1. Introduction
The Arctic regions are experiencing unprecedented changes of climate (IPCC, 2014). Mountainous areas of the Arctic are the remotest, less studied but provide the largest share of Arctic runoff (Hinzman et al., 2005; Viviroli et al., 2011). Recent studies have shown that due to climate warming Arctic runoff is changing too (Makarieva et al. 2019a; Rawlins et al., 2010; Stuefer et al., 2017; Tananaev et al., 2016) but the mechanisms behind observed changes are not fully understood.
The lack of data can partly be compensated by hydrological modelling. Models are also used for projections of future states of hydrological system in the Arctic (Krogh & Pomeroy, 2018; Pohl et al., 2006; Rasouli et al., 2014).
The problematic issue of future projections is that large-scale, relatively simple, conceptual hydrological models are being calibrated against streamflow series in gauging stations of large rivers (Hudson & Thompson, 2019; Nijssen et al., 2001), while more process-based ones, require detailed observational information for their parametrization and are usually applied for well-studied research basins (Changing Cold Regions Network project, Improving Processes & Parameterization for Prediction in Cold Regions Hydrology project; Marsh et al., 2020; Zhang et al.. 2008). It is not very often that hydrological models are tested if they are really able to reproduce currently observed changes before issuing the future projections. These problems undermine the ability of hydrological community to deal with Arctic warming challenge.
The study advocates the approach to hydrological modeling presented in earlier papers (Semenova & Beven, 2015; Semenova et al., 2013; Vinogradov et al., 2011) which suggest a priori or based on expert judgement estimation of model parameters and extensive verification of models and the sets of their parameters as the tool of comprehension of hydrological process in ungauged basins.
The tasks of the study are:
• Compile the database of available historical observations (1957-1959) for remote mountainous river basin located in the zone of continuous permafrost with long-term streamflow series and pronounced changes of hydrological regime in recent decades.
• Describe runoff generation processes; parameterize the hydrological model using compiled data and the results of previous regionalization of the model parameters.
• Verify the model based on available observations of variable states of snow and frozen ground.
• Verify the model by streamflow for the continuous period of observations (1956-2012).
• Assess the ability of the model to reproduce the recent changes of streamflow.
• Investigate the factors of streamflow changes using the hydrological model.
The novelty of the study is the approach that allow for continuous long-term simulations of streamflow and active layer dynamic in remote basin with complicated mountainous permafrost environment based on process understanding and scarce data of short-term observations conducted more than 60 years ago.