Download 12 - Chinese Academy of Sciences

BCAS
Vol.23 No.4 2009
Impacts of Climate Change
on Locust Outbreaks in
China’s History
YU Ge
(Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences,
Nanjing 210008, China)
Global warming is causing the climate to change,
lakes to dry up and less rain to fall. In population
ecology, researchers have found that climate change
plays an important role in controlling the size of species
populations. To proof this model, long-term observational
data are crucial, making researchers to turn to historical
records of locust outbreaks. [1]
The locust is one of the most serious pests to
Gramineae plants, one major family of popular Chinese
foods of cereal, wheat, corn, and rice. Its outbreaks in
history greatly decreased China’s crop output, causing
serious food shortages and famines. This was widely
documented in detail in historical literature. The earliest
record could be found in The Book of Songs, a book
already in circulation in East-Zhou Dynasty (770–476
B.C.), which introduced methods of building bonfires to
lure locusts to their death and burning grass to destroy
their eggs on farmlands. Emperor Fu Jian (338–385 A.D.)
sent thousands of his soldiers to assist locals in erasing
locusts in Yellow River regions in 382 A.D., which was
taken down in History as a Mirror (published during
1019–1086 A.D.), the first historical annals in China.
Yu Ge, received her PhD from the Department of Quaternary Geology, Lund University
in 1996. Now she is a research professor with the Nanjing Institute of Geography and
Limnology, Chinese Academy of Sciences. Her research focuses on physical geography,
geomorphology, Quaternary geology, lacustrine sedimentology, polynology and
paleoclimate simulations. She had taken charge of international research projects in
these fields with support from the US National Oceanic and Atmospheric Administration,
the EU framework program, the Max Planck Society, and the Environment Canada; and
has chaired research programs from the Chinese Academy of Sciences and the National
Natural Science Foundation of China.
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Bulletin of the Chinese Academy of Sciences
Vol.23 No.4 2009
As locust outbreaks caused serious food shortages and
threatened the stabilization of political power, likely “long
years of locust outbreaks caused the peasant uprising and
the destruction of West-Han Dynasty” (recorded in History
of East-Han Dynasty, a book published circa 25–220 A.D),
the first law of locust control in China was issued in 1075
A.D. and the second in 1182 A.D. by emperors of NorthSong Dynasty (960–1127 A.D.). There have been special
books describing the locust ecology and control methods,
for example, Methods of Locust Capture in 1193 A.D.
and Complete Methods of Locust Control in 1857 A.D.
According to historical records, there were 796 disastrous
locust outbreaks between 707 B.C. and 1935 A.D., during
which smaller locust outbreaks occurred once every 2–3
years and severe outbreaks every 7–8 years.
The locusts are mostly born and grow in floodplains,
lake overbanks, swamps, and coastal lowlands in eastern
China. These places become dry lands when water levels
and rainfalls are low and they are submerged when water
levels and rainfalls are high. “Lake drying helps locust
multiply and triggers its outbreaks,” notes An Agricultural
Encyclopedia of Ming Dynasty (1562–1633 A.D.); “changes
to low water levels in ponds, lakes and rivers lead to rapid
locust growth,” reads Complete Methods of Locust Control;
and “rainstorms in spring and summer could cause locust
dying,” observes History of Song Dynasty (circa 960–1127
A.D.). These documents reflect the facts that locust eggs
are multiplied in wet soil but not in a fully submerged
place, and locust migration and dispersal need dry
conditions, as rainfall restrains wing vibration and flight.
Modern bioecology studies have proven that the best soil
for a locust to lay its eggs is the soil with water content of
10–20%, where the eggs could reach to 200,000–400,000
grain/m2 [2]. As a locust egg needs 5–10 days to develop,
submergence for 15 days continuously can drown 100%
of them. Therefore, in terms of bioecology, the lake/river/
coast lands above water level are favorable places for
locusts to develop, while spring and summer dry conditions
lead to locust outbreaks.
Research into the question whether the locust
outbreak variability is consistent with climatic change
has been undertaken in China. Many studies indicated
that, on the basis of the records of the past 50 years,
a warm winter year, (higher January temperature
Opinions
Map of study areas and information for locust and climate
data. (a) The middle-lower reaches of Yellow River (N. region)
are marked by a light-blue area for the GCM grid boxes and
blue dots for the climate gauging stations. (b) The middlelower reaches of Yangtze River (S. region) are marked by light
pink for the GCM grid boxes and red pluses for the climate
gauging stations. Annual index of locust outbreaks during the
past 1000 years for the (c) N. region and (d) S. region, in which
coarse lines are 10-year mean series.
Comparisons of fast Fourier transform spectral power
spectrum of 10-year mean locust index series and proxy
temperature time series in N. region (a) and S. region (b).
than average) and a warm-summer -half year (higher
April–September temperatures than average), and a drysummer-half year (lower April–August precipitation
than average), normally lead to locust outbreaks in
eastern China [3, 4]. Locust outbreaks with relationship
to past climate changes were studied, and found a basis
for linkage of locust outbreaks with warm and drought
climate in Chinese history.
To probe if greenhouse-effected climate warming
strengthens severe locust outbreaks that would cause
continental-scale crop failures in China, we studied their
statistical relationships in history and examined the impacts
of climate change on the long-term locust outbreaks [4].
Analysis of Chinese historical records stretching back for
over a thousand years shows that locust outbreaks are more
likely to occur in warmer and drier weather.
Bulletin of the Chinese Academy of Sciences
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BCAS
Vol.23 No.4 2009
According to the analysis for interannual time
Table1. Aanalysis of strength of locust outbreaks over several
periods of the past 1000 years.
series during the past 100 years, the most severe
locust outbreak years were in the warm-dry years
Strength>90th percentile
Strength>70th percentile
year (AD)
locust index
locust index
with warm-dry summers and warm-wet winters in the
N. region
S. region
N. region
S. region
Yellow River–Haihe River region, northern China,
1000-1250
20%
32%
12%
24%
and warm-wet years with warm-wet springs in the
16%
36%
12%
16%
1250-1500
Yangtze River–Huihe River region, southern China.
44%
36%
28%
32%
1500-1750
Checking wavelet-analyzed variance series, these
45%
15%
35%
10%
1750-1950
interannual time scale synchronous changes with 2–10
1850-1950
60%
30%
50%
20%
periodicity years were 58–60% among the total locust
outbreak years of the past 1000 years.
so as to suggest that greenhouse-effected climate warming
Locust outbreak correlation analysis with decadal
would increase the severe locust outbreaks in the area.
time scale temperature proxy and general circulation
Climate change may increase the frequency of locust
model–simulated climate during the past 1,000 years
plagues in China. The results ring an alarm bell for yet
shows significant correlations in warm-winter-half years
another serious consequence of climate change, which is
and in warm-dry May–June and annual means in the
an important contribution to our understanding of climate
northern region (p < 0.05), where p is probability, and
impact on locust plagues, and will help to devise mitigation
in warm years and warm-dry August–September years
strategies in response to global warming. Given that China
in the southern region (p < 0.10), while these decadal
is the largest agricultural nation in the world, the findings
time scale synchronous changes with 20–110 periodicity
hint at a looming threat that needs to be addressed to ensure
years were 56–65% of the total locust outbreak years
global food security [5].
of the past 1000 years. Historical records on “drought
Acknowledgements: Financial support for this
locust” were true, as we found that the drought of springwork was provided by Key Directional Program of the
summer season in the northern region caused the highest
Knowledge-innovation Project of the Chinese Academy
regional locust outbreaks, but it is not a sensitive factor for
of Sciences: High-resolution lake records and the
locust outbreaks in the wet-humid Yangtze River region.
environmental hydrology simulations during the past 3,000
Although warm winter condition is a key factor for locust
years in China (KZCX2-YW-338-2).
egg survival and preservation, it works well when winter
n
temperatures reach to -10° to -30°C in the northern region
but is not a limiting factor for locust survival in the warm
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Highlights
frequency of locust outbreaks over the past 1,000 years,
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Bulletin of the Chinese Academy of Sciences