Evaluation Of The Impact Of Climate Change On China's Grain Output

At present, the global climate has being significant change which warming is its main characteristics. The global warming has brought or will bring key effects to the ecological system, agricultural environment and crop yields. Exploring and assessing climate change and it impacts are one of important issues in the fields of climate change. Rice is the largest crop in China; the effects of climate change on rice yields are close related to the food safety in China. (I) Meteorological observation data are applied to analysis the spatial distribution of temperature change in the growing season in different rice zones from 1981 to 2000. The technology of low frequency filter the waves is applied to extract the information of rice climate yields from the observed rice yields record. The correlations between anomalous temperature of rice growing season and the index of rice climatic yields are explored in different rice zones from 1981 to 2000. The temporal change of rice actual yields, trend yields and climate yields, the spatial distribution of the tendency of rice climate yields and the contribution of climate yields to rice actual yields are analyzed from 1981 to 2000. Comparing the frequency and intensity of extreme temperature in rice growing season in 90s(1991-2000) with those in 80s (1981-1990). (II) Assessing impacts of climate change on rice growing duration (flowering duration) and yields against IPCC SRES A2 and B2 in 2071-2100 by connecting regional climate model outputs with crop model including impacts of high and low temperature on empty grain of rice in growing duration low and in the main rice zones of China. The main conclusions are as following: 1. In recent 20 years, temperature of growing season on single rice increase by 0.1~0.7oC/20y in the Northeast China and the Northern Yangtze Rive and on the early rice in the Southern Yangtze Rive and the South China, and on the late rice decreased by 0.1~0.3 oC/20y in the Southern Yangtze River and the South China. 2. In recent 20 years, rice climatic yields increase in the Northeast China, rice climate yields decrease including single rice in the Northern Yangtze Rive, late rice the Southern Yangtze Rive, early rice and late rice in the South China. The variability of inter-annual climatic yields increases in 90s. The correlations between the anomalous temperature and the index of climatic yields show that increasing temperature has a positive effect on rice yields in the Northeast China, and on late rice in the Southern Yangtze Rive and the South China; The increasing temperature has a negative effect on climatic yields when its distances of rice growing season temperature is larger than the values of inflexion (the Northeast China: +0.8oC; the Northern Yangtze Rive: +0.1oC; early rice in the South Yangtze Rive: +0.04oC; Guangxi: +0.8oC), and has a positive effect on climatic yields when its rice growing season anomalous temperature is less than the value of its inflexion. The increasing temperature has a negative effect on early rice climatic yields in Fujian and Guangdong provinces. The increasing temperature has a negative effect on late rice climatic yields in the Southern Yangtze Rive and the South China. 3. In recent 20 years, single rice climate yields increase in most parts of the Northeast China, Sichuan Plain and few parts of Guangxi province. Others decrease. 4. Comparing the frequency and intensity of relative extreme temperature events in the growth season in 1990s with that in 1980s, the frequency and intensity of daily high temperature for early rice increase in the Northern Yangtze Rive and the Southern Yangtze River, and that for early rice decrease in south China; the frequency and intensity of daily low temperature for late rice increase in the Southern Yangtze River. The frequency of daily low temperature for late rice in the South China decreases, and the intensity increases. Empirical equation is defined between extreme temperature and the ratio of empty grain using observation data. 5. Adjusting crop genetic parameters, calibrating and validating on crop model. Crop model can simulate flowering duration rice yields using local crop genetic parameters. The corrected RCM outputs can improve the ability of modeling and decrease uncertainty of impacting assessment of climate change. 6. Comparing the 2080s (2071-2100) under A2 and B2 scenarios with baseline year (1961-1990), the results of impact of climate change on rice growth duration and yields are as following: (1) Temperature of growth season increase by 2.3~6.5oC (A2 scenario) and 1.6~5.1oC (B2 scenario). The order of increase temperature: the first is the Northeast China, and the second is the Northern Yangtze River. The extent of increase temperature for late rice season is less thanthat for early rice season in the same rice zones. (2) The flowering days of rice decrease by 10~30 days (A2 scenario) and 10~25 days (B2 scenario). (3) Without CO2 direct effects, under A2 scenario, rice yields decrease by 8~40% () and 10~20% (B2 scenario). The extent of decreasing rice yields in the Northeast is more than that in others. The extent of decreasing rice yields for early rice yields is more than that for late rice yields. The extent of rice yields decrease under A2 scenario is much more than that under B2 scenario. (4) With CO2 direct effects, CO2 fertilization effect may offset negative impacts of climate change on rice yields. Double rice yields would increase, however, a part of single rice yields still decrease. (5) The ratios of empty grains of early and middle rice which induced by extreme high temperature increase by 10~30%(A2 scenario) and 5~20% (B2 scenario) in the Northern Yangtze Rive, the Southern Yangtze River and the South China. The ratios of empty grains of late rice which induced by extreme low temperature decrease by 10~20%(A2 scenario) and 10% or so (B2 scenario) the Southern Yangtze River and the South China, and increase by 0-10% (B2 scenario) in a small parts of Guangdong and Guangxi provinces.