The impact of climate variability and land use/cover change on the water balance in the Middle Yellow River Basin, China

Climate variability and land use/cover change have a significant impact on hydrological regimes, especially in arid and semi-arid regions, which have critical water shortage problems. Using the Mann-Kendall's test methodology, trends in hydro-climatic variables including precipitation, temperature, land use, and water balance indicators have been detected during the last 60 years in the Middle Yellow River Basin (MYRB). Generally, the MYRB has become much warmer and drier. Compared with 1980, the land use has also changed - to a small degree by 2000 and to a significant degree by 2015, with an increase in vegetation coverage. There are decreasing trends for streamflow and water resources and a shift in water balance, with less precipitation generating streamflow and more water being evaporated, especially after 2000. The response of water balance to climate change and land use/cover change, and the attribution for streamflow decrease was analyzed in the 10 sub-regions of the MYRB, based on the regionalization of parameter w of Fu's Formula. The results indicate that with an increase of E-0/P (potential evaporation/precipitation) or w, there is an increase of ET/P (evapotranspiration/precipitation) and a decrease of R/P (streamflow/precipitation). But, the increasing rate of ET/P decreases with an increase of E-0/P or w. Based on the "natural period" streamflow of 1956-1979, climate variability accounts for 75.8% of streamflow decrease in 1980-2000. But in 2001-2016, land use/cover change is the main factor in streamflow decrease, accounting for 75.5% of the decline. The results are useful for understanding what has happened and what will happen under climate change and land use/cover change, for adaption to future water resources management.