The impact of tephra on agriculture: systemic analysis of farms’ structure and functioning to better understand vulnerability by Sophie Malherbe

Young volcanic soils developed on tephra deposits have an outstanding agronomical potential and, as such, attract a large and dense population that draws its livelihood from their use. However, being collocated with Holocene volcanoes, agriculture on volcanic soils is threatened by widespread deposition of tephra during explosive eruptions. Agriculture is often the economic sector most impacted by this volcanic hazard.

To this day, a few studies have considered said impact on crops, mainly proposing a “dose-response” model where the expected crop loss is calculated based on the thickness of the tephra deposit. However, considering that agriculture comes down to crops alone is insufficient, as agriculture is a system, encompassing not only fields but cattle, water, buildings, tools, and the many interactions between them.

When crops fail, fodder becomes an issue and when animals die, fertilizer is lacking. Taking such interactions into account is, we deem, crucial when it comes to estimating the damage caused by an eruption. Using a systemic approach would allow to better understand the tephra’s various impacts on agriculture and its’ vulnerability.

We aim to use such an approach on the farming systems near the Taal volcano in the Philippines, one of the most active volcanoes in the world, in a densely populated and rural area, as well as on the farming systems near the Mayon volcano in the Philippines. We conducted interview on the field in seven and eight farms, respectively, to collect information on the internal workings of each farm, what they produced and how, what they needed to buy for it to run properly, and their financial health. With this data, we want to underline the farms’ vulnerability to tephra using a System Network Analysis (SNA) to describe the farming systems and assess their resilience, efficiency, and productivity.