MORE DROUGHT AND FLOODS Wait. How can it be both? Well, warmer temperatures evaporate moisture from the land faster and warmer air has the capacity to hold more water vapor. So droughts are getting longer and more severe and storm events are causing more flooding. See one piece of highly-cited research here. Even the difference between 1.5° and 2.0° C rise in temperatures is expected (with medium to high confidence) to result in a substantial difference in the severity and frequency of drought and flooding events (source). As NASA research concludes, “From 1958 to 2016 heavy rainfall events have increased in the northeastern states by 55 percent, midwestern states by 42 percent, and southeastern states by 27 percent. The western states have also seen modest increases in heavy rain events that can overwhelm the local watershed’s capacity to absorb excessive water.” Globally, the impacts of climate change caused 12% more record-breaking rainfall events between 1981 and 2010. Essentially, science predicts that dry places will get even drier and wet places will become wetter.

As emissions continue to rise, increasing the degree of global warming, the likelihood of a megadrought (think dust bowl) in the southwest and central US increases and the length of the drought would be more prolonged… up to 30 years. Research from NASA concludes, “the current likelihood of a megadrought, a drought lasting more than three decades, is 12 percent. If greenhouse gas emissions stop increasing in the mid-21st century, … the likelihood of megadrought to reach more than 60 percent. However, if greenhouse gas emissions continue to increase along current trajectories throughout the 21st century, … there is an 80 percent likelihood of a decades-long megadrought in the Southwest and Central Plains between the years 2050 and 2099.” As with many of the calculations of the severity of impacts from climate change, the sooner and more dramatically humans reduce GHG emissions, the lower the likelihood of catastrophic consequences, whether it is sea level rise or drought.

Naumann and co-authors put it matter of factly in the abstract of their 2018 research, “the magnitude of droughts is likely to double in 30% of the global landmass under stringent mitigation policies. If global warming continues at the present rate, water supply-demand deficits would increase fivefold while current 1-in-100-year droughts would occur every two to five years for most of Africa, Australia, southern Europe, southern and central United States, Central America, the Caribbean, north-west China, and parts of Southern America. Approximately two thirds of the global population will experience a progressive increase in drought hazard with warming. In drying areas, drought durations are projected to rise rapidly with warming.”

The image above shows the predicted percent change in precipitation, summer runoff, and soil moistures by 2100. Blue represents increases. Brown decreases. [source]

Increased droughts and major precipitation events also cause agriculture output decline, infrastructure damage, migration and conflict. In 2018, in the midst of a severe drought, Cape Town, South Africa nearly ran out of water (literally) for its 4 million residents. Not every drought is caused by climate change, but there is sufficient scientific evidence to indicate that in many cases, droughts are getting worse.

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