Land management for sustainable water yield under future climate conditions in semiarid regions with over-utilized water resources: A case study of Xiong’an New Area

The growing water extraction due to the economic development and population growth has caused over-utilization of water resources worldwide, especially in semiarid regions. In these regions, the sustainable water availability has often been sought and maintained by managing land, but it is highly uncertain in future climate conditions. Besides, prediction of water availability in such region is still challenging due to non-stationary rainfall-runoff relationship caused by intensive human interferences and poor ET simulation by hydrological models. Therefore, accurate estimation and maintaining of sustainable water availability under future climate conditions are important for the ecological conservation and social development of semiarid regions. In this study, impacts of land use and climate changes on vegetation dynamics (canopy LAI) and water cycle (ET and runoff) of the Xiong’an New Area (XNA) are investigated using an ecohydrological model (i.e., WAVES). The XNA, a typical semiarid region located in North China, is expected to need more water in order to increase the vegetation coverage from 10% to 40% by 2035. The WAVES model is chosen because it can simulate ET well by coupling water-carbon-heat. Here, water use (ET) and water yield (runoff) of three typical ecosystems (i.e., cropland, grassland and forestland) in different future periods (i.e., near-future: 2030s (2021-2040), mid-future: 2050s (2041-2060) and far-future: 2080s (2061-2100)) are assessed using projected future climate forcing from 18 GCMs under three RCPs (i.e., RCP2.6, RCP4.5 and RCP8.5). Projected precipitation (P) and air temperature (T_a) indicate the XNA will become warmer and wetter in the future. The WAVES model is capable to simulate the ecohydrological process well in the XNA with NSE ≥ 0.62, R² ≥ 0.65, RMSE ≤ 0.86 in LAI and NSE ≥ 0.61, R² ≥ 0.66, RMSE ≤ 0.71 mm·d^-1 in ET. During the baseline period of 1982-2012, modeling results show that the forested land evaporates more water (32 mm a⁻¹) than cropland while grassland use almost same water as cropland. Under future climate conditions, both cropland and the grassland will have more water use and water yield due to increased precipitation and suppressed vegetation growth due to warming. Forested land will use more than 20% water (76 mm a⁻¹) compared with that during the baseline period in the XNA, but it will generate more than 10% (12 mm a⁻¹) water yield in the 2050s and 2080s under RCP4.5 and RCP8.5 due to greater increases in precipitation. For the purpose of land management, it is recommended to plant crop or grass in the near-future and to plant forest in the mid-future and far-future to expand vegetation coverage in the XNA. This study highlights that both climate change and land management are of critical importance for sustaining water yield in semiarid regions with over-utilized water resources.