Investigation of the plants' water stress status in north of Iran under Covid-19 virus pandemic

Background and objectives: As the occurrence of water stress in plants and agricultural crops is affected by the drought, global warming, population growth and the urban heat islands, the lack of traffic and human activities in natural environment during the Covid-19 virus pandemic can be considered as a factor reducing plants’ water stress. As water stress is typically described by physiological plant responses to water deficiency due to the lack of soil moisture or high demand for evaporation in the atmosphere, the use of remote sensing data as a rapid and economical tool in monitoring climate change during Covid-19 virus pandemic has been considered.
Materials and methods: In this study, the efects of applying the limitations according to the Covid-19 virus is investigated on the plants water stress status in the spring of 2020 compared to three years ago. For this purpose, visible, near-infrared and short wavelenght infrared spectral bands of Sentinel-2 multispectral satellite images taken from a region in the east of Mazandaran province and in the 2017 to 2020 time interval were used. In the first step of the proposed method in this paper, by combining the normalized difference vegetation indices in near-infrared and short-wavelength infrared ranges, a vegetation map of the study area was produced. Then, three water stress indices of SRWI, NDWI and SIWSI in the vegetation map were calculated and the percentage of vegetation pixels that are under water stress was estimated in the 2017 to 2020 time interval.
Results: The obtained results of monitoring the plants water stress status in the study area in this research indicate the fact that despite a 35% decrease in annual rainfall in the rainy year of 2019-2020 compared to the same period in the last rainy year, the percentage of pixels under water stress has decreased by about 2%. In general, the area under water stress shows a decrease of one percent compared to the total vegetation area.
Conclusion: The results of the analysis showed that from 2017 to 2019, the annual rainfall was an effective factor in increasing or decreasing the percentage of pixels under water stress, especially in the plant leaf water content index (NDWI). An important point in analyzing the results of 2020 is that despite a -35% reduction in annual rainfall, the results of all three spectral indicators show a decrease in water stress in the region, which is one of the main effects of limitations and restricting the entry of vehicles and passengers to Mazandaran province and as a result the temperature has decreased.