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Previous studies have mostly focused on the annual CO2 emissions from drawdown areas on a global scale. However, in drylands, which are more sensitive to global change, finely characterizing the relative importance of drawdown areas on waters (RIDW) in CO2 emissions at the spatio-temporal scale remains unclear. Here, we found that the total drawdown area of drylands could reach 22% of the waters area. From 2004 to 2020, the shrinking of the drawdown area of temperate lakes and reservoirs was the main factor leading to the decline of the total drawdown area. As a result, the mean total CO2 emissions from drawdown areas during 2013-2020 decreased by 18% compared with 2004-2012. The expansion of waters area led to a 29% increase in CO2 emissions from waters. The mean annual CO2 emissions from drawdown areas in drylands was as high as 132.3 ± 23.1 Tg C yr-1, which is equivalent to 61% of estimated CO2 emissions from waters, but its share of CO2 emissions of non-perennial waters shows a significant downward trend. Our study suggests that the spatio-temporal heterogeneity of CO2 emissions caused by the change of drylands waters area is an important part of the global carbon cycle.

Ecological water conveyance is an important way to promote the restoration of degraded ecosystems in arid watersheds. However, there are few previous research results on how to quantitatively evaluate the effect of ecological water conveyance on ecological restoration. In this regard, this paper selects the Tarim River Basin as a typical area, analyzing the changes of desert riparian vegetation and hydrological elements, constructing a watershed ecological environment quality evaluation system, and comprehensively evaluating the ecological water conveyance effect of the damaged desert forest ecosystem. The conclusion showed that the proportion of the pixel area with an upward trend of Fractional Vegetation Cover (FVC) from 2000 to 2021 is as high as 84.3%. The plant diversity index in the ecological water conveyance area showed the characteristics of first obvious increase and then stable. The main body of groundwater depth showed an upward trend, and the Temperature Vegetation Dryness Index (TVDI) showed a downward trend of pixel area accounting for 57.0%, which indicated that ecological water conveyance had played a positive role in groundwater recharge and ecological restoration along the Tarim River. The ecological environment quality of the river basin showed a trend of transition from low-grade to high-grade, and the area with excellent ecological quality had increased from 4,635.50 km2 in 2000 to 12,335.0 km2 in 2021. The above research provides important scientific reference for the protection and restoration of vegetation degradation in arid watersheds.