Hot Spots and Climate Trends of Meteorological Droughts in Europe–Assessing the Percent of Normal Index in a Single-Model Initial-Condition Large Ensemble

Andrea Böhnisch,Martin Leduc,Ralf Ludwig,Magdalena Mittermeier

doi:10.3389/frwa.2021.716621

Andrea Böhnisch, Martin Leduc + Show 2 more

Open Access

https://doi.org/10.3389/frwa.2021.716621

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Abstract

Drought, caused by a prolonged deficit of precipitation, bears the risk of severe economic and ecological consequences for affected societies. The occurrence of this significant hydro-meteorological hazard is expected to strongly increase in many regions due to climate change, however, it is also subject to high internal climate variability. This calls for an assessment of climate trends and hot spots that considers the variations due to internal variability. In this study, the percent of normal index (PNI), an index that describes meteorological droughts by the deviation of a long-term reference mean, is analyzed in a single-model initial-condition large ensemble (SMILE) of the Canadian regional climate model version 5 (CRCM5) over Europe. A far future horizon under the Representative Concentration Pathway 8.5 is compared to the present-day climate and a pre-industrial reference, which is derived from pi-control runs of the CRCM5 representing a counterfactual world without anthropogenic climate change. Our analysis of the SMILE reveals a high internal variability of drought occurrence over Europe. Considering the high internal variability, our results show a clear overall increase in the duration, number and intensity of droughts toward the far future horizon. We furthermore find a strong seasonal divergence with a distinct increase in summer droughts and a decrease in winter droughts in most regions. Additionally, the percentage of summer droughts followed by wet winters is increasing in all regions except for the Iberian Peninsula. Because of particularly severe drying trends, the Alps, the Mediterranean, France and the Iberian Peninsula are suggested to be considered as drought hot spots. Due to the simplicity and intuitivity of the PNI, our results derived from this index are particularly appropriate for region-specific communication purposes and outreach.

Highlights

With progressing climate change droughts have become a critical high-impact hydro-meteorological hazard globally, and in Europe, in recent years (Spinoni et al, 2018)
Seasonal percent of normal index (PNI) values are calculated for 1955–2019 with the E-OBS gridded dataset and the Canadian regional climate model version 5 (CRCM5)-LE with respect to 1955–1974
These time series give a good indication of the amount of inter-annual variability that is to be expected within the depicted regions: whereas for the Alps and British Isles PNI variability in all seasons is low (PNI values of 50–150% during most seasons), the Iberian Peninsula is affected by large PNI variability, ranging from almost 0 to >200%

Summary

Introduction

With progressing climate change droughts have become a critical high-impact hydro-meteorological hazard globally, and in Europe, in recent years (Spinoni et al, 2018). Due to the complexity of drought impacts on diverse different sectors like water supply, agriculture, and ecosystems (Spinoni et al, 2018; Liu et al, 2019), a universal definition of droughts that satisfies all users is impractical (Lloyd-Hughes, 2014). A less complex index for meteorological droughts is the Percent of Normal Index (PNI; Werick et al, 1994; Willeke and Hosking, 1994). It directly represents the percentage of precipitation of a specific period compared to the long-term mean. Due to its simple calculation and intuitive meaning it can serve for communication and outreach purposes (Smakhtin and Hughes, 2004; Nikbakht et al, 2013)

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Discussion

Conclusion