The summer rainfall over the middle-lower reaches of the Yangtze River valley (YRSR) has been estimated with a multi-linear regression model using principal atmospheric modes derived from a 500 hPa geopotential height and a 700 hPa zonal vapor flux over the domain of East Asia and the West Pacific. The model was developed using data from 1958–92 and validated with an independent prediction from 1993–2008. The independent prediction was efficient in predicting the YRSR with a correlation coefficient of 0.72 and a relative root mean square error of 18%. The downscaling model was applied to two general circulation models (GCMs) of Flexible Global Ocean-Atmosphere-Land System Model (FGOALS) and Geophysical Fluid Dynamics Laboratory coupled climate model version 2.1 (GFDL-CM2.1) to project rainfall for present and future climate under B1 and A1B emission scenarios. The downscaled results provided a closer representation of the observation compared to the raw models in the present climate. In addition, compared to the inconsistent prediction directly from different GCMs, the downscaled results provided a consistent projection for this half-century, which indicated a clear increase in the YRSR. Under the B1 emission scenario, the rainfall could increase by an average of 11.9% until 2011–25 and 17.2% until 2036–50 from the current state; under the A1B emission scenario, rainfall could increase by an average of 15.5% until 2011–25 and 25.3% until 2036–50 from the current state. Moreover, the increased rate was faster in the following decade (2011–25) than the latter of this half-century (2036–50) under both emissions.
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