Impacts of wildfire and post‐fire land management on hydrological and sediment processes in a humid Mediterranean headwater catchment

• Published in: Hydrological processes 2020-12, Vol.34 (26), p.5210-5228
• Main Authors: Nunes, João Pedro, Bernard‐Jannin, Léonard, Rodríguez‐Blanco, María Luz, Boulet, Anne‐Karine, Santos, Juliana Marisa, Keizer, Jan Jacob
• Format: Article
• Language: English
• Subjects: Afforestation; Agricultural land; Agricultural practices; Agricultural production; Agriculture; Agroforestry; Catchment area; Catchment scale; Catchments; Conservation practices; Downstream; Downstream effects; Drought; Erosion features; Exhaustion; Fires; Forests; headwater catchment; Headwater catchments; Headwaters; Hydrologic data; Hydrologic processes; hydrological response; Hydrology; Land management; Mediterranean; Meteorology; post‐fire management; Rain; Rainfall; Reforestation; Sediment; Sediment concentration; Sediment dynamics; sediment processes; Sediment transport; Sediment yield; Soil conservation; Soil erosion; Soil loss; Soil management; Storms; Stream discharge; Stream flow; Traditional farming; Water quality; wildfire; Wildfires
• ISSN: 0885-6087; 1099-1085
• DOI: 10.1002/hyp.13926

The extensive afforestation of the Mediterranean rim of Europe in recent decades has increased the number of wildfire disturbances on hydrological and sediment processes, but the impacts on headwater catchments is still poorly understood, especially when compared with the previous agricultural landscape. This work monitored an agroforestry catchment in the north‐western Iberian Peninsula, with plantation forests mixed with traditional agriculture using soil conservation practices, for one year before the fire and for three years afterwards, during which period the burnt area was ploughed and reforested. During this period, continuous data was collected for meteorology, streamflow and sediment concentration at the outlet, erosion features were mapped and measured after major rainfall events, and channel sediment dynamics were monitored downstream from the agricultural and the burnt forest area. Data from 202 rainfall events with over 10 mm was analysed in detail. Results show that the fire led to a notable impact on sediment processes during the first two post‐fire years, but not on streamflow processes; this despite the small size of the burnt area (10% of the catchment) and the occurrence of a severe drought in the first year after the fire. During this period, soil loss at the burnt forest slopes was much larger than that at most traditionally managed fields, and, ultimately, led to sediment exhaustion. At the catchment scale, storm characteristics were the dominant factor behind streamflow and sediment yield both before and after the fire. However, the data indicated a shift from detachment‐limited sediment yield before the fire, to transport‐limited sediment yield afterwards, with important increases in streamflow sediment concentration. This indicates that even small fires can temporarily change sediment processes in agroforestry catchments, with potential negative consequences for downstream water quality. Hydrological and sediment data was collected before and after a small wildfire in a small Mediterranean agroforestry catchment. Erosion was high in the burnt area when compared with croplands, especially where it was ploughed for tree replanting. Sediment export increased, with a time lag after erosion, and most sediments came from the burnt area despite its small size.