在全球变暖的背景下，极端天气和气候事件（如干旱、高温等）频繁发生，对粮食安全带来了巨大的威胁。干旱的发生往往会伴随着高温热浪的出现，两者彼此紧密联系，相互影响。干旱和高温同时发生一般被定义为复合高温干旱事件，相较于单一干旱或者单一高温而言，复合事件可能会对农业生产、生态系统等带来更加严重的影响。随着全球人口的增长，对粮食需求也在显著上升，为了满足人类日益增长的粮食需求，有必要加强复合高温干旱事件对粮食产量影响的认识。本研究首先识别了复合高温干旱事件多特征的时空变化趋势（即发生频率、持续时间、严重程度和幅度），同时通过多个干旱指数结合高温指数定义复合高温干旱事件，评估了复合高温干旱事件变化趋势的不确定性。为了进一步量化复合高温干旱事件对玉米的影响，本研究采用高斯模型，建立了极端气候变量与玉米产量的联合分布，在全球尺度和国家尺度上探究了复合高温干旱事件对玉米减产的影响。同时利用相关系数探究了产量与气候关系的时间变异特征，并进一步探究了变化环境下复合高温干旱事件对玉米减产影响的非平稳特征。主要结论如下：

   （1）分析全球尺度复合高温干旱事件多特征的变化规律。在全球尺度上，复合高温干旱事件的发生频率、严重程度、持续时间以及幅度在时间和空间上都呈现显著上升的趋势，主要集中在中非、欧洲和地中海等地区。

   （2）评估全球复合高温干旱事件变异的不确定性。在全球玉米种植区上，基于不同干旱指标的三种复合高温干旱事件在近60年里发生频率总体呈现显著增加趋势，但增加的幅度差别较大。在玉米产量最高的前10个国家中，多个国家同时遭遇复合高温干旱事件的频率也在增加。

   （3）探究复合高温干旱事件对产量的影响。在全球尺度上，复合高温干旱事件比单一极端条件对玉米产量的影响更大。在主要玉米产区上，与单一极端干旱（高温）相比，复合高温干旱条件导致玉米减产概率从0.07增加到0.31（从0.04增加到0.31）。

   （4）量化复合高温干旱事件对玉米减产的贡献。当十大玉米生产国出现玉米减产时，三种极端气候事件（干旱、高温和复合高温干旱）的贡献各不相同，但多数国家复合高温干旱事件对作物减产的贡献最高，这与各国降水与温度的相关性紧密联系。此外，随着作物减产严重程度的增加，复合高温干旱事件的贡献也越来越高。

   （5）识别变化环境下复合高温干旱事件对产量影响规律的非平稳特征。过去60年全球十大玉米生产国的气候与玉米产量之间的关系发生了变化。随着干旱（高温）条件和作物产量之间关系增强，作物减产的风险一般会增加。在复合高温干旱条件下作物减产的可能性既取决于干旱-产量关系的变化，又取决于高温-产量关系的变化，二者协同变化导致全球大多数玉米生产国玉米减产的风险增加。

Under global warming, weather and climate extremes (e.g., droughts and heatwaves) occur frequently, which pose a threat on food security. Drought is often accompanied by high temperature and the two extremes are closely related to each other. The simultaneous occurrence of drought and hot extremes is commonly defined as compound dry and hot events (CDHEs), which may have larger influence on agricultural production than do single extremes. With the population growth, the global food demand is expected to increase significantly. Thus, it is desirable to improve understanding of the impacts of CDHEs on food production to meet the increased food demand under global warming. The objective of this study is to explore the spatial and temporal variation of CDHEs characteristics (i.e., frequency, duration, severity and magnitude). In addition, we also use different drought indices with temperature index to define different CDHEs and assess the uncertainty of CDHEs changes. To further quantify the impact of CDHEs on maize yields, we select the Meta-Gaussian model and build the join distribution between climatic variables and maize yield.We then explore the contribution of CDHEs to maize yield reduction at the global and national scale. In addition, the temporal variations of the relationships between climate extremes and crop yield are explored using correlation analysis to explore the changed pattern of CDHEs impacts on maize yield under a changing climate. The main conclusions are as follows:

(1) The frequency, severity, duration and magnitude of CDHEs show an increased trend in most regions across global land area (e.g., Central Africa, Europe and the Mediterranean).

(2) The frequency of three types of CDHEs significantly increases over global maize-producing areas during the last 60 years. For the top ten maize-producing countries, the frequency of CDHEs at the same time also increases from 1949-1980 to 1981-2012 for these three types of compound events.

(3) The CDHEs have larger influence on maize yield than that from isolated extremes. Compared with ndividual extreme droughts (or hot extremes), the probability of maize yield reduction could increase from 0.07 to 0.31 (from 0.04 to 0.31) over the major maize producing countries.

(4) The likelihood of occurrences of the aforementioned three extremes on yield reduction varies among ten maize-producing countries. The impact of compound dry-hot conditions on crop yield is the highest for most countries, which is shown to be closely related to the precipitation-temperature dependence. Moreover, the likelihood of compound dry-hot condition becomes higher with increased severity of crop yield reduction.

(5) The relationship between climate extremes and maize yield has changed over the past few decades for the top ten maize-producing countries. The risk of crop yield reduction generally increases with enhanced dependence between dry (hot) conditions and crop yield. The risk of maize yield reduction increases for the majority of these countries under compound dry-hot conditions due to concurrent changes in climate-yield relationships.

This study reveals variations of CDHEs and their imapcts on maize yield, which provides technical support for relevant departments to formulate management measures. In addition, these findings provide new insights for crop yield prediction and agricultural management development to cope with weather and climate extremes under global warming.