Influencing Mechanism of Tidal Disasters on Locust Breeding Area Evolution in the Eastern Coastal Area of China during the Ming and Qing Dynasties

Abstract

Locust plagues and tidal disasters are primary natural hazards in China’s eastern coastal regions, yet their interrelationship remains unclear. This study, drawing on historical documents from the Ming and Qing dynasties (1368–1911 AD), focuses on Zhejiang Province and its Hangzhou Bay coastline, areas typically affected by tidal disasters. Employing advanced quantitative analysis and spatiotemporal models, the research aims to reveal the mechanisms behind tidal disasters and their impact on locust population dynamics. The findings indicate a limited spatiotemporal correlation between locust plagues and tidal or drought disasters but a significant association with flooding. The relationship between locust infestations and floods is notably strong in the unique geographical context of Hangzhou Bay’s northern shore. The ‘hydromarginal’ nature of the north coast creates an ideal habitat for locusts. This study pioneers in identifying flooding as a crucial mediator between tidal disasters and locust plagues, shedding light on the ‘typhoon-tidal-flood-locust’ disaster sequence and offering new insights into understanding and mitigating natural disasters in the region. In this study, we primarily employ a quantitative methodology, utilizing advanced data analysis and sophisticated spatiotemporal modeling to investigate the interplay between locust plagues and tidal disasters. Although some progress has been made in the study of historical natural disasters, systematic studies of the relationship between tidal floods and locust breeding sites along the east coast of China during the Ming and Qing dynasties are still scarce. This study fills this gap by employing advanced GIS and time series analysis techniques, combining traditional historical documentary studies with modern scientific methods and providing a new methodological approach to the analysis of historical disaster patterns.

1. Introduction

In this paper, we delve into the nuanced definitions of ‘natural disasters’ and ‘catastrophes,’ two terms frequently used interchangeably in natural hazard discourse but with distinct meanings. As elucidated by Yu Liangju and Ma Wantong, ‘natural disasters’ encompass events triggered by abnormal or extreme natural phenomena, resulting in life loss, property damage, and disruptions to ecosystems and socio-economic activities. On the other hand, ‘catastrophes’ refer to larger-scale events with profound environmental, economic, or social effects [1]. This study aims to clarify these terminologies for general understanding, focusing on their differences and impacts in natural hazard scenarios, particularly in the context of China’s eastern coastal region, historically affected by tide-related disasters and locust plagues.

The impact of global climate change on the geographical environment and ecosystems is becoming increasingly apparent, leading to a range of complex environmental and social problems [2]. In particular, the unique geographical features and ecological characteristics of China’s eastern coastal region, where the Asian–European continent meets the Pacific Ocean, are particularly sensitive to environmental change [3]. According to the literature, the region suffered from frequent tidal disasters during the Ming and Qing dynasties [4,5,6,7]. It also suffered from persistent locust plagues.

In recent years, the interaction between locust plagues and the aquatic environment has become a focus of research. According to Chen Yonglin, “water” is considered a key factor in locust plague control, providing favorable breeding and migration conditions for locusts in East Asia [8]. Ma Shijun’s pioneering classification of locust areas highlights the close relationship between locust plagues and the water environment [9]. Li Gang found that the historic locust plagues along the Jiangsu coast are closely linked to the distribution of lakes and rivers, a finding that underlines their obvious ‘water-bound’ character [10]. In addition, Kong Dongyan et al. showed how tidal disasters in the Ming and Qing dynasties affected locust plagues by changing the pattern of the water system and the hydrological environment [11]. The above studies show that although existing studies have confirmed the influence of the hydrological environment on locusts in East Asia [7,9,10,11,12,13], it is still controversial and unknown how the relationship between tidal disasters and locust infestation is specifically affected.

This study focuses on the relationship between tidal plagues and locust plagues during the Ming and Qing dynasties, aiming to reveal the interaction mechanism between the two and their impact on the eastern coastal region of China. By combining historical document analysis with modern scientific methods, this paper not only fills the research gap on the interaction between tidal plagues and locust plagues, but also aims to provide a more scientific disaster prevention and control strategy for the region. This study is important for understanding historical environmental–ecological interactions and for developing future strategies to cope with climate change.

2. Data and Methods

2.1. Research Data

2.1.1. Data Sources

As shown in Figure 1 and Figure 2, the research data come from a continuously constructed database of historical locust plagues in China, which filters historical records of tidal disasters, flood disasters, locust plagues, and drought events from 1368–1911 [14,15]. This paper selects the Zhejiang area, a high-incidence area for tidal disasters, and its coastal areas along Hangzhou Bay as the research subjects to build a database of historical disasters in Zhejiang. After pre-processing such as removing duplicate values, comparing ancient and modern place names, and converting administrative regions, data including the time of occurrence (year, season, and month), region, level, and disaster situation were extracted. This dataset encompasses many attributes, including the time (year, season, and month), the region where the disaster took place, the classification of the catastrophe, and its corresponding situation. The ultimate compilation included 322, 368, 2326, and 375 records of locust plagues, tidal disasters, floods, and droughts, respectively.

2.1.2. Data Pre-Processing

• The number of disasters.

The same disaster is regarded to be a disaster of the same sort occurring in the same year and on the same or subsequent days. When the same sort of disaster occurs in the same year but on different dates, it is recognized as a distinct incidence of the disaster. If the same sort of disaster happens in the same year and the time of occurrence is documented only in terms of months or seasons but not precise days, yet the occurrences are in nearby counties or no more than three counties away, then it is deemed to be the same disaster process.

• Spatial units.

Using the most stable county based on historical continuity as the fundamental spatial units [16,17], the data are quantitatively pre-processed according to pre-designed semantic measurement standards, and time sequences of disasters are then constructed.

• Level of locust outbreaks.

Based on the differences in vocabulary descriptions in the literature, the original record descriptions of locust plagues in Zhejiang were classified into three levels (

Table 1. Grade division standards of historical locust outbreaks [18].

Description	Locusts Occurred without Damage	Locusts/Slight Damage	Locusts/Reduce Half/Famine Appears/Delay the Tax	Serious Locusts/without Harvest/Heavy Agricultural Damage/Relieve the Tax
Local/one generation	I	II	II or III	III or IV
Local/two generations	/	II or III	III	III or IV
Local/many years	/	III	III or IV	IV
Regional/one or two generations	I or II	II or III	III or IV	IV
Regional/many years	II	III	III or IV	IV

Note: Northeast China usually has two outbreaks of locusts per year, one in summer and one in autumn. I for occurrences, II for interferences, III for hazards, and IV for disasters.

), level I occurrences, level II interferences, level III hazards, and level IV disasters, taking into account the duration, spread, and degree of damage and social impact.

• Index.

The disaster index used in this study is the cumulative number of years in which a given disaster occurs within a given 10-year period. The index is intended to quantify the frequency and persistence of disasters within each decadal period.

2.2. Methods

2.2.1. Time Series Analysis

Time series analysis attempts to analyze variations in trends, cycles, seasons, and magnitudes in the construction of disaster time series. This study largely takes on time series scales of one year or ten years. The trend changes are fitted using moving averages and polynomial trends. Using wavelet analysis, significant periods can be analyzed for periodic fluctuations.

2.2.2. Spatial Analysis

Utilizing robust spatial analysis capabilities in ArcGIS 10.2, we perform a spatial analysis of various disasters including flooding, waterlogging, locust plagues, and drought. This reveals the areas characterized by high and low risks of these disasters and investigates the correlation between the distribution of locust plagues and hydrographic systems, tidal disasters, and droughts.

Additionally, the utilization of kernel density analysis is implemented. This study abstracts locust plagues that took place within a particular county during a specific year as points. The approach was employed to describe the spatial distribution of locust plagues in Zhejiang. The identification of areas that are prone to locust plague is followed by the implementation of a comparative spatial analysis. And according to events of flood, drought, locust, and tidal disasters for each county in Zhejiang, they are classified into five levels using the natural break approach, with the highest level reflecting greatly high-risk disaster areas.

3. Results

This study shows the temporal and spatial distribution characteristics of locust plagues in Zhejiang during the Ming and Qing dynasties. Based on different locust regions, a quantitative analysis of locust disasters, droughts, and waterlogging was conducted, especially regarding the year, month, and scale of the locust disasters. The correlation between tidal disasters and locust outbreaks is also discussed.

3.1. Temporal Dynamics of Locust Plagues

3.1.1. Month Distribution of Locust Plagues

In the Ming and Qing dynasties, the locust plague in Zhejiang showed noticeable monthly distribution features (Figure 3), with a high concentration from June to August, a peak in June, and a total of 30 occurrences. The locusts were more concentrated between June and August, with a total of 78 locust plagues, accounting for 70.2%. Locust plagues occur in all seasons but are predominantly concentrated in summer and autumn, which constitute 79.27 percent. The most significant concentration of locusts occurred in the summer with 78 outbreaks and 59.4% of the year’s locusts. Further examination of the summer and autumn locusts in Zhejiang throughout the Ming and Qing dynasties revealed that summer locusts made up 36% of the locusts. By contrast, autumn locusts accounted for 64%, suggesting that the seasonal distribution of locusts in Zhejiang during the Ming and Qing dynasties was dominated by autumn locusts (Figure 4).

Therefore, during the Ming and Qing dynasties, the incidence of locusts in Zhejiang had a particular monthly distribution, with a high concentration from June to August, while June was the most plentiful month. The seasonal distribution of locusts was dominated by summer and autumn locusts, the summer locusts being the most prevalent.

3.1.2. Level Patterns of Locust Plagues

According to the distribution of locust plague levels (Figure 5), it can be seen that in Zhejiang throughout the Ming and Qing dynasties, counties affected by level I, level II, and level III locust plagues accounted for 18%, 45%, and 37% of the total number of counties, respectively. The bulk of the affected counties were in level II and level III. The incidence of locust plagues exhibited various temporal patterns. In Stage I (1368–1525 CE) of the Ming and Qing dynasties, there was a low occurrence of locust plagues during the early Ming dynasty. In Stage II (1526–1559 CE), the middle to late Ming period had an increased incidence of locust plagues. In Stage III (1560–1634 CE), the late Ming dynasty was characterized by a high frequency of locust plagues. In Stage IV (1635–1717 CE), the late Ming and early Qing periods had a high incidence of locust plagues. In Stage V (1718–1804 CE), the mid Qing dynasty was distinguished by a high frequency of locust plagues lower than the last. In Stage VI (1805–1911 CE), the late Qing dynasty saw an extremely high level of locust plagues. Significant variances were observed in the occurrence periods of locust plagues among different levels. Large and medium-sized locust plagues were more common during the Ming and Qing dynasties., while hazard locust plagues were particularly prevalent in the early Qing dynasties (1616–1641 CE) and the late Qing dynasties (1805–1911 CE). The level of locust plagues rapidly escalated in the years 1540 CE, 1670 CE, and 1837 CE.

Locust plagues during the Ming and Qing dynasties showed significant historical patterns and ranges in hazards. Stage II (1526–1559 CE) of the locust plagues, which occurred in the middle to late Ming dynasty, was characterized by a high incidence rate. At Stage IV, the late Ming and early Qing (1635–1714 CE) and the late Qing (1805–1911 CE) periods saw an increase in the frequency of hazard locust plagues.

3.1.3. Trend, Phase, and Cyclical Characteristics of Locust Plagues

The “10-year locust index” (the number of years with locusts in 10 consecutive years) and the “10-year locust frequency” (the sum of the number of locusts in each of the 10-years) are used to depict long-term patterns in locust plagues, usually from 0–9 years. The analysis spans from 1370 to 1910 CE, as it provides an in-depth representation of the period (Figure 6). The “10-year locust index” and “10-year locust frequency” show a positive correlation, indicating that as the “10-year locust index” increases, so does the “10-year locust frequency”. Both the “10-year locust frequency” and the “10-year locust index” exhibit a gradual and fluctuating rising trend.

The frequency of locust plagues (Figure 6) demonstrates the significant currency of locust plagues across several time periods, specifically in the years 1520 CE, 1540 CE, 1630 CE, 1670 CE, 1730 CE, 1750 CE, 1850 CE, and 1870 CE.

Figure 7 illustrates the locust index series for Zhejiang from 1368–1911 CE. The average value of this index in the Ming and Qing dynasties is 0.81, while the highest recorded value of 21 occurred in the late Ming dynasty in the year 1540. The sixth-order polynomial demonstrates the presence of distinct fluctuations within the entire series. Specifically, the 10-year moving average exhibits a pattern characterized by “one peak and three hills”. Notably, the period of the Ming and Qing dynasties in Zhejiang represents the most prevalent period of locust plagues, as evidenced by the reigns of various Ming and Qing emperors. The period from 1539–1542 CE, known as the Jiajing period, was marked by a border conflict with Mongolia, signifying a significant phase in the middle and late Ming dynasty. Additionally, the “three peaks” of historical significance occurred during the years 1638–1642 CE (Chongzhen period), 1671 to 1672 CE (Kangxi period), and 1851 to 1859 CE (Xianfeng period). These peaks corresponded to events such as the peasant revolt at the end of the Ming dynasty, the preparation for the Three Feudatories Rebellion, the Taiping Rebellion, and the Second Opium War, respectively.

The locust plagues in Zhejiang throughout the Ming and Qing dynasties fluctuated from 1368–1911 CE. The occurrence of locust plagues followed a specific pattern, characterized by a single peak between 1539 and 1542 CE and three distinct periods of elevated locust plagues during 1638–1642 CE, 1671–1672 CE, and 1851–1859 CE.

Figure 8 shows an analysis of variance (ANOVA) of the decadal locust outbreak data recorded in Zhejiang Province between 1638 and 1911 using the continuous wavelet transform technique, showing variation at different time scales. This analysis highlights significant peaks in the 160-year and 230-year cycles, with the higher significance of the 160-year cycle suggesting that it is the dominant cycle of change and that this periodic oscillation reflects the dominant pattern of change in locust activity in this time series. The relatively long 230-year cycle is recognized as a secondary cycle of change. The shorter cycles have a duration of about 50 years. These cycle intervals indicate the cyclical fluctuations of locust plagues in Zhejiang during the Ming and Qing dynasties, which occurred mainly about every 160 and 230 years, while these long cycle intervals were interspersed with shorter fluctuation cycles of about 50 years.

3.2. Spatial Distribution of Locust Plagues

3.2.1. Spatial Distribution of Locust Plagues on the County

Based on the complete research presented in Figure 9, it is apparent that the northern coast of Hangzhou Bay, particularly the Hangjiahu Plain, situated above the latitude of 31° N, constitutes a significant proportion of 67.7% (218 out of 322 cases) of the locust plagues in Zhejiang. The locust plagues exhibited a significantly clustered distribution within the northern coastal area of Hangzhou Bay. The spatial distribution of locust plagues displays notable spatial disparities in frequency. The region with the most severe locust plagues is the northern coast of Hangzhou Bay. In the southern coastal areas, the Ningshao Plain’s elevated topography contributes to a comparatively lower occurrence of waterlogging when compared to that of the Hangjiahu Plain. Moreover, the southern plain indicates a somewhat reduced expanse, encompassing a smaller agricultural cultivation area, thus leading to a diminished occurrence of locust plagues in comparison to that of the Hangjiahu Plain. The middle and southern areas of Zhejiang, which are predominantly mountainous and hilly, exhibit an inadequate ecological habitat for the proliferation of locusts. Consequently, the occurrence of locust outbreaks tends to be less common as the distance between the locust plague source and the affected area increases.

Therefore, it can be shown that the prevalence of locust plagues in Zhejiang between the Ming and Qing dynasties displayed notable spatial variations. The Hangjiahu Plain, situated on the northern coast of Hangzhou Bay, exhibited a higher incidence of locust plagues compared to the Ningshao Plain on the southern coast and the steep terrains of the middle and southern areas, where the frequency of locust outbreaks was relatively lower.

3.2.2. Spatial Dynamics of Locust Breeding Areas

From the analysis presented in Figure 10, it can be observed that there is a high correlation between the spatial distribution of high-incidence locust plague areas and areas with high rates of tidal disasters, floods, and droughts. This correspondence suggests that the formation of disasters in the coastal area of Hangzhou Bay, situated in the transitional zone between northern and southern China, is characterized by a complex and erratic environment. The concentration of tidal disasters and waterlogging disasters has a significant connection to the trumpet-shaped Hangzhou Bay and the adjacent coastal plains, including the Hangjiahu Plain and Ningshao Plain. All areas along the shore of Zhejiang are classified as coastal locust breeding areas. The Hangzhou-Jiaxing-Hu Plain, situated on the northern shore of Hangzhou Bay, possesses a distinctive geographical setting. It is characterized by its adjacency to a lake, a river, and the sea, as well as its low-lying topography, which makes it an ideal habitat for locust breeding. Similarly, Huzhou, located on the southern shore of Taihu Lake, also falls within the low-lying lakeside area conducive to locust breeding. The regions of Jiaxing and eastern Hangzhou, situated along the northern coastline of Hangzhou Bay, are characterized as coastal locust breeding areas. The Tianmu Mountain, oriented northeast-to-southwest, exhibits a notable influence on precipitation patterns. Specifically, the eastern side of the mountain, characterized by low elevation and inadequate drainage, gives rise to an area prone to flooding, commonly referred to as a waterlogged locust breeding area. The western area of Hangzhou is characterized by its susceptibility to river flooding and locust plagues.

Thus, Zhejiang can be classified into four distinct locust breeding areas. The Hangjiahu Plain, situated on the northern coast of Hangzhou Bay, is characterized by its low elevation and proximity to the lake, river, and sea. This area has a diverse distribution of locust breeding areas.

4. Effects of Tidal Disasters, Flooding, and Droughts on Locust Plagues

4.1. Time Dimension Effects and Correlations

From the analysis of Figure 11 and

Table 2. Correlation analysis of locust plagues, tidal disasters, floods, and droughts in Zhejiang during the Ming and Qing dynasties, 1368–1911.

Disaster Comparison	Tidal Disasters Index	Floods Index	Drought Index
10-year scale locust index	−0.100	0.451 **	0.488 **

Note: ** Significant at 0.01 level.

, it can be observed that in Zhejiang during the Ming and Qing dynasties (1368–1911 AD), which spanned 544 years, locust plagues occurred in 131 of those years, accounting for approximately 24.01% of the time. During the Ming dynasty, locust plagues were recorded for 54 years, approximately 19.5% of the era, while in the Qing dynasty, they were recorded for 77 years, about 28.83% of the time, indicating a higher incidence of locust plagues in the latter period. The correlation analysis revealed a very weak association between locust plagues and tidal disasters with a correlation coefficient of −0.100, indicating a negligible relationship. In contrast, the correlation coefficient with floods is 0.451, suggesting a more substantial connection. Waterlogging disasters have been identified as a significant contributing factor to locust plagues, serving as a mediator through which the effects of locust plagues are seen. Notably, for the years of drought, which accounted for 29.6% of the period, the correlation coefficient with locust plagues is 0.488, signifying a moderate-to-strong relationship, which is statistically significant at the 0.01 level.

Therefore, the frequency of locust plagues in the Zhejiang region in the Qing dynasty was higher than that in the Ming dynasty; locust plague incidence in the Zhejiang region in the Ming and Qing dynasties was closely related to flood disaster, but the correlation with tidal plague was weaker, and there was some correlation with drought disaster.

This is known from the analysis of Figure 12 and

Table 3. Mann–Kendall trend analysis of locusts, tidal disasters, floods, and droughts in Zhejiang during the Ming and Qing dynasties, 1368–1911.

Period	Locust Plague (Tau/p-Value)	Tidal Disaster (Tau/p-Value)	Drought (Tau/p-Value)	Flooding (Tau/p-Value)
1368–1524	0.098/0.134	0.032/0.626	0.285/0.0000136	0.066/0.313
1525–1736	Not Significant	Not Significant	Not Significant	Not Significant
1737–1775	Not Significant	Not Significant	Not Significant	Not Significant
1776–1891	Not Significant	Not Significant	Not Significant	0.190 / 0.0129
1892–1911	Not Significant	Not Significant	Not Significant	Not Significant

:

First period (1368–1524): During this period, neither locust plagues, tidal disasters, nor floods showed statistically significant trends, suggesting that the occurrence of these plagues may have been part of natural variability rather than a clear upward or downward trend. However, droughts showed a significant upward trend, which may indicate some early signs of climate change during this period. Second period (1525–1736): The Mann–Kendall trend test found no statistically significant trend for any of the hazard types, although the observed data showed an increase in the frequency of the four hazards in the same year. This may indicate that although there was an increase in the volatility of disaster frequency, it did not rise to the level of a significant change in trend. Third period (1737–1775): There was no significant trend in the frequency of any of the disaster types during this period, suggesting that a period of relatively calm climate cycles or effective disaster management strategies may have played a role in reducing the frequency of disasters. Fourth period (1776–1891): During this period, only floods showed a statistically significant upward trend, suggesting a significant increase in the frequency of floods in the mid-to-late Qing period, which may be related to climate change or geographical shifts during this period. For locust plagues, tidal disasters, droughts and floods, the Mann–Kendall trend test showed no significant trend change. Fifth period (1892–1911): At the end of the Ming and Qing dynasties, the occurrence of all types of disaster showed no significant trend. This may reflect the fact that changes in environmental or socio-economic factors played a positive role in reducing the frequency of disasters at the end of this period. During the Ming and Qing dynasties, the variety of natural calamities in Zhejiang and their frequency fluctuated. Especially during the late Ming and early Qing dynasties, as well as the middle and late Qing dynasty, events like locust plagues, tidal disasters, floods, and droughts occurred with relatively high frequency. However, the correlation between locust plagues and floods was more pronounced than with tidal disasters and droughts.

4.2. Spatial Dimension Effects and Correlations

Based on Figure 13’s spatial superposition, the kernel density map is categorized into five distinct regions, each reflecting unique disaster frequencies and patterns:

The Hangzhou-Jiaxing-Huzhou plain, notably, the southern shore of Taihu Lake and Jiaxing, experiences a high incidence of floods, droughts, locust plagues, and tidal disasters (level 5), with these events being widespread and consistent.

The Ningshao Plain has a lower overall susceptibility to natural hazards, yet Ningbo is particularly drought-prone (level 5). Floods, locust plagues, and tidal disasters increase in frequency from Shaoxing to Ningbo. The plain’s low elevation, coupled with estuarine tidal disasters, results in flooding, underlining a definitive causal link with tidal events, which also foster conditions conducive to locust breeding.

The lower Jiaojiang River in Taizhou is not commonly affected by natural disasters, with only its lower stretches being highly sensitive to drought (level 5). These areas are impacted by floods, locusts, and tidal disasters.

In the Jinqu Basin, notably, Jinhua, droughts occur with significant regularity (level 5), while floods and locusts appear in an ‘island-like’ distribution.

The coastal region of Wenzhou sporadically faces tsunamis, floods, locust plagues, and droughts with a scattered presence.

Furthermore, the study delves into Hangzhou Bay’s geographical traits and their impact on locust breeding, particularly concerning tidal disasters and flooding. The low-lying Hangjiahu Plain is especially vulnerable to these disasters, which, while beneficial for agriculture, also amplify the adverse effects on farming and ecosystems. Significant correlations between flooding and locust breeding cycles, particularly on the Hangjiahu Plain, support prior time series analysis outcomes. Locust plagues along the Zhejiang coast may be incited by riverine floods and hydrological shifts ensuing from typhoon-induced storm surges.

4.3. Comprehensive Impact Mechanism

In the previous section, we analyzed in detail the increase in the frequency of tidal disasters and floods and the spatial and temporal distribution of locust plague activity in Zhejiang. We particularly demonstrated the correlations between typhoons, tidal disasters, floods, and locust plague outbreaks through temporal analyses.

Based on these findings, this section further explores the geographical features of Hangzhou Bay and their interaction with the breeding patterns of locust plagues as well as the incidence of tidal disasters and floods. The Hangjiahu Plain, located on the northern shore of Hangzhou Bay, features a wider, flatter topography and more low-lying landscapes than the southern shore (Ningshao Plain). This increases its susceptibility to tidal disaster flooding. Additionally, the dense river network and proximity to Taihu Lake make the region highly suitable for agriculture, but also amplify the impact of tidal disasters and flooding on agriculture and ecosystems.

These characteristics resonate with our previous analysis of locust plague activity patterns, showing a direct impact of tidal disaster flooding on locust breeding cycles. Our study found that tidal disaster flooding creates a favorable environment for locust plague breeding, especially in low-lying areas like the Hangjiahu Plain. There is a significant correlation between flooded areas and the occurrence of locust plague infestations, further supporting the conclusions of our previous time series analysis.

Compared to the spatial relationship between tidal disasters, flooding, and droughts, the relationship between flooding and locust plague infestations is more evident. Locust-prone areas along the Zhejiang coast showed significant spatial and temporal correlations. Typhoons lead to storm surges, causing river flooding, lake overflow, and waterlogging. These factors together result in severe water-related disasters, affecting the hydrological conditions of wetland rivers and leading to environmental changes in coastal areas, floodplains, lake shores, and waterlogged areas. These changes potentially impact locust plague outbreaks.

Taken together, our study indicates that tidal disaster flooding influences the establishment and development of locust plague breeding sites by altering the dynamics of the water system. This ultimately affects locust plague outbreaks. These comprehensive analyses deepen our understanding of the interaction mechanism between tidal flooding and locust plagues outbreaks in the Hangzhou Bay area. This provides an important scientific basis for the prevention and management of related disasters in the future.

5. Discussion

This study combed in detail the locust plagues in Zhejiang from 1368–1911 CE, especially the temporal and spatial evolution of locust plagues, and revealed their temporal and spatial connections with related disasters.

This study found that locust plagues are related to the southeast monsoon activity. The locust plagues are highly concentrated in the summer half-year from April to September, and the seasonal distribution is mainly across summer and autumn. The main locust plague levels were secondary and tertiary, consistent with the findings of other studies [12,19,20,21]. The northern coast of Hangzhou Bay (Hangzhou-Jiaxing-Hu Plain), which is low-lying and adjacent to lakes, rivers, and the sea, is a major breeding area for locusts, and all four types of locust breeding areas are distributed there. The locust breeding areas are characterized by their “hydrophilic characteristics” nature, consistent with the findings of other studies [8,10,13,19,22,23,24,25]. Zhejiang and Anhui during the Qing dynasty locust plagues were closely related to the year when the waterlogging disaster occurred, consistent with the findings of other studies [18]. The locust plagues caused by waterlogging caused by typhoon storm surges were consistent with the study results of Kong et al. [11]. In terms of spatial distribution, the high frequency of tidal disasters, waterlogging disasters, and drought was highly concentrated along Hangzhou Bay, which is consistent with the results of Cao et al. [5].

These findings have improved our understanding of locust plagues and their interactions with other hazards and given us more information about the environmental factors behind their occurrence. But while we have made some important discoveries, many questions still require further research. For instance, a better understanding is needed of why there is a strong correlation between the years of occurrence of locust plagues and floods but a relatively weak correlation with tidal disasters and droughts. We also need to better understand the various environmental factors that influence the occurrence of hazards, such as locust plagues, and how these environmental factors can be modified to prevent or mitigate the effects of these hazards.

The aforementioned studies hold substantial importance in facilitating an in-depth understanding of the occurrence of locust plagues in the locust-prone region along the eastern coast of China. Through a thorough investigation and comprehensive analysis of the relationship between locust plagues and occurrences of tidal, flood, and drought events, we have successfully developed a theoretical framework for understanding the interconnectedness of these phenomena. Our research has yielded significant findings and insights into the mechanisms underlying the development of the vicious circle between tidal disaster and floods, droughts, and locust plagues. Nevertheless, it is imperative to acknowledge that numerous unresolved matters exist that necessitate additional detailed investigation. For instance, it is imperative to enhance the awareness of the underlying factors contributing to the robust association shown between the temporal occurrences of locust plagues and waterlogging, while comparatively weaker associations are observed with tidal and drought-related disasters. Furthermore, it is imperative to use a more thorough approach when examining the diverse environmental elements that contribute to the occurrence of locust plagues and other disasters. This will enable a more profound analysis of their reaction mechanisms and subsequent impacts.

There are, however, certain limitations to our study. In particular, in terms of statistical analysis, we relied mainly on historical documentary records, which to some extent limits the application of traditional statistical methods. Future studies have the potential to delve into the intricate dynamics of tidal disasters and their impact on hydrographic environments and ecosystems. This can be achieved through the utilization of simulation experiments and field surveys. By doing so, a more integrated understanding of the interconnections between tidal disasters, water environments, ecosystems, and locust plagues can be attained. Furthermore, the integration of data from several disciplines, like meteorology, hydrology, and geology, can provide a more comprehensive understanding of the intricate processes that contribute to a given phenomenon. This research will enhance our comprehension of the mechanisms behind the occurrence of locust plagues in coastal areas and offer scientific backing for the formulation of more accurate methods for prevention and management. In summary, the findings of this research offer valuable perspectives and recommendations for the continued investigation of the interconnectedness between locust plagues and different disasters, alongside their ramifications on the natural ecosystem and human culture.

6. Conclusions

Through careful analysis of historical documents, this study focuses specifically on the locust plague and its complex interactions with tidal disasters, floods, and droughts in the eastern coastal region of China between 1368 and 1911. This study not only reveals the temporal and spatial dynamics of these disasters, but also probes deeply into the underlying environmental factors, providing us with profound insights into the occurrence and development of historical disasters.

Key findings and their important implications:

Revealing temporal dynamics: This study accurately identifies the seasonal pattern of the locust plague at different historical stages, especially during the high-incidence period from June to August in the Zhejiang region. The discovery of this pattern not only demonstrates the important role of natural environmental factors in the occurrence of locust plagues in historical periods, but also provides a new perspective for understanding the long-term development trend and cyclical changes of natural disasters.

In-depth spatial distribution analysis: This study thoroughly investigated the spatial distribution characteristics of locust plagues, especially the concentration trend on the north coast of Hangzhou Bay. This analysis not only highlights the influence of geographical factors on the distribution of locust breeding, but also reveals the complex spatial relationship between locust plague and other types of disasters, highlighting the crucial role of environmental factors in disaster formation.

Importance of innovative findings: This study reveals for the first time a new mechanism by which tidal disasters indirectly affect locust reproduction by altering the water system. This groundbreaking discovery not only provides a profound new perspective on the environmental contextual analysis of historical disasters, but also offers important insights for addressing the current ecological challenges facing the globe.

In addition, this study highlights the critical role of historical data in predicting and managing modern disaster risks and points the way to future research directions in environmental and disaster management.

These important findings from this study not only deepen our understanding of historical natural hazards, but also provide valuable guidance for future environmental policymaking and disaster prevention, highlighting the significant value of historical research in modern applications.