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Over 40,000 glaciers are located in the Himalaya, which are crucial reservoirs for 800 million people living in downstream valleys. Meltwater is crucial as a balance for water supply and irrigation, especially during drought years. Due to climate change, many glaciers lost important ice volumes except in one region (Karakoram) where positive mass balances are found. This phenomenon is called the Karakoram anomaly. By using temperature and precipitation outputs from the Global Climate Model CESM, run with and without irrigation, we can observe the irrigation-induced temperature and precipitation changes showing a gradual pattern from East to West. By inserting past climatic data from ERA5 into a glacier mass balance (PyGEM), we can reproduce the observed negative mass balances over the Himalaya and positive mass balances in the Karakoram. Furthermore, when running PyGEM with irrigation-induced differences of climatic variables, we can detect the impact of irrigation on the mass balances, mainly resulting in losing less mass or even growing glaciers. A sensitivity analysis reveals that the Karakoram is more influenced by the precipitation, and the rest of the Himalaya by temperature. Precipitation shows a North-South pattern over the Karakoram, corresponding respectively to an increase-balanced amount of snow. The rest of the Himalaya shows a gradient with a warming more to the East, in Hengduan Shan, and a cooling in West to Central Himalaya. Irrigation, although located at the bottom of the mountain range, can have an impact on glaciers and as such indirectly determines the water supply from glaciers with consequences for the hydro-economy of the Himalaya.
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Concurrent extreme events exacerbate adverse impacts on humans, economy, and environment relative to those from independent extreme events. However, while the effects of climate change on the frequency of individual extreme events have been highly researched, the impacts of climate change on compound events have not been extensively investigated, particularly in East Africa. Here, we investigate the joint occurrence of six categories of extreme events in East Africa, namely: river floods, droughts, heatwaves, crop failures, wildfires and tropical cyclones using bias-adjusted impact simulations under past and future climate conditions. We show that the pronounced increase in the probability of joint occurrence of these extreme events in the region can be explained by combined changes in frequency, spatial distribution, and dependence of these extreme events induced by climate change. The analysis demonstrates that there is a higher positive correlation between most co-occurring pairs of extremes in the region under end-of-century global warming conditions leading to more frequent concurrence in comparison to the early-industrial period. Our results further highlight that the most affected locations in the region by concurrent extremes are the Nile basin and parts of the Congo basin, whereby river floods and heatwaves emerge as the main driver(s) for concurrent extremes. Our results overall highlight that these concurrent extremes will become the norm rather than the exception in East Africa, even under low-end warming scenarios.
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