Resilience of ecosystem service delivery in grasslands in response to single and compound extreme weather events.

Extreme weather events are increasing in frequency and magnitude with profound effects on ecosystem functioning. Further, there is now a greater likelihood that multiple extreme events are occurring within a single year. Here we investigated the effect of a single drought, flood or compound (flood + drought) extreme event on temperate grassland ecosystem processes in a field experiment. To assess system resistance and resilience, we studied changes in a wide range of above- and below-ground indicators (plant diversity and productivity, greenhouse gas emissions, soil chemical, physical and biological metrics) during the 8 week stress events and then for 2 years post-stress. We hypothesized that agricultural grasslands would have different degrees of resistance and resilience to flood and drought stress. We also investigated two alternative hypotheses that the combined flood + drought treatment would either, (A) promote ecosystem resilience through more rapid recovery of soil moisture conditions or (B) exacerbate the impact of the single flood or drought event. Our results showed that flooding had a much greater effect than drought on ecosystem processes and that the grassland was more resistant and resilient to drought than to flood. The immediate impact of flooding on all indicators was negative, especially for those related to production, and climate and water regulation. Flooding stress caused pronounced and persistent shifts in soil microbial and plant communities with large implications for nutrient cycling and long-term ecosystem function. The compound flood + drought treatment failed to show a more severe impact than the single extreme events. Rather, there was an indication of quicker recovery of soil and microbial parameters suggesting greater resilience in line with hypothesis (A). This study clearly reveals that contrasting extreme weather events differentially affect grassland ecosystem function but that concurrent events of a contrasting nature may promote ecosystem resilience to future stress.

Spatial co-localisation of extreme weather events: a clear and present danger.

Extreme weather events have become a dominant feature of the narrative surrounding changes in global climate with large impacts on ecosystem stability, functioning and resilience; however, understanding of their risk of co-occurrence at the regional scale is lacking. Based on the UK Met Office's long-term temperature and rainfall records, we present the first evidence demonstrating significant increases in the magnitude, direction of change and spatial co-localisation of extreme weather events since 1961. Combining this new understanding with land-use data sets allowed us to assess the likely consequences on future agricultural production and conservation priority areas. All land-uses are impacted by the increasing risk of at least one extreme event and conservation areas were identified as the hotspots of risk for the co-occurrence of multiple event types. Our findings provide a basis to regionally guide land-use optimisation, land management practices and regulatory actions preserving ecosystem services against multiple climate threats.