Flexible design of a helipad network for forest firefighting helicopters, applied to the case of Sardinia

Abstract

Cost-effective strategic management of aerial forest fire suppression resources involves decisions about fleet location, in order to efficiently match supply and demand. In this study, we explore the flexible design of such a system, pooling the demand of several bases into a “zone”, and analyzing alternative partitions of the territory into zones. Feasible partitions consider an upper limit on the distance between bases, and require their adjacency, within the same zone. Then, we classify the feasible partitions according to a set of six criteria and explore the non-dominated partitions. Finally, we select the preferred partition, with the support of several experts, by applying the AHP method. The considered criteria evaluate, for each partition, the (c1) mean and the (c2) value at risk of the number of unattended active fires, the (c3) helicopter idleness, and the (c4-6) Gini index for each of the previous three criteria. We apply this strategy to the island of Sardinia, where helicopters play a central role in the suppression system, and compare the results with the current design, in which each base is autonomous (i.e., each zone has only one base). Sardinia has eleven helipad operational bases, where the helicopters are allocated at the beginning of the fire season, with the objective of fighting wildfires located in each base’s coverage area. We used fire occurrence and helicopter flight data from 2006 to 2010, which revealed spatiotemporal asymmetries in the forest fire patterns, along the island, and thus the existence of effective opportunities to benefit from demand pooling. The AHP method was applied with Portuguese experts, and our results point towards an improvement in the values related to unattended fires, as well as the Gini indexes, if the proposed strategy of reorganizing the territory in larger zones (with more than one base) is applied. We explore the results of our approach, and identify efficiency gains, potential fire management implications, limitations, and opportunities for additional research. In the scope of the latter, as the optimal value for helicopter idleness is naturally achieved with the current design (partition in zones with one base), this criterion provides a key trade-off with the other five, that can be used, for instance, to examine a flexible strategy for helicopter location-allocation along the years, with annual partition redefinitions, considering all data available up to that point of decision.