Yunlong Cai

Climate change and agriculture in China

Abstract The implications of climate change for agriculture and food are global concerns, and they are very Important for China. The country depends on an agricultural system which has evolved over thousands of years to intensively exploit environmental conditions. The pressures on the resource base are accentuated by the prospect of climate change. This paper synthesizes information from a variety of studies on Chinese agriculture and climate. Historical studies document the impacts of past climate changes and extremes, and the types of adjustments which have occurred, the vulnerability of Chinese agriculture to climate change. Climate change scenarios are assessed relative to the current distribution of agro-climatic regions and farming systems. Notwithstanding the yield enhancing effects of warming and elevated CO 2 levels, expected moisture deficits and uncertain changes in the timing and frequency of critical conditions indicate that there are serious threats to the stability and adaptability of Chinas food production system.

Rocky Desertification, Antidesertification, and Sustainable Development in the Karst Mountain Region of Southwest China

The karst mountain region of Southwest China is one of the largest karst geomorphologic distributing areas in the world (1). It is estimated that the karst geomorphology covers about 620 000 km in this region, involving Sichuan province, Hunan province, Hubei province, Guangdong province, and Chongqing municipality, but largely Guizhou province, Guangxi autonomous region, and Yunnan province (Fig. 1). In the extremely fragile karst geological environment, together with the pressure of overpopulation and lagged social economy, local people have to overexploit land for subsistence, leading to serious land degradation in the form of karst rocky desertification. It is a progressive process where soil is seriously or thoroughly eroded and bedrock exposure is widespread. Productive capability of land declines and, finally, a landscape similar to desert appears under human impact on a vulnerable ecogeoenvironment (2). This major type of desertification finally results in extensive exposure of bedrock. The photo shows different kinds of karst rocky desertification in Southwest China. Because karst rocky desertification is seriously constraining local sustainable development, the productivity of agriculture, forestry, and livestock husbandry are threatened. This issue has attracted widespread social attention. In 1994 and 2003 the Division of Geosciences of the Chinese Academy of Sciences put forward suggestions for comprehensive melioration of karst rocky desertification. The central government also coordinated and organized different rehabilitation for antidesertification at different government levels (state, province, and county) and departments (such as agriculture, forestry, and water conservancy departments) (3, 4). Table 1 provides statistical data about karst areas collected by Ministry of Land Resource, PR China, in 2005 (5). It shows that nearly 22.3% of the karst areas have been developed into karst rocky desertification with an annual increasing rate of 2500 km y 1 in the past 10 y. And three karst-concentrating provinces, i.e., Yunnan province, Guizhou province, and Guangxi Zhuang autonomous region, account for 25.3% of the total karst rocky desertification. The situation is being aggravated further, especially in the southern part of Guizhou province and west part of Guangxi Zhuang autonomous region. The causes behind rocky desertification are rather complex. Several factors such as fragile ecoenvironment, limited natural resources, and backward agricultural economy contribute to the development of karst rocky desertification. Although annual precipitation is 1000 mm or so in this region, runoff often leaks and buries deeply because of the leaking characteristic of limestone. Water resources on the land surface are scarce. This results in both barren cultivated land and scattered and low productivity. Vegetation is hard pressed to survive because of the lack of water. In addition, the potable water facilities for people and livestock are insufficient. In karst-concentrating counties of Yunnan province, Guizhou province, and Guangxi Zhuang autonomous region, the cultivated land per capita is only 0.06 ha. Furthermore, sloping cultivated land accounts for 70% of the total, of which 20% has a slope more than 258. More than 50% of the cultivated land has medium or low productivity. The average yield of grain is only about 2265 kg ha , much lower than the national average (9285 kg ha ). Disasters such as drought and flood are frequent in this region. Cultivated land in karst mountainous regions is mainly located in basins and valleys. In dry seasons or years with low precipitation, cultivated land often suffers from drought because of surface runoff leakage. The drought cultivated land in the middle Guangxi Zhuang autonomous region, for example, reaches about 51 530 000 ha in 2002, all being the medium or low productivity farmland. In rain seasons or years with high precipitation, however, because of water saturation the karst basin and valley are often flooded, usually lasting for a few days, but sometimes as long as several months. Frequent disasters cause enormous losses of topsoil and economic losses leading to poverty. Under the pressure of population growth, local people have to destroy forests and reclaim mountain lands in order to make a living. They also tend to cultivate steeper lands, which leads to soil erosion and rocky desertification. In this way, the localities fall into a so-called poverty, population, and land-degradation