Fire connectivity across the WUI: the interplay between increased drought events and active landscape management strategies

Global warming and land-use/land-cover changes, together with the expansion of the wildland-urban interface (WUI), have increased wildfire risk and exposure within Euro-Mediterranean countries. From a landscape-scale perspective, the scientific community has highlighted the interest of recovering the historical agro-forest mosaics to reduce wildfire risk within WUI areas by increasing land-cover discontinuity and fuel structure heterogeneity. Yet, up to date current and forecasted land-use change scenarios point out to the reverse pattern: i.e. an increasing abandonment of rural activities and forest encroachment. Furthermore, an increase in drought-driven tree mortality episodes is also occurring, potentially leading to changes in forest cover and in the amount of highly available fuels. However, it is unknown how the effects of drought events may interact with active landscape planning to reduce wildfire risk in the long-term.

Here, we analyze current and future fire connectivity patterns within the Barcelona Metropolitan Region (NE Spain), one of the most populated Mediterranean WUI areas. First, we assess the effect of different levels of drought-driven tree mortality episodes over fire connectivity in the long-term. Then, we analyze to which extent these disturbances combined with active landscape management strategies (LMS) can contribute to reduce fire connectivity.

We used a process-based model (MEDFATELAND) to simulate forest dynamics until 2050 under two climatic scenarios (low- vs high-drought). Next, we applied a circuit-based algorithm (OMNISCAPE) to model current (2020-2024) and future (2040-2050) fire connectivity (i.e. the spatial arrangement of areas with similar fuel properties that could facilitate contiguous fire spread). We analyzed drought effects over fire connectivity by comparing the results of both low- and high-drought climatic scenarios. Then, we analyze the effects on fire connectivity of drought impacts combined with three active LMS: (i) recovery of former agricultural lands recently abandoned, (ii) increase of current wood extraction rates under a bioeconomy-oriented strategy, and (iii) limited salvage-logging of drought-affected forest stands.

Overall, we observed a fire connectivity reduction in the long-term (2040-2050), passively mediated by high-drought climate effects (tree mortality) which ultimately diminish forests fine fuel loads. Regarding the active LMSs, we observed the greatest fire connectivity decrease by increasing land-cover discontinuity through the recovery of former agricultural areas. However, this LMS also produced fire connectivity increases in some areas that remained as fuel corridors between croplands. In contrast, a limited salvage-logging strategy in drought affected forest areas reduced wildfire connectivity through the whole study area by diminishing the amount of highly available fuels. Interestingly, we did not observe significant effects from an increased wood harvesting LMS, probably due to departing from extremely low current extraction rates within the study area. In conclusion, in this presentation we will explore through an innovative methodology to which extent passive (i.e. drought-driven tree mortality episodes) combined with active landscape management strategies can contribute to improve the prevention of large wildfire events in WUI areas.