Overview

Project Highlights:

  • Comprehensive analysis of drought across the globe
  • Climate modelling with state-of-the art Earth system model
  • Reconstructing past climate

 

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. 

Reconstructed summer Palmer drought severity index (PDSI) for 1146 – 1155 AD and 1951-1960 AD (from Woodhouse et al. 2010).

Methodology

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.

Training and Skills

The project gives the chance to work on cutting-edge problems in hydrology and palaeoclimate modelling using supercomputers, state-of-the-art climate models, and advanced statistical methods.  Training in climate modelling, data assimilation and statistical methods will be provided at the University of Birmingham. The student also has the opportunity to attend related lectures on the MSc program ‘Applied Meteorology and Climatology’. Co-supervision by and visits to the Max Planck Institute for Meteorology (MPI-Met) in Hamburg, where the simulations will be performed, will strongly contribute to training in climate modelling, and co-supervision by CEH will complement the hydrological expertise of the Birmingham supervisors. The student will also benefit from strong links of the supervisors to international projects such as PAGES2k and PMIP.

CENTA students are required to complete 45 days training throughout their PhD including a 10 day placement. In the first year, students will be trained as a single cohort on environmental science, research methods and core skills. Throughout the PhD, training will progress from core skills sets to master classes specific to the student's projects and themes. 

Timeline

Year 1:  Collect existing palaeoclimate simulations and empirical drought reconstructions. Calculate drought indices from simulations and validate against recent drought data and empirical reconstructions. Analyse model biases and their reasons. If and where bias correction is suitable, apply bias correction.

Year 2:  Analyse simulation-based drought indices and determine influence of forcings. Analyse joint occurrence of droughts in different regions.  Learn how to run the MPI-Met Earth System Model in data assimilation mode.

Year 3:  Perform and analyse data assimilation simulations for periods when large droughts have been reconstructed. Present the results at scientific conferences and in papers.

Partners and collaboration (including CASE)

The School of Geography, Earth and Environmental Sciences at the University of Birmingham includes  strong groups in climate science as well as hydrology, which makes it ideal to conduct this interdisciplinary project. The specific expertise is in climate modelling, palaeoclimate, dynamical meteorology, statistical climatology, downscaling, as well as in surface and sub-surface hydrology, with a focus on droughts. The MPI-Met is one of the world-leading climate modelling centres and adds to the expertise in climate modelling. CEH is the leading UK centre for hydrological research and strengthens the expertise in this field. The supervisors are part of the international PAGES2k and PMIP initiatives, which recently have started specific activities on hydroclimate and on data assimilation, and of the UNESCO-FRIEND and IAHS Panta Rhei initiatives focussing on understanding and quantifying (changes in) drought.

Further Details

Applicants should have a background in a related field such as climatology, meteorology, hydrology, geosciences, physics or mathematics. Sound mathematical and statistical skills and programming experience are essential. Working experience with UNIX, FORTRAN, and climate modelling would be beneficial. For further details please contact M.Widmann (m.widmann@bham.ac.uk).