A novel scale-adaptive ensemble approach for drought persistence and variability assessment under climate change

Climate change has escalated uncertainties in hydroclimatic projections. Consequently, this challenges the reliability of Global Climate Models (GCMs) in representing spatiotemporal precipitation variability. This study presents an integrated framework combining multi-resolution analysis, scale-dependent ensemble weighting and advanced probabilistic modeling for drought assessment over the Tibetan Plateau. Historical monthly precipitation (1961–2014) for reference and 18 GCMs is used for GCMs evaluation and three SSPs for the period 2015–2100 are used for drought assessment. Using Maximum Overlap Discrete Wavelet Transform (MODWT), precipitation is decomposed into multiple temporal scales with the Daubechies wavelet identified as optimal for signal preservation. A strong scale-dependent variability is evident in precipitation and GCM performance varies significantly across temporal resolutions. These findings led to the development of an enhanced Scale-Dependent Wavelet-based Multi-Scale Multi-Objective Performance Ensemble (SD-WMMPE) that incorporates scale-specific variability and multi-error optimization. The results reveal significant improvements over traditional ensemble frameworks with reduced bias and improved consistency across grid stations. It is also evident in the improved representation of precipitation distributions under K-Component Gaussian Mixture Model (K-CGMM). It captures skewness, heavy tails and multimodality features more precisely over the traditional univariate distributions particularly under high-emission scenarios. Drought characteristics are further assessed using proposed Gaussian Mixture-Based Scale-Weighted Standardized Precipitation Index (GMSW-SPI). Under steady state probabilities of Markov chain, normal drought prevails. However, results reveal increasing persistence, severity and variability of droughts from SSP1-2.6 to SSP5-8.5. Overall, the study introduces a robust multi-scale framework for climate risk assessment and water resource management under climate change.