  Microscopic corrugations are ubiquitous in graphene even when placed on
atomically flat substrates. These result in random local strain fluctuations
limiting the carrier mobility of high quality hBN-supported graphene devices.
We present transport measurements in hBN-encapsulated devices where such strain
fluctuations can be in situ reduced by increasing the average uniaxial strain.
When $\sim0.2\%$ of uniaxial strain is applied to the graphene, an enhancement
of the carrier mobility by $\sim35\%$ is observed while the residual doping
reduces by $\sim39\%$. We demonstrate a strong correlation between the mobility
and the residual doping, from which we conclude that random local strain
fluctuations are the dominant source of disorder limiting the mobility in these
devices. Our findings are also supported by Raman spectroscopy measurements.
