The changing characteristics of propagation time from meteorological drought to hydrological drought in a semi-arid river basin in India

This study employs an event-based approach to analyse drought propagation from meteorological to hydrological drought via agricultural drought in the semi-arid Krishna River basin of India. The Standardized Precipitation Evapotranspiration Index (SPEI), Standardized Soil Moisture Index (SSMI) and Standardized Streamflow Index (SSI) representing meteorological, agricultural and hydrological drought, respectively, were estimated. Two different cases of drought propagation are analysed: meteorological-to-agricultural (SPEI-to-SSMI) and agricultural-to-hydrological (SSMI-to-SSI). The drought propagation is analysed using three-time matrices, namely the time difference between initiation ($∆t_{i2i}$), peak ($∆t_{p2p}$) and termination ($∆t_{t2t}$) at multiple timescales of 1, 3, 6, 9 and 12 months using different drought threshold values 0, −0.5, −1 and − 1.5, respectively, to delineate shifts from mild to extreme drought conditions in detail. The results indicate that the propagation time from SPEI-to-SSMI drought decreased for most of the tributaries using multiple timescales at different threshold values, whereas it increased significantly for SSMI-to-SSI drought. The drought propagation changes with respect to time as well as magnitude (intensity and severity). The propagation factor (PF), defined as the ratio of the average value of succeeding drought to preceding drought characteristics, has also been studied. For SPEI-to-SSMI drought, the duration PF shrinks across all tributaries using multiple timescales at different threshold values, whereas it expands for SSMI-to-SSI drought. On the other hand, the severity and intensity PF magnify for SPEI-to-SSMI drought, whereas it experiences dampening effects for SSMI-to-SSI drought. Thus, the proposed study provides valuable insights into drought propagation dynamics, aiding in managing and mitigating droughts in the semi-arid river basin and elsewhere.