Spatio‐temporal and time series analysis of bluetongue outbreaks with environmental factors extracted from Google Earth Engine (GEE) in Andhra Pradesh, India

Abstract

This study describes the spatial and temporal patterns of bluetongue (BT) outbreaks with environmental factors in Andhra Pradesh, India. Descriptive analysis of the reported BT outbreaks (n=2697) during the study period (2000‐2017) revealed a higher frequency of outbreaks during monsoon and post‐monsoon months. Correlation analysis of Normalized Difference Vegetation Index (NDVI), Normalized Difference Water Index (NDWI), rainfall, and relative humidity (RH) displayed a significant positive correlation with BT outbreaks (p<0.05). Retrospective space‐time scan with unadjusted, temporal, and spatial adjusted analysis detected two, five, and two statistically significant (p<0.05) clusters, respectively. Time‐series distribution lag analysis examined the temporal patterns of BT with climate, biophysical factors and estimated that a decrease in 1 unit of rainfall (mm) was associated with 0.2% increase in the outbreak at lag 12 months. Similarly, a 1ºC increase in land surface temperature (LST) was associated with 6.54% increase in the outbreaks at lag 12 months. However, an increase in 1 unit of wind speed (m/s) was associated with a 16% decrease in the outbreak at lag 10 months. The predictive model indicated that the peak of BT was from October ‐ December, the post‐monsoon season in Andhra Pradesh region. The findings suggest that environmental factors influence BT outbreaks, and due to changes in climatic conditions, we may notice higher numbers of BT outbreaks in the coming years. The knowledge of spatial and temporal clustering of BT outbreaks may assist in adopting proper measures to prevent and control the BT spread.