Estimation of surface energy fluxes in the Arctic tundra using the remote sensing thermal-based Two-Source Energy Balance model

Jordi Cristóbal,Anupma Prakash,Martha C Anderson,William P Kustas,Eugénie S Euskirchen,Douglas L Kane

doi:10.5194/hess-21-1339-2017

Abstract

Abstract. The Arctic has become generally a warmer place over the past decades leading to earlier snow melt, permafrost degradation and changing plant communities. Increases in precipitation and local evaporation in the Arctic, known as the acceleration components of the hydrologic cycle, coupled with land cover changes, have resulted in significant changes in the regional surface energy budget. Quantifying spatiotemporal trends in surface energy flux partitioning is key to forecasting ecological responses to changing climate conditions in the Arctic. An extensive local evaluation of the Two-Source Energy Balance model (TSEB) – a remote-sensing-based model using thermal infrared retrievals of land surface temperature – was performed using tower measurements collected over different tundra types in Alaska in all sky conditions over the full growing season from 2008 to 2012. Based on comparisons with flux tower observations, refinements in the original TSEB net radiation, soil heat flux and canopy transpiration parameterizations were identified for Arctic tundra. In particular, a revised method for estimating soil heat flux based on relationships with soil temperature was developed, resulting in significantly improved performance. These refinements result in mean turbulent flux errors generally less than 50 W m−2 at half-hourly time steps, similar to errors typically reported in surface energy balance modeling studies conducted in more temperate climatic regimes. The MODIS leaf area index (LAI) remote sensing product proved to be useful for estimating energy fluxes in Arctic tundra in the absence of field data on the local biomass amount. Model refinements found in this work at the local scale build toward a regional implementation of the TSEB model over Arctic tundra ecosystems, using thermal satellite remote sensing to assess response of surface fluxes to changing vegetation and climate conditions.

Highlights

Air temperatures in the Alaskan Arctic have shown a significant increase, especially in past decade (Serreze and Barry, 2011)
Since the mean root mean square error (RMSE) for all fluxes compared to unclosed and closed turbulent fluxes and for all parameterizations and sites was around 50 W m−2 (Tables 5 and 6), which is commensurate with errors typically reported in other surface energy balance studies (Kalma et al, 2008), these results suggest that a generalized αPTC value of 1.26 in global Two-Source Energy Balance model (TSEB) applications may adequately reproduce energy fluxes in Arctic tundra during the growing season, from leafout until senescence, while capturing inter- and intraannual dynamics
Parameterizations for Rn, G and αPTC used in the TSEB model were evaluated and refined for applications in different tundra types in Alaska over the full Arctic tundra growing season

Summary

Introduction

Air temperatures in the Alaskan Arctic have shown a significant increase, especially in past decade (Serreze and Barry, 2011). The Arctic has become a warmer place, leading to an acceleration of the hydrologic cycle, earlier snow melt and drier soils due to permafrost degradation (AMAP, 2012; Elmendorf et al, 2012; Rawlins et al, 2010; Sturm et al, 2001; Overduin and Kane, 2006). The hydrologic response of the Arctic land surface to changing climate is dynamically coupled to the region’s surface energy balance (Vörösmarty et al, 2001), and the partitioning of energy fluxes plays an important role in modulating the hydrologic cycle of Arctic basins (Rawlins et al, 2010). J. Cristóbal et al.: Estimation of surface energy fluxes in the Arctic tundra

Objectives

Results

Conclusion