João Pedro Nunes
Researcher (CCIAM Group)
Forests are normally associated with the provisioning of hydrological services such as soil protection, flood regulation and water quality control. Mediterranean plantation forests, however, are associated with recurrent wildfires, a problem which could be exacerbated by climate change. Fires negatively impact the hydrological services of forests by destroying vegetation and litter cover, and by changing soil properties; but is this a sporadic effect, or can repeated fires lead to a long-term degradation of the hydrological services usually expected from forest landscapes?
The destruction of vegetation and litter by fires leads to the creation of an ash layer and the presence of water-repellent components in the soil. In consequence, less water is loss to vegetation evapotranspiration, and a larger fraction of rainfall is exported as surface runoff. As a result, burnt forests can experience severe erosion rates, and downstream rivers can experience fire-induced floods and strong turbidity. Moreover, ashes contain toxic compounds such as heavy metals and PAHs, which can contaminate streams, harm aquatic ecosystems and affect the quality of water for human consumption.
Despite these effects, there is little information on their consequences. Firstly, the impacts of fire are difficult to measure due to their sporadic and unpredictable nature. Secondly, the processes connecting burnt hillslopes and streams are still poorly understood, as the field of water and sediment connectivity is still in its infancy. Finally, large-scale Mediterranean forest fires are relatively recent events and there is therefore a lack of long-term datasets. However, recent research has produced sufficient data to help understand the basic processes, and also to parameterize fire-adapted hydrological models which can be used for studies at larger spatial and temporal scales. This presentation will address these problems, focusing on:
- an introduction to this topic: afforestation, fire regimes, and how they can affect hydrological processes and services;
- an introduction to hydrological field research methods and numerical models, with examples of my research in different Portuguese landscapes;
- my research on the impacts of afforestation on hydrology in northern Portugal, without fires, in comparison with the previous agricultural landscape;
- my research on the added impacts of fires on hydrology, and long-term consequences for expected ecosystem services of Portuguese forested landscapes;
- my research project SCONEFIRE: “Stream CONtamination by forEst FIREs – pathways, impacts on water resources, and future vulnerability”, which will be developed in CE3C in the coming years.
