Drought indices revisited – improving and testing of drought indices in a simulation of the last two millennia for Europe

Abstract

Over the past decades, different drought indices have been suggested in the literature. This study tackles the problem of how to characterize droughts by defining a framework and proposing a generalized family of drought indices that is flexible regarding the use of different hydrological fluxes in the water balance. The sensitivity of various indices and its skill to represent drought conditions is evaluated using a regional model simulation for Europe spanning the last two millennia as test bed. The framework combines an exponentially damped memory with a normalization method based on quantile mapping. Both approaches are more robust and physically meaningful compared to the existing methods used to define drought indices. Still, the framework is flexible with respect to hydrological fluxes used for the water balance, enabling users to adapt the index formulation to the data availability of different locations. Based on it, indices using different hydrological fluxes in the water balance are compared with each other showing that a drought index considering only precipitation in the water balance is sufficient for western to central Europe. In the Mediterranean, temperature effects via evapotranspiration rather than potential evapotranspiration, need to be considered to produce meaningful indices representative of water deficit. In addition, our results indicate that in north-eastern Europe and Scandinavia, snow and run-off effects need to be considered simultaneously in the index definition to obtain accurate results.

Impact of strong and extreme El Ni~nos on European hydroclimate

“…A further limitation is that there is no universal interpretation of what drought is, there are many existing definitions, and there was no standard procedure that allows the different definitions to be compared consistently. Raible et al (2017) proposed a standard and flexible template of calculations that allows different drought definitions to be calculated so that they can be assessed together in their true reflections of droughts. Such extensive analyses and inter-comparisons of different drought indices is beyond the resources of our current study; but we note that PDSI is already a more sophisticated/complex drought index compared to the others.…”

Impacts of surface boundary conditions on regional climate model simulations of European climate during the Last Glacial Maximum

“…Regional climate models (RCMs) can both add value to [Feser et al, 2011;Hackenbruch et al, 2016] and reduce the biases in the GCM simulations [Diaconescu and Laprise, 2013], as the higher resolution permits a better representation of relevant physical processes for regional weather and climate. So far, RCMs have only been scarcely used for past climate simulations in Europe, e.g., for the Common Era [e.g., Gomez-Navarro et al, 2015;Raible et al, 2017], the Younger Dryas [Renssen et al, 2001], and the LGM [Strandberg et al, 2011]. In this study, the influences of the SSTs in the eastern North Atlantic on the regional LGM climate over Europe are investigated with RCM simulations.…”

Projected drought risk in 1.5°C and 2°C warmer climates

“…Current research indicates that many historically drought-prone regions will face increased drought risk with continued anthropogenically driven global warming [Held et al, 2005;Dai, 2011a;Hoerling et al, 2012;Fu and Feng, 2014;Prudhomme et al, 2014;Kelley et al, 2015;Duffy et al, 2015;Ault et al, 2016] and that this increase is robust across models since it is primarily driven by mean temperature change. However, there exist considerable uncertainties in observed and projected drought related to the choice of drought index, model structural differences, emissions scenarios, and internal variability [Intergovernmental Panel on Climate Change, 2012;Burke and Brown, 2008;Sheffield et al, 2012;Orlowsky and Seneviratne, 2013;Trenberth et al, 2014;Scheff and Frierson, 2015;Smerdon et al, 2015;Swann et al, 2016;Berg et al, 2016;Raible et al, 2017]. In particular, the risk of multidecadal "megadroughts" remains challenging to constrain, due to the long records needed [Coats and Mankin, 2016 benefits for future drought risk, but such benefits are regional and in some cases highly uncertain…”