Colombian climatology in CMIP5/CMIP6 models: Persistent biases and improvements <span class="so-article-trans-title" dir="auto"> Translated title: La climatología colombiana en modelos CMIP5/CMIP6: Sesgos persistentes y mejoras </span>

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Abstract

ABSTRACT Northern South America is among the regions with the highest vulnerability to climate change. General Circulation Models (GCMs) are among the different tools considered to analyze the impacts of climate change. In particular, GCMs have been proved to provide useful information, although they exhibit systematic biases and fail in reproducing regional climate, particularly in terrains with complex topography. This work evaluates the performance of GCMs included in the fifth and sixth phases of the Coupled Model Intercomparison Project (CMIP), representing the annual cycle of precipitation and air surface temperature in Colombia. To evaluate this, we consider different observational and reanalysis datasets, including in situ gauges from the Colombian Meteorological Institute. Our results indicate that although the most recent generation of GCMs (CMIP6) show improvements with respect to the previous generation (CMIP5), they still have systematic biases in representing the Intertropical Convergence Zone and elevation-dependent processes, which highly determine intra-annual precipitation and air surface temperature in Colombia. In addition, CMIP6 models have larger biases in temperature over the Andes than CMIP5. We also analyze climate projections by the end of the 21st century according to the CMIP5/CMIP6 simulations under the highest greenhouse gases emission scenarios. Models show projections toward warmer air surface temperatures and mixed changes of precipitation, with decreases of precipitation over the Orinoco and Colombian Amazon in September-November and increases over the eastern equatorial Pacific during the entire year.

Translated abstract

RESUMEN El norte de Suramérica es una de las regiones más vulnerables ante cambio climático. Los Modelos de Circulación General (MCG) son las herramientas más empleadas para identificar los posibles impactos del cambio climático. Los MCG proveen información útil, aunque presentan sesgos sistemáticos, principalmente en zonas de topografía compleja. Se evalúa la habilidad de los modelos de la quinta y sexta fase del Proyecto de Comparación de Modelos Acoplados (CMIP) para representar el ciclo anual de precipitación y temperatura superficial del aire en Colombia. Se consideran diferentes bases de datos, incluyendo estaciones in situ del Instituto de Hidrología, Meteorología y Estudios Ambientales (IDEAM). Los modelos de última generación (CMIP6) mejoran su desempeño con respecto a los modelos de la generación anterior (CMIP5), aunque siguen presentando sesgos sistemáticos como dificultades para representar la Zona de Convergencia Intertropical y procesos que dependen de la elevación, fundamentales para el comportamiento intra-anual de la precipitación y la temperatura en Colombia. Los modelos CMIP6 presentan mayores sesgos simulando la temperatura sobre los Andes Colombianos que los modelos CMIP5. Las proyecciones climáticas para finales del siglo XXI considerando los escenarios de mayores emisiones de gases de efecto invernadero sugieren condiciones futuras más cálidas y cambios mixtos de precipitación en Colombia, con reducciones de precipitación en el Orinoco y el Amazonas Colombiano en septiembre-noviembre, e incrementos en el este del Pacífico ecuatorial durante todo el año.

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An Overview of CMIP5 and the Experiment Design

Karl E. Taylor, Ronald J Stouffer, Gerald Meehl (2012)

The fifth phase of the Coupled Model Intercomparison Project (CMIP5) will produce a state-of-the- art multimodel dataset designed to advance our knowledge of climate variability and climate change. Researchers worldwide are analyzing the model output and will produce results likely to underlie the forthcoming Fifth Assessment Report by the Intergovernmental Panel on Climate Change. Unprecedented in scale and attracting interest from all major climate modeling groups, CMIP5 includes “long term” simulations of twentieth-century climate and projections for the twenty-first century and beyond. Conventional atmosphere–ocean global climate models and Earth system models of intermediate complexity are for the first time being joined by more recently developed Earth system models under an experiment design that allows both types of models to be compared to observations on an equal footing. Besides the longterm experiments, CMIP5 calls for an entirely new suite of “near term” simulations focusing on recent decades and the future to year 2035. These “decadal predictions” are initialized based on observations and will be used to explore the predictability of climate and to assess the forecast system's predictive skill. The CMIP5 experiment design also allows for participation of stand-alone atmospheric models and includes a variety of idealized experiments that will improve understanding of the range of model responses found in the more complex and realistic simulations. An exceptionally comprehensive set of model output is being collected and made freely available to researchers through an integrated but distributed data archive. For researchers unfamiliar with climate models, the limitations of the models and experiment design are described.