Riv ers originating in the high mountains of Asia are among the most meltwater-dependent river systems on Earth, yet large human populations depend on their resources downstream 1 . Across High Asia’s river basins, there is large variation in the contribution of glacier and snow melt to total runo 2 , which is poorlyquantified.Thelackofunderstandingofthehydrological regimes of High Asia’s rivers is one of the main sources of uncertainty in assessing the regional hydrological impacts of climate change 3 . Here we use a large-scale, high-resolution cryospheric‐hydrological model to quantify the upstream hydrological regimes of the Indus, Ganges, Brahmaputra, Salween and Mekong rivers. Subsequently, we analyse the impacts of climate change on future water availability in these basins using the latest climate model ensemble. Despite large dierences in runo composition and regimes between basins and between tributaries within basins, we project an increase in runo at least until 2050 caused primarily by an increase in precipitation in the upper Ganges, Brahmaputra, Salween and Mekong basins and from accelerated melt in the upper Indus Basin. These findings have immediate consequences for climatechangepolicieswhereatransitiontowardscopingwith intra-annual shifts in water availability is desirable. In general, the climate in the eastern part of the Himalayas is characterized by the East-Asian and Indian monsoon systems, causing the bulk of precipitation to occur during JuneSeptember (Supplementary Fig. 4). The precipitation intensity shows a strong northsouth gradient caused by orographic eects 4 . Precipitation patterns in the Hindu Kush and Karakoram ranges in the west are characterized by westerly and southwesterly flows, causing the precipitation to fall more equally distributed over the year 5 (Supplementary Fig. 4). In the Karakoram, up to two-thirds of the annual high-altitude precipitation occurs during the winter months 6,7 . In addition, basin hypsometry determines the ratio of solid and liquid precipitation within a basin. Solid precipitation can be stored long-term as perennial snow, and ice or short-term as seasonal snow before turning into runo by melting, whereas liquid

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Consistent increase in High Asia's runoff due to increasing glacier melt and precipitation

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Response of debris-covered glaciers in the Mount Everest region to recent warming, and implications for outburst flood hazards

We study the properties of precipitation in the Hindu-Kush Karakoram Himalaya (HKKH) region using currently available data sets. We consider satellite rainfall estimates (Tropical Rainfall Measuring Mission), reanalyses (ERA-Interim), gridded in situ rain gauge data (Asian Precipitation Highly Resolved Observational Data Integration Towards Evaluation of Water Resources, Climate Research Unit, and Global Precipitation Climatology Centre), and a merged satellite and rain gauge climatology (Global Precipitation Climatology Project). The data are compared with simulation results from the global climate model EC-Earth. All data sets, despite having different resolutions, coherently reproduce the mean annual cycle of precipitation in the western and eastern stretches of the HKKH. While for the Himalaya only a strong summer precipitation signal is present, associated with the monsoon, the data indicate that the Hindu-Kush Karakoram, which is exposed to midlatitude qwestern weather patternsq, receives water inputs in winter. Time series of seasonal precipitation confirm that the various data sets provide a consistent measurement of interannual variability for the HKKH. The longest observational data sets indicate a statistically significant decreasing trend in Himalaya during summer. None of the data sets gives statistically significant precipitation trends in Hindu-Kush Karakoram during winter. Precipitation data from EC-Earth are in good agreement with the climatology of the observations (rainfall distribution and seasonality). The evolution of precipitation under two different future scenarios (RCP 4.5 and RCP 8.5) reveals an increasing trend over the Himalaya during summer, associated with an increase in wet extremes and daily intensity and a decrease in the number of rainy days. Unlike the observations, the model shows an increasing precipitation trend also in the period 1950-2009, possibly as a result of the poor representation of aerosols in this type of GCMs. Citation: Palazzi, E., J. von Hardenberg, and A. Provenzale (2013), Precipitation in the Hindu-Kush Karakoram Himalaya: Observations and future scenarios, J. Geophys. Res. Atmos., 118, 85-100, doi: 10.1029/2012JD018697.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2012JD018697

Precipitation in the Hindu‐Kush Karakoram Himalaya: Observations and future scenarios

About 800 million people depend in part on meltwater from the thousands of glaciers in the high mountains of Asia. Water stress makes this region vulnerable to drought, but glaciers are a uniquely drought-resilient source of water. Here I show that seasonal glacier meltwater is equivalent to the basic needs of 221 ± 59 million people, or most of the annual municipal and industrial needs of Pakistan, Afghanistan, Tajikistan, Turkmenistan, Uzbekistan and Kyrgyzstan. During drought summers, meltwater dominates water inputs to the upper Indus, Aral and Chu/Issyk-Kul river basins. This reduces the risk of social instability, conflict and sudden migrations triggered by water scarcity, which is already associated with the large, rapidly growing populations and hydro-economies of these basins. Regional meltwater production is, however, unsustainably high—at 1.6 times the balance rate—and is expected to increase in future decades before ultimately declining. These results update and reinforce a previous publication in Nature on this topic, which was retracted after an inadvertent error was discovered. Glaciers in the high mountains of Asia provide a uniquely drought-resilient source of water, supplying summer meltwater sufficient for the basic needs of around 200 million people.

Asia's shrinking glaciers protect large populations from drought stress.

The size, distribution, and mobility of landslides caused by the 2015 Mw7.8 Gorkha earthquake, Nepal

[1] Precipitation is one of the main factors which controls surface processes and landscape morphology. Large orogenic belts such as the Himalayas control precipitation distribution as a result of orographic effects due to their prominent relief. However, precipitation is difficult to monitor because mountain regions are largely inaccessible and therefore not sufficiently covered by ground‐based gauge stations. The complexity of orographic effects resulting from the interaction between elevation and climatic processes and the lack of precise meteorological data thus limit our understanding of climatic influence on landscape formation. Therefore, high‐quality precipitation observations with good spatiotemporal coverage are needed. Here we evaluate five gridded precipitation data sets derived from remote sensing and interpolation of rain gauge data with ground‐based precipitation measurements. First, we evaluate the bulk error of each data set, then we evaluate the temporal quality of data within five watersheds, and last we compare the spatial performance along seven swath profiles across strike to the Himalayan range in Nepal. Our evaluation shows that the data sets vary significantly along the orographic front and get more consistent toward the adjacent low‐relief domains, while bulk errors are largest during monsoon season. In particular, where topographic gradients are important, the resolution of gridded data sets cannot incorporate small‐scale spatial changes of precipitation. We show that the data set derived from interpolation of gauge data performs best in the Himalayas. This study gives an overview on the applicability of precipitation data sets within the Himalayan orographic domains where relief has a pronounced impact on precipitation.

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Cristoff Andermann

Papers

Evaluation of precipitation data sets along the Himalayan front