More than half a million children under five years old die of diarrheal disease every year, according to the World Health Organization. Deaths and serious illness are most common in regions without access to clean water. Local climate fluctuations can be tied to outbreaks, but researchers have struggled to predict how climate change will affect diarrheal disease prevalence because diarrhea does not have a single root cause. Bacteria, viruses, and protozoa are all potential culprits of the underlying intestinal infection. Each potential cause can react differently to changes in rainfall, temperature, and other climate variables.