Ai2 HiRO-ACEv2 Simulates Extreme Weather at 3 Km for 1/300th the Cost
Ai2's HiRO-ACEv2 generates global 3 km climate data at 1/300th of X-SHiELD's cost, accurately modeling rare rain, wind and pressure extreme events globally.
Summary
Ai2 introduced HiRO-ACEv2 on October 14, 2026, combining an updated ACE climate model at 100 km resolution with HiROv2, which converts coarse output into 3 km rain, wind and pressure fields. When fed coarsened X-SHiELD data, HiROv2 matches high-resolution statistics within 3%, including extremes occurring once per million data points. It estimates tropical cyclone energy for storms unseen during training, creates realistic hurricane eyes and rain bands, and reproduces mountain downslope winds, although eye winds and pressure remain more lopsided than X-SHiELD.
Updated ACE matched X-SHiELD hurricanes, average climate and rain, wind and pressure distributions over 10 years. The combined system generated a full year of global 3 km data from ACE alone with closely matching statistics, while its 10-year hurricane energy was comparable to X-SHiELD. Global generation costs about 1/300th as much, regional savings can exceed 100 times depending on area, and a planned streamlined HiROv2 could run more than 10 times faster.
Because HiROv2 learned from X-SHiELD, it currently works only with the ACE version tuned to that model, excluding warmer climates and historical datasets such as ERA5. Ai2 plans training data for a world 4°C warmer, plus near-surface temperature, snow and ice outputs supporting uses such as snowpack prediction. Downloadable models, tutorial notebooks and a web demo compare pre-generated HiROv1 and HiROv2 precipitation, wind and sea-level pressure with X-SHiELD.
Positives
- HiROv2 matched X-SHiELD high-resolution statistics within 3% for extremes occurring only once per million data points.
- Global 3 km climate data costs about 1/300th as much to generate with HiRO-ACEv2 as with X-SHiELD.
- Ten-year HiRO-ACEv2 hurricane energy was comparable to X-SHiELD, while updated ACE aligned on hurricanes and major climate distributions.
- Regional simulations can deliver savings exceeding 100 times, depending on the selected area's size.
- Downloadable models, tutorial notebooks and a web demo make HiROv1 and HiROv2 outputs available for inspection and analysis.
- A streamlined HiROv2 under development could increase generation speed by more than tenfold.
Risks & concerns
- HiROv2 currently works only with the ACE version specifically tuned to reproduce X-SHiELD.
- Warmer future climates and historical records such as ERA5 cannot yet be downscaled by the system.
- Hurricane winds and pressure around simulated eyes remain more lopsided than in X-SHiELD.
- Near-surface temperature, snow and ice outputs remain planned rather than available.