Slight mass gain of Karakorum glaciers in the early 21st century

International audienceThere is a severe lack of observations to assess the state of health of Hindu Kush-Karakoram-Himalaya glaciers and constrain their contribution to regional hydrology and global sea-level rise1. In the context of a negative globally-average mass balance of glaciers and ice caps1,2,3, an anomalous behaviour of Karakoram glaciers has been suggested2,4,5,6, but not confirmed by recent mass balance measurements. Furthermore, the presence of numerous glacier surges in the region7,8,9,10,11 complicates the interpretation of the few observations available (e.g., length and velocity changes). Here, we observe the regional mass balance of glaciers in the central Karakoram between 1999 and 2008 by differencing two digital elevation models. The spatial pattern of glacier elevation changes is highly heterogeneous, confirms that glacier surges are widespread and shows that high ice thinning and ablation rates can occur on debris-covered glacier tongues. The regional mass balance is slightly positive (+0.11 ± 0.22 m a-1 water equivalent) and in agreement with a decreasing runoff from rivers originating in this area12. We thereby confirm the so-called "Karakoram anomaly" and show that the sea-level rise contribution of glaciers in this mountain range was -0.01 mm a-1 during 1999-2008, a reduction by 0.05 mm a-1 compared to a recent estimate1

Evolution and development of the Indian monsoon

© Springer Nature Switzerland AG 2020. The Indian monsoon is a complex oceanic-atmospheric-coupled mechanism of the tropics that plays a key role in inter-hemispheric heat transfer on Earth. The summer monsoon brings moisture to the highly populated South Asian countries and affects the livelihood of more than a billion people. The intensity of the monsoon significantly influences the ecological diversity and hydrological reservoirs across the South Asian region. However, the intensity of the monsoon greatly varies spatially and temporally, driven by both external and internal forcing factors. Modeling and palaeoclimatic studies indicate several phases of strong and weak summer monsoon rainfall caused by changes in solar insolation, snow accumulation in western Europe, El Niño-Southern Oscillation, North Atlantic Oscillations and sea surface temperature in the Indian and Pacific Oceans. The initiation and strengthening of the Indian monsoon during the middle-late Miocene are sometimes linked with phases of major surface uplift of the Himalayan and/or Tibetan Plateau. The Plio-Pleistocene glaciation prompted a strong winter monsoon and a weak summer monsoon. During the early Holocene, the summer monsoon strengthened and subsequently weakened with two major phases of sudden rainfall reduction at ~8.2 and ~4.2 kyr BP; the latter event caused significant societal impact including the migration of population of the Indus Valley Civilization. In the last millennium, the Indian summer monsoon (ISM) was strong during the Medieval Warm Period (MWP) now designated as Medieval Climate Anomaly (MCA) and Current Warm Period (CWP), punctuated by a weak phase during the Little Ice Age (LIA). Meteorological records indicate an increasing trend in the intensity and frequency of extreme rainfall events in the last few decades leading to widespread floods and droughts. High-resolution climatic records from marine as well as continental archives improve our understanding of Indian monsoon variability and its forcing factors on different time scales