Warming Accelerates and Intensifies Meteorological-to-Agricultural Drought Propagation in the Northern Great Plains

Abstract

Drought propagates from atmospheric water deficits into root-zone soil–moisture stress, yet the extent to which warming will alter the severity and speed of this transition in cold, semi-arid regions remains poorly quantified, and most propagation studies rely on a single linkage measure. This study assessed meteorological-to-agricultural drought propagation across a 1.74 million km2 transboundary domain in the Northern Great Plains using 11 km projections from the Canadian Regional Climate Model version 5 driven by Coupled Model Intercomparison Project Phase 6 Earth system models (CRCM5-CMIP6) and a calibrated cold-region Soil and Water Assessment Tool (SWAT) model. Climate simulations were bias-corrected by quantile delta mapping, and meteorological and agricultural droughts were characterized using the Standardized Precipitation Evapotranspiration Index (SPEI) and Soil Moisture Deficit Index (SMDI), respectively, for a historical baseline and three future periods under three Shared Socioeconomic Pathway (SSP) scenarios: intermediate (SSP2-4.5), high (SSP3-7.0), and very high (SSP5-8.5) emissions. Propagation was evaluated using multiscale Spearman correlation, run-theory event matching, copula-based conditional probabilities, and lower-tail dependence. Quantile delta mapping increased climate-variable correlations with observations to approximately 0.85–0.95, while SWAT reproduced daily warm-season soil moisture with Kling–Gupta efficiencies of 0.575–0.731. Both SPEI-12 duration and severity of meteorological drought increased with forcing and time; under far-future SSP5-8.5, local increases reached approximately 20–22 months and 60–67 severity units. Basin-mean SMDI declined to −1.08 under far-future SSP5-8.5, with the strongest drying in the southern and southeastern sectors of the region. Although the mean SPEI-3–SMDI correlation weakened slightly from 0.62 in the near future to 0.57 in the far future, the mean propagation time shortened from 2.37 to 1.81 months. The probability of agricultural drought during extreme meteorological drought was 0.69–0.82, and the translation rate increased from approximately 54–58% under SSP2-4.5 to 63–68% under SSP5-8.5. These results indicate that warming intensifies soil-moisture drought while reducing the response time available for agricultural drought preparedness. They also imply that adaptation to a warming climate will require an emphasis on agricultural practices that preserve soil moisture.