Porres, Maru 
  
INFLUENCE OF TOPOCLIMATIC VARIABLES DERIVATED FROM DIGITAL TERRAIN MODELS 
OVER THE VEGETATION REGENERATION PROCESSES IN BURNED AREAS 
Porres de la Haza, M. J. & Pardo Pascual, J.E. 
Departamento de Ingeniería Cartográfica, Geodesia y Fotogrametría 
Universidad Politécnica de Valencia (Spain) 
Mporres@cgf.upv.es, jepardo@cgf.upv.es 
Key words: DTM, NDVI, curvature maps, direct solar radiation maps, upslope catchment area, regenertion vegetal 
cover. 
ABSTRACT 
In this work, the signification of some topo-climatic variables deduced from a DEM over vegetation regeneration 
processes after wildfires monitored on a semi-arid region from Landsat TM images has been analysed. Ten DTMs — 
associated to hydrological (slope, terrain curvature, upslope catchment area) and thermal conditions of terrain (potential 
direct solar radiation )—hhas been extracted from a grid DEM (25x25m) and it has correlated with NDVI values of two 
dates (1987 and 1994) and its differences. The slope, curvature profile, curvature surface and mean curvature has been 
calculated using different and neighbourhood (3x3 and 5x5 pixels) but in all the cases the relationship with the NDVI 
has been very poor. The upslope catchment area also presents a very low correlation with the vegetation. Only the 
potential solar radiation shows a very clear relationship. It has been concluded that thermal factor present the main 
influence on the regeneration processes due the physical conditions of the area (semi-arid Mediterranean climate and 
soils little deep and very poor). Also it has been observed a clear relation of the significance of the potential solar 
radiation with the regeneration vegetal cover associated to the lithology. Over permeable geologic substratum 
(calcareous areas) the relationship is less clear that on impermeable substratum (marls, clays and gypsum). 
The work presented here shows that the employment of MDE and their MDT derived from satellite images allow us to 
explore environmental relationships on a microscale. This could, with difficulty, be carried out with other 
methodologies, which could, in turn, establish deductions of great significance in the functioning of ecosystems. 
1. INTRODUCTION 
The increased availability to users of digital elevation models is allowing detailed analyses to be carried out which 
would have been difficult to imagine only a few years ago. One example is provided by the analysis of vegetation 
evolution in semi-arid climates, such as the case presented here. The dynamics of vegetation is complex and subject to 
many factors, not just endogenous characteristics (availability of seeds, competition between species,...) but also it is 
strongly associated with abiotic factors in the biotopo (microclimatic factors, soils, human uses) In Mediterranean 
semi-arid areas, characterised by long dry periods and irregular rainfall patterns, the main limiting factor in the 
development of vegetation is the lack of available water, for which reason the humidity distribution is a first order 
factor for knowing how the vegetation is distributed and with what density This limiting factor, which is evident 
throughout the vegetation wherever there is a dry Mediterranean climate, is even more notable when the vegetation 
cover is removed by forest fires. In the region of Valencia forest fires can be considered a problem of great magnitude 
since in the past decade as much as 25% of the forest has been damaged in this way. 
Based on digital elevation models it is possible to define a series of parameters that could quantify the spatial variations 
that potentially influence the distribution of the humidity associated with thermal and hydrological processes. In this 
study the significance of these factors, both hydrological — cross-section curvature, cross-section area, accumulated 
basin area and slope — and thermal — potential direct solar radiation— has been analysed to see the effect that they have 
over the recuperation of the vegetation mass after a fire. 
Previous studies had indicated that for the area in question the fundamental parameter to take into account is the 
potential solar radiation, but it was also expected that it would be necessary to look in more detail at the influence that 
hydrological parameters may have. For this, firstly, for each pixel in the model the specific basin area has been 
calculated and, secondly, the curvature and slope have been considered for different neighbourhoods (3x3 and 5x5). The 
vegetation has been characterised using the NDVI calculated from Landsat TM images corresponding to June 1987 and 
June 1994 which had been radiometrically corrected with respect to each other. 
  
1170 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B7. Amsterdam 2000.