Photonirvaehak Journal of the Indian Society of Remote Sensing, Vol. 29, No. 1&2, 2001

Landuse/Landcover Change Detection Through Remote Sensing and its Climatic Implications in the

Godavari Delta Region V V L N SARMA, G MURALI KRISHNA, B HEMA MAL1NI* AND K NAGESWARA RAO

Dept. of Geo-Engineering, Andhra University, Visakhapatnam-530 003. *Dept. of Geography, Andhra University, Visakhapatnam-530 003

Introduction

The satellite remote sensing data with their repetitive nature have l~roved to be quite useful in mapping land use/land cover patterns and changes with time. Quantification of such changes is possible through GIS techniques even if the resultant spatial datasets are on different scales/resolutions. Since the advent of Landsat 1 in the early 1970s, many attempts have been made to map land use/land cover patterns. Such studies have helped in understanding the dynamics of human activities in space and time.

Recd. 30 Feb., 2001; in final form 20 Sept., 2001

The present study has been taken up in order to understand the changes that have taken place in land use/land cover in the Godavari deltaic region and its probable implications on the climate of the region.

Landsber& (1984) has indicated that when deforestation Occurs and swamps or water bodies are drained, the climate is invariably altered due to change in albedo. It is generally known that water bodies and wetlands have a property to buffer the heat and thereby reduce the daytime air temperature of the surrounding areas. Earlier studies on the urban climate of Visakhapatnam by Hemamalini and Rao (1991), and in parts of

86 V.V.L.N. Sarma et al.

Eastern Ghat region by Hemamalini & Rao (1994) have indicated changes in climate as a result of altered land use/land cover. The present paper is an attempt to find out changes, if any, in the local climate of the Godavari deltaic region on the east coast of India, which is experiencing a large-scale land cover changes, recently.

Study area

The Godavari deltaic region is located between 16~ 17~ N latitudes and 81030 ' and 82~ longitudes, covering an area of about 5100 km 2. With its apex near Rajahmundry at about 85 km inland from the coast, Godavari Delta has an arcuate shoreline stretching for about 160 km from the Upputeru river mouth in the south to the Uppada village in its north- eastern corner (Fig. 1).

Data and Methods

In order to analyse the land use/land cover patterns in the study area, Landsat MSS image of 1973 on 1:250,000 scale and IRS-LISS-II imagery of 1992, LISS III imagery of 1997 and 1999 (each on 1:50,000 scale) have been used. For the purpose of this study, land use/land cover features are categorized into three broad types namely, intensive agriculture/plantation, seasonal fallow/barren land and wetland. These three types were identified based on the visual interpretation of the satellite imagery coupled with field checks. These datasets were digitized and analysed through GIS to obtain land use/land cover statistics for the areas under each of these categories for all the four years i.e., 1973, 1992, 1997, and 1999. Data on daily maximum and minimum temperatures as welJ as monthly rainfall for the period 1970-98'Xvere collected from three stations in the Godavari deltaic region. In addition, monthly rainfall data for the period of 1980-98 were also collected from four more stations in the area.

The decadal averages of maximum as well as minimum temperatures and rainfall of each station were computed to find out the trends for

1970-79, 1980-89, and 1990-98 decades for comparison. The linear trends for the annual average maximum and minimum temperatures have been computed using the least square method.

Results and Discussion

Land use~land cover changes

Fertile deltaic alluvial soils and the availability of water through canals as well as ground water sources support intensive agricultural activity in the region. The Godavari deltaic region is one of the densely populated zones of the country with a population of 3.1 million (in 1991) at 550 persons per km 2. The population pressure, economic potential of the region and the entrepreneurial attitude of a majority of the farmers in the region have significantly transformed the land use/land cover pattern of the area, especially during the recent years.

Earlier Subrahmanyam and Rao (1981) have reported that nearly 62% of the harvested area in the Godavari delta was under paddy during Kharif followed by sugarcane, while the paddy was also grown during Raby season in certain pockets. Later, Rao et al. (1991) based on the interpretation of IRS-1A LISS-I image on 1: 250,000 scale have observed that due to changes in cropping pattern from seasonal crops to long term crops, there has been an increase in the cropping intensity by about 160% in the deltaic region during 1980s when compared to the earlier period. In the present study also the Landsat imagery of 1973 are found to be useful, especially for identifying broad categories of land use/land cover of 1970s required for the purpose of this study.

Large-scale exploitation of groundwater resources during the recent years has made cultivation of three crops possible instead of one or two crops earlier. Further, the area under plantation crops such as coconut, Casuarina, cashew, mango, etc., has increased during the

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past one decade: This is evident from the observation of the satellite imagery. While 1973 image (Fig. 2a) shows maximum area under seasonal fallow/barren .land, the 1997 satellite image (Fig. 2c) shows a dense vegetative cover in many parts of the deltaic area even in the month of May during mid-summer. Moreover, the aquaculture boom in recent years has completely altered the face of t h e lower Godavari deltaic region, which appears with mottled blue on 1997 and 1999 imagery.

The progressive increase in the cropping intensity as well as wetland extent in the delta is revealed by the area statistics obtained from the G1S analysis of the four datasets (Table 1). During the period between 1973 and 1999, there has been an increase in the area under intensive agriculture/plantation by 2041 km 2 and wetland by 280 km 2, respectively, while the extent of seasonal fallow/barren land has decreased by 2321 km 2. The increase in the wetland extent, is mainly due to the large-scale aquaculture

practices in the coastal parts of the delta. In fact, an area of about 395 km 2, which was mainly occupied in 1973 by seasonal agricultural lands and/or barren, dry tidal mudflats, besides mangrove swamps, has been converted into prawn/fish ponds that contain water almost throughout the year. As such, the extent of wetlands, albeit artificially, has increased considerably in the deltaic region.

Temperature trends

The linear trends computed for the annual average maximum temperature values, using the least square method at 99% confidence level, show a decreasing trend from 1970 to 1998 at all the three stations, namely, Kakinada, Maruteru and Nidadavole. On the other hand the minimum temperatures reveal an increasing trend except at Nidadavole (Fig. 3). On the whole, the decadal averages of maximum temperatures have decreased while the minimum temPeratures have increased in the area (Table 2).

Table 1: Land use/land cover changes in the Godavari deltaic region during 1973-1999

Land use/land cover

Type 1973

Intensive agriculture/Plantation 1459

Seasonal fallow/Barren land 3069

Wetland 368

River/Tidal channel 225

Total extent (km 2) 5121

Area (kin 2)

1992 1997

�9 2655 3011

1710 1271

531 614

225 225

5121 5121

1999

3500

748

648

225

5121

Table 2: Variations in decadal temperature in the Godavari deltaic region

Decades Kakinada Maruteru Nidadavole

Maximum Minimum Maximum Minimum Maximum Minimum (oc) (oc) (oc) (oc) (oc) (~

1970-79 32.9 23.9 31.8 23. I 21.8

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33

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1990-98 32.4 24.4 31.6 22.4 32.4 22.8

Difference -0.5 +0.5 -0.2 +0.6 -0.7 -0.3 (1970-98)

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Maximum Temperatures

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Fig. 3. T rends in annua l average m a x i m u m and m i n i m u m tempera tu re in the Godavar i deltaic region dur ing 1970-1998

90 V.V.L.N. Sarma et al.

Table 3: Variations in decadal rainfall in the Godavari deltaic region

Station

Maruteru

Nidadavole

Kakinada

Bhimavaram

Ambajipeta

Rajahmundry

Razole

Rainfall(mm)

1970-79 1980-89 1990-98 Difference

1107 1174 1365 +258*

1125 1154 1469 +344*

1153 1016 1228 +75*

NA 1016 1221 +205

NA 1045 1357 +312

NA 1045 1436 +391

NA 1078 1557 +479

* Difference between 1970-79 and 1990-98

Rain fa l l t rends

The decadal analysis of rainfall has indicated an overall increasing trend at aN the seven stations during the past three decades (Table 3). It may be noted that the rainfall data for three stations, namely, Kakinada, Maruteru and Nidadavole were available for the period 1970-98, while for the remaining stations the data pertaining to 1980-98 period only were available. Nevertheless, the increasing trend of rainfall ranging between 75 to 479 mm is notable at all the stations.

Several studies have revealed that the micro- level changes of climate in terms of rainfall and temperature variations are related to albedo changes, which in turn could be due to land use/ land cover modification. Charney et al. (1977) based on their model experiments have stated that when an area is experiencing appreciable evaporation, an increase of albedo causes reduced absorption of solar radiation by the ground leading to a continuous flow of latent heat into the atmosphere which lead to decrease of the cloud cover and rainfall. Based on similar experiments, Chervin (1979) has concluded that although there may not be any change of the global average, precipitation changes locally due to alteration of albedo. Meher-Homji (1994) has observed that under barren conditions the albedo

is as high as 30% as a result of which most of the solar radiation is reflected back to the atmosphere heating the upper layers of the atmosphere and thereby increasing the subsidence i.e. the downward sinking motion of the air leading to a reduction in the incidence of precipitation. Taking the same analogy into consideration, it can be stated that the reverse should be true where there is an increase in vegetation cover and wetland extent. In such areas, the decreased albedo should lead to increased convective activity resulting in more rainfall. Similarly, as the vegetatio n and wetlands tend to absorb heat, the ambient air temPeratures are likely to decrease. This is especially true in the case of day time (maximum) temperatures, since during the day a greater proportion of solar energy is transformed into latent heat due to plant transpiration, thus reducing the air temperature (Mocsenyi, 1985). Similarly, during nights, the water bodies/wetlands, being warmer than the land portions, influence the night time (minimum) temperatures. Perhaps this principle holds good in the case of the Godavari deltaic region. Growth of crops almost throughout the year and raising of plantation crops have led to a definite increase in vegetation cover in the Godavari deltaic region during the recent years. It is evident from Table 1 that there was more than a two-fold increase in the area under

Land Use/Land Cover Change Detection... 91

intensive agriculture/plantation. It is also evident from Table 1 that there was an increase of wetland by 280 km: during the past 26 years from 368 km 2 in 1973 to 648 km 2 in 1999. The spatial increase in the vegetation cover and wetland extent can be expected to influence the climate of the area as evident from the temperature and rainfall trends. Hence, the land use/land cover changes in the Godavari deltaic region may be considered as responsible for the increased rainfall as well as temperature variations in the region.

Conclusions

The present study suggests that human activities in terms of land use/land cover alterations might be responsible for local level climatic changes. The decreasing trend in day time temperatures and increase of night time temperatures, besides increased rainfall during the past three decades in the Godavari deltaic region are the result of large-scale increase in vegetation cover as well as wetlands in the form of shrimp/fish ponds in the region.

Acknowledgements

The authors are grateful to the Department of Ocean Development, Government of India for funding a project entitled "Remote sensing studies on coastal biogeomorphological environments in the Godavari Delta region", under Land-Ocean Interaction in Coastal Zone (LOICZ) programme of IGBP. The present study forms a part of this on-going Project (DOD/25/ LOICZ/IGBP/1/95). Thanks are also due to the anonymous reviewer whose invaluable comments and suggestions have helped in the improvement of the manuscript.

References

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regions, J. Atmospheric Sciences, 34: 1366-1385.

Chervin, R. M. (1979). Response of the NCAR general circulation model to changed land surface albedo. Report of the JOC Stady Conference on Climate Models: Performance, Intercomparison and Sensitivity Studies, GARP Publication Series No. 22, World Meteorological Organization, Geneva.

Hemamalini, B. and Nageswara Rao. K. (1991). Warming of temperatures due to change of land condition in Visakhapatnam city, India. Proc. Symp. Environmental Change and GIS, held at Asahikawa, Japan during Aug. 25-28, 1991, pp. 37-46.

Hemamalini, B. and Udayabhaskara Rao, Ch. (1994). Impact of deforestation on rainfall patterns in a part of Eastern Ghat region of India. In: Geography of Environment (Eds.: M. Shaft and M. Raza). Rawat Publications, New Delhi, pp. 148-157.

Landsberg, H. E. (1984). Global climatic trends. In: The Resourceful Earth (Eds.: J.L. Simon and K. Herman). Basil Backwell Publications Ltd., New York, pp. 272-303.

Mehar-Homji, V. M. (1994). Rural development and concern for the environment. In: Geography of Environment (Eds.: M. Shaft and M. Raza). Rawat Publications, New Delhi, pp. 173-184.

Mocsenyi, M (1985). The effects of urbanisation on landscape elements and woodland cover. In: Pollution Control and Conservation (Ed.: M. Kovacs). Ellis Horwood Ltd., Chichester, pp. 267-283.

Rao, D. P., Raghavaswamy, V., Gautam, N. C., Ravishankar, G., Suresh, L. S. and Mujtaba, S. M. (1991). Land use patterns in deltas of east coast with special'reference to Godavari and Krishna river deltas, Memoirs Of Geol. Soc. of India, No. 22, pp. 51-56.

Subramanyam, A. R. and Venkata Rao, A. (1981). Eco-climate of rice crop in the deltaic districts of Andhra Pradesh, Abstract volume, 9th International Congress of Bio-meteorology, pp. 257-260.