Temporal and Spatial Variability of Soil-Vegetation Variables in the West Region of Santa Catarina State

The western region of the state of Santa Catarina (SC) has suffered several episodes of drought, thus impacting vegetation, agricultural production and water availability. This study aimed to evaluate the spatial and temporal variability of soil-vegetation parameters in the region. Monthly data of evapotranspiration, precipitation, radiation, air and soil moisture and temperature were obtained from the NASA-funded Famine Early Warning Systems Network (FEWS NET) project, Land Data Assimilation System (FLDAS). The study focused on the western region of SC. Evapotranspiration anomalies showed that the years 2015 and 2020 had the lowest values in the last years (i.e. 1990 and 2022). Precipitation had greater variability in recent years, having months of high rainfall combined with periods of severe drought. An evaluation for the Xanxerê city region showed that the year 2020 presented records of low precipitation, evapotranspiration, soil moisture and NDVI, compared to the entire time series. Spatial correlation of the evapotranspiration controlling variables showed that precipitation, air temperature and humidity, and short-wave radiation presented variable correlations in different regions of SC. Soil moisture, however, had the highest positive correlation in the entire territory, showing that this is the main controlling variable of local evapotranspiration and therefore an indicator of the importance of vegetation transpiration in the latent heat fluxes. Equivalent water thickness obtained from the GRACE satellite show that after a maximum occurred in December 2015 its magnitudes steadily decreased, reaching very low groundwater values in 2022. This trend represents a 3.3 mm decrease per year. These results show that the region is undergoing a change in these soil-vegetation parameters that needs to be better monitored and understood.