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J.P. Nunes et al. 2010. Impacts of wildfires on catchment hydrology
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The impact of wildfires on hydrological processes at small spatial (e.g. microplots, plots,
hillslopes) and temporal scales (e.g. rainstorms, a few years) has received much attention from
researchers in recent years. Shakesby and Doerr (2006) review some of the main conclusions
from these studies. Wildfires reduce vegetation cover and can change soil properties, such as
reducing soil aggregate stability and increasing soil water repellence. This can lead to an
increase in overland flow generation and sediment detachment, and to the formation of an
extensive rill and gully system in burnt areas with additional erosion impacts. These impacts
were also observed in northwestern Iberian burnt forests (e.g. Ferreira et al., 2008; Keizer et al.,
2008).
At larger spatial scales, especially catchments, Shakesby and Doerr (2006) report that forest
fires can increase peak runoff rates, but there are few studies on consequences for total runoff.
Erosion responses at this scale are more complex, as they appear to depend on smaller-scale
changes to runoff and soil erosion, and are poorly studied. At larger temporal scales, studies
have focused on the post-fire “window of disturbance” (c. 2 to 5 years in this region) during
vegetation regrowth, but there have been few studies of long-term impacts, particularly the
cumulative consequences of multiple wildfires.
There is therefore a knowledge gap when upscaling measured results to larger scales and
impacts. Modeling has been viewed as an approach to overcome this difficulty (Shakesby and
Doerr, 2006). Recent comparisons of existing hydrological models with measured data in burnt
areas, however, have revealed their limitations in representing the most important processes (e.g.
Larsen and MacDonald, 2007) although suggesting ways to improve them. This has limited
modeling applications at large spatial and temporal scales to perform watershed-scale, long-term
assessments. However, this assessment is feasible provided that existing measured data can be
combined with modeling tools in a coherent approach.
This work will present ongoing research and results of research projects studying burnt
catchment hydrology in northwestern Iberia, including:
1. research at the hillslope scale conducted in central Portugal (Albergaria, Vouga basin);
2. research at the micro-catchment scale in central Portugal (Mondego basin) and western
Galicia (Esteiro), the latter focusing on a paired catchment study;
3. modeling for meso-scale watersheds in central Portugal (Águeda basin).
The results will be discussed in terms of their indication on the impacts of wildfires on
watershed-scale water resources provisioning,
2. Study areas
The research presented in this work focuses on the northwestern Iberian Peninsula
(Figure 1), a region characterized by a humid climate (aridity index, i.e. the ratio of
rainfall over potential evapotranspiration, above 1) with a south-north transition from
Wet Mediterranean to Maritime Temperate. There are good conditions for vegetation
growth, and a large part of this region is covered by forests; in many cases, and
especially in Portugal, there are large areas of commercial forestry where eucalypt and
maritime pine are planted. However, the seasonal and interannual variability of climatic
conditions, particularly the existence of a dry summer season (Figure 2), leads to the
recurrence of appropriate conditions for wildfires.
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.