Changes in the amount of stratospheric water vapor can affect both the chemistry and climate in the stratosphere and troposphere. Convectively lofted ice near and above the tropopause can evaporate and contribute to stratospheric water vapor. Here we conduct several experiments using a trajectory model driven by two chemistry-climate models (CCMs) to study the contribution of lofted ice to stratospheric water vapor. We show that the largest amount of evaporation of convectively lofted ice occurs in the Tropical Tropopause Layer (TTL) and above the Lagrangian cold point, and we find two key regions for lofted ice evaporation: the Asian monsoon region during JJA (June, July, and August) and the tropical western Pacific during DJF (December, January, and February), regions where convection frequently occurs and the evaporation rate of lofted ice is high. The distribution of net contribution is mainly determined by the degree of subsaturation in the TTL, and the net contribution of lofted ice is then transported to the rest of the stratosphere by the general circulation. Over the 21st century, an increase of subsaturation leads both the lofted ice evaporation rate and the net contribution to increase. It explains part of the increase of stratospheric water vapor over the 21st century.
