Risk of crop failure due to compound dry and hot extremes estimated with nested copulas

Abstract

Abstract. Drought and heat events stress agricultural systems and may threaten food security. The interaction between co-occurring drought and hot conditions is often particularly damaging to crop's health and may cause crop failure. In this context, traditional univariate analyses may not be adequate for reliable risk assessment of crop failure associated with compound hazards. Climate change exacerbates such risks due to an increase in the intensity and frequency of dry and hot events in many land regions. Here we model the trivariate dependence between spring maximum temperature, spring precipitation and wheat and barley yields, respectively, over two province clusters in Spain with nested copulas. Based on the full trivariate joint distribution, we (i) estimate the impact of compound hot and dry conditions on wheat and barley loss and (ii) estimate the additional impact due to compound hazards compared to individual hazards. We find that crop loss increases when drought- or heat-stress aggravates to compound dry and hot conditions and that an increase in the severity of compound conditions leads to larger damages. For instance, compared to moderate drought only, compound dry and hot conditions increase the likelihood of crop loss by 8 to 11 %, while when starting with moderate heat, the increase is between 19 to 29 % (depending on the cereal and region). This means that the likelihood of crop loss is driven primarily by drought stress than by heat stress, suggesting that drought plays the dominant role in the compound event, that is, drought stress does not require to be so extreme as heat stress to cause a similar damage. Furthermore, when compound dry and hot conditions aggravate from moderate to severe or extreme stress, crop loss probabilities increase 5 to 6 % and 6 to 8 %, respectively (depending on the cereal and region). Our results highlight the additional value of a trivariate approach for the estimating the compounding effects of dry and hot extremes on of crop failure risk. Therefore, this approach can effectively contribute to design management options and guide the decision-making process in agricultural practices.

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