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Landuse change analysis of three selected panchayats in Kuttanad using Remote Sensing data and GIS


The major environmental issues in the study area can be titled into following points.
  1. Degradation in the quantity and quality of water due to water pollution and stagnant nature or lack of flow, leading to increasing incidence of water borne diseases.
  2. Problems due to lack of tidal flushing and salinity intrusion - weed menace, increase of poisonous snakes etc.
  3. Lack of fertility and productivity of both wetland and dryland soil.
  4. Agricultural pollution - pesticide and fertiliser. Nutrient enrichment of water bodies, weed menace and eutrophication - inland destruction of earthworms.
  5. Frequent floods and droughts.
  6. Conversion of traditional natural freshwater ponds and other water bodies acting as the local source of safe drinking water.
  7. Threats of biologically rich zones of the area like mangroves and the consequent reduction of Biodiversity.

Methodology
The whole methodology adopted for the study is presented in the fig.1. The detailed methodological details are as follows.

First, the different data products such as cadastral maps, aerial photographs and resource maps were acquired. This is followed by the collection of secondary data from various departments, libraries and offices like village office, Panchayat office, Kerala State Land Use Board, Kerala Agricultural University, Directorate of Economics and Statistics, Fishermen co-operative societies etc.

Land use/ land cover mapping was done through actual field study. For that the land use classification scheme adopted in all the three panchayats is given in the table (1.1). Here the paddy double crop means, they are the popular puncha lands, and they are not regularly double cropped in the literal spirit. They are much lower than the virippu paddy lands. Traditionally the Puncha lands are double cropped, so they are designated as paddy double crop. Paddy with Aquaculture category includes both paddy cultivation and aquaculture in an alternative way as a part of the Integrated Farming System. There are people inhabited areas and these are settlements with mixed trees and mixed crops categories, which forms the main habitational areas. The marsh category in this study only means the uncultivable waterlogged fallow areas and not the conventional marshy ecosystem.

Table 1.1 Land use classification scheme adopted
Sl.No. Landuse Classes
1

Paddy - Double Crop (Puncha)
2 Paddy - Single Crop (Virippu)
3 Paddy with Aquaculture
4 Mixed Crops
5 Coconut
6 Cocoa
7 Plantain
8 Mango
9 Settlement with Mixed Trees
10 Pond
11 River
12 Lake
13 Marsh
14 Culturable waste

The whole technical methodology included the following activities.
  1. Collection of Data and Preparation of Maps.
    1. Preparation of Base Map Base maps of the study areas were prepared in the cadastral scale of 1:5000 using the village cadastral maps of each panchayats. All other thematic maps were prepared based on this base map.
    2. Data Interpretation of Basic Tax Register The plot wise information on land use from Basic Tax Register of Revenue Department procured from village offices in each panchayats were encoded, interpreted and transferred to the base map for identifying the survey number / plot wise land use pattern.
    3. Interpretation of Aerial Photographs Interpretation of Aerial photographs of the study areas for the period of 1990-’91 was also carried out at Kerala Forest Research Institute, (KFRI), Peechi, Thrissur. Altogether 14 Photographs were interpreted in the scale of 1:15000.
    4. Field Survey In the field survey, both field mapping of land use, and Participatory Rural Appraisal (PRA) was done.
      The mapping of recent land use (1997) in all the three panchayats were conducted using the base map prepared from the village cadastral maps in the scale of 1:5000. This field reality formed the basis to interpret the Aerial photographs. The mapping was done by identifying the survey plot in the ground and in the cadastral base map by comparing the survey plot number and other land marks shown in the base map.

      The Information on the causes and consequences of the land use changes were gathered through the technique popularly known as Participatory Rural Appraisal (PRA) which involved field observations, interviews and discussions with local people.

      Data Products Used For the Study
      Pallipad
      1. Cadastral maps (1:5000) of 1988
      2. Basic Tax Register (BTR) of 1988
      3. Aerial photographs of 1990-’91 (1:15000)
      Ramankary
      1. Cadastral maps (1:5000) of 1988
      2. Aerial photographs 1990’-91 >
      Kumarakom
      1. Cadastral map (1:5000) of 1988
      2. Basic Tax Register (BTR) of 1936 and 1988
      3. Aerial photographs of 1990-’91 (1:15000)
      4. Panchayat Resource Map of 1992 (1:5000).
    5. Preparation of Thematic Maps Time series thematic maps on Land use / Land cover has been prepared based on the interpreted data and the field survey. Thematic map depicting the accessibility and drainage were also prepared as a separate coverage for overlaying on the Land use map.
    List of Maps Generated
    Pallipad
    1. Land Use - 1988 (BTR)
    2. Land Use - 1990 (Aerial photographs)
    3. Land Use - 1997 (Field survey)
    4. Accessibility and Drainage>
    Ramankari
    1. Land use - 1990 (Aerial photographs)
    2. Land use - 1997 (Field survey)
    3. Accessibility and Drainage
    Kumarakom
    1. Land use - 1936 (BTR)
    2. Land use - 1988 (BTR)
    3. Land use - 1990 (Aerial photographs)
    4. Land use - 1992 (Resource Map)
    5. Land use - 1997 (Field survey)
    6. Accessibility and Drainage
     
  2. Digitisation of Maps The various thematic maps of 1:5000 scale were reduced to a scale of 1: 23,000 (Ramankari and Pallipad) and to 1: 25,000 (Kumarakom) using the `Optical Pantograph’ at KFRI, Peechi, Thrissur. These were scanned and a raster to vector conversion was carried out in AutoCAD (R14). A preliminary editing of these vectorised maps was done using AutoCAD itself and exported in DXF format.

    Analysis using ARC / INFO The digitised thematic maps in the DXF format were imported to ARC/INFO as coverages. After executing ‘CLEAN ‘ command for topology creation, the dangle node errors were removed interactively in ARCEDIT module. After all offshoot / undershoot errors have been removed, Feature Attribute Table (FAT) was created using `BUILD’ in ARC prompt. A master TIC file has been created and projected to UTM. The coverages were then transformed to the copies of the projected TIC file with output unit in metres. Then each land use/land cover category was assigned a code and these codes were attached to appropriate records of FAT interactively. A Look - Up Table (LUT) was also created to assign a shade symbol for each land use / land cover category.
To find out the temporal changes in the conversion of paddy during a specific time period, the area under paddy at an earlier time and the land use other than paddy at a recent time were extracted as separate coverages using `RESELECT’. Then, to find out the actual conversion of paddy areas during the period (e.g.: - 1936 to 1997 in the case of Kumarakom), on GIS, the two coverages were intersected using the overlay command `INTERSECT’. The `INTERSECT`’ command extracts those parts of input coverage falling within intersect coverage to a new coverage. Then the area statistics of Landuse/ Land cover of selected time periods and the intersected coverage which gives the actual conversion, were extracted from the Feature Attribute Tables of respective coverages. This was done using the ‘TABLES’ module of ARC/INFO. The flow chart of GIS analysis is given in the figure (1.1).

Flowchart of Paddy Area Change Analysis in a GIS Environment


Results and Observations
The comparative analysis of land use changes through the Overlay operation of ARC/INFO given the following datials. This will also give a comparison between the three study areas representing the total entity of Kuttanad wetland ecosystem.

Pallipad The comparative analysis of land uses of 1997 with the status in 1988 clearly defines the changes taken place during the last decade. The changes are mainly in the form of reclamation, conversion and degradation of paddy cultivating areas comprising both puncha and virippu fields to other non paddy land uses such as coconut, mixed crops, plantain, mixed crops and marsh. The total area of paddy which occupied 742.18 ha. (56.6 percent of total geographical area of 1311.21 ha) in 1988 has been reduced to 652.01 in 1997 and this shows a 12.15 percent reduction in paddy area i.e., the paddy area which was represented in about 56.6% of the total area in 1988 has been reduced to 49.72% in 1997.

The major change from paddy was to settlements with mixed trees category coming to about 73.69 percent of the total paddy change, i.e., from 541.55 ha. in 1988 to 608 ha. in 1997. The area of paddy cultivation changed to coconut comes about 13.24 percent (from 1.25 ha. to 16.89 ha) ,to mixed crops comes to about 2.66 percent, to plantain 0.31 percent and to the water areas which comes to about 1.03 percent. About 8.93 percent of the change was to marsh. A slight increase in area of pond, and river is noticed from 3.02 to 3.54 hectares and 23.21 to 23.55 hectares respectively. The new categories of land uses evolved mainly through the conversion of paddy are mixed crops, comprising 2.71 ha, plantain comprising 0.37 ha. and marsh comprising 10.27 ha.



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