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Regional climate models are used for multi-decade simulations, but spin-up adds cost and full equilibrium is often impractical. Two overlapping WRF dynamical downscaling runs over the contiguous US compare convergence. The shorter run begins 20 years after the longer reference initialization and is assessed over their common period. After initialization, the shorter run shows cooler surface and nearsurface temperatures and higher soil moisture; differences weaken over the first three months, then re-emerge with secondary peaks during spring and summer as evaporation and evaporative cooling increase. Results support at least one year of spin-up, and some regions suggest 1–4 years to remove spurious top-layer soil-moisture effects.",{"@graph":69,"@context":122},[70,84,105],{"@type":71,"itemListElement":72},"BreadcrumbList",[73,77,79,82],{"item":74,"name":75,"@type":76,"position":8},"https://docshare.wps.com","Home","ListItem",{"item":78,"name":9,"@type":76,"position":14},"https://docshare.wps.com/document/",{"item":80,"name":40,"@type":76,"position":81},"https://docshare.wps.com/document/research-report/",3,{"item":83,"name":65,"@type":76,"position":19},"https://docshare.wps.com/document/examining-spin-up-behaviour-within-wrf-dynamical-downscaling-applications/505282/",{"url":83,"name":65,"@type":85,"image":86,"author":91,"headline":65,"publisher":94,"fileFormat":97,"inLanguage":63,"description":67,"dateModified":98,"datePublished":99,"encodingFormat":97,"isAccessibleForFree":100,"interactionStatistic":101},"DigitalDocument",{"url":87,"@type":88,"width":89,"height":90},"https://docshare.wps.com/thumbnails/examining-spin-up-behaviour-within-wrf-dynamical-downscaling-applications/505282.png","ImageObject",300,407,{"name":92,"@type":93},"gewufjwa","Person",{"url":74,"name":95,"@type":96},"DocShare","Organization","application/pdf","2026-10-18","2026-10-04",true,{"@type":102,"interactionType":103,"userInteractionCount":44},"InteractionCounter",{"@type":104},"ViewAction",{"@type":106,"mainEntity":107},"FAQPage",[108,114,118],{"name":109,"@type":110,"acceptedAnswer":111},"What does “spin-up” mean in regional climate model simulations?","Question",{"text":112,"@type":113},"Spin-up is the period after initialization when initial-condition influence diminishes and the model approaches dynamic equilibrium driven by boundary forcing and internal physics.","Answer",{"name":115,"@type":110,"acceptedAnswer":116},"How did the study compare convergence related to spin-up behavior?",{"text":117,"@type":113},"It used two overlapping dynamically downscaled WRF simulations (31-year and 11-year integrations) over the contiguous US, initializing the shorter run 20 years after the longer reference run and analyzing only the period covered by both.",{"name":119,"@type":110,"acceptedAnswer":120},"What minimum spin-up time does the study recommend for RCM applications?",{"text":121,"@type":113},"The results support using at least one year of spin-up time. Some regions indicate that 1–4 years may be needed to exclude spurious behavior in top-layer soil moisture.","https://schema.org",{"og:url":83,"og:type":124,"og:title":65,"og:site_name":95,"og:description":67},"article",{"robots":126,"canonical":83},"index,follow",{"doc_id":128,"site_id":62},505282,1791158593,{"code":4,"msg":5,"data":131},{"doc_id":128,"user_id":132,"nickname":92,"user_avatar":133,"doc_module":4,"category_id":39,"category_name":40,"doc_title":65,"doc_description":67,"doc_content":134,"file_id":135,"file_url":136,"file_type":137,"file_size":138,"view_count":44,"is_deleted":4,"is_public":8,"is_downloadable":8,"audit_status":8,"page_count":139,"language":140,"language_code":63,"site_id":62,"html_lang":63,"table_of_contents":141,"faqs":142,"seo_title":143,"seo_description":67,"update_tm":144,"read_time":36},3985747882900,"https://ap-avatar.wpscdn.com/davatar_9964176cb1d06d4a9deccf72a44ae3dc","Geosci. Model Dev., 19, 579–594, 2026  \n[https://doi.org/10.5194/gmd-19-579-2026](https://doi.org/10.5194/gmd-19-579-2026)[ ](https://doi.org/10.5194/gmd-19-579-2026)© Author(s) 2026 . This work is distributed under the Creative Commons Attribution 4 .0 License.  \nExamining spin-up behaviour within WRF dynamical downscaling applications  \nMegan S. Mallard 1 , Tanya L. Spero 1 , Jared H. Bowden2 , Jeff Willison 1 , Christopher G. Nolte 1 , and Anna M. Jalowska 1  \n1US Environmental Protection Agency, Research Triangle Park, North Carolina, USA  \n2North Carolina State Climate Office, Raleigh, North Carolina, USA Correspondence: Megan S. Mallard ([mallard.megan@epa.gov](mallard.megan@epa.gov))  \nReceived: 19 May 2025 – Discussion started: 3 June 2025  \nRevised: 15 December 2025 – Accepted: 29 December 2025 – Published: 19 January 2026  \nAbstract. Spin-up is the period after initialization when a model transitions away from its dependence on initial conditions toward a dynamic equilibrium between driving boundary conditions and its own internal dynamics. Regional climate models (RCMs) are often used to simulate conditions over several decades to inform local adaptation and resilience activities. The spin-up period represents added cost to already resource-intensive simulations, and it is often infeasible to use a spin-up period that produces complete model equilibrium. Therefore, a pragmatic compromise is desired to minimize the effects of spin-up. Here, two overlapping dynamically downscaled simulations (31 year and 11 year integrations) using the Weather Research and Forecasting model over the contiguous US (CONUS) are used to explore convergence associated with model spin-up. The shorter simulation is initialized 20 years after initialization of the longer (reference) run, and the runs are analysed over the period covered by both simulations, giving the reference simulation a 20 year period to attain spin-up prior to comparison. After initialization, the shorter run features cooler surface and nearsurface temperatures and greater soil moisture compared to the reference simulation. Differences between the runs decrease in magnitude over the first 3 months as autumn transitions to winter; however, these differences re-emerge and reach a secondary peak during the proceeding spring and summer. During this warm season, evaporation and accompanying evaporative cooling increase and temperature differences between the simulations re-emerge. These results support using at least one year of spin-up time in RCM applications to account for the seasonality of spin-up behaviour. Results from some regions of the CONUS indicate that spin-  \nup durations of 1–4 years are needed to exclude spurious behavior in top-layer soil moisture, which exhibits prolonged spin-up compared with other near-surface variables examined here.  \n1 Introduction  \nRegional climate modelling, or dynamical downscaling, applications provide data to inform adaptation and resiliency at local and community scales, including extremes in nearsurface temperature or precipitation. One benefit ofusing dynamical downscaling (as opposed to statistical downscaling) is that a dynamically consistent suite of three-dimensional (3D) fields is created at sufficient temporal frequency to drive other environmental models, such as air quality or hydrology models. Generating credible dynamical downscaling outputs can present several challenges to serve a variety of applications while remaining computationally manageable.  \nIn general, a spin-up period follows model initialization to allow the model solution to transition from being strongly influenced by the initial condition to a state of dynamic equilibrium between the model physics and boundary forcing from the driving dataset (Giorgi and Mearns, 1999; Denis et al., 2002) . Therefore, the spin-up is a period over which the model initial conditions are “forgotten” as information from the lateral boundaries and the model's internal physics gene","cbCaibz4Vmkh6Rkc","https://ap.wps.com/l/cbCaibz4Vmkh6Rkc","pdf",3096773,16,"English","# Abstract\n## Introduction\n## Spin-up in dynamical downscaling\n## Factors influencing spin-up duration","[{\"question\":\"What does “spin-up” mean in regional climate model simulations?\",\"answer\":\"Spin-up is the period after initialization when initial-condition influence diminishes and the model approaches dynamic equilibrium driven by boundary forcing and internal physics.\"},{\"question\":\"How did the study compare convergence related to spin-up behavior?\",\"answer\":\"It used two overlapping dynamically downscaled WRF simulations (31-year and 11-year integrations) over the contiguous US, initializing the shorter run 20 years after the longer reference run and analyzing only the period covered by both.\"},{\"question\":\"What minimum spin-up time does the study recommend for RCM applications?\",\"answer\":\"The results support using at least one year of spin-up time. Some regions indicate that 1–4 years may be needed to exclude spurious behavior in top-layer soil moisture.\"}]","Examining spin-up behaviour within WRF dynamical downscaling applications | PDF",1791095021]