Transcript Earth Hydrological Cycle - Department of Meteorology and Climate

METR112 Global Climate Change – Lecture 3: Earth Hydrological Cycle
Prof. Menglin Jin, San Jose State University
Earth Hydrological Cycle
What is hydrological cycle
Major components of
hydrological cycle
Precipitation
Evaporation & evapotranspiration
Atmospheric transport
Runoff and ground water flow
Water reservoir (ocean, lake,
glacier, soil water, etc.)
The hydrological cycle. Estimates of the main water reservoirs, given in
plain font in 103 km3, and the flow of moisture through the system,
given in slant font in103 km3/yr, equivalent to Exagrams (1018 g) per
year. (Trenberth et al. 2006a).
Precipitation:
Standard rain gauge used in
observing precipitation
Rain gauge
Precipitation:
Radar detecting the cloud by collecting
reflected microwaves
Radar & satellite
Satellite observe earth in microwave or
infrared channels from space and estimate
precipitation using retrieval techniques
Precipitation:
Observations show great spatial variation
Bosilovich et al. DOI: 10.1175/2008JAMC1921.1
Precipitation: Observations show decadal variation of
precipitation change
Precipitation: Observations show decadal variation of
precipitation change
alternative
Precipitation:
Changes are not spatially uniform
General increase of
precipitation in most areas
in mid- and high latitude,
Decreased precipitation
in the Western, Southern
Africa and Sahel
With mixed signs in
Eurasia
Precipitation increases in
Northwest India
IPCC AR4
Precipitation variation is complex over the land
Increases
Decreases
Source: IPCC AR4 - Chapter 3, Adopted from: Richard CJ Somerville,
APRU World Institute Workshop, 2007
Precipitation:
Changes in zonal averaged
precipitation
Positive anomalies in tropics , negative anomalies in
extra-tropics
Precipitation:
(Chen et al. 2002)
Changes in seasonal variations
vary spatially
Precipitation:
Intensified extreme precipitation in
mid-latitudes
More wet days (upper 5%) and
heavy precipitation (upper 5%
percentile) in US and most Europe
Increased possibility of intense
precipitation in most extratropical
regions
Decrease of heavy precipitation in
central Africa, south east Asia, west
Europe and west Australia
IPCC AR4
Significant decrease in East Asian Monsoon index
since 1976/77 climate shift
Figure 3.35. Annual values of the East Asia summer monsoon index derived from MSLP gradients between land
and ocean in the East Asia region. The definition of the index is based on Guo et al. (2003) but was recalculated
Figure 3.35
based on the HadSLP2 (Allan and Ansell, 2006) data set. The smooth black curve shows decadal variations.
East Asian summer monsoon index: Sum of mean sea level pressure differences
between 110o and 160oE for 20o to 50oN with 5o difference.
Current global climate a boon for Australian Monsoon?
Statistically significant rainfall show up in predominantly northern parts of Australia
Primarily due to additional southern Australian land heat up while no/cold
Anomalous changes in oceans
Figure 3.36. Time series of northern Australian (north of 26°S) wet season (October–April) rainfall (mm) from 1900/1901 to
2004/2005. The individual bar corresponds to the January of the summer season (e.g., 1990 is the summer of 1989/1990). The
smooth black curve shows decadal variations. Data from the Australian Bureau of Meteorology.
African Monsoon shows clear signal due to changes
in ENSO
Figure 3.37. Time series of Sahel (10ºN –20ºN, 18ºW–20ºE) regional rainfall (April–October) from 1920 to 2003 derived
from gridding normalised station anomalies and then averaging using area weighting (adapted from Dai et al., 2004a).
The smooth black curve shows decadal variations.
Figure 3.37
Both tropical Pacific and Atlantic SSTs have effects on African Monsoon
Many studies show deforestation would amplify draught signals
Evaporation (evapotranspiration)
observations are limited
Pan evaporation observes the
potential evaporation
Bowen ratio system observes
evapotranspiration using energy balance
Would distribution of annual averaged Latent
heat flux from 1979 to 2001 from reanalysis
(Trenberth and Stepaniak 2003)
Trend of pan evaporation in US from 1950 to 2001
annual
Blue (red)
is decrease
(increase),
circle is sig
at 90%
Warm
season
Hobbins and
Ramirez 2004
Zonally-averaged annual evaporation shows an Mshaped distribution
15-year
ECMWF
reanalysis
Garnier et
al. 2000
ERA15 (solid curve), COADS (dashed), CE91-95 (dotted curve)
One way of measuring soil moisture: gravimetric method
Two types of augers used for gravimetric soil moisture
observations, sitting on a neutron probe. The one on
the left is pounded into the ground and used when the
ground is frozen. The one on the right is twisted into
the ground
Robot et al. 1999
Major soil moisture climate regimes
soils.usda.gov/use/worldsoils/mapindex/smr.html
Seasonal cycles of soil moisture for various areas
Robot et al. 1999
The most recent monthly averaged soil moisture for US
Snow:
Decreased spring snow covered area in
Northern America
Statistically significant decline in annual SCA for 2.7x10^4 km^2
SCA maximum shift from February to January and earlier snow melt
Melting season shift two weeks earlier from 1972 to 2002
Snow cover anomalies in from 1966 to 2006 for
northern America
http://www.arctic.noaa.gov/detect/ice-snow.shtml
Snow cover anomalies in from 1966 to 2006 for
Eurasia
http://www.arctic.noaa.gov/detect/ice-snow.shtml
Sea ice: Arctic sea ice extent decreases in the last 20
years
annual: -2.7%/dec
The annual sea ice extent decrease steadily from 1980
Summer sea ice decrease in tremendous in the
last 20 years
summer: -7.4%/dec
Most remarkable change is the summer sea ice diminish, in which the interannual to
decadal variability is associated with the variability of atmospheric circulation
Glacier:
Glacier and ice cap mass loss in response to
1970 warming
(Science basis, Chap.4, Fig.4.15)
Strong negative specific mess balances in Patagonia, Alaska after mid 90s,
cumulative balance equivalent to 10m of water (11m of ice)
Total mass loss are contributed mainly from Alaska (0.24 mm/yr of SLE), Arctic (0.19
mm/yr of SLE) and Asia high mountains (0.1 mm/yr of SLE)
Muir glacier ， Alaska
1941
2004
Decreased ice extent
in Kilimanjaro
Ice sheet:
Melting of ice sheets in Greenland and
Antarctic
Increasing melting near the coast overwrites the thickening in the central during the
last 10 years and a recent acceleration in overall shrinkage
Ice sheet mass loss explains the sea level rise over the last 10 years: Antarctica -0.14
to 0.55 mm/yr from 1993 to 2003
Aggressive retreat of Antarctica peninsula ice
shelf
Ice sheet:
Melting of ice sheets in Greenland and
Antarctic
Ice sheet mass loss explains
the sea level rise over the
last 10 years: Greenland:
0.14 to 0.28 mm/yr SLE
from 1993 to 2003
Greenland melt extent seeing from satellite
2005 summer ice extent set a record during 27-year period. 2005 also shows
a especially long melting season (until late Sep) compared to previous years
according to Steffen et al. 2004, Hanna et al. 2005
Greenland melt area during summer
time increases from 1979 to 2005
What could happen in future: IPCC 21 century model projections
Continuous sea ice decrease in 20th and 21st
centuries in multi-model simulation
Intensified precipitation intensity in 21st century
Shrinking of Greenland ice-sheet in a warmer climate
Evolution of Greenland surface elevation and ice sheet volume versus time in
the experiment of Ridley et al. (2005) with the UKMO-HadCM3 AOGCM coupled
to the Greenland Ice Sheet model of Huybrechts and De Wolde (1999) under a
climate of constant quadrupled pre-industrial atmospheric CO2.
Extra Credit (2 points)
Take a look at a useful reference about glaciers
http://www.grid.unep.ch/glaciers/
Write a 2-page review comments.
Due Feb. 17