Photoevaporation rate per unit radius, dΣ/ dt, as a function of radial distance from the central star for different stellar X-ray luminosities, L _X . The evaporation rate peaks in the region 20 AU and at high values of L _X can compete with the inward viscous flow, starving the inner disk of the replenishing gas from the outer disk that contains the bulk (~90%) of the total disk gas mass.