Landuse Change and Environmental Degradation in Dhaka City

Abstract

The present research documents the extent and impact of land use change since 1960 to 2008. Topographical maps of 1960 and two images of different years (Landsat TM image, 1991 and Google image, 2008) were used and analyzed to accomplish the expected research outcomes. The study reveals that a large portion of land has been changed, and the rate of decrease of vegetation and wet/lowlands has appeared to be quite alarming. During 1960-2008, the Dhaka city lost 39.94% (5354 ha) of cultivated land, 66% (5026 ha) of vegetation, 44.48% (1657 ha) of water-bodies and 47.32% (42.50 ha) of wet/lowlands. During the period 1960-1991, the cultivated areas decreased to about 22.45% (97 ha/year), vegetation cover decreased to about 28.85% (71 ha/year), water­bodies to about 14.20% (17 ha/year) and wet/lowlands to about 35.10% (102 ha/year). During 1991 to 2008 Dhaka lost 22.56% (138 ha/year) of cultivated land, 52.21 % (166 ha/year) of vegetation, 35.29% (66 ha/year) of water-bodies and 18.82% (65 ha/year) of wet/lowlands. Maximum changes were found to be concentrated on certain land uses such as in cultivated land (about 112 hectares were under change per year) and vegetation (105 hectares were under change per year) during the study period 1960-2008. Rate of decrease in case of wet/lowlands 89 hectares per year during the same period. It has been observed that wet/lowlands were converted predominantly into built-up areas. The transformation of cultivated land, vegetated lands and wet/lowlands were strongly related with the high rate of growth of urban settlement. Three areas to represent the research were selected viz. Ashulia, Uttara and Amin Bazar. These areas grew and developed mostly during 1960 to 2008. It is important to observe that the increase for Ashulia was 218 .2% during 1960 to 1991. It was true also in case other two areas during 1960-2008. Growth of Uttara region was about 540.4% continuously almost steadily during the same period. It means, the rate of urbanization is much faster in Uttara than in Ashulia. It has been observed that a cultivated lands has been reduced due to urbanization in Uttara. It has also been observed that in Uttara vegetated lands increased for about (159.2%) during 1960-1991. But it has decreased in Ashulia and in Amin Bazar This research presents a dynamic change of land use in Dhaka city, based on selected physical and social factors. Land Change Modeler (LCM) was used to analyze the land use changes between various land use classes during the period 1960-1991 and 1991-2008. The land use change was assessed through evaluation of gains and losses by those classes. It was noted that most of the land use categories experienced loss and gain to some extent. But the pattern was different. During 1960-1991, cultivated/agricultural land lost 76.51 % and gained 68.45%, with a net loss of 8.06%. And in 1991-2008 it lost 78.31 % and gained 63. 72%, with a net loss of 14.59%. Vegetation lost 67.53% and gained 25.34 % in 1960-1991 with a net loss of 42.19 %. In 1991-2008 the loss was 36.28% and the gain was 19.36% with a net loss of 16.92%. Wet/lowlands lost 57.45% and gained 12.53 % in 1960-1991 with a net loss of 44.92 %. In 1991-2008 the loss was 23.57 % and the gain was 24.85% with a net gain of 1.28% and water-bodies neither gained nor lost and land (the loss of water bodies was already completed before that period). Built-up area lost to about 27.61 % and gained 93.58%, with a net gain of 65.97 % during 1960-1991. During 1991-2008 the loss was 56.42% and gain was 71.26% with a net gain of 14.84%. Net gain for bare soil/landfill was 10.58 % and in transport and communication it was 18.24% in 1960-1991. During 1991-2008 similar trends have been noticed for the rest of the classes, with the exception of bare soil/landfill, which seems to be stable. Transport, communication and others categories have gained to some extent. But however, there are always some scopes of checking the result in GIS environment. The location accuracy in land use change model using Landsat TM image of 1991 and Google Earth image of 2008 was done using the clear and visible roads. In case of classifying bare soil/landfill, cultivated/agricultural land and vegetation, the user accuracy were 59%, 49% and 61 % respectively. The prediction of land use change was done on Neural Network, a built-in module in the Andes version of ID RISI. Iterations considered were 5000, considered sufficient for running the data. The lowest accuracy obtained was 57 .30 for all the conversion types. The transition probability matrix records the probability of future changes in which each land use category indicates in relation to other category. This matrix was produced by the multiplication of each column in the transition probability matrix where the numbers of cells of corresponding land use showed the later scenario. Though this matrix can be used to predict future land use in any period, it was specially designed for the predictions for the years 2020 (short term) and 2050 (long term). This research attempted to bring light to the perception of local people regarding change of land use through questionnaire survey. It is evident from the views and opinions of the local people that real estate companies, unplanned urbanization, industrializai10n an<l government organizations are responsible for the change of land use pattern. They also claimed that flooding and drainage congestion, air and water pollution, traffic congestion, water, sanitation and health problems are the main effect of unplanned land use. The air and water pollution, traffic congestion and water-logging are becoming an acute problem for the inhabitants of Dhaka city and creating adverse physical and social environmental impact. Intem1ption of daily life, traffic congestion, scarcity of drinking water, disruption of sanitation, unhygienic situation and the spread of air-and water-borne diseases are the outcomes of land use changes. The local people viewed that to address the socio-environmental problems, it is immediately necessary to control rapid population growth, control unplanned urbanization, control air and water polluting industries and to remove all illegal structures from the wet/lowlands and to raise environmental awareness programs widely. The investigation undertook for this study reveals that the present land use management practices of government organizations are very weak and not systematic. The existing legal tools for different agencies are not exercised properly. Overlapping of functions among the agencies creates conflicts in land use management. The coordination among government organizations is poor, and there sincerely is questionable as well. This study delivers the essence that combined effort is necessary from the part of involved stakeholders such as local people, NGOs, local government body, central government and civic organizations to implement the conservation strategies of land use. Political will and government commitments are also needed essentially. In conclusion, suggestions have been made regarding proper demarcation of land use change, strengthening the relevant GOs, developing appropriate regulations and proper enforcement of laws towards sustainable land use.