A comparison between the effects of snow albedo and infiltration of melting water of Eurasian snow on East Asian summer monsoon rainfall

The effect of Eurasian spring snow amount on East Asian summer monsoon (EASM) rainfall has previously been studied on the basis of both observations and numerical simulations. The results indicate that information on the Eurasian spring snow amount could be important for seasonal prediction of EASM rainfall. Although previous studies identified the effects of snow albedo and melting water of Eurasian snow on global climate, their individual contributions to the prolonged snow effect on early summer regional climate have not been evaluated quantitatively. In this study, the relative importance of the effects of snow albedo and snowmelt water over the Tibetan Plateau on the simulated EASM rainfall is investigated using a regional climate model. Three ensemble simulations were conducted. The first ensemble simulation considers the actual snow cover in the initial condition. The second ensemble simulation ignores the snow effect on the surface albedo in the radiation budget. The third ensemble simulation ignores the infiltration of snowmelt water. A detailed comparison of these simulations indicates that the albedo effect is significant and its effect on rainfall amount over the Yangtze River basin is about three times that of the effect of snowmelt water from May to June. The albedo effect decreased from July to August, while the effect of snowmelt water increased. Eventually, the difference between the two effects became insignificant. Overall, the snow albedo effect over the central and western Tibet appears to dominate the observed relationship between the spring snow anomaly and the EASM rainfall anomaly.