1227 The numerical and graphical evidence (Table 3 and Figure 2) confirms that incorporating transient hydroclimatic variability qualitatively changes the “type” of response: from a smooth and cumulative evolution (scenario 2) to a behavior dominated by pulses (scenario 1). This pattern coincides with field observations reported for acid drainage/acid rock, where during prolonged dry periods acidity and metals gradually increase, and during the initial phase of rainfall events, especially after droughts, sudden increases (“first flush”) are observed due to the dissolution and entrainment of accumulated soluble salts; Subsequently, concentrations may decrease due to dilution and temporary depletion of the salt reservoir, before restarting the concentration cycle during the next dry period. Likewise, reviews on climate change and acid drainage indicate that changes in seasonality and hydrological extremes can modify the composition, transport, and magnitude of pollutant loads, reinforcing the need to evaluate scenarios with non-stationary hydrology. Figure 2 - Annual geochemical response of the system under climate-induced hydrological changes versus steady state. The results show that explicitly incorporating climate projections into reactive geochemical modeling substantially modifies the system's temporal signal, increasing interannual variability and generating extreme events that are not reproduced by average climate approaches. 4. CONCLUSIONS The results show that explicitly including transient hydroclimatic forcing in a reactive transport model shifts the risk assessment from a focus on “average values” to a focus on ‘events’ and “peak loads.” Although the pH averages for both scenarios remain close (4.57 vs. 4.56), the scenario with variable hydroclimate exhibits substantially greater intra-annual variability and the occurrence of years with high pH amplitudes, including maximums above 5.0. In terms of acid drainage, this range is consistent with reports
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