Assessment of drought time-frequency relationships with local atmospheric-land conditions and large-scale climatic factors in a tropical Andean basin

This study analyzed in the Tomebamba subbasin the relationships between droughts, the condition of the vegetation, global scale climatic indices and local atmospheric variables. The variability of monthly meteorological and hydrological droughts, as well as the condition of the vegetation, were characterized using the standardized precipitation index (SPI), the standardized streamflow index (SSI), and the vegetation condition index (VCI). The wavelet coherence method was used to establish time-frequency relationships. The results indicate that the vegetation in good condition reduces the impact of hydrological drought events when there are no sudden precipitation impacts. The atmospheric variables at the local scale with the highest significant correlation are cloud cover, relative humidity, specific humidity, temperature and specific rainwater content between 500 and 750 hPa. The Multivariate ENSO Index (MEI), ENSO 3, the Southern Oscillation Index (SOI), the Pacific Decadal Oscillation (PDO), and the Pacific North American Index (PNA) are strongly linked to SPI and the ENSO 4 index to SSI. Vegetation does not show strong relationships with any climate indices, obtaining the best relationship with the PNA. The results provide a basis for the analysis of variability and propagation of the droughts in Andean basins, their relationships with local and large-scale factors, and the influence of drought on vegetation.