Center for Climate Sciences

The influenza, or flu, virus infects millions of people in the United States each year, mostly during winter. To help limit the impacts of seasonal flu outbreaks, scientists have been trying to anticipate when the outbreaks occur using a variety of information. Laboratory studies have pointed to humidity playing an important role in the transmission of flu. The average amount of water vapor in the air we breathe varies widely across the U.S., but even in the most humid areas, it begins to drop as winter approaches.

Researchers at NASA’s Jet Propulsion Laboratory and the University of Southern California have used NASA satellite data from the Atmospheric Infrared Sounder (AIRS) to illuminate the relationship between low humidity and the outbreak of flu in the U.S. They compared AIRS measurements of water vapor in the lower atmosphere with flu case estimates over a twelve year period. For each state, they identified specific levels of low humidity that signal the start of a flu outbreak. These threshold levels of low humidity vary between the states but follow regional patterns and are tied to each state’s average climate. States with humid climates, such as those in the Southeast, have higher threshold values than arid states, including those in the West and Southwest.

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When designing a space mission, there are many parameters to take into account. For instance, a space-borne instrument will observe a swath of the Earth’s surface as it orbits, and the width of that swath depends on the instrument itself, as well as high above the Earth it flies. There are also often trade-offs between different design parameters. For example, the same instrument can be used in a mission that acquires very fine features on the surface infrequently, or it can focus on larger features but visit them more often. It can be difficult to optimize these design decisions for missions that produce many products in different science focus areas (e.g. the design best for studying water is probably not the same as the design best for land).

NASA’s Earth System Observatory will include a mission to map Earth’s Surface Biology and Geology. The mission will monitor volcanic eruptions, snow-melt, water quality, vegetation health, and more. Each of these areas prioritize different instrument parameters. This study proposed a new metric by which to optimize mission design parameters: intrinsic dimensionality. This is a mathematical metric independent of application area, and can be used to design a mission that provides the best compromise between the needs of different areas.

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Heat stress is a rapidly increasing threat to human health and energy demand across the US and the globe. Both high temperatures and high moisture levels are important contributors to heat stress, and it is well-known that future temperature increases will generally be larger in mountains due to there being much less snow and drier soils. But with moisture increasing rapidly at low elevations, which factor will dominate the total response?

Scientists at JPL and several other institutions looked at all available high-resolution climate-model data and found that the temperature effect best explains the total change in heat stress. However, the more humid a climate zone, the more moisture matters in explaining the magnitude of the changes. These findings help understand where and why heat stress is likely to increase most dramatically, and motivate efforts to make investments and other preparations in the areas of greatest change, such as the southern Appalachians and southern Rocky Mountains.

For more, see the full article.

Sequences of extreme climate events, or multiple ones occurring simultaneously, can have impacts that are ‘larger than the sum of their parts’. For example, bad harvests in several major crop-growing areas can lead to shortages, price shocks, and malnutrition, while oscillations between wet and dry years create larger wildfire risks than dry years alone, by increasing the quantity of vegetation available for burning. Using many versions of the same climate model to represent these events increases the confidence with which scientists can draw conclusions about them.

JPL scientists and colleagues looked at 100 end-of-century climate-model outputs for specific sets of conditions that have been linked to impacts on, for example, food security and wildfire risk. The heat-and-drought levels that historically cause bad harvests will occur simultaneously in the six major corn-growing areas about every 4 years, versus every 18 years now. The chance of a very wet year followed by a very dry year will increase by about 25% in California and many other wildfire-prone areas. Such multi-part interactions are critical to take into account for societal resilience in a warming climate.

For more, see the full article.