Expanding grassland coverage to maintain ecohydrological sustainability in the agro-pastoral ecotone of northwest China

Abstract. To achieve ecological sustainability, the Chinese government is conducting large-scale vegetation restoration projects to increase grasslands to 60 % by 2035. However, excessive vegetation restoration has undermined ecohydrological sustainability, leading to soil drying in the agro-pastoral ecotone of Northwest China (APENWC), where grasslands made up 52.0 %, barren land 29.9 %, and croplands 12.5 % in 2015, with other classes accounting for 5.6 %. The potential impacts of future land use and cover change (LUCC) on ecohydrological sustainability over the APENWC are unclear. To address this gap, the Community Land Model (version 5.0, CLM5.0) was implemented for the historical period from 2000 to 2015 under a real LUCC scenario (reference scenario) and several synthetic LUCC scenarios. The impacts of the LUCC on regional water fluxes and temperature were assessed by comparing the spatially averaged annual land surface temperature (LST) and evapotranspiration (ET) simulated using different model setups. The reference scenario revealed two main LUCC types in the region: conversions from bare land to grasslands and from croplands to grasslands, with a total increase in grassland cover from 44.8 % in 2000 to 52.0 % in 2015. The conversion from bare land to grasslands reduced LST by 0.17 °C and increased ET by 53.32 mm yr−1. Conversely, the conversion from croplands to grasslands increased LST by 1.18 °C and reduced ET by 190.89 mm yr−1. Despite these significant local LUCC impacts, the overall effect of the historical LUCC resulted in limited variations in LST (−0.06 °C) and ET (9.70 mm yr−1) when the complete APENWC region is considered. Future scenarios assuming 60 % grassland cover with varying proportions of bare land and cropland suggest that none of the scenarios showed significant adverse effects on water conservation (WC), suggesting that vegetation restoration will not intensify drying conditions. These results indicate that increasing grassland coverage to 60 % by 2035 supports ecohydrological sustainability without introducing drying.