def hydrographs(ds):
    """Return a graphic showing the discharge simulations and observations."""

    basin_name = ds.basin_name.values[0]  # selected basin name
    g = ds.q_sim.hvplot.line(
        x="time",
        line_width=1,
        label="Simulations",
        ylabel="Streamflow (m³/s)",
        xlabel="Time",
        title=basin_name,
    )

    # Plot the observed streamflows if available
    if hasattr(ds, "q_obs"):
        g *= ds.q_obs.hvplot.line(
            x="time", line_width=1.5, color="k", label="Observations"
        )

    return g