Impacts of droughts and floods on agricultural productivity in New Zealand as measured from space

Abstract

We estimate the impact of precipitation extremes on the productivity of agricultural land parcels in New Zealand using satellite data. This type of post-disaster damage assessment aims to allow for the quantification of disaster damage when an on-the-ground assessment of damage is too costly or too difficult to conduct. It can also serve as a retroactive data collection tool for disaster loss databases where data collection did not happen at the time. We use satellite-derived observations of terrestrial vegetation (the enhanced vegetation index (EVI)) over the growing season, with data at the land parcel level identifying five land use types (annual and perennial crops, and three types of pasture), and with precipitation records, which we use to identify both excessively dry (drought) and excessively wet (flood) episodes. Using regression analyses, we examine whether these precipitation extremes had an observable impact on agricultural productivity. We find statistically significant declines in agricultural productivity that are associated with both droughts and floods. The average impact of these events is usually less than 1%, but the impacts are quite heterogeneous across years and across regions, with some parcels experiencing a much more significant decline in the EVI. We also identify several impact patterns related to the varying drought and flood vulnerability of the analysed land use types.