Evaluation of vegetation–water mutual suitability in Helong Region of the Loess Plateau

Since the implementation of the Grain for Green Project, the vegetation coverage of Loess Plateau has been greatly improved. However, the contradiction between the increasing vegetation water demand (VWD) and the regional rainwater utilization potential (RUP) has become an important factor threatening the sustainable development of vegetation. In order to figure out whether the available water can support the water consumption of vegetation restoration, it is necessary to quantitatively explore the balance between the RUP and the VWD. Based on these, this study utilized the Soil and Water Assessment Tool (SWAT) and Penman–Monteith (PM) method to quantitatively evaluate the vegetation–water mutual suitability of a typical area in the Loess Plateau's Helong Region (HLR). The results showed that both RUP and VWD exhibited significant increasing trends (95 % confidence level) from 1982 to 2018, with a rate of 18.19 mm/10a and 25.22 mm/10a, respectively. Spatially, RUP was lower in the northwest and higher in the southeast and south regions, whereas VWD decreased from the southeast to the northwest. According to the evaluation results, the annual average vegetation–water mutual suitability matching degree was 0.64 in Period I (1982–1999) and 0.67 in Period II (2000–2018). The matching degree was higher in the northwest and middle regions, lower in the southeast, and above 0.60 in most regions. Under the future climate scenarios of RCP 2.6 and RCP 8.5, the matching degree of water supply and demand also improved to 0.69 and 0.72. Overall, the available water resources can basically support vegetation growth in the HLR. Future vegetation restoration in HLR should try to select annual herbaceous plants that consume less water, and it is not recommended to continue vegetation restoration in the southeast. The results of this study can provide scientific guidance and reference for vegetation restoration policies in HLR.