Identifying the dominant effects of climate and land use change on soil water balance in deep loessial vadose zone

Identifying the dominance of climate and land use in soil water balance (SWB) is critical for developing water resource management strategies in agriculture and in environment. The large soil water reservoir in the thick vadose zone of China's Loess Plateau has been depleting in recent years; however, the connection of climate and land use changes with SWB has rarely been differentiated. An experimental site from China's Loess Plateau with different land uses including farmland and apple trees of different ages (approximately 20 and 30 years old) were considered to partition the SWB components under the current (1957-2017) and future (2011-2040) climate using the HYDRUS-1D model. Simulated with three land use types and 20 climate change scenarios, 60 SWB scenarios were used to differentiate the role of climate and land use in SWB changes. For the climate change impacts, precipitation played an important role in SWB variability than temperature. Further, the variance of precipitation had greater effects than mean precipitation on SWB components. The changes in the actual evapotranspiration were dominated by precipitation and temperature, but the change in groundwater recharge was largely controlled by the conversion from farmland to apple trees. This study provides information to guide the implementation of the revegetation program on the Loess Plateau, and highlights the importance in differentiating the influences of climate and land use changes to sustain agriculture and water resources in the future