In the World Bank's follow up report to Turn Down the Heat , the authors predict numerous water crises in the three areas of the world they examine in detail, South East Asia, South Asia, and Africa. Each crisis would be a true crisis if combined with poor human choices and political and economic instability. They predict a 2 degree world within our lifetime and at least a 40% chance of reaching 4 degrees or more by the century's end. At that point, they estimate that the total hyper-arid and arid areas in Africa will have expanded by 10% compared to 1986-2005. Where aridity increases, crop yields decline as the growing season shortens. In South Asia, seasonality is predicted to amplify, with a decrease of up to 30% precipitation during the dry season and a 30% increase during the wet season under a 4°C world. South East Asia faces a combination of effects, with sea level rise, urbanization, and rainfall patterns all changing to create a massive vulnerability in the Mekong Delta particularly.
The report cautions great uncertainty but huge concern about the pattern of the Monsoon. "For global mean warming approaching 4°C, a 10% increase in annual-mean monsoon intensity and a 15% increase in year-to-year variability of Indian summer monsoon precipitation is projected compared to normal levels during the first half of the 20th century. Taken together, these changes imply that an extreme wet monsoon that currently has a chance of occurring only once in 100 years is projected to occur every 10 years by the end of the century." But the report stresses the devastating impacts of changes that are likely in the next two decades, exacerbating existing vulnerabilities to that combination of poor choices and hard to manage precipitation. Without action, these changes will undermine efforts to reduce poverty.
The probability is too high and the likely impacts are too catastrophic for a wait and see approach. Many sensible policy, institutional and investment actions can be taken now that will help now. The new information in this report makes those actions more valuable in the longer term as well.