Now it seems to me that for a State with a high population and a very big agricultural sector (which has presently been getting by on diminishing groundwater), a 35 year drought would be a very big problem indeed. How are economists and their models on the effects on GDP dealing with that scenario?
More generally, a paper just out in Nature Climate Change explains that changes to tropical rainfall are shown under all modelling of the future climate under AGW, but the problem is working out where. As the abstract explains:
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 infrastructure1. There is widespread disagreement among climate model projections of how and where rainfall will change over tropical land at the regional scales relevant to impacts2, 3, 4, with different models predicting the position of current tropical wet and dry regions to shift in different ways5, 6. Here we show that despite uncertainty in the location of future rainfall shifts, climate models consistently project that large rainfall changes will occur for a considerable proportion of tropical land over the twenty-first century. The area of semi-arid land affected by large changes under a higher emissions scenario is likely to be greater than during even the most extreme regional wet or dry periods of the twentieth century, such as the Sahel drought of the late 1960s to 1990s. Substantial changes are projected to occur by mid-century—earlier than previously expected2, 7—and to intensify in line with global temperature rise. Therefore, current climate projections contain quantitative, decision-relevant information on future regional rainfall changes, particularly with regard to climate change mitigation policy.Again, I wonder how economic forecasts over the coming decades can take this uncertainty into account.