Young stars emit strong flares of X-ray radiation that penetrate the surface layers of their associated protoplanetary disks .
It is still an open question as to whether flares create significant changes in disk chemical composition .
We present models of the time-evolving chemistry of gas-phase H _ { 2 } O during X-ray flaring events .
The chemistry is modeled at point locations in the disk between 1 and 50 au at vertical heights ranging from the mid-plane to the surface .
We find that strong , rare flares , i.e. , those that increase the unattenuated X-ray ionization rate by a factor of 100 every few years , can temporarily increase the gas-phase H _ { 2 } O abundance relative to H can by more than a factor of \sim 3 - 5 along the disk surface ( Z/R \geq 0.3 ) .
We report that a “ typical ” flare , i.e. , those that increase the unattenuated X-ray ionization rate by a factor of a few every few weeks , will not lead to significant , observable changes .
Dissociative recombination of H _ { 3 } O ^ { + } , H _ { 2 } O adsorption and desorption onto dust grains , and ultraviolet photolysis of H _ { 2 } O and related species are found to be the three dominant processes regulating the gas-phase H _ { 2 } O abundance .
While the changes are found to be significant , we find that the effect on gas phase water abundances throughout the disk is short-lived ( days ) .
Even though we do not see a substantial increase in long term water ( gas and ice ) production , the flares ’ large effects may be detectable as time varying inner disk water ‘ bursts ’ at radii between 5 and 30 au with future far infrared observations .