ecological modelling 200 ( 2 0 0 7 ) 321–333 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/ecolmodel Mapping lightning/human-caused wildfires occurrence under ignition point location uncertainty Giuseppe Amatulli a,b,c,∗ , Fernando Per´ ez-Cabello a , Juan de la Riva a a University of Zaragoza, Department of Geography and Spatial Management, Calle Pedro Cerbuna 12, 50009 Zaragoza, Spain b University of Basilicata, Department of Crop Systems, Forestry and Environmental Science, Campus Macchia Romana, 85100 Potenza, Italy c European Commission-DG Joint Research Centre, Institute for Environment and Sustainability, Via E. Fermi, 21020 Ispra (VA), Italy article info Article history: Received 9 September 2005 Received in revised form 18 July 2006 Accepted 9 August 2006 Published on line 19 October 2006 Keywords: Fire occurrence Kernel density Fire ignition points Fire atlas Fire spatial patterns Location uncertainty abstract Fire managers need to study fire history in terms of occurrence in order to understand and model the spatial distribution of the causes of ignition. Fire atlases are useful open sources of information, recording each single fire event by means of its geographical position. In such cases the fire event is considered as point-based, rather than area-based data, com- pletely losing its surface nature. Thus, an accurate method is needed to estimate continuous density surfaces from ignition points where location is affected by a certain degree of uncer- tainty. Recently, the fire scientific community has focused its attention on the kernel density interpolation technique in order to convert point-based data into continuous surface or surface-data. The kernel density technique needs a priori setting of smoothing parameters, such as the bandwidth size. Up to now, the bandwidth size was often based on subjective choices still needing expert knowledge, eventually supported by empirical decisions, thus leading to serious uncertainties. Nonetheless, a geostatistical model able to describe the point concentration and consequently the clustering degree is required. This paper tries to solve such issues by implementing the kernel density adaptive mode. Lightning/human- caused fires occurrence was investigated in the region of Arag´ on’s autonomy over 19 years (1983–2001) using 3428 and 4195 ignition points respectively for the two causes of fire origin. An analytical calibration procedure was implemented to select the most reliable density sur- faces to reduce under/over-density estimation, overcoming the current drawbacks to define it by visual inspection or personal interpretation. Besides, ignition point location uncertainty was investigated to check the sensitivity of the proposed model. The different concentra- tion degree and the dissimilar spatial pattern of the two datasets, allow testing the proposed calibration methodology under several conditions. After having discovered the slight sen- sitivity of the model to the exact point position, the obtained density surfaces for the two causes were combined to discover hotspot areas and spatial patterns of the two causes. Evident differences in spatial location of the origin causes were noted and described. The general trend follows the geographical features and the human activity of the study areas. The proposed technique should be promising to support decision-making in wildfire pre- vention actions, because of the occurrence map can be used as a response variable in fire risk predicting models. © 2006 Elsevier B.V. All rights reserved. ∗ Corresponding author. E-mail address: giuseppe.amatulli@jrc.it (G. Amatulli). 0304-3800/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolmodel.2006.08.001