Download Indian Monsoon Variability in the context of Global Warming Debate

Indian Monsoon Variability &
Global Warming
Madhav Khandekar CANADA
Expert Reviewer IPCC 2007 Climate Change
Heartland Conference on Climate Change Chicago
May 21-23 2012
Abstract

An analysis of Indian Summer Monsoon
Rainfall (ISMR) reveals that droughts and
floods have occurred irregularly
throughout a 200-year long excellent
dataset with NO Link to “global warming
OR climate change” at this point in time.
Heartland Conference on Climate
Change Chicago May 21-23 2012
Monsoon: General Notes



Indian/Asian monsoon is the largest seasonal abnormality in the
global climate system
Indian/Asian monsoon affects about 4 billion people of south Asia.
Timely arrival and well distributed rainfall during the summer season
(May-October) is critical for agriculturally dominated countries of
south Asia.
Climate models have achieved only a limited success so far in
simulating many features of global and regional monsoon. Most
climate models project monsoon circulation to intensify in a warmer
future climate. In reality, Monsoon circulation has weakened in the
last fifty years.
Heartland Conference on Climate
Change Chicago May 21-23 2012
Basic Facts on Indian Summer
Monsoon
1.
2.
3.
4.
5.
Summer (June-September) rains most important for whole of
India for agriculture & water supply
Mean rainfall ~90 cm; On west coast ( Mumbai-Goa-Kerala
Coast)~ 150-200 cm; central India ~100-125 cm; northwest India
~50 cm
Monsoon onset on west coast tip of India ~June 7th
Despite year-to-year variability, this onset date is robust: Over
Bay of Bengal & northeast, monsoon arrival ~1-12 June
By 25 June, monsoon spreads over most of India
Heartland Conference on Climate
Change Chicago May 21-23 2012
Heartland Conference on Climate
Change Chicago May 21-23 2012
Highest/Lowest Rainfall




Highest One Year Rainfall: Cherrapunji 2646 cm
Aug 1860- July 1861
Highest One Month Rainfall: Cherrapunji 930 cm
July 1861
Highest 2-day Rainfall: 41 in ( ~105 cm) Mumbai
July 2005
Lowest seasonal Rainfall: 33mm (1918), 49mm (1899) in West Rajasthan:
Both the years ( 1899 &1918 ) were severe drought years over whole of
India
Heartland Conference on Climate
Change Chicago May 21-23 2012
Major Flood Years 1892, 1917, 1933, 1961, 1970, 1975
Major drought years 1868, 1877, 1899, 1918, 1951, 1972, 1987
Heartland Conference on Climate
Change Chicago May 21-23 2012
Large-scale controls of Indian
Monsoon

ENSO phase in the equatorial Pacific (El Nino linked to drought)

Eurasian snow cover, previous winter (Heavy snow cover weakens
monsoon)

Equatorial stratospheric wind oscillation (QBO: quasi-biennial
oscillation)

Indian Ocean Dipole (IOD)
These large-scale controls and their various phases, produce major
droughts/floods in summer monsoon
Heartland Conference on Climate
Change Chicago May 21-23 2012
Regional controls of Monsoon
Depressions traveling along Monsoon trough
Heartland Conference on Climate
Change Chicago May 21-23 2012
ENSO (El Nino-Southern Oscillation)
phases in the equatorial Pacific
Heartland Conference on Climate
Change Chicago May 21-23 2012
The 1997/98 El Nino structure at about Sep 1997
Heartland Conference on Climate
Change Chicago May 21-23 2012
Equatorial stratospheric wind oscillation (QBO) at ~20-22 km level
with about 26-month (east-west) period.
Heartland Conference on Climate
Change Chicago May 21-23 2012
A schematic of Indian Ocean Dipole (IOD)
Positive phase: warmer SSTs in west equatorial ocean
Heartland Conference on Climate
Negative phase: warmer SSTs in east equatorial ocean
Change Chicago May 21-23 2012
Eurasian winter snow cover




Blanford (1884) first identified adverse impact of heavy
winter snow cover on subsequent monsoon rains
Sir Gilbert Walker used snow cover as one of the
important parameters
Barnett et al (1989) simulated snow/monsoon adverse
relationship using climate models
In general, heavier snow cover produces weaker
monsoon and vice-versa
Heartland Conference on Climate
Change Chicago May 21-23 2012
This jet (peak winds ~100 knots at 15 km level) is due to reversal
of north-south temperature gradient. The jet disappears by October.
Heartland Conference on Climate
Change Chicago May 21-23 2012
Indian Monsoon Rainfall standardized values 1871-2001 (Top)
Cramer’s t-statistic for 11-year running mean depicting decadal
variability and epochs (Bottom)
Indian monsoon exhibits decadal variability
and is not influenced by Global Warming at
this time
Heartland Conference on Climate
Change Chicago May 21-23 2012
Major floods/droughts (1813-2010)

FLOODS

1818 (1036 mm)

1861 (1051 mm)





1874 (1033 mm)

1878 (1039 mm)

1892 (1050 mm)

1894 (1032 mm)

1916 (1034 mm)

1917 (1079 mm)

1933 (1042 mm)












1942 (1037 mm)

1956 (1007 mm)




1961 (1088 mm)—Most Severe Flood

1971 (1002 mm)

1988 (1047 mm)






Mean 1041mm
DROUGHTS
1823 (795 mm)
1824 (770 mm)
1832 (775 mm)
1840 (774 mm)
1844 (788 mm)
1848 (688 mm)
1851 (744 mm)
1860 (733 cm)
1864 (748 mm)
1868 (777 mm)
1877 (609 mm)—Most Severe Drought
1899 (695 mm)
1918 (661 mm)
1920 (786 mm)
1941 (785 mm)
1965 (741 mm)
1972 (708 mm)
1979 (723 mm)
1982 (788 mm)
1986 (780 mm)
1987 (739 mm)
2002 (715 mm) Heartland Conference on Climate
2009 (698 mm) Change Chicago May 21-23 2012
Mean 739 mm
IPCC 2007: Global temperature declined between 1945-77, present
Warming since 1980 to 2005
Heartland Conference on Climate
Change Chicago May 21-23 2012
Summer Monsoon Variability:
1951-1975 vs 1981-2005




1951-1975
4 floods, 3 droughts
Mean rainfall:917 mm
Only 8 years below
normal





1981-2005
2 floods, 4 droughts
Mean rainfall:888 mm
12 years below normal
2 years close to normal
Summer monsoon was stronger during 1951-75,
weaker in recent years in a warming climate
Heartland Conference on Climate
Change Chicago May 21-23 2012
Drought
IOD Indian Ocean Dipole
Negative phase
Flood
IOD Indian Ocean Dipole
Positive phase
Heartland Conference on Climate
Change Chicago May 21-23 2012
Severe Drought
Heartland Conference on Climate
Change Chicago May 21-23 2012
Floods in Pakistan and NW India
Heartland Conference on Climate
Change Chicago May 21-23 2012
Summary & Conclusions





Indian Monsoon is a robust system and its inter-annual variability is
governed by large-scale atmosphere-ocean patterns.
Droughts/floods have occurred irregularly throughout a 200-year long
dataset.
Indian Monsoon appears to exhibit a decadal variability with approximately
30-year period of above/below rainfall.
Indian (and by extension Asian) monsoon is NOT impacted at this time by
the modest warming of the earth’s climate. Indian and global monsoon
circulations have weakened, in general, in the last 30 years or so.
A conceptual drought/flood model of Indian Monsoon based on selected
large-scale indices can help predict future droughts and floods with a lead
time of few weeks
Heartland Conference on Climate
Change Chicago May 21-23 2012