Morphoclimatic controls of contemporary chemical and mechanical denudation in a boreal-oceanic drainage basin system in central Norway (Homla drainage basin, Trøndelag)

Abstract

ABSTRACT Based on existing meteorological records, increases of annual air temperatures, annual precipitation sums, annual wind speeds, and of the frequencies and intensities of heavy rainfall and storm events in Norway are postulated. From a process-geomorphological point of view it is of growing importance to obtain an improved knowledge of the complex relationships between contemporary geomorphologic processes, vegetation cover and present-day climatic conditions to arrive at more realistic assessments of possible geomorphic effects of ongoing and future climate changes. This study analyzes the morphoclimate of a boreal-oceanic drainage basin system in central Norway and presents aspects of the contemporary wind, air temperature and precipitation regimes that control the type, frequency, intensity and duration of relevant denudational surface processes operating in the area. The work is based on statistical analyses (magnitude-frequency analyses) of existing meteorological data and process-geomorphologic field work conducted over a five-year investigation period (November 2011–October 2016) in the Homla drainage basin (156.3 km2) in central Norway. Due to the distinct characteristics of the present-day morphoclimate, runoff occurs year-round and chemical denudation clearly dominates over mechanical denudation. Mechanical denudation is strongly event-controlled and the highest share of annual fluvial transport occurs in May during the peak of spring snowmelt. Both chemical denudation (12.1 t km−2 yr−1) and mechanical denudation (3.6 t km−2 yr−1) are of low intensity which is explained by the cool climate combined with a nearly closed and continuous vegetation cover, small thicknesses of sedimentary covers, a high weathering resistance of the predominant bedrock and only low topographic relief in the upper parts of the Homla drainage basin. It is expected that the postulated changes of the wind, air temperature and precipitation regimes will lead to increasing chemical and mechanical denudation rates in the study area.