Persistent multiyear drought (MYD) events pose a growing threat to nature and humans in a changing climate. We identified and inventoried global MYDs by detecting spatiotemporally contiguous climatic anomalies, showing that MYDs have become drier, hotter, and led to increasingly diminished vegetation greenness. The global terrestrial land affected by MYDs has increased at a rate of 49,279 ± 14,771 square kilometers per year from 1980 to 2018. Temperate grasslands have exhibited the greatest declines in vegetation greenness during MYDs, whereas boreal and tropical forests have had comparably minor responses. With MYDs becoming more common, this global quantitative inventory of the occurrence, severity, trend, and impact of MYDs provides an important benchmark for facilitating more effective and collaborative preparedness toward mitigation of and adaptation to such extreme events.

Glaciers in High Mountain Asia, many of which exhibit surface debris, contain the largest volume of ice outside of the polar regions. Many contain supraglacial pond networks that enhance melt rates locally, but no large‐scale assessment of their impact on melt rates exists. Here we use surface energy balance modeling forced using locally measured meteorological data and monthly satellite‐derived pond distributions to estimate the total melt enhancement for the four main glaciers within the 400‐km² Langtang catchment, Nepal, for a 6‐month period in 2014. Ponds account for 0.20 ± 0.03 m/year of surface melt, representing a local melt enhancement of a factor of 14 ± 3 compared with the debris‐covered area, and equivalent to 12.5 ± 2.0% of total catchment ice loss. Given the prevalence of supraglacial ponds across the region, our results suggest that effective incorporation of melt enhancement by ponds is essential for accurate predictions of future mass balance change in the region.

Ice cliffs might be partly responsible for the high mass losses of debris-covered glaciers in the Hindu Kush-Karakoram-Himalaya region. The few existing models of cliff backwasting are point-scale models applied at few locations or assume cliffs to be planes with constant slope and aspect, a major simplification given the complex surfaces of most cliffs. We develop the first grid-based model of cliff backwasting for two cliffs on debris-covered Lirung Glacier, Nepal. The model includes an improved representation of shortwave and longwave radiation, and their interplay with the glacier topography. Shortwave radiation varies considerably across the two cliffs, mostly due to direct radiation. Diffuse radiation is the major shortwave component, as the direct component is strongly reduced by the cliffs’ aspect and slope through self-shading. Incoming longwave radiation is higher than the total incoming shortwave flux, due to radiation emitted by the surrounding terrain, which is 25% of the incoming flux. Melt is highly variable in space, suggesting that simple models provide inaccurate estimates of total melt volumes. Although only representing 0.09% of the glacier tongue area, the total melt at the two cliffs over the measurement period is 2313 and 8282 m³, 1.23% of the total melt simulated by a glacio-hydrological model for the glacier’s tongue.

The thinning patterns of debris‐covered glaciers in High Mountain Asia are not well understood. Here we calculate the effect of supraglacial ice cliffs on the mass balance of all glaciers in a Himalayan catchment, using a process‐based ice cliff melt model. We show that ice cliffs are responsible for higher than expected thinning rates of debris‐covered glacier tongues, leading to an underestimation of their ice mass loss of 17% ± 4% in the catchment if not considered. We also show that cliffs do enhance melt where other processes would suppress it, that is, at high elevations, or where debris is thick, and that they contribute relatively more to glacier mass loss if oriented north. Our approach provides a key contribution to our understanding of the mass losses of debris‐covered glaciers, and a new quantification of their catchment wide melt and mass balance.

Many glaciers are thinning rapidly beneath melt-reducing debris cover, including Kennicott Glacier in Alaska where glacier-wide maximum thinning also occurs under debris. This contradiction has been explained by melt hotspots, such as ice cliffs, scattered within the debris cover. However, melt hotspots alone cannot account for the rapid thinning at Kennicott Glacier. We consider the significance of ice cliffs, debris, and ice dynamics in addressing this outstanding problem. We collected abundant in situ measurements of debris thickness, sub-debris melt, and ice cliff backwasting, allowing for extrapolation across the debris-covered tongue (the study area and the lower 24.2 km² of the 387 km² glacier). A newly developed automatic ice cliff delineation method is the first to use only optical satellite imagery. The adaptive binary threshold method accurately estimates ice cliff coverage even where ice cliffs are small and debris color varies. Kennicott Glacier exhibits the highest fractional area of ice cliffs (11.7 %) documented to date. Ice cliffs contribute 26 % of total melt across the glacier tongue. Although the relative importance of ice cliffs to area-average melt is significant, the absolute area-averaged melt is dominated by debris. At Kennicott Glacier, glacier-wide melt rates are not maximized in the zone of maximum thinning. Declining ice discharge through time therefore explains the rapid thinning. There is more debris-covered ice in Alaska than in any other region on Earth. Through this study, Kennicott Glacier is the first glacier in Alaska, and the largest glacier globally, where melt across its debris-covered tongue has been rigorously quantified.

Ice cliffs and ponds on debris-covered glaciers have received increased attention due to their role in amplifying local melt. However, very few studies have looked at these features on the catchment scale to determine their patterns and changes in space and time. We have compiled a detailed inventory of cliffs and ponds in the Langtang catchment, central Himalaya, from six high-resolution satellite orthoimages and DEMs between 2006 and 2015, and a historic orthophoto from 1974. Cliffs cover between 1.4% (± 0.4%) in the dry and 3.4% (± 0.9%) in the wet seasons and ponds between 0.6% (± 0.1%) and 1.6% (± 0.3%) of the total debris-covered tongues. We find large variations between seasons, as cliffs and ponds tend to grow in the wetter monsoon period, but there is no obvious trend in total area over the study period. The inventory further shows that cliffs are predominately north-facing irrespective of the glacier flow direction. Both cliffs and ponds appear in higher densities several hundred metres from the terminus in areas where tributaries reach the main glacier tongue. On the largest glacier in the catchment ~10% of all cliffs and ponds persisted over nearly a decade.