During the exceptionally hot summer of 2022， an extreme hydroclimatic event in July led to widespread flooding and enhanced sediment mobilization across the southern Alborz Mountains （northern Iranian Plateau）， temporarily altering erosion dynamics. This study examines how such an extreme climate event influenced decadal erosion patterns and abrupt hydro-geomorphic responses by integrating four decades of meteorological and hydrometric data （1980-2022） with satellite-based geomorphic indicators and field observations. Decadal sediment-derived erosion proxies， calculated using area-normalized suspended sediment yield， range from ～3×10
-6 to ～0.058 mm/yr at hydrometric stations. High values in the less-urbanized western and eastern Alborz are consistent with steep terrain， weak lithology， and sparse vegetation cover. Regionally， mean decadal erosion rates are estimated at ～0.0138 mm/yr in Qazvin （western Alborz）， ～0.0030 mm/yr in Karaj and ～0.0054 mm/yr in Tehran （central Alborz）， and ～0.0105 mm/yr in Semnan （eastern Alborz）， highlighting lower values in the more urbanized central Alborz due to surface sealing， drainage reorganization， and reservoir trapping. The July 2022 flood， associated with a strong Indian Summer Monsoon （ISM） incursion and large-scale atmospheric circulation anomalies， generated highly non-linear sediment responses: ～39 times the decadal July mean in the western， ～26 times in the central， and ～0.18 times in the eastern Alborz， reflecting dam regulation and spatially variable erosional patterns. Simultaneously， NDVI declined by ～5% across the semi-arid northern Iranian Plateau， most pronounced in the western and central Alborz， while increasing by up to ～15% near the ISM core. These findings reveal scale-dependent erosion and vegetation responses to extreme climate events， modulated by anthropogenic modification， with implications for erosion assessment in semi-arid mountain-front regions under intensifying climate variability.
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