Simulated Tropical Precipitation Assessed across Three Major Phases of the Coupled Model Intercomparison Project (CMIP)

Abstract

The representation of tropical precipitation is evaluated across three generations of models participating in the Coupled Model Intercomparison Project (CMIP), phases 3, 5 and 6. Compared to state-of-the-art observations, improvements in tropical precipitation in the CMIP6 models are identified for some metrics, but we find no general improvement in tropical precipitation on different temporal and spatial scales. Our results indicate overall little changes across the CMIP phases for the summer monsoons, the double-ITCZ bias and the diurnal cycle of tropical precipitation. We find a reduced amount of drizzle events in CMIP6, but tropical precipitation occurs still too frequently. Continuous improvements across the CMIP phases are identified for the number of consecutive dry days, the representation of modes of variability, namely the Madden-Julian Oscillation and the El Niño Southern Oscillation, as well as the trends in dry months in the 20th century. The observed positive trend in extreme wet months is, however, not captured by any of the CMIP phases, which simulate negative trends for extremely wet months in the 20th century. The regional biases are larger than a climate-change signal one hopes to use the models to identify. Given the pace of climate change as compared to the pace of model improvements to simulate tropical precipitation, we question the past strategy of the development of the present class of global climate models as the mainstay of the scientific response to climate change. We suggest to explore alternative approaches such as high-resolution storm-resolving models that can offer better prospects to inform us about how tropical precipitation might change with anthropogenic warming.

Contrasting Southern Hemisphere Monsoon Response: MidHolocene Orbital Forcing versus Future Greenhouse Gas–Induced Global Warming

“…Based on the PMIP3-CMIP5 multimodel mean (9 models), we find a weakening and contraction of the SH monsoon in the midHolocene and a strengthening and expansion in RCP8.5, consistently with results based on the newest generation of PMIP4-CMIP6 (Brierley et al 2020;Fiedler et al 2020). The change is less than 10%, which is smaller than the intermodel range in some areas.…”

Earth System Models Are Not Capturing Present‐Day Tropical Forest Carbon Dynamics

“…CMIP6 ESMs are able to reproduce total annual precipitation in the African tropics, but show a dry bias in Amazonia and a wet bias in SE Asia. Models reproduce the historical trends in precipitation, yet struggle with reproducing rainfall seasonality (Fiedler et al., 2020). Improving ESM to better simulate tropical precipitation will improve future ESM vegetation modeling.…”

A diagnostic model for the large-scale tropical circulation based on moist static energy balance

“…In addition to the importance of understanding tropical circulation changes in climate change scenarios, it is important to understand why CMIP simulations create mean tropical circulation patterns that are significantly different from the observed (Lian et al 2018;Stassen et al 2019;Chemke and Polvani 2019). A prominent example is the double (Intertropical Convergence Zone) ITCZ problem in model simulations (Li and Xie 2014;Adam et al 2016;Samanta et al 2019;Fiedler et al 2020). Another example of limitations in tropical atmospheric circulations is how CMIP models simulate the El Niño-Southern Oscillation (ENSO), the dominant mode of interannual climate variability.…”