possible solar forcing of late holocene mega-droughts in...
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Possible Solar Forcing of Late Holocene
Mega-Droughts in India
Ashish SinhaCalifornia State University Dominguez Hills
Kevin G. Cannariato, Lowell D. Stott, & Hongchun LiUniversity of Southern California
Hai Cheng & Larry EdwardsUniversity of Minnesota
Ramesh Rengaswamy & Madhusudan G. YadavaPhysical Research Laboratory, India
Indra-Bir Singh
Lucknow University, India
The Indian Monsoon is the Largest Global Hydrologic
Anomaly on Inter-Annual Timescales
The East Asian
Monsoon Regime
The Indian
Monsoon Regime
Has the Instrumental record captured the fullHas the Instrumental record captured the full
range of the Indian Monsoon Variability?range of the Indian Monsoon Variability?
How have the frequency and magnitude of droughts varied beforeHow have the frequency and magnitude of droughts varied before
the instrument record began?the instrument record began?
Is there a link between the Indian Monsoon rainfall and the SolarIs there a link between the Indian Monsoon rainfall and the Solar
Variability on decadal to centennial timescales?Variability on decadal to centennial timescales?
Droughts
MEAN RAINFALL = 870 mmFloods
Available Proxy Records of the Indian MonsoonAvailable Proxy Records of the Indian Monsoon
Most Marine and Lake sediment records (# 1-14) provide a historyMost Marine and Lake sediment records (# 1-14) provide a history
of long-term temporal changes (orbital to tectonic timescales).of long-term temporal changes (orbital to tectonic timescales).
Morill et al., 2003
Speleothems as Climate ProxySpeleothems as Climate Proxy
18O of dripwater
Cave Temp, Kinetic, Water-Rock interactions
Air Temp, Amount, Source, Evap, etc
negative higher rainfalllower rainfall positive 18Orain
Tropical and Monsoon
Regions
variations reflect mainly precipitation changes
18Ospeleothem
Dongge
Current Network of the Indian/Asian MonsoonCurrent Network of the Indian/Asian Monsoon
Speleothem RecordsSpeleothem Records
Hulu
Hoti & Qunf
(Oman) Dandak
(Current Study)
TimtaCherrapunji
Our Sites
Others
The Study Area: Dandak Cave, Central-Eastern India
Sub-Tropical Climate
with dense Teak Forests
Abundunt Rainfall
in Monsoon Months
Stalagmite DAN-D
collected at growth position
Speleothem Speleothem 1818O ResultsO Results
DAN CAVEDAN CAVE
Dandak
Bay of Bengal (BoB) Trajectoryof the Indian Monsoon
Modern ClimatologicalCharacteristics of the Study Area
0
100
200
300
400
J F M A M J J A S O N D
Mean Monthly Rainfall (mm)
(1910-1990)
MAT =25.5oC
18Omonsoon~ -3.0± 1.0
18Onon ~ 0
MAR =1530 mm
Dandak Cave
Suitability of the Cave SiteSuitability of the Cave Site
Local or Regional Precipitation Signal?Local or Regional Precipitation Signal?
Although considerableAlthough considerable
spatial and temporalspatial and temporal
variability exist in thevariability exist in the
ISM rainfall patternsISM rainfall patterns
over Indiaover India……..
Monsoon rainfallMonsoon rainfall
variability at Dandakvariability at Dandak
seems to be reflectiveseems to be reflective
of the overall strengthof the overall strength
of ISM because of itsof ISM because of its
location.location.
Bay of Bengal Branch of the Indian Monsoon
800
1000
1200
1400
1600
1800
800 1000 1200 1400 1600 1800
R= 0.70
All India Monsoon Rainfall (mm)
Da
nd
ak
Mo
ns
oo
n R
ain
fall
(m
m)
Th Age yr. B.P.
Dep
th (
mm
) fr
om
to
p
50
0 500 1000 1500
0
100
150
200
250
300
Th dating of
Stalagmite DAN-D
Variable Growth
Rate, ranging from
0.1 to 0.85 mm/year
Temporal
resolutions range
from <1 year
to ~ 10 years
?
Universal
Famine 879 AD
Great Famine
940-950 AD
11 year Famine
1148-1159 AD
1344-46 AD
Famine
Durga Devi Famine
1396-1407 AD
1661 AD Famine
Source: The Demography of Famines: An Indian Historical Perspective. Arup Maharatna, Oxford University Press, 1996
Theoretical and Observational Considerations
Suggest Rainfall Reduction of 15-30% Compared
to the Present - amounting to ‘Mega-Droughts’
< 1 yr. Resolution ~ 1 yr. Resolution
Durga Devi
1396-1407 AD
Longer intervals of more reduced rainfall during LIA
compared to MWP
Dongge
Is there a Sun-Monsoon Connection?Is there a Sun-Monsoon Connection?
Hoti & Qunf
(Oman) Dandak
(Current Study)
Recent Speleothem 18O Records from Oman and China
suggest the Sun-Monsoon Connection on multi-decadal timescales
2000 1500 1000 500
YEAR A.D.
Dis
tan
ce
Fro
m t
op
(cm
)
TunedAge
Sun-Monsoon Connection?Sun-Monsoon Connection?
Neff et al., 1999
Drier
Wetter
Speleothem 18O record from Hoti Cave, northern Oman
Coherent changes in the Indian monsoon ( 18O) and
solar variability ( 14C) on decadal to centennial timescales
Stronger
Sun
Weaker
Sun
on tuned age model
Sun-Monsoon Connection?Sun-Monsoon Connection?
Fleitmann et al., 2003
Coherent changes in the Indian monsoon ( 18O) and
solar variability ( 14C)on decadal to centennial timescales
r = 0.48
Speleothem 18O record from Qunf Cave, southern Oman
18O (on tuned age model)14C
SunSun––Monsoon Connection?Monsoon Connection?
Wang et al., 2005
Speleothem 18O record from Dongge Cave, southern China
Coherent changes in the East Asian monsoon ( 18O) and
solar variability ( 14C)on decadal to centennial timescales
18O (on tuned age model)14C
Dri
er
Wett
er
Weaker
Str
on
ger
ConclusionsConclusions
Our record suggests persistent failures in theOur record suggests persistent failures in the
Indian monsoon had occurred in the recent past.Indian monsoon had occurred in the recent past.
Compared to recent, some past episodes ofCompared to recent, some past episodes of
monsoon failures were of longer durations andmonsoon failures were of longer durations and
were significantly stronger (mega-droughts).were significantly stronger (mega-droughts).
If If 1414C is indeed a proxy of solar variability, ourC is indeed a proxy of solar variability, our
record (albeit, inconclusively) hints of a possiblerecord (albeit, inconclusively) hints of a possible
Solar Forcing of Indian Monsoon on multi-Solar Forcing of Indian Monsoon on multi-
decadal timescales.decadal timescales.
Residual 14C Versus 14C Production
Rate Record
Which one is a better proxy for the Solar Variability?