基于信息扩散和分形技术的玉米干旱特征分析

为研究区域农业干旱时空分布特征,以及干旱对作物产量的影响,建立了基于信息扩散和分形技术的农业干旱特征量化分析模型。以西安市为典型研究区,根据1951—2010年降水、气温资料和1949—2015年玉米产量等数据,利用该文提出的评估指标和技术方法对西安市玉米干旱特征分析计算,验证了模型的有效性。结果表明:1)60年来,西安市玉米共发生30次气象干旱,平均2年1次。2001—2010年以来,频次增多,平均1.25年1次。气象干旱发生的时间具有分形特征,经大量试验,发现当计算样本数量约14时,重标极差方法可取得很好效果。2)玉米气象干旱的程度呈现很缓慢上升趋势,Hurst指数0.930 7,而玉米趋势产量波动上升,玉米当前(2011—2015年)平均趋势产量为5 468 kg/hm~2,作物干旱程度(减产率)呈缓慢下降趋势。3)玉米气象干旱程度和作物干旱程度相关性不明显,但两者变化周期基本相同,经信息扩散技术处理后,趋势呈现明显波峰、波谷交替变化。4)预测西安市2023年(第40个干旱年)气象干旱程度约1.2,按照当前的抗旱能力和技术水平,产量损失估计约1.35%,预估玉米单产约5 394 kg/hm~2。该研究尝试基于信息扩散和分形技术对西安市玉米干旱发生时间和程度的特征进行分析,为该地区玉米干旱防灾减灾提供技术参考。

Characteristic analysis of drought for corn based on information diffusion and fractal technology

Abstract: It is significant to research the drought occurring and extent regularities to provide technical supports for disasters prevention. The new meteorological drought evaluation index was suggested, which fully considered the matching degree between precipitation process and crop water requirement. Based on daily mean temperature and precipitation data from 1951 to 2010, the meteorological drought occurring features for corn in Xi''an City, Shaanxi Province were analyzed by the fractal analysis method. Meanwhile, the crop production loss caused by drought was calculated based on information diffusion technology, according to the unit yield data of corn in Xi''an from 1949 to 2015. Firstly, the values of meteorological drought extent for corn in historical year were calculated by the new meteorological drought index. According to the rescaled range analysis method, the trend values of meteorological drought extent for corn were calculated and the time characteristics were analyzed. The occurrence time of meteorological drought had fractal characteristics. The rescaled range method could achieve good results when the number of samples was about 14 according to a large number of tests. In the past 60 years, the meteorological droughts occurred for 30 times in Xi''an, once every 2 years on average. From 2001 to 2010, the frequency increased to once every 1.25 years on average. The extent of meteorological drought for corn mainly showed a very slow upward trend, and the Hurst index for meteorological drought extent sequence was 0.930 7. Secondly, according to the moving average method improved by information diffusion technology, the values of trend production of corn were calculated. The tendency of trend production of corn was described by information diffusion regression method. On basis of trend production calculation, the values of yield reduction rate of corn that were considered to reflect the extent of crop drought were analyzed by information diffusion fitting technology. The trend yield of corn increased in fluctuation, and the average trend yield of corn from 2011 to 2015 was 5 468 kg/hm2. The crop drought degree showed a slow downward trend. Comparing the extent of meteorological drought and the features of crop drought for corn in Xi''an, it was found that the correlation between the meteorological drought degree of corn and the drought degree of crops was not obvious, but their cycles of change were basically the same, and after treatment by using information diffusion technology, the trend presented a feature of alternation of obvious peaks and troughs. Finally, the meteorological drought degree in Xi''an in 2023, which is about the fortieth drought year, is estimated to be about 1.2. The yield loss is estimated at about 1.35%, according to the current drought resistance ability and technical level, and the estimated corn yield per unit area is about 5 394 kg/hm2. This research is of guiding implications to the prevention of disaster and yield reduction of corn in Xi''an City.