Is it possible to calculate flow accumulation using google earth engine?

EE does not provide a way to compute flow accumulation out of the box, the reason is that a significant amount of iterative operations is required.

You can either use a 90m global version from the above HAND link (reference). But the problem is that dataset is that the flow accumulation is computed only up to sub-catchment limits, then it resets to zero. An alternative is to use a 90m HydroSHEDS FA generated from LDD, see the following post on the development forum and the script with a flow accumulation dataset generated using this method here: https://code.earthengine.google.com/ae9664cd08e21a474f7c93fa6c0d325d.