Mapping rainfall interception by shrubs in an Arctic tundra watershed using L-band SAR data

Abstract:

Rainfall interception by shrub canopy is a key component of the summer water balances in the Arctic tundra ecosystem (Zwieback et al. 2019). Interception reduces the effective rainfall and redistributes soil water and chemicals (Ward and Robinson 2000). With the expanding shrub cover and extended summer season driven by climate change across the Arctic tundra, rainfall interception by shrubs is predicted to further increase (Wrona et al. 2016). Furthermore, interception exhibits spatial variations across the tundra as it is controlled by the highly heterogeneous shrub canopy cover. A cost-effective tool is therefore necessary to quantify the amount of rainfall interception and capture its variability at broad spatial scales.

In this study, we examined the applicability of L-band SAR data in interception modelling to yield spatially distributed interception estimation across the Trail Valley Creek watershed in Northwest Territories. ALOS-2 derived maps of canopy storage capacity and fractional cover of dwarf birch were fed into the Gash analytical model to capture the spatial heterogeneity of the shrub canopy. Comparison between the model estimates and in-situ measurements at two field sites resulted in a relative error of 4.1% at site A and 0.9% at site B. On average, 16.6 ± 3.2 % of incoming rainfall was intercepted by dwarf birch during the study period of 23 June to 28 August 2018. These results suggest the potential of utilizing SAR-based shrub canopy products to map the interception loss across broad spatial scale, ultimately providing a quantified understanding on their roles in regional water balances.