Welcome on behalf of the Royal Society and by Professor Jim Hall FREng
Professor Jim Hall FREng, University of Oxford, UK
Drought risk in the Anthropocene: from the Jaws of Death to the Waters of Life
Sir James Bevan, Environment Agency England, UK
In his opening address, Sir James Bevan, Chief Executive of the Environment Agency, will set the scene on the Anthropocene: looking at what this new epoch means for humans and nature, how we got here, and where we need to go next. Sir James’ speech will set out the alarming impact that the epoch’s most important feature, climate change caused by human activity, is having on drought risk and extreme weather. In response to these challenges Sir James will look ahead to COP26 and beyond, setting out what needs to be done to mitigate the worst impacts of runaway climate change, and to adapt to impacts that are irrevocable. In particular he will examine what needs to be done to escape what in 2019 he called ‘the Jaws of Death’, the point on water companies’ planning charts some 20 years from now where if we don’t intervene water demand will outstrip supply. He will set out what the Environment Agency is doing alongside business, government, civil society, and what the Royal Society can do to help. Finally he will argue why we should be optimistic we can turn the climate crisis into an opportunity that creates a better place for all.
Global drought trends and future projections
Dr Sergio M Vicente-Serrano, Instituto Pirenaico de Ecología, Consejo Superior de Investigaciones Científicas (IPE-CSIC), Spain
Drought is one of the most difficult natural hazards to be measured and monitorised, which strongly affects the assessment of recent drought changes and future scenarios. This talk first illustrates some key conceptual issues, which are necessary to be considered when assessing drought changes and related uncertainties; among them it includes the need of considering the different behaviour of different drought types. Secondly, it shows trends in meteorological droughts considering a long-term perspective using precipitation records and also the possible role of global warming processes on trends in drought severity. Finally, the talk shows a review of studies analysing drought projections for future climate scenarios and it stresses the key concepts and uncertainties that are necessary to consider when assessing drought processes under climate change, including the use of different metrics and modelling approaches. The necessity of establishing differences between the behaviour of the mean climate and the frequency, duration, and spatial extent of droughts, considered as an extreme natural hazard, are emphasised when determining drought changes and future projections.
Droughts in a changing climate: Evidence from the IPCC AR6
Professor Sonia I Seneviratne, ETH Zurich, Switzerland
This presentation will provide an overview of the main conclusions of the 6th Assessment report (AR6) from the Intergovernmental Panel on Climate Change (IPCC) on observed and projected changes in droughts. For the first time, a full chapter of the IPCC assessment report (Chapter 11; Seneviratne, Zhang, et al, in press) was dedicated to the topic of weather and climate extremes, including extensive assessments on changes in droughts. The drought assessment was subdivided in changes in meteorological, agricultural and ecological, and hydrological droughts. It was also informed from cross-chapter assessments with AR6 chapters assessing changes in a) the water cycle (Chapter 8), b) climatic impact drivers (Chapter 12), and the c) carbon cycle (Chapter 5), as well as d) the Atlas chapter. Regional assessments were also provided for all considered AR6 regions. Observations reveal that agricultural and ecological droughts have increased in several regions, and that human influence has contributed to increases in some regions due to increases in evapotranspiration. With every increment of global warming, changes in agricultural and ecological droughts become larger in several regions, including West-Central Europe and the Mediterranean region, as well as the Amazon region, among others.
Did aerosols delay the emergence of greenhouse gas-forced drought in Southwestern North America?
Dr Kate Marvel, NASA Goddard Institute for Space Studies and Center for Climate Systems Research, Columbia University, USA
Greenhouse gas emissions have likely contributed to current drought conditions in southwestern North America, which is experiencing one of its driest periods on record. But greenhouse gas emissions have risen steadily since the beginning of the Industrial Revolution: why then, have these drought conditions only emerged recently? In fact, in the latter part of the twentieth century regional soil moisture anomalies were unprecedentedly wet. In this talk, Dr Marvel will present a Bayesian method for detection and attribution that quantifies uncertainties, handles multiple external forcings, and can be used for model evaluation. The evidence suggests that aerosol forcing, aided by the eruption of Pinatubo in 1991, partially counteracted greenhouse gas-driven decreases in soil moisture, delaying the emergence of the current anthropogenically forced drought.