Water resources planning for a river basin with recurrent wildfires

• Wildfire impact on river water quality
• Relationship between wildfire frequency and fire risk
• Modeling phosphorus concentration in water after wildfire
• Forest management designed for reduction of wildfire risk

Situated in the north of Portugal, the Beça River basin is subject to recurrent wildfires, which produce serious consequences on soil erosion and nutrient exports, namely by deteriorating the water quality in the basin. In the present study, the ECO Lab tool embedded in the Mike Hydro Basin software was used for the evaluation of river water quality, in particular the dissolved concentration of phosphorus in the period 1990–2013. The phosphorus concentrations are influenced by the burned area and the river flow discharge, but the hydrologic conditions prevail: in a wet year (2000, 16.3 km2 of burned area) with an average flow of 16.4 m3·s− 1 the maximum phosphorus concentration was as low as 0.02 mg·L− 1, while in a dry year (2005, 24.4 km2 of burned area) with an average flow of 2 m3·s− 1 the maximum concentration was as high as 0.57 mg·L− 1. Phosphorus concentrations in the water bodies exceeded the bounds of good ecological status in 2005 and between 2009 and 2012, water for human consumption in 2009 and water for multiple uses in 2010. The River Covas, a right margin tributary of Beça River, is the most appropriate stream as regards the use of water for human consumption, because it presents the biggest water potential with the best water quality. Since wildfires in the basin result essentially from natural causes and climate change forecasts indicate an increase in their frequency and intensity in the near future, forestry measures are proposed to include as a priority the conversion of stands of maritime pine in mixed stands of conifer and hardwood species.