outline

The Tibetan Plateau is called the third pole of the earth after the North and South Poles, and is expected to show the effects of global warming sooner and more dramatically than other parts of the globe. Consequently, we have installed an automated weather station (AWS) at a place in Dam-gzhung (DNX) at the altitude of 4,300 meters in the central part of the Tibetan Plateau, and are observing the general meteorological elements, radiation balance and heat balance. In addition, we have set up simplified weather monitoring units at 10 locations along a line transect up to the altitude of 5,530 meters to monitor changes in meteorological elements in relation to rise in altitude (Fig. 2). Through these observations, we are studying what impact global warming will have on the physical environment of the ecosystem.

East Asia is a region with high cultivation intensity. Approximately one quarter of the land area between 20°N and 60°N and between 100°E and 170°E is farmland, a large portion of which is accounted for by rice paddies, a characteristic of agriculture in monsoon Asia, as well as by grassland (including pasture). In Japan, too, rice paddies represent 12.4% of the total land area. In order to respond to the full carbon accounting required in the second commitment period pursuant to the Kyoto Protocol, it is necessary to quantify the carbon balance in rice paddies, which is the agricultural ecosystem most representative of monsoon Asia, and in grasslands and pastures. For this purpose, carbon dioxide and other gas flux monitoring is being continued at rice paddies and grasslands/pastures under varying cultivation and meteorological conditions (Fig. 1, Fig. 3). Simultaneously, research is ongoing to increase the accuracy of flux measurement, to improve the accuracy of carbon balance assessment and to standardize observation methods. These observation and research activities are conducted in cooperation with related organizations as an activity of AsiaFlux, an international monitoring network for carbon balance in monsoon Asia.

Relevant Outcomes to Date

In the rice paddy site (MSE) in Tsukuba, Ibaraki, Japan and some other monitoring sites, multi-year observation data are becoming available. In a well-managed rice paddy, carbon dioxide flux is known to present clear seasonal fluctuations of strong absorption in the rice growth period and weak release in the non-growth period. We have begun to find, however, that year-to-year fluctuations in weather conditions and other factors cause year-to-year fluctuations in the carbon dioxide flux, at times causing as much as 2t-C/ha variance in annual absorption (Fig. 4). In addition, in the highland grassland site (QHB), where the plant growth period is very short, it has been found that the meteorological conditions in early spring when plants start to grow have a significant impact on the total carbon dioxide absorption throughout the growth period. We plan to keep accumulating multi-year data also for other monitoring sites and clarify yearly fluctuations of GHG flux and carbon balance as well as inter-site differences.

The data obtained by our research are registered into various databases and are made available to the general public through the Internet (Fig. 5). The data are utilized as actual measurement data in studies on inter-site comparison of carbon balance and the development and verification of carbon circulation models in the ecosystem.