pcolor plot with non-linear axis

I have the n*m matrix 'HMB'. I plot this with pcolor right now as:

    subplot(1,1,1);
    pcolor(HMB);
    shading flat;
    colormap(hot)
    colorbar;
    caxis([0, 1])
    axis ij image;
    xlabel('x');
    ylabel('y'); 
    title('Half-Maximum Bounds');
    daspect([1 0.2 1])

I want the x dimensions to scale linearly like usual, but I want the y dimension to scale as sqrt(y). This will stretch out the y dimension near y=0 and contract them for high values of y. How can this be done?

Thanks