Iraqi Geological Journal Mzuri Et Al
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Iraqi Geological Journal Mzuri et al. 2021, 54 (1A), 110-126 Iraqi Geological Journal Journal homepage: https://www.igj-iraq.org Spatiotemporal Analysis of Vegetation Cover and Its Response to Terrain and Climate Factors in Duhok Governorate, Kurdistan Region, Iraq Rebar Tahseen Mzuri 1, *, Abdulla Amir Omar1, and Yaseen Taha Mustafa2 1Department of Geology, College of Science, Salahaddin University, Erbil, Kurdistan Region, Iraq 2Department of Environmental Science, Faculty of Science, University of Zakho, Kurdistan Region, Iraq *Correspondence: [email protected]; Tel.: +964 750 448 9752 Received date: 24 September 2020; Accepted: 22 November 2020; Published: 31 January 2021 Abstract The integration of remote sensing techniques and Geographic Information System has a wide use to quantify the spatial and temporal distribution of vegetation cover. Over the last decade, a remarkable change was noticed in both climate and vegetation cover in Duhok. The Modified Soil Adjusted Vegetation Index (MSAVI2) was extracted from Landsat satellite images over the 20 years (2000 to 2019). For analyzing the vegetation changes, the terrain data including elevation, slope, and aspect and climate data temperature and precipitation are used. The result shows that from 2000–2019, the average mean MSAVI2 is 0.361 and the trend increased in 77.9% of the study area. The northern and northeastern areas of the study area revealed a significant increase in vegetation, while in the low land areas it is decreased. The amount of precipitation and temperature degree affect the spatiotemporal distribution of vegetation cover. The MSAVI2 showed a positive relationship with precipitation and temperature. At elevation less than 2000 m, with increasing elevation the MSAVI2 is increasing, but when the elevation reaches 2000 m, the MSAVI2 is decreasing and negatively related to elevation. The vegetation has a positive relation with slopes less than 45°, and at slopes higher than 45°, the MSAVI2 is decreased. The impact of aspect on the vegetation figured out that the largest MSAVI2 is detected in the shady slope due to relatively less evapotranspiration. Keywords: Vegetation cover change; Terrain factor; Climate factor; Statistical analysis 1. Introduction The spatial distribution of vegetation in high-altitude areas is very important as it reduces soil erosion and affects climate change. Vegetation cover effectively protects the environment against the risk of natural hazards such as rockslide, floods, shallow landslides, and debris flows (Brang et al. 2001). Spatial and temporal variations in vegetation cover are significant in the ecosystem changes (Shi et al., 2019). Terrain factors (elevation, slope, and aspect) and climate factors (rainfall and temperature) have an impact on the spatiotemporal distribution of vegetation cover and vegetation growth (Jirjees et al. 2020; Liu et al. 2018). Therefore, understanding the spatial and temporal distribution of vegetation growth along with the affecting factors have been studied worldwide (Zhu et al. 2011; Chen et al. 2006; Othman et al. 2020; Mustafa and Ismail, 2019). To have a comprehensive overview of spatial and temporal analysis of vegetation analysis within a large area, satellite remote sensing data and Geographic information system (GIS) would be the most suitable techniques to be used. Remote sensing (RS) and DOI: 10.46717/igj.54.1A.10Ms-2021-01-31 110 Iraqi Geological Journal Mzuri et al. 2021, 54 (1A), 110-126 GIS are appropriate techniques for analyzing the spatiotemporal distribution of vegetation and other natural resources (Ochege et al. 2017). This can be performed by using mathematical relationships between and among satellite bands to create so-called indices. Among the many RS indices, Modified Soil Adjusted Vegetation Index (MSAVI2), is used to identify the vegetation cover and growth. The MSAVI2 is a widely used vegetation index, derived from reflectance measurements in the red and near- infrared spectral bands (Qi et al., 1994). The MSAVI2 corrects the reflection of areas with a large amount of exposed soil. When applied to areas with a high level of the exposed soil surface, it aims to resolve some of the shortcomings of the Normalized Different Vegetation Index (NDVI). In bare soil areas, the MSAVI2 index is more powerful than the NDVI for vegetative area delineation. This behavior of MSAVI2 is more useful for vegetation studies in the Iraqi Kurdistan Region, where much of the soil is exposed (Gaznayee and Al-Quraishi, 2020). Gaznayee and Al-Quraishi (2020) used MSAVI2 to identify drought status in Duhok Governorate. Liu and Wang (2005) used MSAVI2 as an indicator to monitor desertification in China. Moreover, MSAVI2 is used to evaluate the impact of drought on the spatiotemporal distribution of vegetation on the San Carlos Apache Reservation in Arizona (Wu et al. 2016). Therefore, this research selected the MSAVI2 index along with climate data from 2000-2019 to analyze the trend and spatiotemporal distribution of vegetation cover in Duhok Governorate. The aim of the research is to assess the spatiotemporal changes of vegetation in Duhok Governorate from 2000- 2019, to explore the responses of MSAVI2 with respect to the elevation, slope, and aspect, and to investigate the relationships between vegetation distribution and climatic factors. 2. The Study Area Duhok is located in the northwestern part of the Iraqi Kurdistan Region. It is located within latitudes 36°18′ - 37°20′N, and longitudes 42° 20′- 44°17′E (UTM 280000 - 400000 Easting and 4080000 - 4140000 Northing), at altitude 291 to 2574 m above sea level, and it covers an area of 6,600 km2 (Fig. 1). Duhok has four Districts; Amadiya, Duhok, Zakho, and Sumail. Geologically; the study area is located in the high folded zone and imbricated zone according to the tectonic division of Iraq. It is characterized by a series of asymmetrical double plunging anticlines trending NW-SE with different extensions (Jassim and Gailani, 2006). The soil of the study area is classified according to chemical composition as a none saline soil (Buringh, 1960). The climate of the study area is similar to that of the Mediterranean region. According to Koeppe and De Long (1959), the Mediterranean climate is characterized by a moderate amount of rainfall in winter and dry summer. It is distinguished by mild to cool wet winter, and warm to hot dry summer. The annual average temperature in Duhok Governorate over the study period ranges from 19.3 to 21.2°C, as in winter between 0°C (min.) and 15°C (max.), and in summer between 20°C (min) and 37°C (max). The average annual precipitation is about 500–1000 mm. The forest ratio in Duhok is 28.4% and the agricultural lands are mostly around the villages (FAO, 2003). 3. Materials and Methods 3.1. Data Sources and Image Pre-Processing The meteorological data including annual rainfall and average temperature were collected over the 20 years (2000-2019) from 15 different weather stations within Duhok (Fig. 1). The climate data were provided by the General-Directorate of Meteorology and Seismology of the Iraqi Kurdistan Region. In this research, a digital elevation image (DEM) of Duhok with 30 m resolution was applied to get information about terrain factors including elevation, slope, and aspect through a GIS spatial analysis tool. The DEM was downloaded from the websites of Earth Data of the National Aeronautics and Space Administration (NASA). 111 Iraqi Geological Journal Mzuri et al. 2021, 54 (1A), 110-126 Fig. 1. The location of the study area, together with the location of weather stations used Moreover, Landsat 5 (TM), 7 (ETM), and 8 (OLI) satellite images with a spatial resolution of 30 m and 16 days’ intervals, for a period of 20 years (2000 to 2019) were used in this research. The imagery scenes with the least cloud cover percentage were found from websites of Earth Explorer of the United States Geological Survey (USGS). The images that have been used are acquired in May and June. They are used to calculate the MSAVI2, and for that purpose, those images passed through image pre- processing. This step has been applied to correct the images from radiometric and atmospheric noises using the Fast Line of Sight Atmospheric Analysis of Spectral Hypercubes (FLAASH) function of the ENVI 5.3 program. The required coefficients were acquired from the metadata of the images. Atmospheric and radiometric corrections are required for deriving accurate quantitative surface information from satellite imagery (Liang et al. 2002). Subsetting the study area and other pre- processing steps were accomplished. These steps were applied for all 20 images. The steps of the methodology are clearly shown in Fig. 2. 3.2. Spatial and Temporal Analysis of the MSAVI2 Vegetation index, representing vegetation information by using different satellite reflectance band combinations that are sensitive to vegetation (Baret et al., 1989). In this research, MSAVI2 was used as the main vegetation index to calculate the spatiotemporal vegetation coverage in the studied area. The values of MSAVI2 ranging from -1 to +1 and are computed upon pixel basis as in equation (1) (Qi et al. 1994). 2 2 × 휌푁퐼푅+1 − √(2 × 휌푁퐼푅+1) − 8 × (휌푁퐼푅 - 휌푅푒푑) 푀푆퐴푉퐼2 = (1) 2 112 Iraqi Geological Journal Mzuri et al. 2021, 54 (1A), 110-126 Where ρ is the reflectance in the NIR and Red bands. According to the basic area calculations, the area of vegetation is calculated for each year. This is conducted by selecting a threshold experimentally for each MSAVI2 image each year. For the 20 years, the threshold values range 0.11 – 0.25. To find the spatial variation in MSAVI2 trends, the linear trends from 2000 to 2019 were examined on a pixel basis. It attempts to model the relationship between variables (x) and time (y), by fitting a linear equation to observed data (equation 2). 푦(푥) = 푎 + 푏푥 (2) where a is the intercept and b is the slope of the line.