Time series satellite data for assessment of drought impacts on vegetation land cover in dryland Constanta County, Romania

In frame of global warming context impact arid regions are affected by increases in temperature and decreases in precipitation, that will trigger water shortages, drought, and further aridification. This paper addresses a number of issues related to current and future climatic change and drought impacts on vegetation land cover, focusing on the Constanta County in Dobrogea region placed in the South Eastern part of Romania near North Western Black Sea coastal area. Remotely sensed monitoring and assessing of drought effects in long term change could provide sound understanding to guide arid agricultural areas ecological restoration and local ecosystem sustainability. This study examined the applicability of MODIS Terra/Aqua time series satellite-based together MERRA -2 reanalysis data in synergy with insitu monitoring of climate observables for aridity assessment. Time series of Normalized Difference Vegetation Index - NDVI, evapotranspiration-ET, land surface albedo-LSA, land surface temperature-LST and air surface temperature-AT at different time scales and other climate parameters (precipitation rate, relative humidity and surface solar irradiance-SI were computed for the period 2000 to 2023. The trend analysis of the time series for ET, NDVI and LST in the Constanta Cunty was conducted using a simple linear regression analysis method. During summer periods (June – August) of 2021-2023 period, LST and NDVI appeared to be linear and negatively correlated in each year ranged from r = - 0.85 with p<0.05 in 2022 year, r = - 0.77 with p<0.05 in 2021 year, and r = - 0.40 with p<0.05 in 2023 year. A high decrease of NDVI values ranged (0.2-0.3) was recorded during summer-autumn droughts periods of years 2022 and 2023 associated with strong heat waves. The results in this study show that large area of Constanta County is highly controlled by drought during summer to autumn seasons. This work demonstrates the importance of satellite remote sensing data conjugated with in-situ data for changes monitoring of dryland vegetation in their response to climate-drying conditions.