Examining the impacts of projected precipitation changes on sugar beet yield in Eastern England

Abstract

Projected increasing temperatures and reduced summer precipitation in the UK raises questions about the sustainability of aspects of the agriculture industry and food security. This study investigates the potential impact of precipitation changes on sugar beet yield in Eastern England. Observations of precipitation was examined for the period 1971-2000 and the expected changes in precipitation were investigated using seven CMIP5 climate models for the historical phase (1971-2000) and RCP45 and RCP85 future scenarios (2021-2050). Three out of the seven models were found to show good agreement with observations but the MOHC ensemble mean was the closest to the observed means and was used for further precipitation analyses. Statistical analysis of the future precipitation changes were performed using the Met Office Hadley Centre (MOHC) model focused on changes between the historical phase and RCP45 and RCP85. Results showed a consistent and significant reduction in annual May-October precipitation under future scenarios. The study then investigated the impact of reduced future precipitation changes on sugar beet yield by applying controlled watering regimes informed by the CMIP5 projections to sugar beet plants in a greenhouse experiment over two seasons – the use of CMIP5 projections in this way is a first. In the first experiment carried out in 2014, a climatological watering regime (i.e. where the total seasonal rainfall for the different scenarios was applied in equal and regular watering events) was applied to the plants, which meant a 16% reduction in precipitation in the “future” category relative to a “control” category. Analysis of the yields indicated a statistically significant reduction in mean tuber wet mass: mean of 360g for the control and 319g for the future (p-value 0.03). This implies a potential yield reduction of 11% by 2050. In the second experiment carried out in 2015, a “realistic distribution” watering regime (i.e. where the total seasonal rainfall is applied in a series of watering events that reflect the analysed sizes and distribution of rainfall events in the different categories), this meant a reduction in precipitation in the months of June (-15.6%), July (-7.7%) and August (-3.7%). This resulted in statistically significant reduction in mean tuber wet mass between control (153g) and RCP85 (113g) with a p-value of 0.01. This implies a reduction of 26% in future yields under RCP85 by 2050. Results in this thesis further show how changes and variation in precipitation are intertwined with changes in soil moisture and yield of sugar beet plants. The findings will enable UK sugar beet farmers to identify potential areas of challenges in order to adapt their management practices to ensure maximum crop yield in future growing seasons. Moreover, from a global perspective, the findings here are also broadly applicable to a variety of agricultural crops in different parts of the world, where changes in yield may have important consequences to food security and food prices.