PhD Research Project: NERC CENTA - Understanding and quantifying drought using climate simulations

Droughts are one of the most devastating climate-related hazards, and in extreme cases have even contributed to the collapse of whole civilisations, such as the Maya (Medina-Elizalde and Rohling, 2012). Quantifying drought probabilities in different parts of the world and understanding the drivers for drought is key for placing recent droughts in a wider context and for estimating the drought hazard in the future. However, the instrumental records are too short to fully address these questions. Therefore drought reconstructions based on palaeoclimatic proxy data, e.g. tree ring records, have been calculated for some regions back more than 1000 years and used for comparison with droughts in climate simulations for the 21. century (e.g. Cook et al. 2009, Woodhouse et al. 2010).

Past droughts can also be calculated from simulations for past climates. Several such simulations with complex General Circulation Models are available for the last 1200 years, some for even longer periods. While the simulated temperatures have been comprehensively analysed and compared with proxy-based reconstructions (e.g. PAGES2k – PMIP3 group, 2015) the simulated precipitation and soil moisture has not been systematically analysed yet. In this project we will address this research gap with a focus on droughts.
Palaeoclimate simulations have been performed so far mainly by prescribing climate forcings such as solar radiation and atmospheric composition. As a consequence of internal climate variability, the temporal evolution of the climate states is not completely determined by the forcings. Therefore such simulations can be expected to provide information about drought probabilities, but not about individual historical droughts. By analysing ensemble simulations it will be possible to distinguish between the influence of climate forcing on droughts and the effect of random weather variability.
A second type of simulations, which have become available recently, combine empirical information from proxy data with numerical simulations This approach is used operationally in meteorology and is known as data assimilation, but adapting it to palaeoclimatic applications is challenging (e.g. Widmann et al. 2010, Matsikaris et al 2016.). Analysing drought from such simulations allows to better understand the meteorological conditions that led to specific historical droughts.

Drought indices will be calculated from palaeoclimate simulations based on the simulated precipitation and temperatures. These will be compared with empirical drought reconstructions, where available, for model validation. Potential biases in the simulated drought characteristics will be removed using multivariate bias correction methods when appropriate.
Standard forced and long equilibrium simulations will be used to quantify probability distributions for local droughts for the entire globe and to analyse their variability on decadal to centennial timescales. The contributions of random variability and the signal of the forcings will be determined by comparing the different simulation types and by conditioning the probabilities on the forcings. The joint occurrence of droughts in different regions will be explicitly analysed.
Data assimilation simulations will be performed for periods when large historic droughts have been reconstructed from proxy data. This can be expected to lead to an unprecedented understanding of the associated meteorological conditions.

Funding Notes

In addition to completing an online application form, you will also need to complete and submit the CENTA studentship application form available from www.centa.org.uk.

CENTA studentships are for 3.5 years and are funded by the Natural Environment Research Council (NERC). In addition to the full payment of their tuition fees, successful candidates will receive the following financial support.

Annual stipend, set at £14,296 for 2016/17
Research training support grant (RTSG) of £8,000

CENTA students are required to undertake from 45 days training throughout their PhD including a 10 day placement.

References

Cook, E.W, R. Seager, R.R. Heim jr., R.S Vose, C. Herweijer and C. Woodhouse, 2009: Megadroughts in North America: placing IPCC projections of hydroclimatic change in a long-term palaeoclimate context. J. Quaternary Science, 25(1), 48-61.
Garner, Grace, Anne F. Van Loon, Christel Prudhomme, and David M. Hannah. "Hydroclimatology of extreme river flows." Freshwater Biology 60, no. 12 (2015): 2461-2476.
Matsikaris, A., M. Widmann, and J. Jungclaus, 2016: Assimilating continental mean temperatures to reconstruct the climate of the late pre-industrial period. Climate Dynamics, 46,3547-3566.
Medina-Elizalde, M. and E.J. Rohling, 2012: Collapse of classic Maya civilization related to modest reduction in precipitation. Science, 335(6071), 956-959.
PAGES2k – PMIP3 group, 2015: Continental-scale temperature variability in PMIP3 simulations and PAGES 2k regional temperature reconstructions over the past millennium. Climate of the Past, 11(12), 1673-1699.
Widmann, M., H. Goosse, G. van der Schrier, R. Schnur and Jan Barkmeijer, 2010: Using data assimilation to study extratropical Northern Hemisphere climate over the last millennium. Climate of the Past, 6, 1-18.
Woodhouse, C. A., D.M Meko, G.M. MacDonald, D.W. Stahle, E.W. Cook, 2010: A 1200 year perspective on 21st century drought in southwestern North America. PNAS, 107 (50), 21283-21288.