The Assessment of
Partial GLADA result to China Land Degradation
China LADA Team
Nairobi, Kenya, 7-9 April 2009
Main Contents
1 - General Opinion
2 - Verification of partial GLADA result to
China land degradation
3 - Comments on several GLADA Indicator
4 - Summary & Suggestion
General Opinion
(1) The utility of RS (Remote Sense) statistic / application of NDVI
to assess the vegetation growth is a common qualitative approach
for the evaluation of environmental situation, which manifests that
the development of RS technology provides the possibility of a
swift assessment of eco-dynamic in the Global-large scope.
General Opinion
(2) In general, the GLADA avails itself of NOAA RS data from 1981 to
2003 as the source of information, through analyses of NDVI, RUE
and EUE, assessing Global Land degradation / improvement with time
sequence. China LADA team believes that it is theoretically correct to
use NDVI to evaluate the Global scale situation, also can be
considered a trend of large-scope assessment of eco-environment.
General Opinion
(3) However, verification of GLADA result indicates some measures
of the assessment may not be perfect, especially deficiencies of
several impact indicators and/or the chosen parameters lead to
discrepancy between the real situation and GLADA assessing
output.
Verification of partial
GLADA Result to
China land degradation
Overall Opinion
(1) Arid regions (North China)
The GLADA report about China pointed that 8% of the country shows
an increase in climate-adjusted (NPP) net primary productivity over
the period 1981-2003, mostly located in the north of the country.
The results matches the general status in North China .Vegetation of
this arid region has been well rehabilitated due to the implementation
of some national eco-construction programs, however, according to
our examination, GLADA results to some specific regions does not
accord with real situation.
For example, Pamier is an oasis located in
west edge of Taklimakan desert, the
dynamic of land improvement is not that
apparent as the GLADA result shows.
Pamier
Minqin
Another example, Minqin is also an oasis; lay in the water-catchment area of
ShiYang River, GanSu Province, in recent 20 years, the over-exploitation of
Upstream leads to devastating decrease of stream flow, as the consequence,
Minqin had to dig and tap the ground water and the following lowing of ground
water level is making a eco-disaster to this city, degradation of all eco-aspect
includes, without limitation, the damp off of vegetation and etc, in year 2007, it
is the Chinese premier who personally deals with the issue occurred in Minqin,
making up his mind to try every attempt to combat degradation as well as
protect the eco-system.
(2) Humid regions (South China)
The report points, in China over the period of 1981-2003,
degrading areas, occupying 23% of the country, located in the
south of China.
While the results does not accord with the current monitoring
results from authorities. It is shown that with well rainfall and
tender temperature and without any sudden special natural
disaster, large-scope of land degradation is somehow, impossible
in this humid area.
(3) About Forest Degradation in China
The GLADA report points out, 39% of the degradation area in China
is forest, in which Broad-leaf forest accounts for 22% while needleleaf is for 17%.
From 1980, The Chinese government has executed several forest
eco-system rehabilitation and preservation projects such as Natural
Forest Protection Project, Conversion from Farmland to Forest /
Grassland (Grain for the Green) etc. It is also other International
Report proves that Forest resources have been under well-
protection and also been rehabilitated in an appropriate way. Some
forests have even not been covered by those projects, is also under
well care. Thereby the GLADA report may not reflect the actual
trend of forest development of China.
GLADA:
Land Degradation in
China from 1981-2003
Forest Resource Distribution Map of China
Some “hot spots” and field photos
Those are either national reserves or natural logging-prohibited zones, the
forest resource has been in well protected and rehabilitated for recent 20
years, the possibility of degradation occurrence is rather limited.
(4) The GLADA report indicates that in China 21% of
degrading land is arable (24 per cent of the arable), it quotes
the time-series data on land use since 1980s published by the
Ministry of Land Resources, P.R.C and remarks that from the
point of view of the environment, many of these changes are
harmful as to prove the result of this report (land is
degrading in south China) is correct.
China LADA Team never deny that cropland may be degraded,
however, we believes that this result is still arguable, at least
the remark shows an misunderstanding to agricultural status
in South China.
Firstly, from 1980s, the grain output (per unit) has a dramatic
increasing trend.
Secondly, China implements strict control for changing land
use from cropland to construction area, as a result, from the
time-series data, it can be seen most land use change
occurred differentiated just from plant species, e.g., from
grain to economic vegetation such as economic timber & fruit.
Thirdly, because of multi-sources of income among peasants in
South China, especially in GuangDong, ZheJiang and JiangSu
provinces, farmer does not depend on cropland that much, the
annual litigation regulation has also changed, typical
phenomenon in some places is seed/plough/harvest only once
in a year, compared with three times in the past, the land got
rehabilitated but a decrease value of NDVI in monitoring.
Comments on Several
GLADA Indicator
(1) Rain-use efficiency
Rain-use efficiency is NDVI/Rainfall, It is positive indicator
when applying in arid region where the growth of
vegetation mostly rely on natural rain-fed, however, when
we need to use this indicator as the adjustment of NDVI,
there are 2 concerns ought to be emphasized.
(1) Rain-use efficiency
(a) For oases or farmlands in arid deserts (e.g., the north of
China) where the rainfall is normally below 100mm annual
sum, all vegetation/crop-plant need irrigation because of
scarce rain and high evaporation.
So for some area RUE value is pretty high, but the
contribution comes from irrigation much more than rainfall,
thus to make RUE meaningless to irrigated farmlands and
oases in arid region.
RUE in oasis in the north of China
RUE is the highest in some irrigated cropland in Northwest China,
comparing relatively low RUE in South China, that means the
application of RUE shall technically integrate the condition of land use
and irrigation, or, it may result some limitation when adjusting NDVI.
(1) Rain-use efficiency
(b) For some areas which enjoy high rainfall, as soon as the
rainfall achieves specific amount, the excessive rain does not
make sense to plants, in this way, the correction from RUE
cannot reflect actual vegetation growth (NDVI).
According to the outcome of relevant researches, the
correlation between NDVI and rainfall is weak (South China),
and it should be scientifically taken into account when
applying RUE to adjust NDVI in those areas.
(2) About the Cloud in South humid area of China
Neither MODIS nor Wind Cloud is based on Radar-Monitoring, which
means their inspection cannot “penetrate through” the clouds, or to
say, the clouds does produce some impacts for the result captured by
these satellites.
According to relevant monitoring, in South China cloud coverage area
is large and the period of covering is pretty long (sometimes it has
lasted for several months). Although GIMMS accomplishes some
treatments / adjustments, since NDVI integrates results every 10 days,
it is believed NDVI may also be under-estimated thus not to correctly
present the growing situation of vegetation in the area hereinbefore.
In some area of South China, the amount
of cloud-covering days reaches 75% of
total annual time that may produce
impact on NDVI.
Not only in China, in the scope of the
whole “world”, the reflection of GLADA
report sees similar, most of land
degradation distributes in the area which
possess high cloud coverage rate.
(3) Limitation of NDVI
About NDVI itself, in high-density plantation area, e.g., wellgrowing forest, NDVI may become “saturated”, which means the
value of NDVI will not increase further after certain amount has
been achieved.
Summary & Suggestion
(1) For GLADA as the assessment to Global land degradation, the
technical application of NDVI is positive in theory.
(2) Because of some inappropriate selection of parameter and/or
indicator as well as for assessing measures, GLADA result
presently shows, no matter in China or in the whole world,
degraded land where forest is abundant, which may not fully tally
with the actual status, so embedded study is required.
Thank you!