Assessing impacts of the Ecological Retreat project on water conservation in the Yellow River Basin

The Ecological Retreat (ER) project significantly impacts water conservation functions in the Yellow River Basin (YRB). However, studies on the impact and benefit of different ER modes on ecological water effects still lack systematic and integral disclosure. In our study, CNLUCC (China land use/cover data sets) and the Markov transition matrix were used to simulate land pattern changes from 2000 to 2018. Water yield was chosen as an indicator of water conservation to explore the impact of the ER project by using the water yield module of the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model. After the ER project, the land pattern changed significantly because massive cropland was transformed into forest and grassland. Thus, the total water yields of the YRB increased by 46.32 × 103 hm3 from 2000 to 2018, and the overall water yield benefit was 12.39% larger than the water loss. Forest rehabilitation (FR) showed the highest average water yield capacity, while grassland restoration (GR) exhibited the most incredible total water conservation benefit. Wetland recovery (WLR) manifested a great capacity to improve average water yield, but its total benefit was far less than FR and GR, while waterbody recovery (WBR) showed a negative impact. The results indicate that FR and GR were effective restoration methods, and WLR showed great potential to improve water yield. By using the random forest and principal components analysis, precipitation (PRE), evaporation (AET and ET0), and variation of forest and grassland proved to be the most critical driving indicators affecting water yield changes. Additionally, the correlation and sensitivity between root depth (R_depth) and water yield indicate that increasing R_Depth can also enhance water conservation. The ER project provides a valuable restoration model for water yield and water conservation benefits. The results can provide theoretical support for eco-hydrology and land ecological restoration studies.