نوع مقاله : مقاله پژوهشی
موضوعات
عنوان مقاله English
نویسندگان English
Aim: Changes in climate parameters, including precipitation and temperature, either alone or together, cause fluctuations in vegetation. The purpose of this research is to determine the relationship between climatic parameters and annual and seasonal fluctuations of vegetation in Sistan and Baluchistan province using spatial and temporal analysis of geographic information systems.
Material & Method: This research used data from terrestrial weather stations and remote sensing images of the Normalized Vegetation Index with a time period of 16 days and a spatial resolution of 250 meters and Land Surface Temperature images with a resolution of one kilometer and a time period of 8 days. The MODIS sensor of the Terra satellite was used from 2001 to 2022.
Finding: The results showed that the average area of vegetation in the region was 3.56%, and the area of vegetation in the province was the lowest in 2001 and 2002, i.e., 1.34 and 1.41%, and the highest in 2010 and 2020 with 4.62 and 9.82%, respectively. The results show that during the statistical period under study, the average vegetation index of the region showed an increasing trend. Correlation results showed that the correlation between the normalized index of vegetation and the temperature of the earth's surface in summer with (r=0.49; p<0.05) and the normalized index of vegetation with the amount of precipitation in winter (r=-0.97; p> 0.05).
Conclusion: The results show that the vegetation cover index significantly correlates with temperature and precipitation in Sistan and Baluchistan province. Based on this, the correlation between vegetation cover and precipitation reaches its maximum with a delay of two to three months in the summer season.
Innovation: The innovation of this research is to investigate the relationship between the vegetation cover of the study area and the fluctuations climatic elements using satellite images and indicators used in it.
کلیدواژهها English
Climate change, characterized by declining precipitation and rising temperatures, has induced widespread drought conditions globally. Droughts exert significant impacts on water resources and vegetation, exacerbating desertification. One of the primary consequences of drought is reduced vegetation cover. With the reduction of vegetation, environmental conditions are provided for the emergence of various hazards such as soil erosion, increased runoff, and flooding. Vegetation, a crucial parameter in arid ecosystems, is influenced by low precipitation, high temperature, and evapotranspiration factors. The Normalized Difference Vegetation Index (NDVI), a proxy for photosynthetic activity, has been widely used in studies examining vegetation changes. Moreover, high-resolution satellite imagery offers a powerful tool for analyzing vegetation dynamics and the effects of climate change.
To investigate the impact of climate variables on vegetation cover in Sistan and Balouchestan province, Iran, this study employed NDVI and Land Surface Temperature (LST) derived from satellite imagery, as well as meteorological station data. The analysis utilized 506 MODIS Terra NDVI images with a 16-day temporal resolution and 250-meter spatial resolution and 1012 MODIS Terra LST images with an 8-day temporal resolution and 1000-meter spatial resolution, spanning a 22-year period (2000-2022). Seasonal and annual averages of NDVI and LST were computed. The spatial distribution of NDVI was analyzed for four time periods: 2001, 2005, 2010, and 2020. Temporal variations in these variables were calculated to assess the influence of temperature and precipitation changes on vegetation, and correlation coefficients and trends in NDVI were determined using regression analysis.
The average vegetation cover in the study area was 3.56%. The provincial vegetation cover reached its minimum in 2001 and 2002, at 1.34% and 1.41%, respectively, and its maximum in 2010 and 2020, at 4.62% and 9.82%, respectively. Based on the fluctuation curve and the annual average trend of the vegetation index, the curve trajectory indicates short-term (3 to 4 years) climatic effects on vegetation changes in the region. The results show that the average vegetation index in the study period increased. The average vegetation index over the study period was 0.154, with a maximum of 0.161 in 2016 and a minimum of 0.150 in 2001.
The relationship between climatic factors and vegetation index was examined at annual and seasonal scales. Overall, the relationship between vegetation index and land surface temperature in the study area was significant. Results from the 22-year seasonal average spatial correlation matrix between the normalized vegetation index and land surface temperature revealed the highest correlation in the summer season (r = 0.49, p < 0.05). In this season, the highest index values were observed in areas with higher temperatures, indicating a positive relationship between the two variables. In contrast, the relationship was negative and significant in other seasons. Additionally, the results of the spatial correlation matrix of the seasonal average of the two variables, vegetation index and precipitation, showed that the highest spatial correlation between the two variables occurred in winter (r = -0.97, p < 0.05).
Based on seasonal analysis findings, variations in the Normalized Difference Vegetation Index (NDVI) are primarily influenced by fluctuations in temperature and solar radiation. While the impact of intra-annual precipitation changes is less apparent, its inter-annual (overall trend) influence is clearly discernible. Spring experiences the highest vegetation cover among the seasons, attributed to increased winter precipitation, replenished water reserves, abundant flow in rivers such as Hirmand, Mashkid, Kajou, and Sarbaz, as well as favorable climatic conditions. Conversely, summer experiences a pronounced decline in vegetation cover due to diminished precipitation, extreme heat, and depleted water resources. Autumn also experiences a reduced vegetation cover due to reduced precipitation and the early onset of cold weather. Additionally, the average NDVI and total area of vegetation classes in the province exhibit a slight upward trend, primarily driven by shifting precipitation patterns towards increased rainfall and human activities such as agriculture and dam construction. A limitation of this study is its sole focus on temperature and precipitation. Consequently, future research should consider other factors influencing vegetation dynamics.
