Abstract
Climate change was projected to have negative effects on water availability and consequently a serious constraint to food production in many areas of the world. However, such effects have not been well understood, particularly over rainfed croplands, partly because of the poor representation of green water in associated assessments. In this study, we develop an integrated agricultural water scarcity index (WSIag) that incorporates blue and green water components to examine the agricultural water scarcity in the baseline (1981–2005) and future (2026–2050) periods under the Representative Concentration Pathway (RCP)2.6 and RCP6.0 scenarios. Results show that ∼3.8 million km2 (∼39% of total) croplands experienced water scarcity in the baseline period and it would expand by more than 3% in the future. Under the two scenarios, WSIag projections are similar overall and are higher than that under the baseline in 83%–84% of global total croplands. Differences are found between the scenarios in Amazonia, Southern Africa, and South Asia. The increases in future WSIag are dominated by the decreased water availability in ∼60% of total croplands and ∼24% of which is dominated by the increased crop water requirement. Changes in green water availability have a significant contribution to changes in WSIag in 16% of global croplands, mostly in arid/semiarid regions (e.g., the South edge of the Sahel, Southern Africa, Northeast China, and Central America). This implies the important role of green water management for agriculture in these regions. The integrated assessment can help develop effective strategies for agricultural water management under climate change.
Plain Language Summary
Future climate change may intensify water scarcity and adversely affect crop productivity in many regions of the world. Traditionally, water scarcity assessment focused on blue water (from rivers, reservoirs, and lakes) or green water (crop evapotranspiration from soil moisture) alone. In order to examine the impact of climate change on water scarcity in croplands, we develop an integrated agricultural water scarcity index (WSIag) that incorporates blue and green water components and calculate WSIag for both historical and future periods. The assessment suggests that nearly 40% of global croplands have experienced water scarcity in the past and the situation would worsen in the future. WSIag is projected to be higher than in the past in 83%–84% of global total croplands. The increased WSIag is mostly caused by less water availability and larger crop water requirement. It is noted that changes in green water availability could also be a dominant factor in some arid/semiarid regions in the South edge of the Sahel, Southern Africa, India, Northeast China, and Central America. Our study highlights the important role of green water for agriculture water management and is expected to provide useful information for agricultural adaptation to future climate change.
Key Points
Agricultural water scarcity will intensify in more than 80% of global croplands
Decreased water availability dominates the aggravation of future water scarcity globally
Green water have a significant contribution to future changes in water scarcity in 16% of global croplands