Influence of water vapor influx on interdecadal change in summer precipitation over the source area of the Yellow River Basin

The source area of the Yellow River Basin (SYRB) is located in the northeastern Tibetan Plateau, and the precipitation in the SYRB is of great importance to the water resources throughout the whole basin. By analyzing the summer precipitation in the SYRB, we found that an 11.4% increase in precipitation occurred during 2003–2019 compared with 1982–2002. Such interdecadal increase of summer precipitation was due to significant changes of moisture contribution from external moisture source. In the past 38 years, 95.4% of the water vapor for summer precipitable water in the SYRB came from local evapotranspiration (10.6%), the Tibetan Plateau area (35.8%), central Eurasian area (22.5%), South Asia-northern Indian Ocean area (14.6%), South China Sea-western Pacific area (6.6%), and North Africa-West Asia area (5.3%). Thus, external water vapor supplied about 84.8% of summer precipitable water in the SYRB. Compared with 1990–2002, the relative growth rates of moisture contribution during 2003–2019 from the central Eurasian area, North Africa-West Asia area and South China Sea-western Pacific area increased by 2.40%, 4.55% and 15.07%, respectively. Such interdecadal changes were verified by evapotranspiration minus precipitation for it can illustrate the supply capacity of the moisture source. Water vapor supplies in these areas increased during 2003–2019, which greatly contributed to the increase of summer precipitation in the SYRB.