An assessment of transformation of land cover and land use in province Lago Argentino (Argentina) by use of digital spatial methods

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An assessment of transformation of land cover and land use in province Lago Argentino (Argentina) by use of digital spatial methods

Grinfeldt Y.S.

Grinfeldt Y.S. Senior Researcher Department of World Physical Geography and Geoecology, Faculty of Geography, Lomonosov Moscow State University, Russia.

Summary: This paper explores the analysis of spatial fragmentation of land cover types of local site of Argentina - the Department of Lago Argentino, Santa Cruz Province. During the period from 2001 to 2012 the structure of land cover and land use undergone significant changes due to population growth, re-orientation of the World markets, increase of the pasture land use. On the basis of remote sensing methods (decoding of Landsat satellite images and processing of the data contained in the data base MODIS Land Cover) for the periods 2001 - 2012 using the program packages ArcGIS 10.4.1 and NextGIS-QGISj happened possible to determine the square of transformation of the land cover, main transitions and the courses of changes.

Key words: land cover classes, land use, change detection, regional level, local level, geoecology, geographic zones, Argentina.

Introduction

Investigated are is the department Lago Argentino of Santa Cruz province (Argentina). It relates to Patagonia physical-geographic area. Department is located at the South-West of the province and bounded by the Chico River from the north, bounded from the south with Guer Aike department, with the Corpen-Aike department at the east, and with Chili territory at the west. The highest point of the El Chalten province (Fitz Roy) - 3405 m is located here. Three large lakes are located in Andes front mountain area: Lago Argentino, Viedma and San Martin. Precipitation in Andes highlands promote ice accumulation formed the South Patagonia ice Plateau. 7000-8000 mm precipitation is falling at the level of the plateau annually [9]. Latitudinal depression free of ice opposing the Argentino Lake separates the ice plateau into two parts - spacious northern and relatively small southern. Excretory glaciers moving from the plateau from the west are mostly end at the lakes (O'Higgins, Viedma, Argentino). At the territory of department the largest excretory glaciers are located: Viedma, Upsala, Perito Moreno. At the Argentinean territory the South Patagonia plateau forms the national park Los Glaciares. Ha Amount of precipitation is decreeing from West to East therefore in the Eastern part o the territory is formed a moderate combinational climate with average precipitation rate of 500 mm per year [8]. The deficit of precipitation promotes the sheep breeding. Preference order of soil is Molisoli. Lack of precipitation suppotys the development of sheep breeding. Preliminary soil types are Molisoli, which supports the agricultural development of the area [2].

Main agricultural specialization of the Santa Cruz province of Argentina is the pasture stock breeding. The only exclusion is the Lago Argentino department, which develop the recreational servicies (National Park Los Glaciares). The historical development the conditional core landscapes of the Lago Argentina department were significantly transformed due to intensive agricultural development mainly because of pasteurizeing [4]. Study of soil cover transformation degree is actual for determining of geo-environmental problems, factors identification and causes of transformation [3].

The problem statement

Land change is considered a major contributor of global environmental change. Estimates indicate that human land change has impacted ~40% of the earth's ice-free terrestrial surface, mostly due to the conversion of natural ecosystems (e.g., forests, savannas, and grasslands) to croplands and pasture. The impacts of land changes over ecosystems are greater across the tropics where land conversion for agriculture mostly occurs over intact forested lands. Central to land-change research is to identify the different land change trajectories (i.e., deforestation and reforestation) and to understand how to balance land conversion to meet human needs while preserving natural ecosystems. Land change is the result of the interaction of multiple social, economic, and environmental factors occurring at multiple and hierarchical spatial scales (e.g., local, regional, global). Human population change, rural to urban migration, consumption patterns, presence and effectiveness of social institutions, and land-use policies are all examples of local factors that can influence patterns of land change. Examples of regional or global factors include the increasing global demand for agricultural products, shifts in regional economies, indirect effects of tourism, and globalization of markets. In addition, climate change and variability (e.g., droughts, tropical storms) are often important factors influencing land change [7].

In the world practices of scientific research for assessment the Degree of Transformation of the Land Cover Structure such degree is wildly used the geo-spatial data bases Land Cover Change, generated on the basis of spectral radiometer MODIS (Moderate-resolution Imaging Spectroradiometer). Data of the Land Cover Change are the secondary images obtained after processing of MODIS data in certain zones and are distributed in free access in Internet network [6]. These data contain information on spatial distribution of vegetation types of natural and anthropogenic geneses, urban and built-up areas, territories free of vegetation (waste grounds, glaciers, etc.), water bodies, water streams, and over moistened areas [1].

The object of the Land Cover Change analysis is the category of land cover, which in reality is only relatively related to belt-zone specifics. For instance, the grassland category can be met both in Arctic and subEquator latitudes, Mixed Forest category exist within the moderate, subtropical and tropical zones. Therefore, to interpret results on the basis of landscape approach, it is necessary to use independent operational territory landscape units, according which the analysis and assessment of measurements could be conducted. The most applicable for such territory unit seems to be the natural zones with the uniform of hydrothermal, soil-geographic and geo-botanic characteristics.

Materials and methods

As mentioned above, as a data source on land cover conditions for 2001-2012 period the publically available data of Land Cover Change [6]. As a media for analysis the GIS package ArcGIS for Desktop Extension Spatial Analyst.

For assessment of degree of transformation of the land cover structure, the aggregated global data with horizontal resolution 5'x5' in geographical coordinate system WGS-84 (World Geodetic System - 1984 were used. Considering that the main goal of the analysis was the calculation of area variations in land cover structure over the globe, the data were projected into Cylindrical Equal Area projection. The projection was carried out with the basic complectation of the ArcGIS for Desktop Basic. The cell size of output raster was determined as 1000, firstly for conformity of further calculations of the areas of land cover variations, and secondly, since it provides the optimal raster dimension and allow not losing the data metallization.

For raster data for preprocessed with the method mentioned above, 2001 and 2012 the instrument Combine of ArcGIS for Desktop Spatial Analyst was used. Each combination of input data of two rasters was distinguished as a unique zone. For each zone the number of included cells was calculated, which in this case is 1 km 2, since the resolution of analysed rasters is equal to 1000 m. The tables obtained were supplemented with the text description of the land surface (Join Field instrument), the percent of existed changes within the initial zone (from the zone in 2001) was also calculated.

The legend for Land Cover Change includes 17 classes (from 0 to 16), corresponding to classification of International Geosphere Biosphere Programme (IGBP): 0 - Water,1 - Evergreen Needleleaf Forest, 2 Evergreen Broadleaf Forest, 3 - Deciduous Needleleaf forest, 4 - Deciduous Broadleleaf Forest - 5Mixed Forest, 6 - Closed Shrublands, 7 - Open Shrublands, 8 - Woody Savannas, 9 - Savannas, 10 - Grasslands, 11 - Permanent Wetlands, 12 - Croplands, 13 - Urban and Built-up, 14 - Cropland and Natural Vegetation Mosaic, 15 - Snow and ice, 16 - Barren or Sparsely Vegetated.

Thus, the data for Land Cover of 2001 and 2012 were compared where the each cell is characterized with corresponding numerical index from 0 to 16 according classification. Whit change of the land cover class from 2012 in comparison with 2001 the change of numerical index is occurred. It allows to segregate a sell (or the number of sells) as an area of certain types of changes. For example, index 12.5 means that the arable lands covered the cell in 2001 were replaced with mixed forest in 2012.

Identification of transformed territories of Lago Argentino department was conducted on the basis of mosaic of Landsat 7 (2001 and 2012) space images. To get the necessary information regarding the changes in the land use system two synthesized images and one timely-different composite image. In the study was used a combination of “artificial color” (channel system 4 - 3 - 2), where the red-brown tints represents vegetation, and green-blue represents damaged territories. For convenience of changes identification the time-different image based on two existing sets of scenes - synthetic red channel (Landsat7 2012) (Land- sat7 2001) and green channel (Landsat7 2012). Variations of rose-purple tints characterize the settled and disturbed territories, and blue - mostly for agricultural areas. Green color is an evidence of chlorophyll oversaturation, rose - absence of chlorophyll. As a media for analysis was used a GIS package ArcGIS Desktop for Desktop Spatial Analyst and combining instruments (Combine) for analysis of raster data Land Cover Change for identification of types and areas of changes occurred within the land cover in 2001 - 2012. Square table (Tabulate Table) for joint analysis of raster and vector data and calculation of transited land cover from 2001 to 2012 and their types in Lago-Argentino department was generated. The data base MODIS Land Cover [6] was a basis of analysis of transformation areas. The study was conducted in the framework of the NextGIS-QGIS program, Images were provided by USGS Earth Explorer and by La Red Geoespacial de America Latina y el Caribe [5].

Goal. The goal of this study is to determine the zones of transformation of land cover in the Lago Ar- gentino department (province Santa Cruz, Argentina) during 2001 - 2012.

To reach the goal the following tasks were determined: to allocate the Santa Cruz province in the structure of the Argentinial land cover, study the natural conditions and current landscapes in Lago Argentino department, determine the social-economic specifics of the studied area, and using remote sensing methods compare the data of 2001 and 2012. And identify the changes in the land cover in the Lago Argentino department. Compare the identified changes with the spatial data base and thematic cartographic materials of the national organizations, identify the causes of land cover transformation.

Results and discussion

Image in combination of “artificial” color for 2001 demonstrates that no vegetation disturbance was observed (Fig. 1).

geodetic argentina land cover

Figure 1. Scheme of Landsat 7 images decoding in 2001

Image in combination of “artificial” color for 2012 identified in the western part of the territory (undis-demonstrate that at the East of investigated area some turbed are relates to National park Los-Glacieres). changes (disturbances of vegetation cover) are observed (Fig. 2), at the same time no disturbances were Thus, after decoding of composite image it is seen that mainly the eastern part of the department is transformed, which oriented primarily on agriculture development (sheep breeding) (Fig. 3).

Figure 2. Scheme of Landsat 7 decoding for 2012

Figure 3. Results of composite image decoding

Since the population density at the department territory is low (0,69 pers/km2), the populated areas are distributed fragmentary and the main areas are covered with agricultural lands.

Comparison of obtained results with results of Change Detected 2001-2012 it is seen that the changes of the land cover types are observed exactly in these areas (Table 1).

Table 1. Dynamics of land cover types square in 2001-2012

Extension of the areas covered with snow and ice confirms the fact of glaciers growth in the Alpine foothills. Appearance of turned over year deciduous broad- leaf forests on the territory of Los Glaciares National Park is caused by natural reasons. Grasslands are included in this category. Areals of mixed forests are in the process of transformation to grasslands. Increase of the areas covered with open shrablands and grasslands has exclusively anthropogenic reasons related to increase of sheep breeding. This fact could be an evidence of harvesting lands shortening. Territories without vegetation in 2001 became grasslands and open shrablands formations in 2012. In the result of this study it became possible to determine the total square of transformed land, which comprised 39,9%. At 2001 - 2012 the territories barren or sparsely vegetated were completely disappeared, and the turned over year deciduous broadlive forests appeared.

References

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