Multi-Timescale Drought Dynamics Under Historical and CMIP6 Future Climate Scenarios

Abstract

Drought evolution in semi-arid watersheds is controlled not only by rainfall deficits but also by the interaction between precipitation variability, temperature-driven evapotranspiration and timescale-dependent moisture propagation. This study investigates historical and future drought dynamics in the Kundaleru watershed, India, using Indian Meteorological Department (IMD) observations for 1951–2019 and bias-corrected CMIP6 projections for 2015–2050 under the SSP2-4.5 scenario. Standardised Precipitation Index (SPI) and Standardised Precipitation Evapotranspiration Index (SPEI) were computed at 3-, 6-, 9-, 12-, 24- and 48-month timescales to examine short-term meteorological stress, seasonal agricultural drought and long-term hydrological drought conditions. A TOPSIS-based framework was used to evaluate seven CMIP6 models and reduce model-selection uncertainty. Historical SPI results showed that mild and moderate droughts dominated across timescales, while severe drought months were highest at SPI-12 and extreme drought months were most evident at SPI-3 and SPI-24. SPEI indicated stronger drought intensification than SPI, with 57 severe drought months at SPEI-12, 25 extreme drought months at SPEI-24 and 41 severe drought months at SPEI-48, highlighting the influence of temperature-driven evapotranspiration on long-term moisture stress. Model evaluation identified EC-Earth3-Veg, MPI-ESM1-2-LR and BCC-CSM2-MR as relatively reliable precipitation models, while MPI-ESM1-2-LR and EC-Earth3-Veg performed better for T_max. Future projections showed uncertain precipitation trends but more consistent warming, with maximum temperature increasing by about 0.04°C/year–0.05°C/year in several models. Long-term SPEI projections indicated prolonged multi-year droughts, with some events lasting up to 192 months, suggesting increased stress on groundwater recharge, streamflow reliability, reservoir storage and rainfed agriculture. Overall, this study enhances understanding of drought-related hydrological processes by linking climatic variability, evaporative demand, drought propagation and climate-model uncertainty within a multi-timescale framework. The findings support climate-resilient water-resource planning and drought-risk management in semi-arid monsoon-dependent watersheds.