Reconstruction of a 1,910-y-long locust series reveals consistent associations with climate fluctuations in China

Abstract

It is becoming increasingly clear that global warming is taking place; however, its long-term effects on biological populations are largely unknown due to lack of long-term data. Here, we reconstructed a 1,910-y-long time series of outbreaks of Oriental migratory locusts (Locusta migratoria manilensis) in China, on the basis of information extracted from >8,000 historical documents. First by analyzing the most recent period with the best data quality using generalized additive models, we found statistically significant associations between the reconstructed locust abundance and indexes of precipitation and temperature at both annual (A.D. 1512-1911) and decadal (A.D. 1000-1900) scales: There were more locusts under dry and cold conditions and when locust abundance was high in the preceding year or decade. Second, by exploring locust-environment correlations using a 200-y moving window, we tested whether these associations also hold further back in time. The locust-precipitation correlation was found to hold at least as far back as to A.D. 500, supporting the robustness of this link as well as the quality of both reconstructions. The locust-temperature correlation was weaker and less consistent, which may reflect this link being indirect and thus more easily moderated by other factors. We anticipate that further analysis of this unique time series now available to the scientific community will continue to provide insights into biological consequences of climate change in the years to come.

Fig. 1.

(A) The locations of locust records (solid points) and research region (gray-lined polygon). (B) Annual locust index. (C) Decadal locust index. Dashed lines connect data points across periods with no locust reports.

Fig. 2.

Periodicity analysis for annual and decadal locust series: (Left) wavelet power spectra and (Right) global wavelet power spectra (estimations of the classical Fourier power spectra). (A) Annual data for A.D. 1512–1911; (B) decadal data for A.D. 1000–1910. In the wavelet power spectra, dark contour lines (and the red lines in their global wavelet power spectra) are the 95% confidence interval based on 2,000 Beta-Surrogate series, white lines materialize the maxima of the undulations of the wavelet power spectra, semitransparent cones indicate the regions influenced by edge effects, and the colors code for power values from dark blue (low values) to dark red (high values).

Fig. 3.

Regression analysis of the effects of climate on annual-scale locust dynamics. (A–C) Estimated effects of previous year locust index, dryness [“dryness”, Table 1; average of regional values ranging from 1 (very wet) to 5 (very dry)], and temperature (“temp.T”, Table 1, unit is °C) on locusts, respectively. Points: partial residuals. Shaded areas: 95% confidence bands. Residual diagnostics reveal no residual trend (D), approximate normal distribution of residuals (E; the quantile plot of residuals forms a nearly straight line), and no significant autocorrelation function (ACF) of residuals (F; autocorrelation marginally surpassed the 5% critical limits indicated by the dotted lines for one out of the 25 time lags considered (lag = 19 y), which is roughly as expected to arise from chance alone).

Fig. 4.

Regression analysis of effects of climate on decadal-scale locust dynamics. (A–C) The effects of previous decade's locust abundance, precipitation (Table 1, σ-unit), and temperature (“temp.Y”, Table 1; σ-unit), respectively, on decadal mean locust abundance. (D) Time series of residuals suggest that reconstructed locust abundance tended to be lower than predicted during the first centuries. (E) Residuals were approximately normally distributed. (F) Autocorrelation function of residuals (ACF) reveals significant positive autocorrelation at lag 3 decades.

Fig. 5.

(A–D) Correlations between the reconstructed locust index and decadal climate reconstructions using a 200-y moving window centered at the x-axis values. The precipitation index is available only from A.D. 500 onward.