High-mass young stellar objects (HMYSOs) gain about half of their mass in about two per cent of their formation time through short (~1 yr) bursts of accretion. Little is known about the effects of these bursts on the evolution of the HMYSO natal environment, as the first HMYSO burst was observed in 2017. We observed the burst in real-time with multi-instrument time-dependent water maser observations. Seven epochs of 22 GHz water masers observations in the bursting source NGC6334I-MM1B with the VLBI Exploration of Radio Astrometry (VERA) array were conducted. Our epochs, from 2014 to 2016, spanned the pre-burst, burst onset (2015.1) and burst stages of the accretion burst. We combined our observations with 2019 321 GHz water maser observations with ALMA, and single dish maser monitoring with Hartebeesthoek Radio Astronomical Observatory (HartRAO). We developed a simple method to distinguish pump and hydrodynamic (random) variability with a 22 GHz single-dish time series. Shock types (C-shocks vs J-shocks) were distinguished through long-term variability patterns, proper motions and the 22 GHz to 321 GHz line ratios. The constant mean proper motion before, v_pre = 50 ± 40 km/s, and after the burst, v_burst = 54 ± 42 km/s indicates that maser variability is due to excitation effects from variable radiation rather than jet ejecta. The northern region, CM2-W2, is likely excited in C-shocks and showed long-term flaring with velocity-dependent excitation of new maser features. We propose that radiative heating of H2 due to high-energy radiation from the accretion burst be the main mechanism for the flaring in CM2-W2. Significant UV and X-ray output from accretion bursts may alter the chemical and dust evolution of the natal HMYSO environment. With JWST observations of H2 line emission and irradiated shock models, we can test this scenario, which would open new avenues of investigation in the rapid time-variable evolution of HMYSOs and their surroundings.
