Assessments of Impacts of Climate and Forest Change on Water Resources Using SWAT Model in a Subboreal Watershed in Northern Da Hinggan Mountains

Water resources from rivers are essential to humans. The discharge of rivers is demonstrated to be significantly affected by climate change in the literature, particularly in the boreal and subboreal climate zones. The Da Hinggan Mountains in subboreal northeast China form the headwaters of the Heilongjiang River and the Nenjiang River, which are important water resources for irrigation of downstream agriculture and wetlands. In this study, long-term (44 years) hydrologic, climate and forest dynamics data from the Tahe were analyzed using the soil and water assessment tool (SWAT) model to quantify the effects of climate and forest change on runoff depth. Meanwhile, downscaled precipitation and temperature predictions that arose from global climate models (GCMs) under four representative concentration pathways (RCP 2.6, RCP 4.5, RCP 6.0 and RCP 8.5) were forced using the SWAT model to investigate the climate change impacts on the Tahe River flows in the future. The results indicated that compared with the 1972–1982 period, the forest biomass in the 1984–1994 period was reduced by 17.6%, resulting in an increase of 16.6% in mean annual runoff depth. On the contrary, with reforestation from the 1995–2005 period to the 2006–2016 period, the mean forest biomass was increased by 9.8%, resulting in the mean runoff depth reduction of 11.9%. The tree species composition shift reduced mean annual runoff depth of 13.3% between the 1984–1994 period and the 2006–2016 period. Compared with base years (2006–2016), projections of GCM in the middle of the 21st century indicated that both mean annual temperature and precipitation were expected to increase by −0.50 °C and 43 mm under RCP 2.6, 0.38 °C and 23 mm under RCP 4.5, 0.67 °C and 36 mm under RCP 6.0 and 1.00 °C and 10 mm under RCP 8.5. Simulated results of the SWAT model showed that annual runoff depth would increase by 18.1% (RCP 2.6), 11.8% (RCP 4.5), 23.6% (RCP 6.0), and 11.5% (RCP 8.5), compared to the base years. Such increased runoff was mainly attributed to the increase in April, July, August, September and October, which were consistent with the precipitation prediction. We concluded that the future climate change will increase the water resources from the river, thereby offsetting the possible decline in runoff caused by the forest recovery. The findings of this study might be useful for understanding the impacts of climate and forest change on runoff and provide a reasonable strategy for managers and planners to mitigate the impact of future climate change on water resources in the subboreal forested watersheds.

The influence of vegetation types on water yields in the Da Hinggan Mountains of China

Climate change and excessive water use are endangering water resources in many areas of the world. As a result there is an urgency to increase available water resources and to improve water supply using vegetation management in catchment areas. The objectives of this study were to determine the effects of four vegetation types (Quercus mongolica F.; QM), Larix spp. plantation; LP), Prunus sibirica L.; PS) and grassland; GL) on water yields by monitoring surface runoff, infiltration, canopy interception and evapotranspiration in the Da Hinggan Mountains, a semi-arid area of China. Surface runoff for each vegetation type was triggered by rainfall of at least 6.6 mm, with surface runoff significantly increasing with rainfall events over 15.8 mm. The QM forest had the highest amount of runoff (1.34 mm), followed by LP (1.06 mm), PS (1.01 mm) and GL (0.69 mm), this accounting for only 0.23% – 0.44% of the total water balance. Infiltration to a soil depth of 10 cm occurred with rainfall events with at least 13 mm, but the depth of infiltration rarely exceeded 30 cm during most rainfall events. More than half of the rainfall was taken up by vegetation during the growing season, with an order of LP > QM > PS > GL. Comprehensive analysis indicated that QM was the most appropriate vegetation for water conservation in this water-limited area, and this vegetation cover could effectively provide more water resources in the local area.