Projection on precipitation frequency of different intensities and precipitation amount in the Lancang-Mekong River basin in the 21st century

In the Lancang-Mekong River basin (LMRB), agriculture, dominating the local economy, faces increasing challenges in water supply under climate change. The projection of future precipitation in this basin is essential for understanding the challenges. In this study, the Weather Research and Forecasting (WRF) model was applied to project the LMRB precipitation. Comparing with the historical period (1986-2005), we analyzed the changes of both the projected precipitation amount and the frequency of rainless (<0.1 mm d(-1)), light rain (0.1-10 mm d(-1)), moderate rain (10-25 mm d(-1)), heavy rain (25-50 mm d(-1)), rainstorm (50-100 mm d(-1)), and heavy rainstorm (>100 mm d(-1)) for three periods, namely the near-term (2016-2035), mid-term (2046-2065), and long-term (2080-2099). The results indicate that the precipitation amount during the wet season (April-October) is expected to increase in most areas of the basin for the three periods. As for the precipitation during the dry season (November-March), an increase is projected in most areas for the near-term, while an increase in the lower reach of the basin and a decrease in the upper and middle reach for the mid-term and long-term. The precipitation reduction is expected to be greatest in Myanmar, Laos, Thailand, and Yunnan province of China for the mid-term. The frequency of precipitation in different intensities has prominent regional and temporal differences. During the wet season, the days of rainless and light rain are expected to decrease in the middle reach, whereas the days of rainstorm and heavy rainstorm increase. This feature is especially strong in southern Thailand, southern Laos and Cambodia in the near-term and in Laos and Thailand for the mid-term and long-term. During the dry season, there are projected increasing rainless days and decreasing days of precipitation for the other intensities in the middle reach, and opposite in the rest area of the basin. These projected precipitation changes have potential various impact in different parts of the basin. The middle reach would likely face increasing flood risks because of more days of rainstorm and heavy rainstorm, as well as more precipitation. Yunnan, Myanmar, Thailand and Laos would probably be the center of drought threatens during the dry season due to the increment of rainless days and the precipitation reduction. Besides, the seawater intrusion during the dry season in the near-term and mid-term would be more serious as a result of the precipitation decrease in southern Vietnam.