Runoff Dynamics in Catchment Areas with Forest Cover Disturbed by Cutting in Angara River Basin

In light of large-scale logging in the regions of Central Siberia, the problem of restoring the hydrological regime in catchment areas seems to be very urgent. The Angara River basin is the most indicative in terms of forest disturbance. The purpose of this work was assessing the impact of the area of forest cover disturbed as well as of post-logging reforestation on the hydrological regime of the Angara tributaries using climate databases and remote sensing data. The paper analyses the runoff dynamics in four Angara tributaries (the Irkineeva, Chadobets, Mura, and Karabula rivers), whose catchment areas were subject to large-scale logging. To solve this problem, we used long-term runoff observations data from hydrological posts and precipitation data from meteorological stations in the region under study. The forest cover changes analysis in the studied catchments, taking into account the clearing areas, was carried out using the data from the Global Forest Change (GFC) 2000-2020 resource (https://earthenginepartners.appspot.com/science-2013-global-forest) and Landsat satellite images. The direction of the reforestation and the forest restoration processes were analysed based on our own forestry research and forest management materials. It was found that logging caused a decrease in the flow of the studied rivers from 1.5 mm (Mura River) to 4 mm per year (Chadobets River) over the past two decades. Relative equalisation of the flow is observed when 16-20 years old clearings are overgrown, when young trees reach the pole wood growth stage. The obtained results and numerical modelling of the runoff’s dependence on the area of forest cover disturbance showed critical values of the fresh cuttings’ share for maintaining the stability of water content of Angara’s medium and small tributaries. For example, for the smallest of the studied rivers (Karabula), the area of non-renewed cuttings should not exceed 2% of the catchment area. Cutting on adjacent units is possible only after the formation of closed young growth in the first cutting. The studies showed some certainty in studying of the conjugation of runoff dynamics and critical transitions of secondary phytocoenoses caused by a gradual change in the vegetation cover in the process of reforestation after disturbance of the forest cover in the catchment area. As a result of constant changes in the structure of the vegetation cover, future scenarios of the rivers’ hydrological regimes after logging are determined by both further climate changes and the direction of vegetation successions.