Snow droughts are a new way to understand changes in snowpack and subsequent runoff. Globally, we do not have a good understanding of the drivers of snow droughts or how those drivers have changed historically. Here, we identify what has been the dominant driver of global snow droughts in mountain ranges, how it shifted historically, and what similarities exist in similar snow types. We explore this in all global mountain ranges, ones that are highly dependent on winter precipitation for summer water, and two regional case studies in the Cascade Range and the Himalayan Mountains. We found that in both the northern and southern hemispheres, dry snow droughts (driven by precipitation) are the most common. In both the northern and southern hemisphere, more mountain ranges shifted to having temperature be the main driver of snow droughts in the historical record. In the northern hemisphere, tundra, boreal, prairie, and ice snow type areas had the most area with dry snow droughts. In the southern hemisphere, all snow types except for tundra had the most area with temperature as the main driver of snow droughts. With this global, multivariate methodology, we were able to identify common drivers and patterns of historical snow droughts that exist across similar geographical areas (i.e., northern and southern hemisphere and mountain ranges) and snow type areas. More research is needed to better understand snow droughts, their drivers, and the risk they pose regionally to food and water security.

Observations of Planet Earth from space are a critical resource for science and society. Satellite measurements represent very large investments and United States (US) agencies organize their effort to maximize the return on that investment. The US National Research Council conducts a survey of earth science and applications to prioritize observations for the coming decade. The most recent survey prioritized a visible to shortwave infrared imaging spectrometer and a multi-spectral thermal infrared imager to meet a range of needs. First, and perhaps, foremost, it will be the premier integrated observatory for observing the emerging impacts of climate change . It will characterize the diversity of plant life by resolving chemical and physiological signatures. It will address wildfire, observing pre-fire risk, fire behavior and post-fire recovery. It will inform responses to hazards and disasters guiding responses to a wide range of events, including oil spills, toxic minerals in minelands, harmful algal blooms, landslides and other geological hazards. The SBG team analyzed needed instrument characteristics (spatial, temporal and spectral resolution, measurement uncertainty) and assessed the cost, mass, power, volume, and risk of different architectures. The Research and Applications team examined available algorithms, calibration and validation and societal applications and used end-to-end modeling to assess uncertainty. The team also identified valuable opportunities for international collaboration to increase the frequency of revisit through data sharing, adding value for all partners. Analysis of the science, applications, architecture and partnerships led to a clear measurement strategy and a well-defined observing system architecture.