Temporal And Spatial Variation In NDVI In Argentina And Its Response To Climate And Human Activity

As a critical“producer”in terrestrial ecosystems,vegetation plays a key role in regulating climate and maintaining ecosystem stability.Vegetation change and its response to climate change are essential for regional ecological protection.Argentina has a large latitude span and a large difference in surface heat,which is very sensitive to climate change.In recent years,affected by heat waves and long-term drought,large areas of forests and natural vegetation in Argentina have been devastated.Human activities have further contributed to extensive changes in vegetation in Argentina,and the ecosystem is facing huge risks and challenges.The Normalized Difference Vegetation Index（NDVI）,temperature,precipitation,Palmer Drought Index（PDSI）,and land use data from 1982 to 2021 were processed.Correlation analysis and multiple regression residual analysis were used to analyze the characteristics and relationship between NDVI and climate change in Argentina,evaluated the response of climate change and human activities to NDVI,extracted the characteristics of drought in Argentina,and explore its impact on vegetation.It can provide the basis for the country’s response to climate change and the impact of human activities on vegetation changes.The main conclusions are as follows:（1）The change of NDVI in Argentina is directly related to the change of climatic conditions.The temperature increased and the precipitation decreased in most regions of Argentina from 1982 to 2021.The average temperature showed a slight upward trend（0.048°C/10a）,accounting for 74.97%of the area,and approximately 90%of the region’s annual precipitation decreased significantly（-22.19 mm/10a）.Climate change causes the NDVI in Argentina decreased at a rate of-1.7×10^-4/a,and the area showing a downward trend accounted for 54.66%,mainly distributed in Patagonia,Pampas,Northeast Argentina（NEA）and Northwest Argentina（NWA）.（2）The change in NDVI in Argentina is closely related to temperature and precipitation.In Pampas,NEA,NWA,and Cuyo,NDVI was positively correlated with temperature and precipitation,accounting for 74.20%and 78%respectively.In Patagonia,vegetation change was more affected by precipitation,and the positive correlation between NDVI and precipitation（16.78%）was greater than that between NDVI and temperature（13.45%）.Water availability was a key limiting factor for vegetation growth in arid and semi-arid areas in Patagonia.Compared with winter and summer,NDVI in spring and autumn had a positive correlation with temperature and precipitation in more than 60%of the country,and precipitation in spring and autumn had a greater impact on NDVI than temperature.The high temperature in summer negatively affected the vegetation growth in the whole range,except for Patagonia;the vegetation growth in summer was mainly controlled by precipitation in most regions.（3）Climate change and human activities in Argentina have a significant inhibitory effect on NDVI.During the period of 2000 to 2020,the area of cropland and construction land in Argentina increased by 82957.45 and 5980.66 km²,respectively,and the area of forest land decreased by 38606.07 km².Deforestation directly caused serious damage to vegetation.Land use change was mainly manifested in the mutual conversion between shrubs,grassland,forest land,cropland,and unused land.Land use changes such as the expansion of agricultural and pastoral land and deforestation have changed the habitat conditions of vegetation to a certain extent,indirectly leading to vegetation loss.Climate change and human activities inhibited NDVI by 76.36%and49.57%,respectively.Under the joint influence of climate change and human activities,the vegetation coverage in Argentina gradually decreased.（4）The reduction of NDVI in Argentina is closely related to drought.The probability of drought in most areas of Argentina from 1982 to 2021 was high and the duration was wide.The average number of drought events was 14,and the average drought duration was 12 months.The positive correlation between NDVI and PDSI accounted for 86.68%.From 2007 to 2009,NDVI,precipitation,and PDSI first decreased and then increased,with the minimum value appearing in 2009.The overall temperature increased first and then decreased.The correlation coefficient between NDVI and PDSI was as high as 0.94.Affected by the drought,the NDVI in the eastern and northeastern areas of Pampas,and Corrientes Province decreased significantly.