The contrasted response of ash to wetting The effects of ash type, thickness and rainfall events Javier León a, ⁎, Merche B. Bodí b,1 , Artemi Cerdà b,1 , David Badía c,2 a Dept. of Geography and Spatial Management, University of Zaragoza, Pedro Cerbuna 12, Zaragoza 50009, Spain b SEDER (Soil Erosion and Degradation Research Group), Dept. of Geography, University of València, Blasco Ibáñez, 28, Valencia 46010, Spain c Technic School of Agricultural Engineering and Environmental Sciences, University of Zaragoza, Ctra. de Cuarte, s/n, Huesca 22071, Spain abstract article info Article history: Received 30 August 2012 Received in revised form 17 June 2013 Accepted 18 June 2013 Available online 8 July 2013 Keywords: Forest fires Black ash White ash Rainfall simulator Infiltration rates After a wildfire the soil is covered by ash. Ash properties depend on vegetation type, amount of fuel and fire intensity. The ash layer controls the post-fire soil hydrologic response, but little is known about the effect of ash thickness and ash type on infiltration, which is relevant for post-fire runoff and soil losses and for ecosystems rehabilitation and restoration. This paper analyses the role of i) ash type (black or white), ii) thickness (5, 15 and 30 mm-thick) and iii) temporal variation (0, 15 and 40 days) under three simulated rain events (55 mm for 1 h) on soil surface hydrology. The rainfall was simulated on 0.25 m 2 plots, and time to ponding, runoff and runoff discharge were measured. The infiltration rates, the initial infiltration rate (f 0 ), the steady-state infiltration rate (f c ), and the infiltration decay factor (k), were calculated and the Horton infiltration equation applied. The results show that soils covered with white ash doubled the runoff rates of soils covered with black ash. In general, runoff decreases as the ash thickness increases and the runoff decreases with the number of rainfall events after the fire in plots covered with white ash. Ponding time and k are positively correlated by the ash thickness and f 0 and f c are correlated by the rainfall events (in three runs). Ash type and ash depth are key factors on the soil hydrology after a wildfire. © 2013 Elsevier B.V. All rights reserved. Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143 2. Materials and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 2.1. Description of the Site and Ashes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144 2.2. Experimental Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 2.3. Rainfall Simulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 2.4. Data Collection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 2.5. Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145 3. Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 4. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 146 5. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150 1. Introduction Soil hydrology changes within the first days or weeks following wildfires, as a result of the sudden changes in vegetation – modification of vegetation cover, loss of surface litter, duff and other organic ground cover – (Cerdà, 1998a; Woods and Balfour, 2008), soil surface cover and soil properties, from heating on the soil structure (Mataix-Solera and Doerr, 2004) and, in some cases, changes in soil water repellency Geoderma 209–210 (2013) 143–152 ⁎ Corresponding author. Tel.: +34 976761000. E-mail address: fcojleon@unizar.es (J. León). 1 Tel.: +34 963864882. 2 Tel.: +34 974239318. 0016-7061/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.geoderma.2013.06.018 Contents lists available at SciVerse ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma