Decreasing Relative Importance of Drawdown Areas on Waters in CO₂ Emissions in Drylands

Previous research has primarily focused on global annual CO₂ emissions from drawdown areas. However, in drylands, which are highly vulnerable to global change, elucidating the spatial and temporal significance of drawdown areas in relation to CO₂ emissions from water remains unclear. In this study, we aimed to characterize the relative importance of drawdown areas on waters (RIDW) in CO₂ emissions at a spatio-temporal scale. We found that the total drawdown area of drylands was estimated to be 127,442 ± 18,474 km² per year, which represents up to 22% of the waters area. Furthermore, the annual variation of drawdown areas (coefficient of variation: 0.64) was higher than that of waters (coefficient of variation: 0.22). Our findings suggest that the shrinking of drawdown areas in temperate lakes and reservoirs has been the main factor in the decline of the total drawdown area from 2004 to 2020. As a result, the mean total CO₂ emissions from drawdown areas during 2013–2020 decreased by 18% compared with 2004–2012, particularly in North Africa and Middle Asia, which saw decreases of 35% and 34%, respectively. Meanwhile, the expansion of waters area led to a 29% increase in CO₂ emissions from waters. Our research further reveals that the mean annual CO₂ emissions from drawdown areas in drylands are as high as 132.3 ± 23.1 Tg C yr-1, equivalent to 61% of estimated CO₂ emissions from waters, but its share of CO₂ emissions of non-perennial waters shows a significant downward trend. These results have important implications for understanding the role of drawdown areas in CO₂ emissions and the impact of global change on dryland ecosystems.