Journal of Natural Disaster Science, Volume 27, Number 1, 2005, pp9-15

Multi-temporal Analysis of Land Cover Changes in Nagasaki City
Associated with Natural Disasters Using Satellite Remote Sensing

1

Asif A. SHAIKH1, Keinosuke GOTOH1 and Kaoru TACHIIRI2
Graduate School of Science and Technology, Nagasaki University
2
Department of Civil Engineering, Nagasaki University(Received for 5 Dec., 2003 and in revised from 29 Aug., 2005)

ABSTRACT
Natural disasters are inevitable and it is almost impossible to fully prevent the damage that they cause.
However, it is possible to reduce the potential risk by developing disaster early warning strategies and to help in
rehabilitation and post disaster reduction. Remote sensing technology has proven its usefulness, not only formonitoring disastrous events, but also to provide accurate and timely information well before the occurrence of adisaster. The study of the temporal changes of spatial patterns is important to understand the underlying factors
and the functional effects.
This paper addresses a multi-temporal analysis of land cover changes from 1986 to 2000 in Nagasaki City.
Nagasaki City was studied using Thematic Mapper (TM) data acquired by Landsat-5. Particular attention is given
to the selection of an appropriate method for land cover classification. A common and reputable unsupervisedclassification method, the Iterative Self-Organizing Data Analysis Technique (ISODATA) is used. The overall
results of the study area show that the amounts of forestland and agricultural land are decreasing and in contrast
the amounts of urban land and barren land are increasing. This trend is especially clear in detailed analysis of typically developed areas such as Tagonoura, Koebaru and Kaminoshima.

1. INTRODUCTION
Land cover change plays a vital role in regional, social andeconomic development and global environmental changes. It contributes significantly to Earth—atmosphere interactions.
Biodiversity loss is a major factor in sustainable development andhuman response to global change, and is important in integrated
modeling and assessment of environmental issues in general.
Scientists, researchers and planners have paid much attention to
the issues of land cover change over the past decade. A number ofstudies have been carried out using various methodologies andalgorithms to derive land cover and change information from different sets of remotely sensed data.
Natural disasters are inevitable, and the Japanese Islands areprone to all type of natural disaster such as flood, drought,typhoon, earthquakes and forest fires. Disasters can be classified
in several ways. Possible sub-divisions are: 1) Natural Disasters,
2) Human made disasters, and 3) Human induced disasters.
Another sub-division is related to the main controlling factors leading to a disaster. These may be meteorological, geomorphological/geological, ecological, technological, global environmental andextra terrestrial. Some disasters strike within a short period withdevastating outcomes; others have a slow onset period with equallyor even more serious repercussions (The Japan Landslides Society,1997).
Recent disasters include torrential downpours aroundKumamoto and Nagasaki in 1972; disasters from Typhoon No. 17in 1976; torrential downpours in Nagasaki in 1982; and disasters
from Typhoon No. 19 in 1991 that hit Nagasaki Pref., and manyothers. Human causalities from these disasters amount to 543
deaths in the 1972 event, 298 deaths in the 1976 event, 493 deathsin the 1982 event and 66 deaths along with 777 persons wounded
in 1991 event (Iseda, T., Ochiai, H. and Tanabashi, Y., 1982).
Among them, the tragedy of 1992 was devastating. The disaster in
Nagasaki in July 1982 had catastrophic effects. Hundreds of people died and many became homeless due to the disaster, which wasfollowed by landslides. Thousands of billions yen of property
were destroyed thus badly effecting the economy of the prefecture(Table 1).
The landslides occurred at various parts of the city during andafter the disaster, mainly focused on the newly constructed areas.
The intensity of landslides can be investigated at Nishi Yama Dai
Township (Iseda et al., 1982) (Fig. 1). The area is surrounded bymountains and after the disastrous event the occurrence of landslides around the New Township caused many deaths and extensive damage. In Fig. 1, points A and B indicate the locations
where the collapses directly hit the front areas of public apartments. Small black circles show the locations where landslides
occurred.
Land cover changes in Nagasaki City have been significant
over the past few decades. The development of new townships inrecent years i.e. Sakura no Sato, Yume ga Oka and Minato Zaka

KEY WORDS: Remote sensing, Land cover, Landslide, Natural disaster, Nagasaki

10A. A. SHAIKH, K. GOTOH AND K. TACHIIRI

Table 1.

Catastrophic Losses of the Disaster in Nagasaki in July 1982 (Iseda et al., 1982)

Nagasaki City
Nishi Yama Dai

Fig. 1Landslides at Nishi Yama Dai area, Nagasaki in the 1982
Disaster (Iseda et al., 1982)

etc. has accelerated the chance of landslides occurring in thoseareas. Landslides generally occur along gently to moderately sloping ground. Such areas tend to include residential and agriculturaluse. Because of these conditions, measures must be taken to protect the slopes from future landslides and failures.
Now we can access information gathering and organizing
technologies such as remote sensing and geographic information
systems (GIS), which have proven their usefulness in disaster management and monitoring. The use of remote sensing data, such as
satellite imageries and aerial photos allow us to map the variability

Fig. 2

Location of the study area (Nagasaki City, Japan)of terrain properties, such as vegetation, water and geology, bothspatially and temporally. Remote sensing also allows monitoring
the event during the time of occurrence while the forces are still inprogress. After the cessation of the disaster event, remote sensing
can help to prevent the occurrence of such disasters again in future.
2. STUDY AREA AND USED DATA
Nagasaki, with the exception of Okinawa, is the westernmost
prefecture of Japan and has a land area and population of 241.2km2

MULTI-TEMPORAL ANALYSIS OF LAND COVER CHANGES IN NAGASAKI CITY ASSOCIATED WITH NATURAL DISASTERS USING SATELLITE REMOTE SENSING

Table 2.

Land Cover Classification Schemeand 426,500 (The World Gazetteer, 2002). Only 10% of the landarea is flatland and 58% of the total area is comprised of forests.
Nagasaki City was selected for analyzing land cover variation(Fig. 2). As other cities, this city includes land cover types of forest, grassland, urban and built-up land, agricultural land, wetland,etc. In the last few decades, due to natural disasters and urbanization, the land cover in this area has changed significantly.
Landsat TM digital data of May 12, 1986, May 12, 1992, andMay 2, 2000 were employed in this study. Criteria to the selectionof the multi-temporal Landsat data set involved assessment ofcloud cover percentage, time of acquisition, and sensor type so thatto optimize the land cover change detection scope. Aerial photographs of Nagasaki taken in December 1982 were used mainly toverify the accuracy of the land cover classification (Nagasaki
Shinbun Sha, 1985).
3. METHODOLOGY
3.1 Data Acquisition and Image Preprocessing
Seven banded remotely sensed data were acquired by TM on
Landsat 5, having 5,965 lines and 6,920 pixels. The data used inthis study were extracted as a sub-scene from the original dataset.
For the purpose of temporal land cover change detection, remotelysensed data were obtained in the same month, i.e. May of 1986,
1992 and 2000.
With constraints such as spatial, spectral, temporal and radiometric resolution, relatively simple remote sensing devices cannot
record adequately the complexity of the Earth’s land and water
surfaces. Consequently, error creeps into the data acquisition
process and can degrade the quality of the remotely sensed datacollected. Therefore, it is necessary to preprocess the remotelysensed data before the actual analysis. Radiometric and geometricerrors are the most common types of errors encountered in remotely sensed imagery. The commercial data provider has removed theradiometric and systematic errors of Landsat/TM data, while theunsystematic geometric distortion remains in the image.
The geometric errors were corrected using ground control
points (GCP). Nearest-neighbor re-sampling method was used tocorrect the data geometrically. A correlation threshold is used toaccept or discard points. The correlation range was within limits
i.e. 1 pixel size. The x and y corrections were below 0.5 pixel.
3.2 Classification Analysis
In this study, the satellite images were classified using a common and popular unsupervised, Iterative Self-Organizing Data
Analysis Technique (ISODATA) classification algorithm. The

11ISODATA clustering method uses spectral distance as in thesequential method, however it iteratively classifies the pixels, redefines the criteria for each class, and classifies again, so that thespectral distance patterns in the data gradually emerge. ISODATA
is iterative in that it repeatedly performs an entire classification
and recalculates statistics. Self-Organizing refers to the way inwhich it locates clusters with minimum user input. The ISODATA
method uses minimum spectral distance to assign a cluster for eachcandidate pixel (Digital Image Processing, 1996).
To perform ISODATA clustering, the following parameters
were specified:● N – the maximum number of clusters to be considered. Since
each cluster is the basis for a class, this number becomes themaximum number of classes to be formed (10 in this study).
● T – the convergence threshold, which is the maximum percentage of pixels whose class values are allowed to beunchanged between iterations (95% in this study).
● M – the maximum number of iterations to be performed (24 inthis study).
Certain classification schemes that can readily incorporate
land use and/or land cover data obtained by the interpretation of
remotely sensed data have been developed (Introductory Digital
Image Processing, 1996). The classification scheme shown in
Table 2 was applied in this study.
3.3 Accuracy Assessment
The most common and typical method to assess classification
accuracy Error Matrix (sometimes called a confusion matrix orcontingency table) was used to assess the accuracy assessment forthis study. Error matrix compares, on a category-by-categorybasis, the relationship between known referenced data and the corresponding results of an automated classification. Such matrices
are square, with the number of rows and columns equal to thenumber of categories whose classification accuracy is being
assessed (Introductory Digital Image Processing, 1996).
In this study, satellite classified image of the year 1986 andaerial photographs of Nagasaki City taken in December 1982, published by Nagasaki Shinbun Sha were compared to assess the accuracy. These aerial photographs were the latest authenticated available source of information for the study area. Further knowledgeof the study area was obtained through field surveys. These investigations provided better detail as to what type of land cover isactually present, especially at the locations of distinctive land
cover change. For computing the accuracy assessment 250 reference pixels were used. The overall accuracy calculated was 82%.
4. RESULTS
4.1 Land Cover Change in whole Nagasaki City
The results of ISODATA classification of Nagasaki City arepresented in Fig. 4-6. The calculated areas of each land cover are
shown in Table 3 and Fig. 3.
The overall results of the area indicate that the amounts offorestland and agricultural land are decreasing and in contrast theamounts of urban land and barren land are increasing. The amountof urban land has been increasing from 1986 until 2000; on theother hand, the amount of barren land has been decreasing from1986 until 1992 and then started increasing from 1992 until 2000.

12A. A. SHAIKH, K. GOTOH AND K. TACHIIRI

Table 3.

Area in km2
Water
Forest land
Range land
Urban land
Agricultural land
Barren land

Land Cover Change in Nagasaki City
Estimated by ISODATA Classification
1986/5/12 1992/5/124
123.7
28.1
33.3
42.6
9.5

3.4
117.5
28.2
49
38.8
4.3

2000/5/2

Overall Change

3.5
106.3
29.2
58.9
35.7
7.6

-0.5
-17.4
1.1
25.6
-6.9
-1.9

Nagasaki City

Water
Rangeland
Agricultural land

Fig. 3Fig. 4

Result of Land Cover Classification, 1986/5/12

Fig. 5Result of Land Cover Classification, 1992/5/12

Fig. 6

Result of Land Cover Classification, 2000/5/2

Forest land
Urban land
Barren land

Land Cover Change in Nagasaki City

Both the forestland and agricultural land within the study area
show an inclination towards decrease. The change of decrease in
the forestland and agricultural land since year 1986 until year 2000
comes up to 17.4km2 and 6.9km2, respectively. Whereas, the overall change of urban land from 1986 to 2000 was calculated as
25.6km2.
4.2 Detailed View in the Typical Areas
Three different sites, within the study area are chosen to show
the typical change in land cover. The locations are shown in Fig.
7. Fig. 8-10 show the land cover classification images of these
distinctive areas within the research site. The land cover change,in terms of percentage, is presented in Figs. 11, 12 and 13.
5. DISCUSSION
The results obtained through analyzing the satellite data wereverified through the ground truth method. The ground truth
method was also used to verify the accuracy of the results obtainedby satellite data. In order to obtain the ground truth, three typicalsites within the research area were visited. The results showed that
all three sites have the same tendency of constructing new towns.
The new towns namely, Sakura no Sato , Yume ga Oka andMinato Zaka were being constructed in Tagonoura, Koebaru andKaminoshima areas respectively (Figs. 8-10). These new towns
have been constructed within the last 15 years.
The construction of new towns has significantly changed theland cover of those areas. Due to Sakura no Sato new town inTagonoura area, the land cover has drastically altered between

ColorClass
Water
Forest land
Range land
Urban land
Agricultural land
Barren land

MULTI-TEMPORAL ANALYSIS OF LAND COVER CHANGES IN NAGASAKI CITY ASSOCIATED WITH NATURAL DISASTERS USING SATELLITE REMOTE SENSINGFig. 7Location of three selected areas

Fig. 8Land Cover Classification Images of Tagonoura in 1986, 1992 and 2000

Fig. 9Land Cover Classification Images of Koebaru in 1986, 1992 and 2000

1314A. A. SHAIKH, K. GOTOH AND K. TACHIIRI

Fig. 10 Land Cover Classification Images of Kaminoshima in 1986, 1992 and 2000

ColorClass
Water
Forest land

Color

Class
Range land
Urban land

Color

Kaminoshima Area

Koebaru Area

1992/5/12

Water
Range land
Agricultural land

2000/5/2

Forest land
Urban land
Barren land

Fig. 11 Land Cover Change of Tagonoura
Area

Area in Percentage

Area in Percentage

Area in Percentage

Tagonoura Area

1986/5/12

Class
Agricultural land
Barren land

1986/5/12

1992/5/12

Water
Range land
Agricultural land

2000/5/2

Forest land
Urban land
Barren land

Fig. 12 Land Cover Change of Koebaru
Area

1986 and 1992. A and A’ in Fig. 8 shows the land cover change
caused by the new township of Sakura no Sato. Yume ga Oka newtown has significantly altered the land cover between 1986 and1992. While noticing B and B in Fig. 9, it is apparent how Yume
ga Oka new town affected the land cover of the Koebaru area. A
new park named, Nagasaki Sogo Koen was constructed in 1998
in the Koebaru area, which helped to convert the barren land into
agricultural land (C and C in Fig. 9). In the Kaminoshima area,Phase 1 and 2 of Minato Zaka new town are largely accountable
for the land cover change. D, D , and D in Fig. 10 show the stepby step conversion of land cover due to Phase 1 of Minato Zaka
new town. Whereas E, E , and E in Fig. 10 illustrate how Phase
2 of Minato Zaka new town altered the land cover of theKaminoshima area.
Vegetation cover is an important factor influencing the occurrence and movement of rainfall-triggered landslides, and changes
to vegetation cover often result in modified landslide behavior.
Landslides occur when pore-water pressures in the regolith
decrease frictional resistance below that required to keep the saturated and heavier regolith in place. When tree roots are absent,

1986/5/12

1992/5/12

Water
Range land
Agricultural land

Fig. 13

2000/5/2

Forest land
Urban land
Barren land

Land Cover Change of
Kaminoshima Area

resistance of the regolith is further reduced, increasing the probability of landslides.
As mountains cover these areas, there is a likelihood of landslides. Due to forest and agricultural land, the water bearing
capacity of soil was significantly high in those areas. But with thedecrease of both forest and agricultural land, the water bearing
capacity of soil also decreased. This results in increased danger oflandslides in those areas, which may cause casualties and also
damage to the infrastructure.
6. CONCLUSION
Land cover is one of the boundary conditions that directly or
indirectly influence natural disasters. For this reason, the impactsof land cover changes are of primary concern. In this study, theeffects of land cover changes in Nagasaki were evaluated using
satellite remote sensing data. There is a reduction of forest andagricultural land mainly due to the construction of new townships
within the study area. In the last fourteen years, the forest andagricultural land was reduced by 123.7km2 and 42.6km2 in 1986 asMULTI-TEMPORAL ANALYSIS OF LAND COVER CHANGES IN NAGASAKI CITY ASSOCIATED WITH NATURAL DISASTERS USING SATELLITE REMOTE SENSING

compare with 106.3km2 and 35.7km2 in 2000, respectively. In contrast, urban land increased from 33.3km2 in 1986 to 58.9km2 in
2000. The dynamic changes are also clearly visible in three typicalsites within the study area.
The current study demonstrates the role of man made land
cover changes in increasing natural disasters risks. It is possible toreduce the potential risks and damage of natural disasters by planning and controlling the development of new townships in thestudy area. If not, the radical land cover changes within the study
area may impact directly on the activities of human beings and also
it may accelerate the damage caused by natural disasters.
ACKNOWLEDGEMENTS
We are grateful to the following organizations for their kind
support for providing the statistical data used in this study: theJapan Landslides Society, Statistics Bureau & Statistics Center,
Ministry of Public Management, Home Affairs, Posts andTelecommunications and The World Gazetteer.
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