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Disasters
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Land Degradation Analysis of Rainfed Agricultural Area in Pakistan using Remote Sensing Data
Satoshi Uchida*, Rakhshan Roohi** and Shahid Ahmad**
* Japan International Research Center for Agricultural Sciences (JIRCAS)
1-2 Ohwashi, Tsuuba, Ibaraki 305, Japan
** National Agricultural Research Centre , Pakistan Agricultural Research Council
P.O. Box BIH, Park Road, Islamabad, Pakistan
Abstract
Pothwar plateau area located in the northern part of Punjab province in Pakistan which is characterized by a high but irregular amount of precipitation has been developed as rainfed agricultural land mainly for wheat cultivation. This area I mostly covered with loess soil which is highly erosive. The objective of this study is to evaluate the capability of satellite remote sensing data for delineating erosive conditions and associated land degradation. Satellite data with three different scales have been employed for this study. GVI data were used to describe the general vegetation conditions of the area SPOT panchromatic data were mainly used to extract the severely eroded areas and LANDSAT TM data were used to calculate indices of soil and vegetation conditions. The conclusions of this multi-staged approach were as follows; 1) GVI data can be applied to distinguish agricultural land from non-agricultural land, 2) severely eroded area can be extracted by digital image processing from SPOT panchromatic data,3) land coverage and soil conditions in severely eroded area can be characterized by some indices calculated from LANDSAT TM data.
1. Introduction
Agricultural lands have been degraded by imppropriate use and management of limited land resources. In the pothwar plateau located in the northern part of Punjabprovince in Pakistan, rainfed agricultural land which is used mainly for wheat cultivation in the Rabi season has covered a considerable area of potentially arable land. The natural conditions of this land may be suitable for crop production provided that rainfall is stable and soil erosion is well controlled. However irregular climatic conditions for a long period of time and inadequate land land management in addition to the existence of highly erosive soils have resulted in the expansion of severely eroded and degraded land in this area.In order to conserve land and imporve degraded ranges, it is necessary to analyze the land conditions and the cause of land degration. For this purpose it is considered that the use of remote sensing and a geographic information system would provide information about ground features.National Agricultural Research Centre (NARC) of Pakistan Agricultural Research Centre (NARC) of Pakistan Agricultural Research Council and JIRCAS started a collaborative research program entitled ''Dynamic behavior of soil erosion/degradation and development of techniques for prevention of erosion in all tropical land uses' in 1991. This paper is a part of the results on the applicability of remote sensing technology to land degradation analysis . This study also takes into consideration the effect of a multi-staged approach using remote sensing data.
2. Objectives
There are three major objective in this study. The first one is to characterize the regional features in terms of vegetation veriation using remote sensing data with relatively low spatial resolution. The second is to delineate the complex topographic patterns in severely eroded areas by analyzing the data with high spatial resolution. And the last one is o distinguish the relation between erosivity and ground surface conditions associated with vegetation , soil and coverage state using multi-spectral information .
3. Study Area
Geographically the pothwar plateau is located on the watershed of the Soan river, which is one of the main tributaries of the Indus river, and its adjoining hilly areas. The elevation of this area ranges between 300 and 500 meters above sea level and the amount of mean annual precipitation varies from about 500 to 1,000 millimeters. There are two peaks of rainfall in a year one in February to March and the second in July to August Crop cultivation usually corresponds to the rainfall pattern and the cropping season from October to March is called Rabi and the other season Kharif. The major soil types are loamy eroded loess and shallow residual with some gullied land Land use type is largely for agricultural purposes without systematic irrigation systems and the intensity of cultivation is relatively low.The scale of the study area foe data processing varies with the objectives. The target area for studies on vegetation variation using data with low spatial resolution was originally the whole country. Thereafter characteristic areas inside the Pothwar plateau were selected. With relatively higher resolution date, the calculated range which should be located in the middle of the Pothwar plateau includes 2,500 lines by 3,300 columns for SPOT data and 750 lines by 1,000 columns for LANDSAT data, respectively.
4. Methods
In this study basic data consist of satellite remote sensing data with three different scales and several kinds of small scale thematic maps. The satellite data with the smallest scale correspond to GVI (Global Vegetation Index) of which the original sensor is NOAA-AVHRR and the mesh size is modified to a larger value to cover the whole surface of the earth in a unit data set. Although GVI data represent weekly normalized vegetation index values, monthly maximum values in 1986 to 1989 have been applied to this study. Tow other satellite data consist of LANDSAT TM and APOST HRV panchromatic data. The data obtained by these satellites were recorded on 9 February 1992 and 2 April 1990 , respectively. Thematic maps are a part of intermediate archives of the agroenvironmental atlas produced by NARC and the scale of the sheet is 13,000,000.
Although seasonal variations of the vegetation are different from area to area, it is assumed that the vegetation state within an area with homogenrous physical and land use conditions may be uniform in general. In this case therefore, unit district of land which is applied to calculate the average value of GVI data is defined by overlaying six subjects of thematic maps as shown in Figure 1.0.02 degree in both latitude and logitude in order to match the position with that of land unit.
Figure 1. Flow of GVI data analysis
Extraction of severely eroded area is performed by using SPOT data and its procedure is illustrated in the upper part of Figure2. Two different methods were applied to this purpose. One was the manual interpretation method which distinguished the severely eroded area of the imagery other was the extraction by a digital image processing of data. For the purpose of facilitating extraction, effects of high path filter and rank order filter were examined in the process shown in figure 2.
Figure 2. Flow of Soil erosion area analysis
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