Grain size modulates volcanic ash retention on crop foliage and potential yield loss

In: Natural hazards and earth system sciences: NHESS, Band 23, Heft 4, S. 1355-1369

Abstract

Abstract. Ashfall from volcanic eruptions endangers crop production and food security
while jeopardising agricultural livelihoods. As populations in the vicinity
of volcanoes continue to grow, strategies to reduce volcanic risks to and
impacts on crops are increasingly needed. Current models of crop
vulnerability to ash are limited. They also rely solely on ash thickness (or
loading) as the hazard intensity metric and fail to reproduce the complex
interplay of other volcanic and non-volcanic factors that drive impact.
Amongst these, ash retention on crop leaves affects photosynthesis and is
ultimately responsible for widespread damage to crops. In this context, we
carried out greenhouse experiments to assess how ash grain size, leaf
pubescence, and humidity conditions at leaf surfaces influence the retention
of ash (defined as the percentage of foliar cover coated with ash) in tomato
and chilli pepper plants, two crop types commonly grown in volcanic regions.
For a fixed ash mass load (∼570 g m−2), we found that
ash retention decreases exponentially with increasing grain size and is
enhanced when leaves are pubescent (such as in tomato plants) or when their surfaces are
wet. Assuming that leaf area index (LAI) diminishes with ash retention in
tomato and chilli pepper plants, we derived a new expression for predicting
potential crop yield loss after an ashfall event. We suggest that the
measurement of crop LAI in ash-affected areas may serve as an impact metric.
Our study demonstrates that quantitative insights into crop vulnerability
can be gained rapidly from controlled experiments. We advocate this approach
to broaden our understanding of ash–plant interactions and to validate the
use of remote sensing methods for assessing crop damage and recovery at
various spatial and time scales after an eruption.