This repository contains Python codes to reproduce the main figures of the paper: "Observation-constrained projections reveal longer-than-expected dry spells" by Petrova I.Y. et al. 2024 (DOI: https://doi.org/10.1038/s41586-024-07887-y)

Author: Irina Y. Petrova

Climate models indicate that dry extremes will be exacerbated in many regions of the world. However, confidence in the magnitude and timing of these projected changes remains low, leaving societies largely unprepared 5,6 . Here we show that constraining model projections with observations using a newly proposed emergent constraint (EC) reduces the uncertainty in predictions of a core drought indicator, the longest annual dry spell (LAD), by 10–26% globally. Our EC-corrected projections reveal that the increase in LAD will be 42–44% greater, on average, than ‘mid-range’ or ‘high-end’ future forcing scenarios currently indicate. These results imply that by the end of this century, the global mean land-only LAD could be 10 days longer than currently expected. Using two generations of climate models, we further uncover global regions for which historical LAD biases affect the magnitude of projected LAD increases, and we explore the role of land–atmosphere feedbacks therein. Our findings reveal regions with potentially higher- and earlier-than-expected drought risks for societies and ecosystems, and they point to possible mechanisms underlying the biases in the current generation of climate models.

• ECpaper_Figure*py files reproduce the corresponding main figures of the paper
• Map2_Corr.py and useful_functions.py are aiding files for data processing and plotting
• EC_KL_div*py files are part of the Emergent Constrain calculation package adopted for this study. The full EC package can be found at https://doi.org/10.5281/zenodo.10886174 and Brient2020: https://doi.org/10.1007/s00376-019-9140-8

Data required to reproduce the figures are available from https://doi.org/10.5281/zenodo.11636527

This Python package has been prepared and run under the following specifications

• Operating System (OS): GNU/ Linux x86_64
• Software: Conda (version = 4.10.3)
• Software: Python (version = 3.7.13)

I.Y. Petrova, Diego G.M., Florent B., Markus G.D., Seung-Ki M., Yeon-Hee K., Margot B. Observation-constrained projections reveal longer-than-expected dry spells. Nature (2024), DOI:10.1038/s41586-024-07887-y