Study On The Impact Assessment Of High Temperature Damage For Rice In The Lower And Middle Reaches Of Yangtze River

The currently global climate has being experienced a significant change characterized as warming up. Varying temperature changed the environmental conditions of agricultural production, and the agro-meteorological disasters which were induced by high temperature effect on crop yield was also increasingly prominent. How to ensure national food security and the stable development of agricultural production was a challenge facing humanity. In this context, it has strong practical significance to assess the impact of climate change caused by hot damage on agricultural production in China. This paper based on the meteorological data of the lower and middle reaches of Yangtze River and the growth period data of rice. Applying statistical analysis, the intensity, frequency and temporal-spatial variation of hot damage was investigated and the high-risk period of high temperature was defined. In order to establish the regional model database, field observations were used to calculate and calibrate the cultivar genetic parameters by put into WOFOST crop model. Then, according to the impacts of high temperature on rice growth, the crop model was improved appropriately. In Different growth periods with the impact of hot damage, the improved model was used to simulate the yield of early rice and medium rice. Meanwhile, the rice yield in both actual weather conditions and average weather conditions were simulated to be contrasted. Using the yield reduction rate as the hot damage evaluation index, the paper assessed the impact of high temperature damage for rice in the lower and middle reaches of Yangtze River. The main results in the article would be presented as following:1. Frequent damage of high temperature weather was occurred in most parts of the southern Yangtze River, but in the western and northeastern regions were relatively less. The high temperature days of maximum temperature≥35℃were more in Hunan, Jiangxi and Zhejiang provinces, and the main high-value areas were in Guixi, Zhangshu, Ji'an of Jiangxi and Lishui, Jinhua of Zhejiang. In addition to the above areas, the high temperature days of average temperature≥30℃also occurred frequently in Jiayu, Huangshi of Hubei. High temperature year is mainly in 1966, 1967, 1971, 1978, 1988, 1994, 1995 and 2003.2. During all developmental stages of rice, when the same intensity hot damage occurred, the level of early rice production cuts were filling stage the maximum, flower stage the second and booting stage the minimum. When the temperature was 30℃, yield decline of both medium rice and early rice were the same. While when the temperature rises to 35℃and the high temperature continuously over 3 days, the medium rice yield of flowering stage was more sensitive to continuous days of higher temperature, and the drop in yield should be greater than the degree of filling stage. As the number of high temperature days continued to increase, the early and medium rice yield of booting stage reduced little, while the yield of flowering and filling stage decreased more significantly. When the same frequency heat damage occurred, the production cuts of early and medium rice were larger than that at filling stage. But when the temperature was high than 34℃, the falling yield of medium rice at flowering stage was greater than that at filling stage, which means that higher temperature strength greater impact on medium rice at flowering period. With the high temperature strength increased, yield loss of early rice also gradually increased. While for medium rice, when temperature was low, the yield reduction increased significantly, but when it is beyond some temperature, the increase in yield reduction would reduce. Under the same growth conditions, the reduced production rate of medium rice was generally larger than early rice, and medium rice was more vulnerable to more serious high temperature weather.3. Compared the rice yield in average weather conditions with actual weather conditions. Changing from the time, the fluctuation of yield reduction rate of early rice was more significant. The years of obvious early rice yield loss were 1967, 1971, 1978, 1988 and 1994. While the fluctuation of medium rice yield was less than that of early rice, but the number of years in which yield declined was much more than that of early rice. The medium rice yield were reduced in1967, 1978, 1994, 1995, 2003, and 2006. Changing from the spatial distribution, in parts of the northern Yangtze River region, the underproduction of early rice presented between 5~6 years in the 60s. And in the 70's, 80's and 90's, the underproduction of most districts occurred between 3~4 years, moreover the south areas has 7~9 years to present the yield loss. After the 2000 the most regions of northeast experienced production cuts between 5~6 years. In the 60's, medium rice yield was most seriously affected between 7~9 years in the south region. In the 70's and 90's, the cut yield occurred in parts of northern areas between 5~6 years. And there was 3～4 years of yields reduction in most west area in 80's. Up to 2000, production cut between 5~6 years appeared in the eastern region.4. In these years which high temperature weather occurred more frequently, yield reduction rate of both early rice and medium rice were more than 30% and there were significant regions of severe disasters. In addition, high temperature days in 1967 had more serious influences on medium rice yield than that of early rice. In 1978, the hot damage regions of early rice were close to that of medium rice. In 1994, high temperature effect on early rice yield was stronger than medium rice yield. While the high temperature in 2003 affected medium rice more seriously than early rice. Generally, in the same high temperature year, the maximum yield reduction rate of medium rice was larger than early rice.