Effects of wildfire on runoff generating processes in northern Mongolia
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Seasonal runoff generation in a headwater (~100 km2) of the mountainous Sugnugr Basin, situated within the discontinuous permafrost zone of northern Mongolia, was investigated. The role of the active layer and the effects of a recent wildfire on runoff generation were elucidated. On the catchment scale, stormflow events were investigated by streamflow hydrograph analysis and stable isotope investigations. Hydrological response parameters indicate increasing recession periods and delayed flow fractions during summer as active layer thickness increases. Isotopic signature revealed a high ratio of meltwater in river baseflow in early summer and a gradual decline until the beginning of September. During a stormflow event in early summer, a high fraction of event water was determined by two-component hydrograph separation. At a taiga-vegetated hillslope, subsurface flow was observed following precipitation events after a relative increase in upper soil volumetric water content (VWC i ) of 0.05 m3 m−3, demonstrating the retarding characteristics of the organic surface layer. Depending on active layer depth, subsurface flow predominantly occurred in the organic surface layer in early summer and subsequently subsided into the underlying mineral layer as soils thawed. After a wildfire, the water retention capacity of the organic surface layer diminished, as was reflected by a VWC i of 0.01 m3 m−3. Here, stormflow water temperatures indicated quickflow in the mineral layer above a degenerated frost table. The results of the study suggest that wildfires increase stormflow runoff while baseflow declines. Hence, the problem of water shortages in downstream areas during dry weather conditions is exacerbated.
KeywordsDiscontinuous permafrost Hydrograph separation Mongolia Stable isotopes Stormflow Runoff generation
This work was funded by a research grant of the German Federal Ministry of Education and Research (BMBF) to the project MoMo (Integrated Water Resources Management in Central Asia—Model Region Mongolia, FKZ: 033L003C) to Prof. Dr. L. Menzel. The authors would like to thank Stefanie Minderlein and Mathias Bents for help during field work and Barbara Herbstritt for assistance in the laboratory. We further thank Chimegsaikhan Altangerel, Nasanbayar Narantsogt, Khuhuu Gunsenbat and Nugonhayaar Gansukh for their support of this study. We further thank two anonymous reviewers and the editors, who certainly helped to improve this manuscript.
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