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The 2009/10 Drought in China: Possible Causes and Impacts on Vegetation

01 Aug 2012-Journal of Hydrometeorology (American Meteorological Society)-Vol. 13, Iss: 4, pp 1251-1267

Abstract: Several provinces of China experienced an intense drought episode during 2009 and 2010. The drought was particularly severe in southwestern and northern China, where the accumulated precipitation from May 2009 to April 2010 was about 25% less than normal. The decline of accumulated precipitation over northern China was mostly noticeable during the summer season of 2009 and it was comparable to recent dry episodes. The southwestern China drought resulted from a sequence of dry months from summer 2009 to winter 2010, corresponding to the driest event since at least 1951. The suppression of rainfall in summer over both regions was in agreement with a weakened broad-scale South Asian summer monsoon, possibly influenced by an El Nino developing phase, whereas the extremely negative phases of the Arctic Oscillation during the winter of 2010 may have contributed to the persistence of the drought in southwestern China. The assessment of the associated impacts indicates that water reservoirs were severely ...
Topics: Monsoon (54%)

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The 2009/10 Drought in China: Possible Causes and Impacts on Vegetation
DAVID BARRIOPEDRO
IDL, Universidade de Lisboa, Lisbon, Portugal, and Departamento de Astrofı´sica y Ciencias de la Atmo
´
sfera/Instituto de
Geociencias, Universidad Complutense de Madrid, Madrid, Spain
CE
´
LIA M. GOUVEIA
IDL, Universidade de Lisboa, Lisbon, and Escola Superior de Tecnologia, Instituto Polite
´
cnico de Setu
´
bal, Setubal, Portugal
RICARDO M. TRIGO
IDL, Universidade de Lisboa, and Departamento de Engenharias, Universidade Luso
´
fona, Lisbon, Portugal
LIN WANG
Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
(Manuscript received 22 June 2011, in final form 16 February 2012)
ABSTRACT
Several provinces of China experienced an intense drought episode during 2009 and 2010. The drought was
particularly severe in southwestern and northern China, where the accumulated precipitation from May 2009
to April 2010 was about 25% less than normal. The decline of accumulated precipitation over northern
China was mostly noticeable during the summer season of 2009 and it was comparable to recent dry episodes.
The southwestern China drought resulted from a sequence of dry months from summer 2009 to winter 2010,
corresponding to the driest event since at least 1951. The suppression of rainfall in summer over both regions
was in agreement with a weakened broad-scale South Asian summer monsoon, possibly influenced by an
El Nin
˜
o developing phase, whereas the extremely negative phases of the Arctic Oscillation during the winter
of 2010 may have contributed to the persistence of the drought in southwestern China. The assessment of the
associated impacts indicates that water reservoirs were severely affected with a ;20% reduction in the na-
tionwide hydroelectrical production during the drought event. Furthermore, an analysis of the normalized
difference vegetation index data reveals that large cropland sectors of northern and eastern China experi-
enced up to 8 months of persistently stressed vegetation between May 2009 and July 2010, while southwestern
China was relatively less affected. Such different regional vegetative responses are interpreted in terms of
the land-cover type, agriculture management, and their dependence on seasonal precipitation and water
availability for irrigation.
1. Introduction
During 2009 and 2010, an intense and prolonged
drought episode affected several provinces of north-
ern (Hebei, Shanxi, and Liaoning) and southwestern
(Yunnan, Guizhou, Guangxi, and Sichuan) China, in-
cluding the municipalities of Beijing and Chongqing
(Qiu 2010). Northern China is an important area of grain
production, while the southwest region represents one
of the major water resources of the country, supplying
water to the Yangtze River, the Pearl River head, and
their reservoirs. According to the Chinese Office of State
Flood Control and Drought Relief Headquarters and
the Ministry of Civil Affairs, the drought affected ;25
million people and ;18 million livestock by shortage of
drinking water, as well as about ;8 million ha of arable
land nationwide, with total economic losses of at least
$3.5 billion U.S. dollars (http://www.chinadaily.com.cn/
china/2010drought/index.html).
Droughts are recurrent phenomena in China, but
they can be associated to different causes and complex
Corresponding author address: David Barriopedro, Instituto
Dom Luiz, Universidade de Lisboa, Departamento de Engenharia
Geogra
´
fica, Geofı
´
sica e Energia, Faculdade de Cie
ˆ
ncias, Univ. de
Lisboa, Campo Grande, Ed C8, Piso 6, 1749-016 Lisboa, Portugal.
E-mail: dbarriopedro@fc.ul.pt
A
UGUST 2012 B A R R I O P E D R O E T A L . 1251
DOI: 10.1175/JHM-D-11-074.1
Ó 2012 American Meteorological Society

processes. For example, the recently severe drought epi-
sode during winter 2008/09 in eastern China was shown
to be partially driven by the 2008/09 La Nin
˜
a episode
and also influenced by the anomalous high tempera-
tures over the Tibetan Plateau (Gao and Yang 2009).
Interannual rainfall variations in China are also asso-
ciated with the Asian monsoon—a complex and multi-
faceted system encompassing the East Asian monsoon
(EAM), the Indian monsoon (IM), and the western
North Pacific monsoon (WNPM) (e.g., Wang et al. 2001;
Wang and LinHo 2002). The EAM (e.g., Ding and Chan
2005) is characterized by a cold, dry East Asian winter
monsoon (EAWM) affecting Japan and southeastern
China (e.g., Zhang et al. 1997) and a warm, rainy East
Asian summer monsoon (EASM), whose main signature
is a meridional rainfall tripole and the quasi-stationary
mei-yu subtropical front (e.g., Chen et al. 2004). Fluctu-
ations in the EASM are often associated with floods
and droughts in the Yangtze River basin (e.g., Huang
et al. 2007). Relatively, other regions of the country are
more affected by interactions between the different sub-
systems of the Asian monsoon, midlatitude processes,
and tropical cyclones (e.g., Wang et al. 2008), which
in turn are subject to remote influences. In particular,
El Nin
˜
o–Southern Oscillation (ENSO) explains a sig-
nificant part of the interannual Asian monsoon vari-
ability by displacing the heat sources in the tropics
(Webster and Yang 1992; Wang et al. 2001), although
such relationship is nonstationary (Kumar et al. 1999;
R. Wu and B. Wang 2002). Other reported factors af-
fecting seasonal precipitation in China are the Arctic
Oscillation/North Atlantic Oscillation (AO/NAO; Gong
and Wang 2003; Sung et al. 2006), the stationary plan-
etary waves (Chen et al. 2005), the Antarctic Oscillation
(AAO; Nan and Li 2003), dynamic and thermal effects of
the Tibetan Plateau (Wu and Zhang 1998; Hsu and Liu
2003), and the Eurasian snow cover (Zhang et al. 2004).
In addition to the assessment of physical mechanisms
associated with extreme events, it is of equal relevance
to quantify their impacts. This is a particularly daunting
task in China, where the area influenced by droughts
reaches nearly 20 million km
2
on average every year,
accounting for about
1
/
6 of the national arable land
(Huang et al. 2000). Given the key role of agriculture
(;13% of China’s GDP) sustaining the huge number of
Chinese people (;1.3 billion), droughts can cause large
economic losses in China (circa 50% of the total losses
induced by climatic hazards on average; Huang et al.
2000). With the advent of satellite-derived products, the
monitoring of droughts and the related assessment of
vegetation health and net primary production have
experienced significant improvements (e.g., Kogan
1995; Fang et al. 2003). Studies based on the normalized
difference vegetation index (NVDI) over China have
shown a nationwide enhancement of vegetation cover-
age during recent decades, which is not only due to the
advance of agricultural technology but also to the re-
gional precipitation and temperature changes that have
caused an extended growing season and more rapid plant
growth (Piao et al. 2010). This general trend in NDVI is,
however, punctuated by severe droughts with spatially
coherent NVDI anomaly patterns (Habib et al. 2009),
which have become relatively frequent and widespread
in northern China since the 1970s (e.g., Zou et al. 2005).
The application of NDVI as a tool to assess droughts’
impacts in agriculture production is also of great interest
in China because the large variety of climate regimes
and crops, together with an uneven distribution of water
resources and agriculture management, make that a given
combination of climate anomalies can produce either
beneficial, irrelevant, or damaging effects on vegetation
(e.g., Tao et al. 2008).
The main goal of this paper is to provide a descrip-
tion of the 2009/10 drought in China from multiple
perspectives by addressing some of the aforementioned
issues. In more detail, the objectives are (i) to charac-
terize the temporal and spatial extent of this extreme
drought event, (ii) to assess the regional precipitation
deficits in terms of the associated atmospheric circulation
anomalies, and (iii) to evaluate some socioeconomic
impacts of this extreme drought episode, particularly on
vegetation greenness and hydroelectrical production.
The data and methods employed in this study are
described in section 2. Section 3 analyzes the spatial and
temporal characteristics of this drought. The associated
anomalous atmospheric circulation is presented in sec-
tion 4. Section 5 then describes the social–economic im-
pacts of this drought, including the impacts on national
hydroelectrical production and on vegetation. Finally, the
main conclusions are presented in section 6.
2. Data and methods
Monthly precipitation data on land surface at 1.083
1.08 resolution grid were provided by the Global Precipi-
tation Climatology Centre (GPCC; Rudolf and Schneider
2005). This dataset has already been used to analyze ex-
treme dry precipitation episodes over different regions,
such as Iberia (Garcı
´
a-Herrera et al. 2007) and the Mid-
dle East (Trigo et al. 2010). The GPCC products are
basedoninsituraingaugedataandcovertheperiod
from 1901 to present through two gridded datasets: the
so-called full data product (1901–2009), which is contin-
uously updated with all available stations, and the mon-
itoring product (2007–present) that only uses a network
of near-real-time stations. Both datasets are subject to
1252 JOURNAL OF HYDROMETEOROLOGY VOLUME 13

similar processing and quality-control steps but they dif-
fer in the number of underlying stations. A preliminary
analysis revealed high consistence between these two
GPCC products during their overlapping period (2007–
09). Therefore, the monitoring product for 2010 was
added to the full data product (available until the end of
2009) to provide full temporal coverage of the drought
episode (2009/10). Since the number of stations over
China experiences a significant decrease before the 1950s,
the period of analysis has been limited to 1951–2010. To
better characterize regional features of the drought ep-
isode, regional precipitation averages have been com-
puted over northern (N) and southwestern (SW) China
(see Fig. 1) after excluding grid points with very dry cli-
mates (e.g., inner Mongolia) and/or at high elevation sites
(e.g., southeasternmost sector of the Tibetan Plateau).
The spatial domain of these sectors is further supported
by a clustering analysis based on observational precipi-
tation stations in China (Song et al. 2007).
The atmospheric data include geopotential height,
temperature, humidity, and zonal and meridional wind
data at different pressure levels obtained from the Na-
tional Centers for Environmental Prediction–National
Center for Atmospheric Research (NCEP–NCAR) re-
analysis in a 2.5832.58 regular grids and for the period
1951–2010 (Kistler et al. 2001). The vertically inte-
grated moisture flux (from the surface to 300 hPa) was
computed following the approach adopted in Trenberth
and Guillemot (1995). This field displayed almost identical
features to the water vapor flux at low levels (e.g., 850 hPa)
for the analyzed period of the drought and it also showed
strong resemblance with the low-level wind, except over
relatively dry land areas of midlatitudes. With the aim
of assessing remote influences in the regional precip-
itation variability, we have used atmospheric circula-
tion indices of ENSO [measured by the El Nin
˜
o 3.4 index
(EN3.4)] and the AO for the 1951–2010 period, as pro-
vided by the Climate Prediction Center of the National
Oceanic and Atmospheric Administration (NOAA; www.
cpc.ncep.noaa.gov/).
Additionally, taking into account the regional mani-
festations of the Asian monsoon, a suite of distinct win-
ter and summer monsoon indices have been computed
from the NCEP–NCAR reanalysis for the period 1951–
2010. The summer indices include (i) the Webster–Yang
Asian Monsoon Index (WYMI; Webster and Yang 1992),
(ii) the Western North Pacific Summer Monsoon Index
(WNPMI; Wang and Fan 1999), and (iii) the Indian
Monsoon Index (IMI; Wang and Fan 1999). In what
concerns the winter season, the strength of the EAWM
was characterized by the East Asian Winter Monsoon
Index (EAWMI) proposed by Jhun and Lee (2004).
Seasonal values are computed from the seasonal mean
fields and then standardized with reference to the 1951–
2008 period. The WYMI reflects the broad-scale South
Asian summer monsoon variability, which is primarily
driven by two relatively independent convective heat
sources over the Bay of Bengal and the Philippine Sea
(Wang and Fan 1999), herein represented by the IMI
and WNPMI, respectively. Although the WNPM is not
exactly the same system as EASM, it is closely related to
the variations of mei-yu and therefore is able to capture
the main features of the EASM (Wang et al. 2008). The
sign of WNPMI used here is reversed compared with the
original index proposed by Wang and Fan (1999) so that
positive value indicates an enhanced mei-yu rainfall.
Other summer and winter monsoon indices (see Wang
et al. 2008 and Wang and Chen 2010a) may capture better
regional precipitation anomalies, but for the sake of
simplicity, the discussion will focus on some of the most
traditional indices that are of standard use in operational
centers.
The response of vegetation was assessed with fields
of NDVI since a close relationship between NDVI and
annual rainfall variations has been reported for different
land-cover types in China (Fang et al. 2001). Meanwhile,
it should be noted that water intensive crops (e.g., rice
and cotton) and areas with multicropping rotations are
more sensitive to seasonal rains, springtime snow, and
glacier melt and water resources (Piao et al. 2010). The
NDVI can also reflect temperature anomalies since low
minimum temperatures during the growing season cause
FIG. 1. Spatial distribution of the accumulated monthly precipi-
tation (in percentage relative to the 1951–2008 norm) during the
hydrological year 2009/10 (i.e., between May 2009 and April 2010).
To avoid misleading results over dry areas, only grid points with
climatological accumulated precipitation above 240 mm (i.e.,
20 mm month
21
) are shown. Black boxes approximately delimit
regions with maximum deficit in accumulated precipitation and
they are referred to as N and SW China in the text.
A
UGUST 2012 B A R R I O P E D R O E T A L . 1253

damage to crops (e.g., Tao et al. 2008). NDVI values were
derived from the so-called 10-day global synthesis
(S10) products of the SPOT-VEGETATION partner
(VITO) database (http://free.vgt.vito.be), which provide
atmospherically corrected and geometrically calibrated
data acquired by the VEGETATION instrument on board
both Satellite Pour l’Observation de la Terre (SPOT)
SPOT-4 and SPOT-5 satellites between September 1998
and August 2010 (Maisongrande et al. 2004; Hagolle et al.
2005). NDVI fields are supplied at the resolution of
0.0089288 (i.e., about 1-km
2
resolution at the equator) in
geographic coordinates and on a 10-day basis, following
the maximum value composite (MVC) method, which
selects the date of maximum NDVI among 10 consec-
utive daily images (Holben 1986). All months are divided
in three 10-day values, the first one corresponding always
to the first 10-day period of that month. For months
with 31 days and February (28 or 29 days), the last 10-
day value actually represents the maximum NDVI within
slightlylonger(11day)orshorter(8or9day)periods.
Monthly fields of the NDVI were subsequently derived
by averaging at each pixel the three 10-day values of the
given month.
It should be noticed that NDVI values tend to un-
derestimate the green biomass of stands over areas with
strong foliage density and high production (Hobbs 1995;
Tucker et al. 1986; Gilabert et al. 1996), causing satu-
ration of NDVI. Despite this caveat, which is expected
to cause relatively lower impacts in the assessment of
droughts, the time series of MVC–NDVI composites
have proven to be a source of valuable information for
monitoring surface vegetation dynamics at the global
and the regional scales (Zhou et al. 2001; Nemani et al.
2003; Gouveia et al. 2008). Therefore, despite the rela-
tively short period analyzed herein, the use of this da-
taset is preferred because the high spatial resolution is
expected to bring a more accurate assessment of the
drought impacts in land-cover types. Information about
the land-cover type associated to each pixel was obtained
from the Global Land Cover 2000 database (http://bioval.
jrc.ec.europa.eu/products/glc2000/products.php).
3. Spatial and temporal characteristics
of the drought
The precipitation regime in China is characterized by
a strong seasonal behavior, with a rainy season mostly
concentrated between May to September and a large
spatial gradient in the annual totals between the wet
monsoonal areas of the southeast and the semiarid re-
gime of northwest (e.g., Song et al. 2007). Therefore, the
hydrological year used in this study is defined as the
period spanning between May of year (yr) and April of
the next year (yr11). Meanwhile, the amount and tim-
ing of the annual maximum of monthly precipitation
varies across China following the penetration and north-
western advance of the Asian monsoonal flows. Thus,
SW China experiences a long-lasting and intense sum-
mer monsoon, with a broad precipitation peak of
;200 mm month
21
centered in June–July that contrasts
with the relatively narrower, delayed (July–August), and
less intense (150 mm month
21
) maximum of N China
(see Figs. 2b,c). However, when annual totals are con-
sidered N China shows a stronger dependence on sum-
mer rainfall, with July–August precipitation accounting
for more than half of the annual totals. This implies that
dry summer conditions in N China are expected to be
reflected on the accumulated totals, while a dry summer
monsoon in SW can be compensated by near-normal
precipitation in other seasons.
To better assess the drought episode, the spatial pat-
tern of accumulated precipitation percentages for the
hydrological year (May 2009–April 2010) has been com-
puted with respect to the corresponding climatological
(1951–2008) norms (Fig. 1). The drought episode was
particularly severe over N and SW China, with both re-
gions recording nearly 25% below the climatological
normal. In addition, relatively less severe drought condi-
tions were observed in other territories, including north-
eastern India and Burma; northern parts of Thailand,
Laos, and Vietnam (not shown); as well as other prov-
inces of southern China such as Hunan and Guangdong
(Fig. 1).
Figure 2a shows the accumulated monthly precipi-
tation averaged over N and SW areas between May 2009
and April 2010, along with the corresponding evolution
of the climatological accumulated monthly precipi-
tation distribution (whiskers plot). At the end of the
considered period, the regional average accumulated
precipitation in SW (;850 mm) was ;25% less than
the long-term mean value (;1100 mm), corresponding
to the lowest accumulated value in any hydrological year
since at least 1951. In relative terms, the N region ex-
perienced a more severe decrease (;30%) in accumu-
lated totals (;350 mm relative to a ;470 mm mean).
However, this region is also characterized by large in-
terannual variability, with the standard deviation (SD)
of annual accumulated totals (69.7 mm) being of similar
magnitude to that in SW (76.2 mm). Consequently, from
a normalized point of view, the 2009/10 drought was
more severe in SW (23.1 SDs) than in N (21.7 SDs). It
is worth noticing that, despite its extreme magnitude,
the 2009/10 drought episode over N China was not
particularly anomalous in the context of recent years
(Fig. 2a), which have been characterized by a relative
recurrence of extreme droughts. This is in agreement
1254 JOURNAL OF HYDROMETEOROLOGY VOLUME 13

with a drying climate trend in northern China (e.g., Hu
et al. 2003) and the increasing tendency for N China to
suffer from severe and long-lasting droughts, which were
particularly acute from 1997/98 to 2002/03 (Zou et al.
2005; Wang et al. 2011).
To better assess the months that specifically contrib-
uted to the marked decline in accumulated precipitation
within the hydrological year, Figs. 2b and 2c show the
temporal evolution of the regional averaged precipi-
tation monthly series during 2009 and 2010 in N and SW
China, respectively. The period with deficit of precipi-
tation started in May 2009 and lasted until October 2009
in N China, further persisting until March 2010 in SW
China. The winter and spring of 2010 were also dry in
the middle and the lower reaches of the Yellow and
Yangtze Rivers (not shown), but slightly wet in N China
(Fig. 2b). A near-normal 2010 monsoon season in SW (N)
China contributed to alleviate (mitigate) the persistent
deficits accumulated throughout the previous hydrologi-
cal year.
Compared with the historical situation, every month
of the May–September monsoon period of 2009 (except
June) exhibited precipitation deficits below the 30th
percentile of the long-term distribution in both N and
SW China (Figs. 2b,c). However, the drought in these
two areas exhibits different features. Thus, in relative
terms, the precipitation deficit over SW China was more
severe (below the 10th percentile of its climatologi-
cal distribution) from September to November 2009
(i.e., after the peak time of local monsoon rainfall). In
contrast, N China received the lowest precipitation
(also below the monthly 10th percentile) during July–
September 2009, which is the peak time of local mon-
soon rainfall. As a consequence, the drought period over
N China was shorter and mainly caused by decreased
summer precipitation, whereas that over the relatively
wetter SW China resulted from the persistence of dry
conditions during several consecutive months.
FIG. 2. (a) Accumulated monthly precipitation averaged over N
and SW China during the hydrological year 2009/10 (black dotted
lines). Gray shaded areas show the overlapping from the corre-
sponding evolution from all grid points embedded in the given area
(defined by the black boxes of Fig. 1). Gray lines indicate the cli-
matological mean evolution in each region, with boxes (whiskers)
representing the 60.5sigma level (10th–90th percentiles) obtained
from all hydrological years between 1951 and 2008. The other two
most severe drought events in each region within the period 1951–
2008 are also indicated with color lines and ranked in the upper-left
corner. (b),(c) Climatological (1951–2008) annual cycle of monthly
precipitation averaged over (b) N and (c) SW China. Two full
annual cycles are shown. The light (dark) shaded areas comprise
the 10th–90th (30th–70th) monthly percentiles obtained from the
1951–2008 precipitation time series, with the median in between.
Dashed line shows the time series for 2009 and 2010, with the
corresponding monthly departure from the climatological mean
being represented in the bottom graphic.
A
UGUST 2012 B A R R I O P E D R O E T A L . 1255

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235 citations


Cites background from "The 2009/10 Drought in China: Possi..."

  • ...Therefore, climatic disasters such as droughts and floods in summer and severe cold surges, freezing rain, and low temperature in winter frequently occur in China (Huang and Zhou, 2002; Huang, 2006; Gu et al., 2008; Huang et al., 2011c, 2012b; Barriopedro et al., 2012)....

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  • ...…2009 to January 2010 (Wang and Chen, 2010b), the particularly severe drought in Southwest China from the autumn of 2009 to the spring of 2010 (Barriopedro et al., 2012; Huang et al., 2012b), severe floods in South China and the Yangtze River basin during May– July, particularly severe floods…...

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  • ...For example, a ∼20% reduction was observed in the nationwide hydroelectrical production due to the depleted water reservoirs during the 2009–2010 Southwest China droughts (Barriopedro et al., 2012)....

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Journal ArticleDOI
Kevin E. Trenberth1, John T. Fasullo1Institutions (1)
Abstract: [1] A global perspective is developed on a number of high impact climate extremes in 2010 through diagnostic studies of the anomalies, diabatic heating, and global energy and water cycles that demonstrate relationships among variables and across events. Natural variability, especially ENSO, and global warming from human influences together resulted in very high sea surface temperatures (SSTs) in several places that played a vital role in subsequent developments. Record high SSTs in the Northern Indian Ocean in May 2010, the Gulf of Mexico in August 2010, the Caribbean in September 2010, and north of Australia in December 2010 provided a source of unusually abundant atmospheric moisture for nearby monsoon rains and flooding in Pakistan, Colombia, and Queensland. The resulting anomalous diabatic heating in the northern Indian and tropical Atlantic Oceans altered the atmospheric circulation by forcing quasi-stationary Rossby waves and altering monsoons. The anomalous monsoonal circulations had direct links to higher latitudes: from Southeast Asia to southern Russia, and from Colombia to Brazil. Strong convection in the tropical Atlantic in northern summer 2010 was associated with a Rossby wave train that extended into Europe creating anomalous cyclonic conditions over the Mediterranean area while normal anticyclonic conditions shifted downstream where they likely interacted with an anomalously strong monsoon circulation, helping to support the persistent atmospheric anticyclonic regime over Russia. This set the stage for the “blocking” anticyclone and associated Russian heat wave and wild fires. Attribution is limited by shortcomings in models in replicating monsoons, teleconnections and blocking.

232 citations


References
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Journal ArticleDOI
Abstract: The National Centers for Environmental Prediction (NCEP) and National Center for Atmospheric Research (NCAR) have cooperated in a project (denoted “reanalysis”) to produce a retroactive record of more than 50 years of global analyses of atmospheric fields in support of the needs of the research and climate monitoring communities. This effort involved the recovery of land surface, ship, rawinsonde, pibal, aircraft, satellite, and other data. These data were then quality controlled and assimilated with a data assimilation system kept unchanged over the reanalysis period. This eliminated perceived climate jumps associated with changes in the operational (real time) data assimilation system, although the reanalysis is still affected by changes in the observing systems. During the earliest decade (1948–57), there were fewer upper-air data observations and they were made 3 h later than the current main synoptic times (e.g., 0300 UTC), and primarily in the Northern Hemisphere, so that the reanalysis is less reliable than for th later 40 years. The reanalysis data assimilation system continues to be used with current data in real time (Climate Data Assimilation System or CDAS), so that its products are available from 1948 to the present. The products include, in addition to the gridded reanalysis fields, 8-day forecasts every 5 days, and the binary universal format representation (BUFR) archive of the atmospheric observations. The products can be obtained from NCAR, NCEP, and from the National Oceanic and Atmospheric Administration/ Climate Diagnostics Center (NOAA/CDC). (Their Web page addresses can be linked to from the Web page of the NCEP–NCAR reanalysis at http:// wesley.wwb.noaa.gov/Reanalysis.html.) This issue of the Bulletin includes a CD-ROM with a documentation of the NCEP–NCAR reanalysis (Kistler et al. 1999). In this paper we present a brief summary and some highlights of the documentation (also available on the Web at http://atmos.umd.edu/ ~ekalnay/). The CD-ROM, similar to the one issued with the March 1996 issue of the Bulletin, contains 41 yr (1958–97) of monthly means of many reanalysis variables and estimates of precipitation derived from satellite and in situ observations (see the appenThe NCEP–NCAR 50-Year Reanalysis: Monthly Means CD-ROM and Documentation

4,106 citations


Journal ArticleDOI
Abstract: The leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep, zonally symmetric or ‘‘annular’’ structures, with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude. The structure and dynamics of the Southern Hemisphere (SH) annular mode have been extensively documented, whereas the existence of a Northern Hemisphere (NH) mode, herein referred to as the Arctic Oscillation (AO), has only recently been recognized. Like the SH mode, the AO can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields. In this paper the structure and seasonality of the NH and SH modes are compared based on data from the National Centers for Environmental Prediction‐National Center for Atmospheric Research reanalysis and supplementary datasets. The structures of the NH and SH annular modes are shown to be remarkably similar, not only in the zonally averaged geopotential height and zonal wind fields, but in the mean meridional circulations as well. Both exist year-round in the troposphere, but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave‐mean flow interaction: midwinter in the NH and late spring in the SH. During these ‘‘active seasons,’’ the annular modes modulate the strength of the Lagrangian mean circulation in the lower stratosphere, total column ozone and tropopause height over mid- and high latitudes, and the strength of the trade winds of their respective hemispheres. The NH mode also contains an embedded planetary wave signature with expressions in surface air temperature, precipitation, total column ozone, and tropopause height. It is argued that the horizontal temperature advection by the perturbed zonal-mean zonal wind field in the lower troposphere is instrumental in forcing this pattern. A companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades.

3,064 citations


"The 2009/10 Drought in China: Possi..." refers background in this paper

  • ...On the other hand, the spatial pattern of temperature anomalies over China resembles that associated with negative phases of the AO (Thompson and Wallace 2000), which in the winter of 2009/2010 exhibited its lowest value (23.0) since the midtwentieth century (Fig....

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Journal ArticleDOI
06 Jun 2003-Science
TL;DR: It is indicated that global changes in climate have eased several critical climatic constraints to plant growth, such that net primary production increased 6% (3.4 petagrams of carbon over 18 years) globally.
Abstract: Recent climatic changes have enhanced plant growth in northern mid-latitudes and high latitudes. However, a comprehensive analysis of the impact of global climatic changes on vegetation productivity has not before been expressed in the context of variable limiting factors to plant growth. We present a global investigation of vegetation responses to climatic changes by analyzing 18 years (1982 to 1999) of both climatic data and satellite observations of vegetation activity. Our results indicate that global changes in climate have eased several critical climatic constraints to plant growth, such that net primary production increased 6% (3.4 petagrams of carbon over 18 years) globally. The largest increase was in tropical ecosystems. Amazon rain forests accounted for 42% of the global increase in net primary production, owing mainly to decreased cloud cover and the resulting increase in solar radiation.

2,765 citations


"The 2009/10 Drought in China: Possi..." refers background in this paper

  • ...…to cause relatively lower impacts in the assessment of droughts, the time series of MVC–NDVI composites have proven to be a source of valuable information for monitoring surface vegetation dynamics at the global and the regional scales (Zhou et al. 2001; Nemani et al. 2003; Gouveia et al. 2008)....

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Journal ArticleDOI
Brent N. Holben1Institutions (1)
Abstract: Red and near-infrared satellite data from the Advanced Very High Resolution Radiometer sensor have been processed over several days and combined to produce spatially continuous cloud-free imagery over large areas with sufficient temporal resolution to study green-vegetation dynamics. The technique minimizes cloud contamination, reduces directional reflectance and off-nadir viewing effects, minimizes sun-angle and shadow effects, and minimizes aerosol and water-vapor effects. The improvement is highly dependent on the state of the atmosphere, surface-cover type, and the viewing and illumination geometry of the sun, target and sensor. An example from southern Africa showed an increase of 40 percent from individual image values tothe final composite image. Limitations associated with the technique are discussed, and recommendations are given to improve this approach.

2,508 citations


"The 2009/10 Drought in China: Possi..." refers methods in this paper

  • ...NDVI fields are supplied at the resolution of 0.0089288 (i.e., about 1-km2 resolution at the equator) in geographic coordinates and on a 10-day basis, following the maximum value composite (MVC) method, which selects the date of maximum NDVI among 10 consecutive daily images (Holben 1986)....

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  • ..., about 1-km(2) resolution at the equator) in geographic coordinates and on a 10-day basis, following the maximum value composite (MVC) method, which selects the date of maximum NDVI among 10 consecutive daily images (Holben 1986)....

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Journal ArticleDOI
Shilong Piao1, Philippe Ciais2, Yao Huang3, Zehao Shen1  +13 moreInstitutions (5)
02 Sep 2010-Nature
TL;DR: It is found that notwithstanding the clear warming that has occurred in China in recent decades, current understanding does not allow a clear assessment of the impact of anthropogenic climate change on China’s water resources and agriculture and therefore China's ability to feed its people.
Abstract: China is the world's most populous country and a major emitter of greenhouse gases. Consequently, much research has focused on China's influence on climate change but somewhat less has been written about the impact of climate change on China. China experienced explosive economic growth in recent decades, but with only 7% of the world's arable land available to feed 22% of the world's population, China's economy may be vulnerable to climate change itself. We find, however, that notwithstanding the clear warming that has occurred in China in recent decades, current understanding does not allow a clear assessment of the impact of anthropogenic climate change on China's water resources and agriculture and therefore China's ability to feed its people. To reach a more definitive conclusion, future work must improve regional climate simulations-especially of precipitation-and develop a better understanding of the managed and unmanaged responses of crops to changes in climate, diseases, pests and atmospheric constituents.

2,100 citations


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