By applying various statistical techniques this study has attempted to identify relationships between crop yield of various crops and dynamics of two hydro-meteorological variables (soil moisture and evapotranspiration reduction) in the period 1975-2001. This study covers 94 NUTS-1-level regions throughout Europe, giving this study a very large-scale scope on the theme.
Exploring the relationship between low soil moisture availability and yields of major crops on the pan-European scale
Global change is projected to result in changes in the hydrological cycle, including regime and extremes. To understand the impacts of these changes on agriculture the relationship between large-scale hydrological dynamics and crop yield needs to be understood. This study focussed on drought. It attempted to analyse this relationship in statistical terms between the drought condition and yields of winter wheat, winter rye, barley, maize, potatoes and sugar beets in the period 1975-2001. This has been done for 94 NUTS-1-level regions throughout the European Union and Switzerland. This study used data of soil moisture and evapotranspiration as modelled by a number of large-scale models forced by the WATCH Forcing Data (EU FP6 project). Data on actual and potential crop yields were obtained from Eurostat and WOFOST respectively. A large-scale analysis based on the ratio of evapotranspiration reduction ratio (ETa/ETp) and an event-based analysis based on soil moisture anomaly were two key approaches applied in this study, both as a seasonal mean and a volume of below-threshold conditions. Crop yield was expressed as the ratio of actual over potential crop yield. AVHRR-NDVI data were used to explore the impacts of dry conditions on overall vegetation in the region. Exploration of the hydrometeorological data indicated the well-known drying trends in southern regions and wetting trends in northeastern regions. Results indicate divergent crop yield responses to dry conditions, with some regions unexpectedly featuring increasing yields in dry years. A geographical clustering of similar crop yield responses was observed for most crops. Southern regions display mostly negative crop yield responses to low moisture availability, while responses in northern Europe are mixed. Given the many factors influencing crop yields it is difficult to identify a statistically meaningful signal of the impact of dry conditions on crop yields.