Exploring the utility of drought and water scarcity indicators to assess climate risks to agricultural productivity in a humid climate

Drought indices have been extensively used by the hydrological research community for understanding drought risks to water resources systems. In a humid climate, such as in England, most agricultural production is rainfed and dependent on summer rainfall, but knowledge of drought risks in terms of their occurrence and potential agronomic impacts on crop productivity remains limited. This paper evaluated the utility of integrating data from three well-established drought indices, including the standardised precipitation index (SPI), standardised precipitation evapotranspiration index (SPEI) and the Palmer drought severity index (PDSI), with simulated yield outputs from a biophysical crop model for potato, a drought-sensitive and high-value crop. The relationships between drought onset and yield response were statistically evaluated. The SPEI-3 drought indicator was found to be most suited to monitoring water availability and hence drought conditions for both rainfed and irrigated production. ‘Heat maps’ were produced to illustrate the strength of the correlation between the modelled SUBSTOR-Potato yields and SPEI for different aggregation periods and monthly lags. Finally, the outputs were used to assess alternative ways in which decision-making could be improved regarding adaptation strategies to reduce agricultural system vulnerability to future drought events.