Many tropical countries are exceptionally vulnerable to changes in rainfall patterns, with floods or droughts often severely affecting human life and health, food and water supplies, ecosystems and infrastructure. There is consensus on likely global-scale future changes of the hydrological cycle under climate change, but widespread disagreement among climate model projections of how and where rainfall will change over tropical land at the regional scales relevant to impacts. This disagreement is largely caused by the diversity of climate model responses of the atmospheric circulation to warming, with different models predicting current tropical wet and dry regions to shift in different ways. Despite uncertainty in the location of future rainfall shifts, such shifts do occur in all models over the 21st century, and so climate models consistently project large rainfall changes for a considerable proportion of tropical land. This is important for climate change mitigation policy, where the exact location of anticipated climate impacts may be less vital than the knowledge that such impacts are likely to occur. More robust predictions of regional rainfall change remain a research priority, and in order to achieve this goal the driving processes must first be better understood. Idealised climate model experiments can isolate the different aspects of anthropogenic forcing and warming that cause precipitation change, and a set of experiments focused on understanding regional climate responses has been included in CMIP6. Results from several modelling groups which have run these experiments with their CMIP5 models will be presented.