Study On The Risk Assessment Of The Main Meteorological Disasters For Maize In Northeast China

The major agricultural areas of China are affected by a variety of meteorological disasters which bring heavy losses for crop yield. Accurate and quantitative assessment of agro-meteorological disaster risk is very meaningful for sustainable agricultural development and development of disaster prevention and mitigation policies. The current research direction in assessment of agro-meteorological disasters is comprehensive assessment of hazard of disaster-forming environment, exposure and vulnerability of the bearing body, capability of mitigation and prevention according to the theory of natural disaster risk assessment and the formation mechanism of the agro-meteorological disaster risk. At present, researches were mainly focused on agro-meteorological disaster hazard and vulnerability of disaster-affected body, and few researches were related to the risk of several meteorological disasters, not exactly reflecting the comprehensive risk faced by agriculture under real meteorological conditions. Meteorological disasters occurred at different crop growth stages have different influence on final crop yield. Present research mainly based on the whole crop growth season. Crop development stages when disaster happens are not usually specified, and few disaster risk assessment throughout the whole crop development process exists.Aimed at the current problems, multivariate data including meteorological data of48meteorological stations across the Northeast China from1961to2010, the maize development record (from1980to2010), sowing areas and yield (from1961to2010), and soil moisture and agriculture disaster data (from1992-2010) collected by48agro-meteorological observation stations, were used. Based on the analysis of meteorological disasters such as chilling, drought and flood during the stages of sowing to seven-leaf, seven-leaf to tasseling, tasseling to milky ripening, and milky ripening to maturation of maize in Northeast China, the risk assessment technology of the main meteorological disasters for maize in Northeast China was studied mainly focused on the index system and model establishment of the main meteorological disasters risk assessment based on natural disaster risk theory and assessment technique. The chilling damage index and the crop water surplus deficit index were first established to identify chilling damage, drought and flood disaster during different growth stages of crop, and the temporal-spatial distribution and the variation rules for different growth stages of the main meteorological disasters were analyzed. According to the theory of natural disaster risk, starting from the formation mechanism of agricultural meteorological disaster risk, a fairly complete index system of the main meteorological disasters risk assessment was then built, and the main meteorological disaster risk assessment models of growth stages and the whole growth period of crop were established using natural disasters risk index method. The values of risk indices of growth stages and the whole growth period were finally regionalized using the method of system cluster. The main conclusions are as following:1. Thermal resource and chilling damage changes during the maize growth stages in northeast China(1) Interdecadal variability of heat index for the four growth stages generally exhibited band distribution rule, the lowest value lay in the Changbai Mountains of the southeast, and the value increased gradually from southeast(or east) to northwest(or west). In recent50yrs, the heat index had an obvious increase, which showed the best thermal condition in the early21st century.(2) The average chilling damage of the whole growth period in all areas experienced a significant decreasing trend, but the intensity varied between areas, basically presenting a stepped rise from southwest to northeast. The chilling damage intensity significantly decreased for areas with maize ripening in the middle of the season. In contrast, the chilling damage intensity increased over the areas with maize ripening late of the season. An in-the-middle situation occurred in the areas with middle-late-season ripening maize.(3) The frequency of chilling damage of the four growing stages showed an overall decreasing trend, and a significant reduction of frequency appeared in the1980s. The frequency of chilling damage reached the lowest degree in the early21st century. The abrupt change of chilling damage intensity during the four growing stages occurred in the middle of1990s, and then decreased obviously.2. Distribution of water demand and supply, drought and flood during the maize growth stages in northeast China(1) The water demand during the whole growing period didn't have an appreciable increase trend in the recent50years. There was an obvious increase trend of drought during the stage from milky ripening to maturation, while during the other three stages and the whole growth period, there was no obvious change of drought or flood.(2) From sowing to seven-leaf and seven-leaf to heading, the frequency of middle drought or above in the most parts of Northeast China was less than10%; while from heading to milky ripening and milky ripening to maturation, the frequency of middle drought or above decreased from northwest to southeast, and the west of Songnen Plain and western part of Liaoning Province were the high-incidence areas, the frequency was between30%and50%.(3) From sowing to seven-leaf, the frequency of middle flood or above was less than10%; while during the followed three stages, it decreased from southeast to northwest, and the southeast part of Liaoning Province and Jilin Province were the high-incidence areas, the frequency was between30%and50%.(4) Widespread and regional middle drought or above and flood or above of growth stages had an obvious interdecadal change. From1980s, the number of widespread and regional middle drought or above and flood or above increased significantly.3. Selection of index and establishment of model of the main meteorological disasters risk assessment during growth stages of maize in northeast China(1) Hazard indices of the main meteorological disasters were selected using multi-index method for environment causing the disaster according to meteorological and biological significance of the main meteorological disaster-pregnant environment index. According to the connotation of exposure and vulnerability for the hazard bearing body, indices were selected for risk assessment. Based on the relative lag situation of disaster prevention and mitigation, the regional agricultural level was used to comprehensively reveal the preventing and mitigating capability, and a fairly complete index system of the main meteorological disasters risk assessment was developed.(2) Using synthetic weighted mark method and analytic hierarchy process (AHP), the model of hazard assessment of growth stages of crop for a single disaster was built. Combining the hazard index of disaster-pregnant environment index and occurrence frequency of the main meteorological disasters, the main meteorological disasters hazard assessment model was built by adopting AHP, and the weight coefficients were determined by the ratio of the frequency of the main meteorological disasters. (3) Using natural disaster risk index method, the model of the main meteorological disasters risk assessment of the growth stages of crop was established. Based on the values of risk index of the main meteorological disasters of the growth stages, according to correlation relationship between yield reduction rate and the values of the main meteorological disasters risk, the weight coefficients were determined, and the model of the main meteorological disasters risk assessment of the whole growth period of crop was established using synthetic weighted mark method. Then, using the system cluster analysis, the risk of the four growth stages and the whole growth period of crop were identified.4. The main meteorological disasters risk assessment and identification of maize in northeast China(1) The distribution of hazard of the main meteorological disasters of the growth stages of crop revealed regional differences and continuity. From sowing to seven-leaf, high values mainly distributed in the southeast of Heilongjiang Province and East of Jilin Province, low values in the middle northern part of Liaoning Province. From seven-leaf to tasseling, the high value areas mainly distributed in the southeast of Liaoning Province, and the low values with poor contiguous. For both growth stages from tasseling to milky ripening and from milky ripening to maturation, the middle-high range lay in the west of Songnen Plain while the low value range lay in the middle-east of Jilin Province.(2) Exposure of maize showed an increase trend from the northeast to the southwest, high value mainly distributed in most part of Liaoning province except the western part and the middle area of Jilin Province; Middle values were located in the Songnen Plain and the northeast of Jilin Province from southeast to northwest, and the low value in the middle-east of Heilongjiang and the northeast of Jilin Province.(3) Continuity of the vulnerability index from sowing to seven-leaf and from seven-leaf to tasseling stages was not obvious. During the next two stages of crop the vulnerability index distributed continuously. And the low values of preventing and mitigating capability were mainly located in the west of northeast China and northeast of Jilin Province, while the high values distributed in the middle of northeast China from northeast to southwest.(4) During the stage from sowing to seven-leaf, the value of the main meteorological disasters risk presented a band distribution from northeast to southwest, with low value areas mainly distributed in the middle of northeast China, while high value areas mainly distributed in the west and east of northeast China. During the stage from seven-leaf to heading, the value of risk mainly increased from northeast to southwest, with low value areas distributed in Heilongjiang Province and the northeast of Jilin Province, and the high value areas mainly situated in the west of the northeast China, southeast of Jilin Province and eastern and southern of Liaoning Province. From heading to milky ripening, milky ripening to maturation and the whole growing period, the value of risk increased from east to west, and the middle-high value areas were mainly located in Songnen Plain and Liaoning Province.