Spatiotemporal variations in eco-environmental quality and responses to drought and human activities in the middle reaches of the Yellow River basin, China from 1990 to 2022

The middle reaches of the Yellow River basin (MYRB) are among the regions most severely affected by soil erosion globally. It has always held a pivotal role in soil and water conservation and ecological restoration efforts in China. Nonetheless, in the face of recurrent drought occurrences and growing human intervention, there have been notable alterations in the eco-environmental quality (EEQ) within the MYRB. However, the influences of drought and human intervention on the EEQ of MYRB remain unclear. In this study, the remote sensing ecological index (RSEI) was applied to quantify the spatiotemporal changes in EEQ and the contributions of drought and land use type transitions to EEQ in the MYRB from 1990 to 2022. The results showed that the EEQ in the MYRB fluctuated significantly and exhibited a weak overall improvement trend over the past 33 years. The proportion of good and excellent grades for EEQ significantly improved, while the proportion of poor and fair grades significantly decreased, especially in the northern regions. The trend of changes in EEQ follows a phased pattern. During the periods of 1990–2002 and 2011–2022, an improving trend is observed, while the period of 2003–2010 shows no significant change in EEQ. Drought had the strongest influence on the EEQ from 2003 to 2010, followed by that from 1990 to 2002, and had a lesser impact in the period from 2011 to 2022. The EEQ was primarily positively influenced by spring, autumn and winter droughts and negatively affected by summer droughts, especially in arid grassland and unused land areas. The EEQ in the MYRB improved primarily during the initial and final phases of the ecological projects, with a lesser impact from drought. The increase in EEQ during the initial phases of ecological project implementation was less noticeable, and drought significantly affected EEQ during this period.