Projected changes in temperature and precipitation
The Brahmaputra basin
Rainfall Future scenarios project a 5–25% increase in summer rainfall over most of the basin up until 2050. According to the wettest scenario (RCP 8.5), the increase could be more than 25%, especially in the northern and far-western parts of the basin. In winter, projections show an increase over the main mountain range. This winter increase is expected to range from 5–25%. However, the southwest part and central northern part show decreases in winter precipitation of up to 25% for both scenarios. Overall, RCP 4.5 and RCP 8.5 project an increase of 10.5% and 9.5%, respectively, for the monsoon season. Temperature Both climate change scenarios show an increase of 1–3°C across the Brahmaputra basin in summer. The RCP 8.5 scenario shows a slightly larger area that will experience a 2–3°C increase. The increase in winter temperature is similar, but occurs over larger areas and with stronger warming (with an increase of more than 3°C in some areas), particularly for the RCP 8.5 scenario. Projections show that winter and summer warming is greater in the north where the increase is mostly more than 2°C.
The regional HKH perspective – Indus, Ganges, Brahmaputra, upper Salween, upper Mekong basins Climate models indicate that both temperature and precipitation patterns are likely to change in the Hindu Kush Himalayas in the future. However, owing to its very diverse topography, the magnitude and extent of these changes will not be uniform over the entire region. There is a high degree of uncertainty in climate projections in the HKH, particularly as global climate models are not able to adequately account for changes relating to topography. 103,104 By 2050, temperatures across the basins are projected to increase by about 1–2°C on average, and winters will see greater warming than summers inmost places. Mountainous and high altitude areas will be particularly affected in both summer and winter, with warming reaching 4–5°C in some places.
Compared to temperature, projected trends in precipitations are more diverse across the whole area and within each basin. By 2050, in the summer, an increase in temperature of about 5% on average is expected, reaching 25% in some areas. But decreases of around –5% are also projected in significant portions of the Brahmaputra, Indus, and Ganges basins, especially in winter – possibly reaching up to –25% in some places. Extremes in precipitation are likely to increase with wet areas getting wetter and dry areas getting dryer. Areas receiving intense precipitation events are likely to see further intensification of such events. Projections are made for the period 2021–2050, compared to the baseline period 1961–1990. The two ensemble scenarios used in this analysis – RCP 4.5 and 8.5 – produce broadly consistent projections. However, RCP 8.5 generally shows stronger increases in temperatures and stronger variability in precipitation.
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