Journal Article

Storylines for Global Hydrologic Drought Within CMIP6

Bjarke, N., Livneh, B., Barsugli, J.

2024

Overview

Future global increases in the duration and severity of hydrologic drought present an emerging challenge for water resource management. However, projected changes to drought within global climate models are often complex, including potentially co‐occurring changes to the timing, duration, and severity of drought. Here, we apply a storyline approach for interpreting projections of future hydrologic drought to identify coherent narratives that include runoff trends, shifts in the seasonal drought timing, increases in multi‐year drought frequency, and increased drought severity within the Coupled Model Intercomparison Project Phase 6. We develop a framework to classify future drought storylines (2015–2100) and quantify model consensus to determine the most‐likely “dominant” storyline under four emission scenarios Shared Socioeconomic Pathways (SSPs) 1–2.6, 2–4.5, 3–7.0, and 5–8.5. Under a low‐emission scenario (SSPs 1–2.6) approximately one third of the land‐area is projected to be impacted by a dominant storyline of minimally detectable runoff trend paired with increased frequency of multi‐year drought. However, under the highest‐emission scenarios (SSPs 5–8.5), the most likely storyline shifts to an increase in multi‐year drought frequency, increased severity of drought, and negative long‐term runoff trends for 62% of the area in those same regions. Shifts in the seasonal timing of drought are a component of dominant storylines for the northern latitudes across all emission scenarios. These results provide an alternative mode of interpretation of co‐occurring changes to the features of future drought, framed in a way to support regional adaptation strategies to mitigate future drought impacts. Plain Language Summary Future hydrologic droughts are projected to become more severe and prolonged through the 21st century, posing challenges for water resource management across the globe. To understand these changes, we analyzed and ensemble of global climate models, focusing on runoff trends, shifts in seasonal drought timing, increased multi‐year drought frequency, and severity. Using a storyline approach, we identified coherent narratives for future drought scenarios from 2015 to 2100 under different emission scenarios. Under low‐emission scenarios, about one‐third of the land may experience minimal runoff changes but increased multi‐year drought frequency. However, under high‐emission scenarios, many global regions are projected to experience widespread multi‐year droughts, intensified drought severity, and decreased runoff. Furthermore, seasonal shifts in drought timing were prominent in northern latitudes across all future scenarios. These findings offer insights to support regional adaptation strategies to address future drought impacts. Key Points Future storylines that include more frequent multi‐year drought occur for at least 23% of the land‐surface in all future emission scenarios Seasonal shifts in the timing of drought occur in the dominant storyline for the northernmost latitudes regardless of emission scenario Hydrologic drought storylines that will most acutely stress water resources become more extensive under higher emission scenarios

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: climate change / Climate models / Climatic changes / CMIP6 / Drought / Droughts / Emission / Emissions / Environment / Environmental impact / Evaluation / Forecasts and trends / General circulation models / Global climate / Global climate models / Hydrologic drought / Influence / Management / multi‐year drought / Precipitation / Resource management / Runoff / Simulation / storylines / Surface water / Trends / United States / Water / Water resources / Water resources management / Water shortages