Periodic temperature-associated drought/flood drives locust plagues in China

Abstract

Global warming is currently of great concern. Yet the ecological effects of low-frequency climate variations remain largely unknown. Recent analyses of interdecadal variability in population abundance of the Oriental migratory locust (Locusta migratoria manilensis) in China have revealed negative associations with temperature and positive associations with Yangtze drought and flood frequencies during the past millennium (AD 957-1956). In order to shed new light on the causal relationships between locust abundance, floods, droughts and temperature in ancient China, we used wavelet analysis to explore how the coherencies between the different variables at different frequencies have been changed during the past millennium. We find consistent in-phase coherencies between locusts and drought/flood frequencies, and out-of-phase coherencies between locusts and temperature and between drought/flood and temperature at period components of 160-170 years. Similar results are obtained when historical data of drought/flood frequencies of the Yangtze Delta region are used, despite flood data showing a weak and somewhat inconsistent association with other factors. We suggest that previously unreported periodic cooling of 160-170-year intervals dominate climatic variability in China through the past millennium, the cooling events promoting locust plagues by enhancing temperature-associated drought/flood events. Our results signify a rare example of possible benign effects of global warming on the regional risk of natural disasters such as flood/drought events and outbreaks of pest insects.

Temperature and precipitation in Northeast China during the last 150 years: relationship to large-scale climatic variability

“…In agreement with these authors, Stige et al (2007) and Zhang et al (2009), in studies concerning the abundance of the oriental migratory locust Locusta migratoria manilensis (recorded in China for over 1000 years) in relation to temperature and precipitation reconstructions from 957-1956 AD, list oscillations of about 40-and 70-year-long periods, resulting from spectral analysis of temperature series, and an oscillation of an about 20-30-year-long period in precipitation. They also detect a longer, almost bicentennial variation in temperature.…”

Periodic climate cooling enhanced natural disasters and wars in China during AD 10–1900

“…Our findings provide quantitative evidence about climate-driven agricultural breakdown owing to droughts and locusts increasing the frequency of internal wars. Droughts have been well recognized as the positive effect on locust plagues in China because they produce favourable wet bank or lake beach environments for locusts to lay eggs (Stige et al 2007;Zhang et al 2009). The positive effect of low temperature on locust plague is obviously indirect through increase of temperature-induced droughts.…”

“…Drought, flood and locust plague have been regarded as the three major natural disasters affecting crop production in ancient China (Zhang et al 2009), suggesting that their detrimental effects on agricultural production may trigger internal uprisings. In the cold period of AD 1840 -1890, agricultural yields in China were reduced by 10 to 25 per cent compared with the relatively warm period of AD 1730 -1770 (Gong et al 1996).…”

“…We focus on identifying associations of high levels of AW, EW or IW with these natural disasters. We have also used wavelet analysis (Cazelles et al 2008; see the electronic supplementary material) that appears suitable for investigating possible causal links of multiple variables within the overlapped coherency in frequency and time domains (Zhang et al 2009). Wavelet coherency analysis was used to identify the time period and the frequency of Periodic cooling increased wars Z.…”

“…A few recent studies have demonstrated that wars and social unrests in the past often were associated with cold climate phases (Zhang et al 2005(Zhang et al , 2007a. Climate cooling may have increased locust plagues through temperature-driven droughts or floods in ancient China (Stige et al 2007;Zhang et al 2009). Therefore, cool temperatures may directly or indirectly be detrimental to agriculture, and thus stimulate wars of rebellion within a dynasty (defined here as the 'internal war hypothesis'; see Zhang et al 2005Zhang et al , 2007a.…”