Comparison of Dryland Climate Change in Observations and CMIP5

Abstract:

Both observations and simulations of 20 models from the fifth Coupled Model Intercomparison Project (CMIP5) reveal that drylands have expanded during the last 58 years (1948-2005). However, the dryland expansion in the simulations (0.4×10⁶ km² ) is only one-sixth of that (2.5×10⁶ km²) in the observations. The large model biases in dryland expansion are accompanied with large uncertainties of aridity index (AI) and poor simulation of precipitation in the models. The precipitation is overestimated by climate models only 7 mm in hyper-arid regions, but 30 mm and 37 mm in semi-arid and dry subhumid regions. The AI also shows large biases in the semi-arid (0.02) and dry subhumid regions (0.04), which is 8 and 15 times as much as that in the hyper-arid regions. We conclude that the semi-arid and dry subhumid regions are two key regions in the models, because they show large biases from the observations.

Key words: aridity, dryland expansion, climate change, CMIP5