54 During normal year, average maximum temperature reached on June and
other monthly period temperature was decreased. However, average maximum of precipitation reached on May and other monthly period until July the precipitation
was decreased, meanwhile in the August to October the precipitation was increased. Distribution NPP value show increased in April and in other monthly
period until August the NPP distribution was stable. Increased of NPP occurs in September followed with increasing in precipitation.
During El Nino year, average maximum of temperature reached on May and other monthly period temperature was decreased. However, average
maximum of precipitation reached on June and other monthly period until October the precipitation was decreased, meanwhile in the October to November the
precipitation was increased. The distribution NPP value show increased until May and in other monthly period until October the NPP distribution was decreased.
Increased of NPP occurs in October to December followed with increasing in precipitation.
During La Nina year, average maximum of temperature reached on May and other monthly period temperature was decreased. However, average
maximum of precipitation reached on March and other monthly period until July the precipitation was decreased, meanwhile in the July to November the
precipitation was increased. The distribution NPP value show increased in March and in other monthly period until July, the NPP distribution was decreased.
However, increased of NPP distribution occurs in August followed with increasing in precipitation during this period.
However, the effects of ENSO to the temporal changes of NPP are small. In comparison to the temperature sensitivity of NPP, the variability of NPP
responses to the historical precipitation was much higher. Refer to the measurement result of NPP estimation in previously explained that decrease in
NPP distribution is mainly related to the precipitation and temperature. Decrease in precipitation will make drought intensified, and affected to limit the
photosynthesis. Meanwhile, the increase in temperature makes respiration and consumption increase, resulting in NPP decline. Therefore, increasing
55 photosynthesis makes NPP increased, and it will make more carbon in the
atmosphere will be absorbed. Spatial and temporal changes of NPP are closely correlated with increase
temperature and changing precipitation. Precipitation will increase in most Sumatera areas during La Nina event. Since increase in precipitation is
accompanied by increasing clouds cover and decreasing sunlight and radiation, the increased NPP is small. The decreased NPP also correlated with the rapidly
increasing of temperature and the decreasing of precipitation. Understanding of responses of ecosystem processes to climate variability
is essential for reducing the uncertainty in the estimates of CO
2
exchange between the biosphere and atmosphere. On an annual basis, our analyses have indicated
that precipitation, especially the amount falling in the drier part of the year, is the primary factor influencing annual carbon storage. Our analysis further indicates
that changes in precipitation combine with changes in temperature to affect soil moisture, a factor we have identified as an important controller of carbon storage.
Reduction in soil moisture can lead to a decrease in net ecosystem production through influencing the availability of nitrogen Raich et al., 1991.
Studies have also found increased NPP at the global scale. Potter et al. 2003a used CASA and AVHRR data to calculate changes in NPP and NEP
during 1982 –1998, determining that NEP increased at the global scale. These
studies are concentrated, using only one or two climate variables temperature and precipitation; Potter et al., 2003.
Nemani et al. 2003a used a PEM developed for the global MODIS GPP and NPP products Running et al., 2000 to study the effects of all three primary
climate controls incoming solar radiation, temperature and water on NPP for the period 1982
–1999, and found that global NPP increased 6, with tropical regions. In addition, Nemani and colleagues found that climate alone was responsible for
more than 40 of the increase in the global NPP. Other factors, such as CO
2
fertilization and nitrogen deposition may also played a role in enhancing NPP. Different climatic responses have been suggested in previous studies to be
the primary cause of ENSO-related terrestrial carbon cycle variation. For
56 example, Kindermann et al. 1996 suggested that the temperature dependence of
Net Primary Production NPP is the most important factor in determining land –
atmosphere carbon flux. However, precipitation has been suggested, alternatively, as the dominant factor for variation of terrestrial carbon cycle Zeng et al., 2005.
4.4.2.1. Interannual and Within-year Variations in NPP
The climate response of ENSO over land lags the tropical sea surface temperature SST signal by several months, resulting in variations in regional
temperature, precipitation and radiation for terrestrial biosphere. The typical El Nino events are characterized by changes in atmospheric circulation and
precipitation patterns that give rise to warmer and drier conditions in the tropical land regions. Potter et al., 2003.
There are complex patterns of wet and dry periods within Sumatera and there is a general seasonal character to precipitation across Island. Between July
and October the whole Sumatra appears to be relatively dry, whereas in the other months it is relatively wet. Variations in NPP across years are tightly to variations
in climate, particularly precipitation. For the tropical forest, annual NPP for the nine-year period was significantly correlated with annual precipitation also
monthly NPP is strongly correlated with monthly precipitation. These results suggest that a small decrease in precipitation during the dry
season can lead to a substantial decrease in NPP, while a similar decrease in precipitation during the wet season might not affect NPP nearly as much. For
example, although annual precipitation decreased in the non-El Nino years of 2002 and 2006, annual NPP remained positive because there was no obvious
decrease in precipitation during the dry season. Increased temperatures in the tropics may reduce carbon storage, especially if higher temperatures are
associated with drier climates and more fires. Zeng et al. 2005 have studied the interannual variability of the terrestrial
carbon and have suggested that the tropical dominance is a result of a „conspiracy‟ between climate and plantsoil physiology. Precipitation and temperature
variations in the tropics drive the opposite changes in vegetation growth and soil decomposition, both contributing to land
–atmosphere flux changes in the same
57 direction. Though the results of these studies emphasizing the dominant factors
influencing the interannual variability of the terrestrial carbon flux vary a lot, they provide insight and opportunities to explore the underlying physical and
biological mechanisms of the interannual variability of atmospheric CO2 growth rate. Most of the studies cited above, however, have primarily focused on the
effect of the climatic factors on photosynthetic processes GPP, NPP. Climatic variability and climatic change can also change the amount of
carbon held on land. Year-to-year variation in temperature and precipitation, in affecting rates of photosynthesis and respiration, is thought to be the major factor
responsible for large year-to-year variation in the growth rate of atmospheric CO2. Over the longer-term, the effects of climate change are not as clear.
Prediction of future terrestrial sinks resulting from climate change requires an understanding of not only plant and microbial physiology, but also the regional
aspects of future climate change.
4.4.2.2. Connection between ENSO and IOD
ENSO is a leading mode of tropical climate variability at interannual timescales and is characterized by sea surface temperature SST and surface
pressure anomalies across the Pacific Ocean. Its positive “El Nino” phase occurs when SSTs are warm in the eastern tropical Pacific Ocean contrasted by its
negative “La Nina” phase when they are cool. ENSO impacts on tropical are believed to occur in part via tropical Atlantic and Indian Ocean teleconnections
Alexander et al., 2002. The IOD is another coupled ocean-atmosphere mode, with a positive
negative phase characterized by warm cool SSTs over the Western Indian Ocean and cool warm SSTs in the eastern Indian Ocean. The Indian Ocean
dipole mode IODM is defined as the difference in SST anomaly between the tropical western Indian Ocean 50
o
E-70
o
E, 10
o
S-10
o
N and the tropical southeastern Indian Ocean 90
o
E-110
o
E, 10
o
S-Equator. A positive IOD brings heavy rain to East Africa and droughts to Indonesia and parts of Australia.
Usually, parts of East Asia including Japan suffer from dry hot conditions during a positive IOD event whereas Southeast Asia suffers from floods. Indian summer
58 monsoon rainfall as a whole remains above normal during a positive IOD Saji
et.al, 2003. During normal conditions in the Indian Ocean, the sea surface temperature
is warmer in the east and cooler in the west. When an Indian Ocean Dipole event occurs, the situation is reversed. Cooling of the eastern part of the Indian Ocean
has resulted in less convection and less rain. Consequently longer drought occurred in western Indonesia during the summer.
Sometimes, the Indian Ocean Dipole can occur together with El-Nino in the Pacific, causing extreme weather and disaster events. When this happened in
1997, there was serious drought and extensive forest fires in Indonesia and Malaysia. When the IOD and El-Nino combined again in 2006, the worst flooding
in 50 years occurred in the Horn of Africa, affecting 1.8 million people. The flooding was followed by outbreaks of cholera, malaria and Rift Valley Fever.
The composite of IOD from SST of El Nino years shows a maximum from October to November associated with a warming cooling of the western
eastern Indian Ocean. The tendency of IOD indicates that a persistent forcing of this positive IOD exists from January to October.
Figure 4.13 show schematic of positive and negative IOD event SST anomalies are shaded red color is for warm anomalies and blue is for cold.
White patches indicate increased convective activities and arrows indicate anomalous wind directions during IOD events.
Figure 4.13. Schematic of Positive and Negative IOD event
59 The influence of IOD on other global climate systems is less explored.
One major difficulty is that many of the positive IOD events in the recent years are associated with strong El Nino events and it is difficult to separate the
influence of IOD from El Nino. Nevertheless, when the influence of ENSO is removed, in the tropical regions surrounding the Indian Ocean, there is a clear
pattern of warm temperature anomalies over land regions to the west and cool anomalies over regions to the east of the Indian Ocean.
Comparing data on climatic temperature and precipitation have resulted that the impact of El Nino and La Nina for NPP distribution is not significant or
only give small effect. However, comparing data between monthly mean NPP and monthly mean SST have resulted the significant effect for the distribution NPP as
show in Figure 4.14.
27 27.5
28 28.5
29
20 40
60 80
M on
th ly
A ver
ag e
SS T
M on
th ly
A ve
rage N
P P
Monthly Period
Correlation between NPP and Indian Ocean Dipole in Sumatra
Mean NPP SST
26 26.5
27 27.5
28 28.5
29
10 20
30 40
50 60
70
112006 212006
312006 412006
512006 612006
712006 812006
912006 1012006
1112006
M o
n th
ly a
v e
r a
g e
S e
a s
u r
f a
c e
t e
m p
e r
a tu
r e
M on
th ly a
ver ag
e N
P P
Monthly Period
Correlation between NPP and sea surface temperature, Year 2006
Mean NPP Mean SST
26.5 27
27.5 28
28.5 29
10 20
30 40
50 60
70 80
112005 212005
312005 412005
512005 612005
712005 812005
912005 1012005 1112005 1212005 M
o n
t h
ly a
v er
a g
e s
ea s
u r
fa c
e t
emp er
a tu
re
M on
th ly
av e
r ag
e N
P P
Monthly Period
Correlation between NPP and sea surface temperature, Year 2005
Mean NPP Mean SST
60
Figure 4.14 Relations between NPP and Indian Ocean Dipole
Figure 4.14 shows correlation between annual and monthly NPP with sea surface temperature SST. Result of analyses between monthly average NPP
distribution with sea surface temperature during normal climate condition non ENSO year has provided information about NPP distribution pattern. NPP has
reached maximum value during April and September. However, SST increased during April and reached maximum value in May and September.
Result of analyses between monthly average NPP distributions with SST during El Nino year has provided information about NPP distribution pattern.
NPP has reached maximum value in May and in other month NPP has decreased. However, NPP has increased during October. The SST also has similar trends
with the NPP during ENSO year El Nino event. Result of analyses between monthly average NPP distributions with SST
during La Nina year has provided information about NPP distribution pattern. NPP has reached maximum value in April and other month NPP has decreased
value. However, during September NPP has increased. The SST has reached maximum value during April but the SST has sharply decreased during September
in La Nina event. There are correlation between SST and NPP. Increased SST during normal
climate condition or abnormal climate condition always followed with increased NPP and the situation is reversed when SST has decreased, it will followed by
decreased NPP.
26.8 27
27.2 27.4
27.6 27.8
28 28.2
28.4 28.6
28.8
10 20
30 40
50 60
70
112007 212007
312007 412007
512007 612007
712007 812007
912007 1012007 1112007 1212007
Monthly Period
M on
th ly av
e r
age s
e a s
u r
fac e
t e
m p
e r
at u
r e
Mo n
t h
ly a
v e
r a
g e
N P
P
Correlation between NPP and sea surface temperature, Year 2007
Mean NPP Mean SST
61
4.4.3. Ground truth of NPP Estimation in Provinces
Administratively Sumatra terrestrial divided into ten provinces. In this study, two provinces have chosen to show the different characteristic of spatial
and distribution NPP in Sumatra terrestrial. The two provinces are Aceh and South Sumatra Province. Aceh province is located in the northern part of the
Sumatra Island meanwhile South Sumatra province is located in southern part of Sumatra Island.
4.4.3.1. Aceh Province
Within the country, Aceh is governed not as a province but as a special territory, an administrative designation intended to give the area increased
autonomy from the central government in Jakarta. Aceh has area around 5635481 ha. Administratively, the province is dividing into 18 regencies and has 5 cities.
The capital and the largest city is Banda Aceh, located on the coast near the northern tip of Sumatra. Estimation of NPP compare to the area in percentage of
Aceh province during years 2001 up to 2009 as shown in Figure 4.15.
Figure 4.15 Estimation of NPP distribution compare to area in Aceh Province
The GIS software has used to overlay NPP estimation within the province. NPP value divided into six groups value, range from 0 to 150 g C m
-2
yr
-1
. Low
25 50
75 100
2001 2002
2003 2004
2005 2006
2007 2008
2009
P er
ce nt
age A
re a
Year Period
Annual NPP Estimation of Aceh Province percentage areas
0-50 50 - 75
75 - 100 100 - 125
125 - 150 150
62 NPP value indicated as low or sparsely vegetation cover and high NPP value
indicated as dense vegetation cover. Figure 4.14 shows, Aceh province mostly dominated with high NPP value.
Based to estimation result, the province indicated has remained areas which covered by densely vegetation. Result estimation NPP show of low NPP value is
below 15 and it has dominated by NPP value with group 1 to 5. Meanwhile the high NPP value has percentage about 85.
However, yearly of total of NPP in average show the fluctuation results. In year 2001 to 2002 there is an increased of NPP value about 4.4. Different
condition occurred in 2002 to 2003; NPP value decreased about 5.8. Decreased of NPP over the province has followed in year 2003 to 2006 with decreased each
year around 5.2, 4.25 and 14.4. However, NPP has increased during 2006 to 2007 and 2008 to 2009 with increased percentage around 18.4 and 8.9.
Meanwhile during 2007 to 2008, NPP has decreased about 8.9.
4.4.3.2. South Sumatra Province
Within the country, South Sumatra is a province of Indonesia. It is on the island of Sumatra and borders the provinces of Lampung to the south, Bengkulu
to the west and Jambi to the north. Off of the coast are the islands of Bangka and Belitung, which are split from South Sumatra province to form the province of
Bangka Belitung in 2000. The capital of South Sumatra province is Palembang. Administratively, the province is subdivided into 10 regencies and 4 cities and has
an area about 8791496 ha. Estimation of NPP values compare to the area in percentage of South
Sumatra province during years 2001 up to 2009 as shown in Figure 4.16. Based to estimation result of NPP value in South Sumatra province, it has shown that NPP
in percentage are well distributed. Result estimation of NPP distribution in South Sumatra province has shown that lowest NPP value has annual average
changes about 1.4 compare to Aceh annual average of lowest of NPP is 1.3. High NPP value in South Sumatra province are dominated with the third group
range of NPP value 50 – 75 g C m
-2
yr
-1
with annual average NPP is 30.7.
