<p>Weather extremes, including flash droughts and wet spells, are increasing in frequency and intensity, yet their timing and sequential impacts on ecosystem stability in subhumid regions remain poorly understood. To investigate how the timing and sequence of hydroclimatic extremes influence ecosystem stability, we used eddy covariance observations (2022–2024) from a central Oklahoma tallgrass prairie and an adjacent juniper-encroached woodland to evaluate ecosystem stability through ‘flashiness’ a metric that quantifies short-term variability in ecosystem carbon and water fluxes. Ecosystem flashiness varied substantially among fluxes, vegetation types, seasons, and meteorological event sequences. Ecosystem respiration (<i>f</i>_Re) and evapotranspiration (<i>f</i>_ET) generally exhibited flashiness values ranging from 0.1 to 0.6, whereas gross ecosystem productivity (<i>f</i>_GEP) showed the highest values (~ 1.1). Seasonal fluctuations in flashiness were most pronounced for <i>f</i>_GEP and net ecosystem exchange (<i>f</i>_NEE), while <i>f</i>_Re and <i>f</i>_ET exhibited smaller seasonal variation. An early-season wet-to-dry sequence in 2022 triggered rapid increases in GEP, Re, and ET followed by abrupt declines with significantly steeper reductions observed in woodland than in grassland (<i>p</i> &lt; 0.05). In contrast, a late-season dry-to-wet sequence in 2024 elicited more moderate responses, with gradual dry-phase declines and similar wet-phase increases. Bootstrap comparisons showed the strongest ecosystem responses in <i>f</i>_NEE, with woodland exhibiting significantly greater flashiness than grassland for both wet spell and flash drought phases in 2022 but not 2024. These findings suggest that preserving native tallgrass prairie and limiting woody encroachment could enhance the stability of terrestrial carbon sequestration under increasingly variable hydroclimate regimes.</p>