Spatiotemporally Coherent Probabilistic Generation of Weather from Climate

Local climate information is crucial for impact assessment and decision-making, yet coarse global climate simulations cannot capture small-scale phenomena. However, to preserve physical properties, estimating spatio-temporally coherent high-resolution weather dynamics for multiple variables across long time horizons is crucial. We present a novel generative approach that uses a score-based diffusion model trained on high-resolution reanalysis data to capture the statistical properties of local weather dynamics. After training, we condition on coarse climate model data to generate weather patterns consistent with the aggregate information. As this inference task is inherently uncertain, we leverage the probabilistic nature of diffusion models and sample multiple trajectories. We evaluate our approach with high-resolution reanalysis information before applying it to the climate model downscaling task. We then demonstrate that the model generates spatially and temporally coherent weather dynamics that align with global climate output. Numerical simulations based on the Navier-Stokes equations, discretized over time and space, are fundamental to understanding weather patterns, climate variability, and climate change. Stateof-the-art numerical weather prediction (NWP) models, which primarily focus on atmospheric processes, can accurately resolve small-scale dynamics within the Earth system, providing fine-scale spatial and temporal weather patterns at resolutions on the order of kilometers [1]. However, the substantial computational resources required for these models render them impractical for simulating the extended time scales associated with climatic changes. In contrast, Earth System Models (ESMs), such as those included in the CMIP6 project [2], incorporate a broader range of processes--including atmospheric, oceanic, and biogeochemical interactions--while operating on coarser spatial scales. This coarse resolution limits the ability of ESMs to fully capture small-scale processes, requiring parameterizations to represent unresolved dynamics as functions of resolved variables. This work introduces a probabilistic downscaling pipeline that jointly estimates spatio-temporally consistent weather dynamics from ESM simulations on multiple variables. The framework is built around a score-based diffusion model and can be understood as a combination of four modules, which can each be adjusted independently of the others. This schematic outlines the framework.