冬小麦在我国的粮食生产结构中占有举足轻重的地位，特别是主产区华北地区的冬小麦产量对于保证我国小麦和粮食总产量的稳定发挥着至关重要的作用。在当前全球与区域气候环境变化的大背景下，如何持续有力地保证华北地区冬小麦产量的稳定就显得尤为重要。海表面温度（Sea Surface Temperature, SST）作为气候系统内部的一个重要因子，可以以大气响应为媒介，通过“大气桥”遥相关作用显著影响远距离地区的局地环流和气候因子变化，进而通过气候因子的异常变化作用于局地农作物的生长发育与产量形成。在研究气候因子变化影响农作物产量的时候，有必要利用一定的数学方法将农作物的原始产量进行趋势产量与气候产量的分离，从而得到用于分析气候因子对粮食产量具有影响作用的那部分气候产量。

为了探究影响华北地区冬小麦气候产量的超前气候因子，本研究利用1949-2015年华北五省区（河北、河南、山东、安徽和山西）的冬小麦单产数据，通过对比计算分析，采用HP滤波（Hodrick–Prescott filtering）方法得到冬小麦的气候产量，并与全球逐月海表面温度（SST）场进行相关性计算，发现并指出了前期远距离海温场影响华北地区冬小麦气候产量的关键局地气候因子以及作用机制，从而初步建立起了“前期远距离SST—同期大气响应信号—同期局地关键气候因子—局地农作物气候产量”的概念模型。主要研究结论如下：

（1）利用4种不同的趋势产量与气候产量分离方法，对1949-2015年华北地区的冬小麦产量进行分离，除线性去趋势法之外，其他三种方法（五点滑动平均法、HP滤波法和高斯滤波法）得到的气候产量相互之间具有极为显著的正相关关系（P < 0.001）和较为一致的变化趋势。同时，利用建立的能够反映农业技术进步革新的综合指标，表明该综合指标与分离得到的冬小麦趋势产量具有极为显著的正相关关系（P < 0.001），而与冬小麦气候产量没有显著关系（P > 0.1）；（2）将利用HP滤波方法得到的1949-2015年华北地区冬小麦气候产量与1948年7月-2015年6月的逐月全球海温场（ER–SST）进行相关性计算，发现在超前冬小麦收获一年的7-12月份，从南印度洋经印太暖池区至西北太平洋地区存在一个“正–负–正–负–正”的五极型高相关区域，并将其定义为印太海温五极子（Indian Ocean–Pacific SST Five–pole, IPF），而利用Hadley–SST海温场数据也得到了类似的计算结果。据此建立印太海温五极子指数（Indian Ocean–Pacific SST Five–pole Index, IPFI），发现超前一年秋季的IPFI与冬小麦气候产量具有极为显著的正相关关系，并且在10月份，IPFI与冬小麦气候产量相关性达到最大（r = 0.692, n = 67, P < 0.001），经过逐点剔除交叉验证与滑动相关检验，表明两者的相关关系不依赖于个别极值点，而是长时间稳定存在的；

（3）超前一年10月份的IPF可以显著影响同期大气位势高度场的异常变化，使之表现出与IPF相类似的五极型分布；IPF与同期华北局地气温有显著负相关关系，但与局地降水量和土壤含水量具有显著正相关关系。合成分析表明，当IPF出现正位相异常时，华北地区近地面大气出现低压异常、而中高空大气出现显著高压异常，有利于形成上升气流，从而使华北地区温度降低、降水增加。同时，华北地区700 hPa出现气旋型环流异常，有利于水汽的辐合和降水的形成，与之对应的降水量和土壤含水量也显著增加。而当IPF出现负位相异常时，华北地区700 hPa出现东风异常，不利于水汽辐合与形成降水，与之对应的降水量和土壤含水量也显著减少；

（4）由于超前一年的10月份（秋季）正好对应着华北地区冬小麦的播种期，该时期的气温变化对于冬小麦气候产量仅有微弱的负相关影响，而降水量和土壤含水量与冬小麦气候产量具有显著正相关关系。从播种期至第二年返青期的合成分析表明，在降水耦合度异常偏高的年份里，冬小麦平均气候产量为0.26 t/ha，显著高于降水耦合度异常偏低年份里的平均值-0.21 t/ha。土壤含水量异常偏高年份里的冬小麦气候产量平均值为0.28 t/ha，显著高于土壤含水量异常偏低年份里的平均值-0.27 t/ha；

（5）在超前一年的冬小麦播种前至播种期（7–10月份）的降水量异常偏多年份里，土壤含水量可以从播种后的出苗期至第二年的返青期（前一年11月至收获当年的3月）持续的保持异常偏多的趋势，而这一阶段正好是华北地区一年之中降水较少的时期。因此，这对于处在冬小麦营养生长阶段的水分供给以及返青后的生长发育至关重要。

综上，超前一年秋季的印太海温五极子对于次年华北地区冬小麦气候产量具有极为显著的影响，进一步的研究发现印太海温五极子通过激发同期大气信号的响应，作用于同期的华北局地环流和气候因子，从而影响到播种期和播种后至返青期的冬小麦生长发育，并最终对冬小麦的气候产量造成影响。该研究可为更好地理解“海温–环流–气候–粮食”四者之间的关系以及为超前一定时期针对粮食产量的预估提供了可能性，并有利于决策者和农业管理者根据前期气候信号，做出更为合理的农业规划部署与及时调整农业种植结构提供了理论支撑与指导建议。

Winter wheat plays an important role in grain production structure in China, especially winter wheat production in North China, which plays a key role in ensuring the stability of total wheat and grain yields in China. Under the background of global and regional climate environment change, it is especially significant to ensure the stability of winter wheat output in North China. Sea surface temperature (SST), as an important factor in the climate system, can significantly influence the local circulation and climatic factor changes in the remote area through the “atmospheric bridge” teleconnection effects, and then the abnormal changes of climatic factors could impact on the growth and production of local crops. When investigating the influence of climatic factors on crop yield, it is necessary to use a certain mathematical method to separate the climatic yield and trend yield of crops from the original yield, so as to obtain the climatic yield that is used to analyze the effects of climatic factors on grain yield.

In order to investigate the previous climatic factors affecting the climatic yield of winter wheat in North China, this study uses the yield data of winter wheat in the five provinces of North China (Hebei, Henan, Shandong, Anhui and Shanxi Province) during 1949-2015. Through comparative calculation and analysis, the climatic yield of winter wheat is obtained by using HP filtering method, and the correlation calculation with the global monthly SST field. The key local climatic factors and its mechanism of influence winter wheat in North China are found and pointed out. Thus, the conceptual model of “previous remote SST–atmospheric response signal–local key climatic factor–local crop climatic yield” is established. The main research results are as follows:

(i) Four different trend yield and climatic yield separation methods are used to separate winter wheat yield in North China from 1949 to 2015. Except for linear detrend method, the climatic yield obtained by the other three methods (five-point moving average method, HP filtering method and Gaussian filtering method) has a very significant positive correlation with each other (P < 0.001) and a relatively consistent change trend. At the same time, the comprehensive indexes which can reflect the agricultural technological progress and innovation are used to show that the comprehensive indexes have very significant positive correlation with the separated trend yield of winter wheat (P < 0.001), but have no significant relationship with the climatic yield of winter wheat (P > 0.1);

(ii) The correlation between the climatic yield (using the HP filtering method) of winter wheat in North China from 1949 to 2015 and the monthly global sea surface temperature field (ER-SST) from July 1948 to June 2015 were calculated, and it is found that in the period from July to December of the previous year, a “positive–negative–positive–negative–positive” five-pole high-correlation region is present from the Southern Indian Ocean to the North-West Pacific region and is defined as the Indian Ocean–Pacific five-pole (IPF) SST, and similar results are obtained using the Hadley-SST data. According to this, the Indian Ocean–Pacific SST five-pole index (IPFI) is set up, and it is found that IPFI in the fall of the previous year has a very significant positive correlation with the winter wheat climatic yield, and in previous October, the correlation between the IPFI and the climatic yield of the winter wheat reachs the maximum (r = 0.692, n = 67, P < 0.001). After point–by–point elimination of cross–validation and sliding related tests, the correlation between them is not dependent on the individual extreme points, but is stable for a long time;

(iii) The previous October’s IPF could significantly affect the abnormal changes of atmospheric potential height field in the same period, making it show a five-pole distribution similar to IPF. IPF has a significant negative correlation with local temperature in North China, but has a significant positive correlation with local precipitation and soil moisture in the same period. The composite analysis shows that when the positive phase anomaly occurs in IPF, there is a low pressure anomaly in the near surface atmosphere in North China, while a significant high pressure anomaly occurs in the middle and upper atmosphere, which is beneficial to the formation of updraft, thus reducing the temperature and increasing precipitation in North China. At the same time, the cyclonic circulation anomaly appeared at 700 hPa in North China, which is beneficial to the convergence of water vapor and the formation of precipitation, and the corresponding precipitation and soil moisture also increased significantly. When the negative phase anomaly occurs in IPF, the easterly anomaly occurs at 700 hPa in North China, which is not conducive to water vapor convergence and precipitation formation, and the corresponding precipitation and soil moisture are also significantly reduced;

(iv) Due to the previous october (autumn) just corresponds exactly to the sowing date of winter wheat in North China, the temperature change in this period has only a weak negative correlation to winter wheat climatic yield, while the precipitation and soil moisture have a significant positive correlation with winter wheat climatic yield. The composite analysis from the sowing date to the next year’s returning green stage shows that the average climatic yield of winter wheat is 0.26 t/ha in the year of unusually high precipitation coupling degree, which is significantly higher than the average value of -0.21 t/ha in the year of abnormally low precipitation coupling degree. The average climatic yield of winter wheat in the year of abnormally high soil moisture is 0.28 t/ha, which is significantly higher than that in the year of abnormally low soil moisture -0.27 t/ha;

(v) During the previous year in which the precipitation is abnormally higher, from ahead of the winter wheat sowing date to the sowing period (July-October), the soil moisture could maintain an abnormally high trend from the seedling stage after sowing to the returning green stage in the following year (from previous November to the harvest year’s March), this stage is just a period of less precipitation in the North China of every year. Therefore, this is very important for the water supply in the vegetative growth stage of winter wheat and the growth and development after returning green;

To sum up, the Indian Ocean–Pacific SST five-pole in the previous autumn has a very significant effect on the following year’s climatic yield of winter wheat in North China, the further research shows that the IPF act on the local circulation and climatic factors in North China in the same period by stimulating the response of atmospheric signals in the same period, thus affecting the growth and development of winter wheat at the sowing date and after sowing to the returning green stage, and finally affecting the climatic yield of winter wheat. This study could provide a better understanding of the relationship between “SST–circulation–climate–grain”, as well as the possibility of predicting grain production in a certain period ahead of time, and is helpful for policymakers and agricultural managers to make more reasonable agricultural planning and deployment and timely adjustment of agricultural planting structure according to the previous climatic signal.