Drought & Deluge in 2018

In a warming world, a supercharged water cycle ramps up evaporation and precipitation. Warmer air creates higher evaporation rates from the soil, which worsens drought, stresses water supplies, and hampers agriculture. Evaporation of surface waters, such as lakes and oceans, also increases. A warmer atmosphere can hold more water before becoming saturated, so more water is available to come down as heavy precipitation during storms. This heavier precipitation can result in more flooding, causing property damage and sending additional pollutants into waterways.

While a persistent weather pattern can lead to dry and wet periods, the background climate can make them more severe. Early research suggests that the warming Arctic may play a role in changing jet stream fluctuations that can lead to these more stagnant weather patterns (the research community is hard at work on this issue). The amount of precipitation in the highest one percent of daily rainfall is increasing in the U.S., with the the largest increases east of the Rockies. In the West, even though a relatively modest increase in the amount of precipitation has been recorded during the heaviest downpours, the bigger story is that droughts are getting more intense over the past century.

This year, drought has intensified across most of the Southwest, with exceptional drought (the highest category in the drought scale) in parts of Arizona, New Mexico, Oklahoma, and Texas. Drought will likely worsen before getting better. The start of the Southwest monsoon season, that time of year that brings bursts of heavy and gusty thunderstorms, is still a month away. Even when rain does come, heavy rain on parched ground often runs off, raising the flood risk. Meanwhile, the additional heavy rain on the saturated soils in the Middle Atlantic and Southern Appalachians has resulted in higher streamflows and flooding. A wetter than average summer east of the Mississippi River is currently forecast by the Climate Prediction Center, which would enhance the risk of summer flooding.

More: Visit our Extreme Weather Toolkits in our Media Library for more resources on the relation between climate change and drought or heavy precipitation. From NASA, See how drought and over-reliance on aquifers have taken a toll on California’s groundwater supply.

Methodology: Nationwide year-to-date precipitation data was gathered from the NWS Advanced Hydrologic Prediction Service tool on May 21. Individual city year-to-date precipitation amounts were calculated through May 20 via the Advanced Climate Information System and compared to the climatological normal through that date. Please contact us if you would like to see the full data set.