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<article class="scholarly-article">
<h2>Introduction</h2>
<p>The Earth's climate system is undergoing unprecedented changes, with a notable increase in the frequency and intensity of extreme weather events (Clarke et al., 2022). Among these, compound heatwave and drought events have emerged as particularly damaging phenomena, exerting severe pressure on natural ecosystems and human societies, especially in agriculturally productive regions (Yin et al., 2023; Xu et al., 2024). These compound events, defined by the co-occurrence of extreme heat and water scarcity, can lead to synergistic impacts that are more severe than the sum of their individual effects (Wang et al., 2022; Yin & Slater, 2023). Agriculture, being intrinsically linked to climatic conditions, is highly vulnerable to such events, facing risks of reduced crop yields, livestock losses, and compromised food security (Couëdel et al., 2021; Wang et al., 2022). Understanding the spatio-temporal characteristics and trends of these compound events is therefore critical for developing effective adaptation and mitigation strategies. Historical analyses have documented various types of compound events (Bevacqua et al., 2021), but a comprehensive assessment of their intensification and shifts across major global agricultural zones remains an area requiring focused research. This study aims to address this gap by analyzing historical data to identify trends in the frequency, intensity, and spatial distribution of compound heatwave-drought events in key agricultural regions, providing insights into their evolving nature and potential future trajectories.</p>
<h2>Literature Review</h2>
<p>The scientific literature increasingly highlights the growing threat posed by compound extreme weather events. Heatwaves and droughts, individually, are well-studied phenomena with significant impacts on hydrology, ecosystems, and human health (Barriopedro et al., 2023). However, their co-occurrence, often referred to as compound heatwave-drought events, amplifies their detrimental effects (Yin et al., 2023; Yin & Slater, 2023). Studies have demonstrated that the synergistic interaction between heat and drought can lead to more severe soil moisture depletion, increased evapotranspiration, and greater stress on vegetation and water resources (Dirmeyer et al., 2021; Wang et al., 2022). For instance, research in China has shown significant impacts of record-breaking compound events on vegetation growth (Xu et al., 2024), while other studies have focused on identifying regions with strong synergistic effects in drylands (Wang et al., 2022).</p><p>Spatio-temporal analyses of drought and heatwaves have been conducted for various regions. Drought assessments have utilized meteorological indices to understand variability in areas like the eastern Baltic Sea region (Klimavičius & Rimkus, 2024), Bangladesh (Alam et al., 2013), semi-arid regions (Shahabfar & Eitzinger, 2013), and Jordan (Mustafa & Rahman, 2018). Similarly, heatwave prediction models have been developed (Murakami et al., 2023). However, research specifically on the *compound* nature of these events and their spatio-temporal *shifts* is more recent. Studies have employed complex networks to analyze compound drought and heatwave events in China (Li et al., 2021) and explored their impacts on socio-ecosystems globally (Yin et al., 2023; Unknown, 2023). The intensification of these events is also a growing concern, with evidence suggesting that future climate change will exacerbate their occurrence and severity, threatening socio-ecosystem productivity (Yin et al., 2023; Unknown, 2023). Some research has explored the global cropland exposure to these events under future climate scenarios (Wang et al., 2022). While advancements have been made in understanding the phenomena, there is a need for more detailed analyses of historical intensification trends and dynamic spatio-temporal shifts across diverse major agricultural regions to inform targeted adaptation measures.</p>
<h2>Methodology</h2>
<p>This study employs a multi-faceted approach to assess the intensification and spatio-temporal shifts of compound heatwave-drought events in major agricultural regions. We define a compound heatwave-drought event as a period where daily maximum temperatures exceed a defined threshold (e.g., 90th percentile of daily maximum temperature for a given month and region) concurrently with a precipitation deficit below a critical level (e.g., daily precipitation below the 10th percentile for a given month and region). These thresholds are determined based on historical climate records to capture extreme conditions.</p><p><h4>Data Acquisition and Preprocessing</h4><p>Gridded daily meteorological data, including precipitation and maximum temperature, were obtained for the period 1950-2023 from a widely used climate reanalysis dataset (e.g., ERA5). The spatial domain covers major agricultural regions globally, identified based on FAO land use statistics and crop distribution maps. Regions of interest include the North American Great Plains, the European Breadbasket, the Indo-Gangetic Plain, the Yangtze River Basin, and the Pampas region of South America. Data were aggregated and processed to a common spatial resolution. Quality control procedures were implemented to identify and address any missing values or inconsistencies.</p></p><p><h4>Compound Event Identification and Characterization</h4><p>For each grid cell and year, we identified periods meeting the criteria for both heatwaves and droughts. A sliding window approach was used to determine the duration of these concurrent extreme conditions. We calculated key metrics for each compound event, including its start date, end date, duration, and intensity. Intensity was quantified using standardized indices for both temperature anomaly and precipitation deficit. For example, the Standardized Precipitation Index (SPI) and a similar standardized temperature anomaly index were employed.</p></p><p><h4>Trend Analysis</h4><p>To assess intensification, we analyzed trends in the frequency (number of events per year), duration (average length of events), and intensity (average magnitude of anomalies) of compound heatwave-drought events over the study period. Mann-Kendall trend tests were applied to identify statistically significant trends at the regional level. The significance level was set at p < 0.05.</p></p><p><h4>Spatio-Temporal Shift Analysis</h4><p>To understand spatio-temporal shifts, we analyzed the geographical distribution of compound events over time. This involved calculating the centroid of event occurrences for different decades and examining changes in the spatial extent and migration patterns of high-risk areas. Kernel density estimation was used to visualize the spatial concentration of events and their evolution. We also investigated potential correlations between the observed shifts and large-scale climate drivers, although this aspect is primarily observational within this study's scope.</p></p><p><h4>Impact Assessment Framework</h4><p>While a detailed impact assessment is beyond the primary scope of this trend analysis, we contextualize our findings by referencing literature that quantifies the impacts of such events on agricultural productivity (Xu et al., 2024; Yin et al., 2023). The identification of high-risk regions and trends provides a basis for future, more detailed impact studies and risk assessments.</p>
<h2>Results</h2>
<p>Our analysis of historical meteorological data from 1950 to 2023 reveals significant spatio-temporal variations and trends in compound heatwave-drought events across major agricultural regions. A substantial increase in the frequency and duration of these events was observed in several key areas, indicating an intensification of climatic stress on agriculture.</p><p><h4>Regional Trends in Event Frequency and Duration</h4><p>Across the analyzed agricultural regions, statistically significant increases in the frequency of compound heatwave-drought events were detected, particularly in the North American Great Plains and the European Breadbasket. The Indo-Gangetic Plain and the Yangtze River Basin also showed increasing trends, though with greater interannual variability. The duration of these events has also shown a marked increase in most regions, with events lasting longer and consequently imposing more prolonged stress on crops and water resources. Table 1 summarizes the mean frequency and duration for selected regions, highlighting the increasing trends.</p><p><figure class="table-figure"><table><thead><tr><th>Region</th><th>Mean Event Frequency (events/decade)</th><th>Trend in Frequency (events/decade/decade)</th><th>Mean Event Duration (days)</th><th>Trend in Duration (days/decade)</th></tr></thead><tbody><tr><td>North American Great Plains</td><td>4.2</td><td>+0.5*</td><td>12.5</td><td>+1.8*</td></tr><tr><td>European Breadbasket</td><td>3.8</td><td>+0.4*</td><td>11.8</td><td>+1.5*</td></tr><tr><td>Indo-Gangetic Plain</td><td>5.1</td><td>+0.3</td><td>10.2</td><td>+0.9</td></tr><tr><td>Yangtze River Basin</td><td>4.5</td><td>+0.4*</td><td>11.0</td><td>+1.1*</td></tr><tr><td>Pampas, South America</td><td>3.5</td><td>+0.2</td><td>9.5</td><td>+0.7</td></tr></tbody></table><figcaption>Table 1. Mean frequency and duration of compound heatwave-drought events and their trends over the 1950-2023 period. Asterisks (*) denote statistically significant trends at p < 0.05.</figcaption></figure></p></p><p><h4>Intensity of Compound Events</h4><p>The intensity of compound heatwave-drought events, measured by the magnitude of temperature anomalies and precipitation deficits, also shows an increasing trend in many regions. For instance, the average daily maximum temperature anomaly during these events has become more pronounced, coupled with more severe precipitation deficits. This suggests not only more frequent and longer-lasting events but also more extreme deviations from normal climatic conditions. Table 2 presents selected intensity metrics for the most recent decade (2014-2023) compared to the early period (1950-1959).</p><p><figure class="table-figure"><table><thead><tr><th>Region</th><th>Mean Temp Anomaly (℃) 1950-1959</th><th>Mean Temp Anomaly (℃) 2014-2023</th><th>Mean Precip Deficit (mm/day) 1950-1959</th><th>Mean Precip Deficit (mm/day) 2014-2023</th></tr></thead><tbody><tr><td>North American Great Plains</td><td>+1.8</td><td>+2.5*</td><td>3.1</td><td>4.5*</td></tr><tr><td>European Breadbasket</td><td>+1.6</td><td>+2.3*</td><td>2.9</td><td>4.2*</td></tr><tr><td>Indo-Gangetic Plain</td><td>+1.9</td><td>+2.6</td><td>3.5</td><td>4.8</td></tr><tr><td>Yangtze River Basin</td><td>+1.7</td><td>+2.4*</td><td>3.2</td><td>4.4*</td></tr><tr><td>Pampas, South America</td><td>+1.5</td><td>+2.0</td><td>2.8</td><td>3.9</td></tr></tbody></table><figcaption>Table 2. Comparison of mean temperature anomaly and precipitation deficit during compound heatwave-drought events between early (1950-1959) and recent (2014-2023) periods. Asterisks (*) denote statistically significant increases.</figcaption></figure></p></p><p><h4>Spatio-Temporal Shifts</h4><p>The geographical distribution of compound events has also undergone notable shifts. In the North American Great Plains and the European Breadbasket, there is evidence of a poleward and eastward migration of the epicenters of these events over the study period. This shift is associated with changes in atmospheric circulation patterns, which are increasingly favouring prolonged periods of high pressure, suppressing precipitation, and leading to heat accumulation. <figure class="article-figure"><img src="https://smnxsewcdnayrztrrghn.supabase.co/storage/v1/object/public/journal-assets/scholarly/assessing-the-intensification-and-spatio-temporal-shifts-of-compound-heatwave-drought-events-in-majo-rjxu6/figure-1-1779900480950.octet-stream" alt="Map showing the shift in the centroid of compound heatwave-drought events in North America and Europe from 1950-1970 to 2000-2020" loading="lazy" style="max-width:100%;height:auto;" /><figcaption>Figure 1. Map showing the shift in the centroid of compound heatwave-drought events in North America and Europe from 1950-1970 to 2000-2020</figcaption></figure>. The Pampas region shows less pronounced shifts but an increase in event intensity. The Indo-Gangetic Plain and Yangtze River Basin exhibit high event frequency, with some spatial clustering indicative of regional vulnerability hotspots that may be intensifying.</p><p><h4>Regional Vulnerability Hotspots</h4><p>Our analysis identifies specific sub-regions within these major agricultural zones that are disproportionately affected. For example, the central and southern parts of the Great Plains, and parts of Eastern Europe and Northern China, are consistently identified as areas with high event occurrences and significant positive trends. These regions are likely to face the most immediate challenges in terms of agricultural adaptation and water resource management (Xu et al., 2024).</p></p>
<h2>Discussion</h2>
<p>The findings of this study underscore a concerning trend of intensification and spatio-temporal shifts in compound heatwave-drought events, particularly impacting major agricultural regions worldwide. The observed increases in frequency, duration, and intensity align with projections from climate models and are consistent with the broader understanding of climate change impacts on extreme weather (Clarke et al., 2022; Barriopedro et al., 2023). The synergistic nature of these compound events, where heat exacerbates drought conditions and vice-versa, leads to amplified impacts on agricultural systems (Yin et al., 2023; Wang et al., 2022). This intensification poses a direct threat to crop yields, potentially leading to significant economic losses and compromising food security, as evidenced by recent events in China (Xu et al., 2024) and the documented impacts on socio-ecosystems globally (Unknown, 2023).</p><p><h4>Mechanisms Driving Intensification</h4><p>The intensification observed in regions like the North American Great Plains and the European Breadbasket can be attributed to complex interactions between global warming and regional climate dynamics. Increased sea surface temperatures, altered atmospheric circulation patterns (e.g., changes in jet stream behaviour), and feedback mechanisms such as reduced soil moisture leading to higher surface temperatures (Dirmeyer et al., 2021) likely contribute to the formation of more persistent and severe heatwaves and droughts. The spatio-temporal shifts, such as the poleward migration of high-risk areas, suggest a reshaping of climate zones and agricultural suitability, necessitating adaptive measures that consider these dynamic changes (Couëdel et al., 2021).</p></p><p><h4>Implications for Agriculture and Food Security</h4><p>The implications for global agriculture are profound. Extended periods of heat and water scarcity challenge crop physiology, reduce water availability for irrigation, and increase the risk of pest outbreaks. The increased variability and intensity of these events make agricultural planning and investment more precarious (Yin et al., 2023). Regions identified as hotspots of compound event activity require urgent attention for developing climate-resilient agricultural practices, including the adoption of drought-tolerant crop varieties, improved water management techniques, and diversified farming systems (Alam et al., 2013; Mahmoud & Gan, 2019). The observed shifts also imply that regions historically less exposed may face increasing risks in the future, requiring proactive planning.</p></p><p><h4>Comparison with Previous Studies and Limitations</h4><p>Our findings are broadly consistent with studies that have analyzed compound events in specific regions like China (Li et al., 2021; Xu et al., 2024) and drylands (Wang et al., 2022), as well as broader assessments of drought and heatwave variability (Klimavičius & Rimkus, 2024; Shahabfar & Eitzinger, 2013). However, this study provides a more comprehensive global perspective on the spatio-temporal dynamics of *compound* events and their intensification across major agricultural zones. Limitations include the reliance on reanalysis data, which have inherent uncertainties, and the definition of compound events, which can vary across studies (Bevacqua et al., 2021). Future research could benefit from incorporating higher-resolution climate model projections and a wider range of impact data to further refine risk assessments. Additionally, exploring the role of anthropogenic factors in driving these specific event types, beyond general warming, would be valuable (AghaKouchak et al., 2021).</p></p>
<h2>Conclusion</h2>
<p>This study provides critical insights into the intensification and spatio-temporal shifts of compound heatwave-drought events in major agricultural regions from 1950 to 2023. Our analysis confirms a significant and concerning trend towards more frequent, longer-lasting, and more intense co-occurrences of extreme heat and drought across agriculturally vital areas, particularly in the North American Great Plains and the European Breadbasket. The observed poleward and eastward shifts in the geographical distribution of these events signal a dynamic recalibration of climate risks, demanding adaptive responses that transcend historical patterns. These findings have direct implications for global food security, agricultural sustainability, and water resource management. The intensification of these compound hazards necessitates immediate and coordinated efforts in policy-making and agricultural practice to build resilience against escalating climate extremes. Further research into the underlying mechanisms and regional-specific impacts will be crucial for refining adaptation strategies and ensuring the long-term viability of agricultural systems in a changing climate. The identification of vulnerability hotspots underscores the need for targeted interventions to protect food production and livelihoods in the most exposed regions.</p>
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