Study Of Effects Of Future Climate Change On Rice Production In The Middle And Lower Reaches Of The Yangtze River

With global warming, the climate in China has changed significantly, and it had a great impact on agriculture. Rice is a staple food crop in China. Assessing the future climate change on rice production in China provides scientific basis for stabilizing international food prices and solving food crisis. This paper aims to examine the potential impacts of future climate change on rice growth duration, rice yield and rice water demand in the middle and lower reaches of the Yangtze River, by inputting future climate data to rice crop model ORYZA2000. Here, climate data generated by the nested regional climate model for the baseline (1961-1990) and future period (2021-2050) under IPCC SRES A2, B2 and A1B scenarios were used. According to the future climate change, I combined the rice growth duration, rice yield and rice water demand in the middle and lower reaches of the Yangtze River, putting forward a series of adaptive measures, in order to reduce the dangers of rice production for climate change. The main research conclusions are as follows:(1) The mean temperature and precipitation of study area would increase by 1.5℃and 5.0% respectively under SRES scenarios during 2021-2050 period, compared to that under Baseline. Rising temperature could mitigate cold-dew-wind injury for late rice, but increase risk of extreme high temperature events for single rice. Summer extremely high frequency of research area increased more than 12 times one year, and it is harmful to rice heading and rice production. Extremely precipitation frequency of research area increased more than 0.5 times one year, and it is easy to form flood disaster, so it is dangerous for rice production. In the future, effective temperature (≥10℃) in rice growing season significantly increased and boundaries of double-rice-cropping and triple-rice-cropping systems have shifted northward. Moreover, relative to the Baseline, the average safe sowing date and safe full heading date would be earlier and later under SRES scenarios during 2021-2050 period, respectively and consequently, the average rice growing season would be longer.(2) Climate warming would shorten the rice growth duration of rice by 4.3d,3.8d and 4.1d under A2, B2 and A1B scenarios respectively in the 2021-2050 period compared to that in the baseline. The shorter days increased from south to north, similar to the temperature change. In this study, rice experimental data at 65 agro-meteorological stations from 1981 to 2006 were used to investigate the performance of ORYZA 2000 model. From ORYZA2000 modelling, we can see that the predicted growing period and yield had a better agreement with the observed values, and the normalized root-mean-square relative error between outputs of crop model and observations was within a reasonable range, below 2% and 15% respectively. Parameter calibration results of litres scale model can reflect the nurseries rice varieties and cropping system differences.(3) Rice yield of study area has an obviously decrease under the raising temperature effect. The number is 13.8%,12.3% and 16.4%, under A2, B2 and A1B scenarios respectively. Because each province has its own cropping system and rice varieties, the rice yield reduction is not the same. Compared to rain-fed rice, irrigated rice could relieve water shortage of rice and generally produced higher yield by over 50% in the north region of the Yangtze River, while it had no much difference in the south where water can meet the demand by rice. CO2 fertilization effect improved the rice yield, but it was still not enough to offset the negative warming effect for single rice. CO2 concentration is still exploiting the main role of improving rice yield in study area.(4) Climate warming increases transpiration rate and leads to a rise of paddy evapotranspiration. Rice water demand increased under A2 and B2 scenarios, but it had increase and decrease under A1B scenario. This could be for the reason of decreasing solar radiation and increasing relative humidity with shortened growth duration. CO2 fertilization effect improved the rice water demand, the increase extent is from 0.5%-1.5%.This paper argues that high CO2 concentration increased rice photosynthesis and rice leaf area, and offset the transpiration reduction caused by stomatal closure to a certain extent.