Declines in Arctic sea ice extent and thickness suggest scientifically important changes in the spatial pattern of the marginal ice zone (MIZ)—a dynamic and biologically active band of sea ice cover close to open ocean. Arctic MIZ widths were measured in satellite era sea ice concentrations over the years 1979–2011 using a recently published MIZ width analysis method. Over the record, the warm season (July–September) MIZ width increased by 13 km decade⁻¹, amounting to a 39% widening. This widening trend resulted from a marked poleward advancement of the MIZ poleward edge into regions where sea ice was increasingly younger and thinner at the beginning of annual melt, while the MIZ's equatorward edge moved comparatively little. The warm season MIZ widening contrasted in sign and strength with a cold season (February–April) MIZ narrowing trend (4 km decade⁻¹, amounting to a 15% narrowing).

We employ dynamical downscaling and pseudo global warming methodologies to evaluate climate change impact on the roles of temperature and precipitation in spring snowpack (S) variability across the western United States (U.S.). The negative correlation between S and temperature weakens linearly with elevation, whereas the correlation between S and precipitation increases asymptotically with elevation. The curvilinear relationship in the latter case was not visible in prior studies because of the observation networks' limited range. In our historical validation, there is a range of threshold elevations (1580–2181 m) across six mountainous regions, above which precipitation is the main driver of snowpack variability and below which temperature is the main driver. Under a moderate end‐of‐century climate change scenario, these thresholds increase by 191 to 432 m. These rising thresholds indicate increasing spatial and elevational vulnerability of western U.S. spring snowpack along with associated impacts to hydrologic and ecologic systems.

Accelerating warming, changes in the amount, timing, and form of precipitation, and rapidly growing populations highlight the need for improved predictions of snowmelt‐driven water supplies. Although decadal‐scale trends in reduced streamflow are common, minimal progress has been made in improving streamflow prediction on the annual time scales on which management decisions are made. Efficient allocation of dwindling supplies requires incorporating rapidly evolving knowledge of streamflow generation into parsimonious models capable of improving prediction on seasonal, annual, and multiyear time scales of water resource management. We address this need using long‐term streamflow and climate records in 12 catchments averaging 90 years of observations and totaling more than 1,080 site‐years of data. These catchments experience similar regional climate forcing each year, but are diverse enough to represent broad ranges in precipitation, temperature, vegetation, and geology characteristic of much of the western US. We find that January baseflow across all catchments exhibits a coherent, quasi‐decadal periodicity that presumably is indicative of groundwater response to decadal climate. Although the direct contribution of this discharge to streamflow is small, interannual variability in groundwater discharge is a consistently strong predictor of runoff efficiency suggesting that antecedent groundwater storage alters precipitation routing to streamflow. Incorporating antecedent groundwater storage with precipitation and melt dynamics in multiple linear regression models reduces uncertainty in annual runoff from approximately 40% to <5%. These simple models, using readily available data, provide immediately useful tools for water managers to anticipate and respond to streamflow variability on time scales of 1 to 10 years.

Leads are a key feature of the Arctic ice pack during the winter owing to their substantial contribution to the surface energy balance. According to the present understanding, enhanced heat and moisture fluxes from high lead concentrations tend to produce more boundary layer clouds. However, described here in our composite analyses of diverse surface- and satellite-based observations, we find that abundant boundary layer clouds are associated with low lead flux periods, while fewer boundary layer clouds are observed for high lead flux periods. Motivated by these counterintuitive results, we conducted three-dimensional cloud-resolving simulations to investigate the underlying physics. We find that newly frozen leads with large sensible heat flux but low latent heat flux tend to dissipate low clouds. This finding indicates that the observed high lead fractions likely consist of mostly newly frozen leads that reduce any pre-existing low-level cloudiness, which in turn decreases downwelling infrared flux and accelerates the freezing of sea ice.

Significance: This study is the first, to our knowledge, to reveal how climate variability drives irruptions of North American boreal seed-eating birds. Patterns of Pine Siskin irruption and associated climate drivers manifest as two modes (North-South and West-East) in which dipoles of temperature and precipitation anomalies push and pull irruptive movements across the continent at biennial to decadal periodicities. Our study accentuates the value of sustained and synoptic biological observations, contributed by citizen scientists in this case, that match the spatial and temporal scales at which climatic phenomena are observed and understood. Such observations can help probe new questions, such as the role of climatic dipoles in other large-scale ecological processes.