The interconnection between land cover and land surface temperature in the arctic and boreal regions

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Hamid Dashti, William K Smith, Andrew M. Fox, Charles J Devine, Xueli Huo and David J.P. Moore, School of Natural Resources and the Environment, University of Arizona, Tucson, AZ

Background/Question/Methods:
Ecosystems in the Arctic and boreal regions (ABR) have been extensively changed over the past decades from shrub encroachment, deforestation caused by wildfire, and the expansion of agriculture. Natural and anthropogenic land cover change (LCC) alters ecosystem interactive controls governing water and energy exchange and either amplify or stabilize warming; albedo and evapotranspiration changes the land surface temperature (LST) which in turn influences ecosystem function. The main question of this study is how does LCC affect the temporal and spatial variations of LST over ABR? We test the hypotheses that the main control on spatiotemporal changes in LST-LCC sensitivity is dependent on the type of ecosystem transition (e.g. forest to shrub vs. forest to wetland). We predict the sensitivity of LST to LCC is spatially and temporally variable and the direction of LST change is predicted by the relative evapotranspiration and albedo of ecosystems before and after the LCC. Our study area is the core region of NASA Arctic and Boreal Experiment which includes entire Alaska and western Canada. We use recently developed high-resolution land cover maps (30m, 2003-2013) for the region and a range of remote sensing, modeled historical datasets, and local biometerological measurements.
Results/Conclusions:
Our results show both LST and LCC are temporally and spatially dynamic and have undergone substantial changes over time. Between 2003 and 2013, about 31% of the region experienced some sort of ecosystem transition which led to changes in annual LST (-2.9 to 2.8 [C°]), albedo (-0.16 to 0.12), and evapotranspiration (-79.5 to 92.6 [mm year-1]). However, these changes depend on the type of transition. For example, conversion of evergreen forests to shrub lead to the reduction of average annual LST (-0.23±1.38 [C°]) while evergreen forests to sparse cover increased LST (0.48±1.5 [C°]). Sensitivity analyses show the strong dependence of LST-LCC sensitivities to the type of ecosystem transition as well. For example, while the sensitivity of LST to shrub-sparse transition is positive (0.0025±0.0004 [C°/unit LCC], pvalue<0.01), sensitivity of LST to shrub-wetland transition is negative (-0.0077±0.0003 [C°/unit LCC], pvalue<0.01). However, the interaction between LST and LCC is complex and we find evidence that the ecosystem transition has different effects in winter vs summer. The findings of this study are of interest to the ecological communities and policymakers designing future warming mitigation strategies in the