Downscaling and Regional Climate Models
Despite improvements to GCM’s, the spatial resolution is still too large to account for processes occurring at relatively small scales, which limits the applicability of GCM predictions at smaller scales. This is especially the case for New Zealand, where our country’s small size, complex mountainous terrain and extensive coastal areas give rise to an incredibly varied climate across relatively small distances. As such, regional climate models have been developed, which utilise GCM results, and apply them to smaller spatial scales in order to provide more informative and relevant climate forecasts. NIWA’s regional climate model (RCM) has a 30 km grid spacing over New Zealand, compared with 100–300 km for a global model (see figure below). NIWA also use statistical downscaling, whereby scientists use statistical relationships between the regional circulation and aspects of the local climate (e.g., temperature, rainfall, wind) to apply global climate model results to a particular place.
This figure illustrates how climate models "see" New Zealand with the typical spatial resolution of a Global Climate Model (GCM, top, ~140km resolution) and a Regional Climate Model (RCM, bottom, ~30km resolution).