<p>The effects of climate change on water resources are partly determined by the size and the spatial distribution of ice reservoirs around the world. While mountain glaciers represent only 1% of today’s global ice volume, they have contributed around 25% to sea-level rise during the last decades, and are expected to contribute within the same proportion during the rest of the 21st century [<em>SROCC, 2019</em>]. Mountain glaciers also represent sources of drinking water for millions of people. The glacierized drainage basins cover around 26% of the global land surface and are populated by more than two billions of people [<em>Huss et Hock, 2018</em>]. However, mountain glacier ice thickness estimates are largely uncertain due to the use of simplified retrieval approaches [<em>Rabatel et al., 2018</em>]. Furthermore, nearly 50% of the global glacier evolution uncertainty comes from the glacier model itself and the initial glacier representation in space [<em>Marzeion et al., 2019</em>]. The objective of this study is to understand the effects of initial glacier conditions, and specifically the ice thickness, on simulations of glacier evolution and their contribution to river runoff.</p><p><br>For that purpose, we used the Open Global Glacier Model [OGGM, <em>Maussion et al., 2019</em>], that simulates the surface mass balance and ice dynamics to estimate the evolution of any glacier in the world. We used three new different ice thickness dataset and proposed a framework to assimilate them within OGGM. We then focused on sensitivity analysis of future glacier evolution using different climate scenarios, initial conditions of ice thickness and internal model parameters such as the creep parameter, the spatial resolution, the spin-up initialization. These experiments were performed for different types of glaciers in terms of location, size and geometry. The results helped us to assess the importance of model initialization with respect to other model parameters, in the glacier evolution during the 21st century and specifically the changes in surface and volume. We also explored the differences induced in terms of glacier contribution to river runoff and peak water timing, which is of great importance for freshwater resources management.</p>