Lake expansion since the middle of the 1990s is one of the most outstanding environmental change events in the Tibetan Plateau (TP). This expansion has mainly occurred in the Inner TP, a vast endorheic basin with an area of about 708,000 km(2) and containing about 780 lakes larger than 1 km(2). The total lake area of the Inner TP has increased from 24,930 km(2) in 1995 to 33,741 km(2) in 2015. The variability of the lake area in the coming decades is crucial for infrastructure planning and ecology policy for this remote region. In this study, a lake mass balance model was developed to describe the lake area response to climate change. First, the model was used to inversely estimate the change in precipitation from the change in lake volume. The result shows that precipitation has increased by about 21 +/- 7% since the middle of the 1990s, as seen in GPCC global data set. Then, the lake size in the coming two decades was predicted by the model driven with either current climate or a projected future climate, showing the lake area would expand continuously, but at a lower rate than before. Both predictions yield a total lake area of 36150 +/- 500 km(2) in 2025 and a rise of average lake level by about 6.6 +/- 0.3 m from 1995 to 2025. However, the two predictions become disparate in the second decade (2026-2035), as the future climate is more warming and wetting than the current climate. It is noted that the prediction of lake expansion is robust for the entire inner TP lake system but not always applicable to individual subregions or specific lakes due to their spatiotemporal heterogeneity.