Monitoring vegetative drought dynamics in the Brazilian semiarid region

Drought is a complex natural phenomenon that can lead to reduced water supplies and can consequently have substantial effects on agriculture and socioeconomic activities that cause social crises and political problems. Different drought indicators are used for identifying droughts. This work explored the applicability of a near-real time drought monitoring methodology using Terra-MODIS Normalized Difference Vegetation Index (NDVI) and land surface temperature (LST) products. This approach is called the Vegetation Supply Water Index (VSWI), which integrates land surface reflectance and thermal properties. The results indicate that during a major drought event from 2012 to 2013, approximately 85% of the Brazilian semiarid region was affected. The number of days of soil moisture deficit, which was derived from a simple water balance model and the daily interpolated precipitation, were used to verify the results. A correlation analysis of VSWI, precipitation and soil moisture deficit shows that VSWI is closely related to rainfall and soil water content, especially under dry conditions, and indicates that the use of VSWI can be a suitable near-real time drought monitoring approach. The evaluation of the 2012-2014 drought considering the VSWI index highlighted two major characteristics of vegetation response to drought conditions, i.e., the recovery and memory effects of vegetation.