Climate change in tropical regions from high-resolution time-slice AGCM experiments



In this study we discuss present-day climate conditions (1961–90) and climate change projections (2071–2100) for four tropical regions as produced with a high-resolution time-slice AGCM experiment. We use the National Aeronautics and Space Agency/National Center for Atmospheric Research finite-volume element global model FVGCM with a horizontal grid interval of 1° latitude and 1.25° longitude. The regions considered are South Asia, tropical South America, Sahel/equatorial Africa, and southern equatorial Africa, and the projections refer to the IPCC A2 emission scenario forcing. We focus on the rainy seasons of the four regions.

In all regions the FVGCM reproduces the rainy season climatologies reasonably well, in both their mean and their interannual variability characteristics. The greatest discrepancies with observations occur over South Asia, where the monsoon precipitation does not penetrate far enough inland. The climate change scenarios can be summarized as follows: (i) an intensification of monsoon precipitation over South Asia; (ii) a decrease in precipitation over the Amazon basin; (iii) a northward shift of the monsoon precipitation band over the Sahel and equatorial Africa; and (iv) a drying over southern equatorial Africa. In most cases these changes are statistically significant at the 95% confidence level. Statistically significant warming is found over all regions, varying from 2 to 5 K across regions.

A robust result of our analysis is a consistent increase in interannual variability for the scenario simulations over all the regions examined and for both precipitation and temperature. Because of the experiment design this increase is not due to an increase in variability of sea surface temperature, but is rather associated either with land–atmosphere feedbacks or with a general intensification of the global hydrological cycle under warmer conditions. We also compare our change projections with previous results from coupled global models. Copyright © 2005 Royal Meteorological Society.