Assessing future drought risks and wheat yield losses in England

D Clarke,T M Hess,D Haro-Monteagudo,M.A Semenov,J W Knox

doi:10.1016/j.agrformet.2020.108248

Abstract

Droughts pose a major risk to agricultural production. By comparing the outputs from an ecophysiological crop model (Sirius) with four drought severity indicators (DSI), a comparative assessment of the impacts of drought risk on wheat yield losses has been evaluated under current (baseline) and two future climate scenarios. The rationale was to better understand the relative merits and limitations of each approach from the perspective of quantifying agricultural drought impacts on crop productivity. Modelled yield losses were regressed against the highest correlated variant for each DSI. A cumulative distribution function of yield loss for each scenario (baseline, near and far future) was calculated as a function of the best fitting DSI (SPEI-5July) and with the equivalent outputs from the Sirius model. Comparative analysis between the two approaches highlighted large differences in estimated yield loss attributed to drought, both in terms of magnitude and direction of change, for both the baseline and future scenario. For the baseline, the average year differences were large (0.25 t ha−1 and 1.4 t ha−1 for the DSI and Sirius approaches, respectively). However, for the dry year, baseline differences were substantial (0.7 t ha−1 and 2.7 t ha−1). For the DSI approach, future yield losses increased up to 1.25 t ha−1 and 2.8 t ha−1 (for average and dry years, respectively). In contrast, the Sirius modelling showed a reduction in future average yield loss, down from a baseline 1.4 t ha−1 to 1.0 t ha−1, and a marginal reduction for a future dry year from a baseline of 2.7 t ha−1 down to 2.6 t ha−1. The comparison highlighted the risks in adopting a DSI response function approach, particularly for estimating future drought related yield losses, where changing crop calendars and the impacts of CO2 fertilisation on yield are not incorporated. The challenge lies in integrating knowledge from DSIs to understand the onset, extent and severity of an agricultural drought with ecophysiological crop modelling to understand the yield responses and water use relations with respect to changing soil moisture conditions.

Highlights

Wheat is the most widely cultivated cereal globally, contributing 20% of total dietary calories consumed (Shiferaw et al, 2013)
In the context of a national research effort to understand the impacts of droughts and water scarcity across a range of sectors including agriculture, this study aimed to assess the impacts of drought on wheat yield under current and future climate conditions via two contrasting approaches; (i) evaluating drought risks on wheat by correlating selected drought severity indicators (DSI) with yield loss response functions and (ii) comparing the outputs from this regression driven modelling with equivalent yield losses derived from a complex ecophysiological crop model
Water limitations on average reduce UK wheat yields by 1 to 2 t ha−1 this can be considerably higher in drought years

Summary

Introduction

Wheat is the most widely cultivated cereal globally, contributing 20% of total dietary calories consumed (Shiferaw et al, 2013). With limited scope for extending current cultivated areas, the emphasis will inevitably be on achieving significant increases in productivity (yield) to assure future food security (Reynolds et al, 2009). In 2018, 1.75 million hectares (40% of the arable area) in the UK were used for wheat production (Fig. 1); the average yield (7.8 t ha−1) contributed to approximately 2% of global output, valued at £2.1 billion (Defra, 2018). A third of the UK wheat crop is grown on drought prone soils, resulting, on average, in a 10 to 20% loss in total production, valued at £72 million (Ober et al, 2011), but this can be considerably higher during drought years. Average yield in 2018 resulted in a 5.1% drop in total production from the previous year (Defra, 2018). The UK wheat industry perceives ‘unpredictable weather’ to be one of the highest risks to production (Ilbery et al, 2013) in combination with short intense periods of drought (Kendon et al, 2013)

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