Global composite drought indices for investigating the effects of climate-driven drought on major crop water requirements

Droughts are expected to increase in warmer climates, significantly affecting global crop production and raising crop water demand. The recurrence of extreme droughts in recent years needs more attention to capture their multifaceted nature. Explaining the impact of general drought indices on water requirements could limit the precision of future water demand estimates. Three composite drought indices were used to investigate the effects of drought on crop water requirement (CWR), irrigation water requirement (IWR), and yields for major crops under the Shared Socioeconomic Pathways (SSPs 245 and 585), to provide a broader view of future water-demand risks. The results indicate that drought distribution is accompanied by wetness, with a higher likelihood of future dryness in regions such as South Asia, Australia, and North and South America. There is an increase in the estimates of the CWRs and IWRs under the SSPs. In extreme cases (SSP 585), maximum fractional changes in total (including rainfed and irrigated) CWR and IWR relative to the baseline period are +80.16 mm/month and +42.68 mm/month for wheat; +52.54 mm/month and +7.09 mm/month for maize; and +14.01 mm/month and +4.98 mm/month for rice, respectively. Overall, the results indicate a significant increase in CWR and IWR under future climate scenarios, underscoring the potential for increased water demand and the urgent need to develop adaptive water management strategies.