Using earth observation to develop a health index for peatlands

Abstract

Globally peatlands are laterally extensive and represent important stores and sinks of atmospheric carbon. The cold humid island hypothesis proposes that damaged peatlands can be distinguished from functioning peatlands by their relatively dark, bare, dry soils with resulting relatively high daytime and low night-time land surface temperatures. Contrasts in bare soil, vegetation cover and land surface temperature can be readily observed by satellite and so we propose that Earth observation, and the cold humid island hypothesis, can be used to survey, manage and monitor peatlands. Using the NASA MODIS Earth Observation (EO) products allowed the study to directly assess both status and trajectory of peatlands over multi-decadal time at a national scale. The predictions of the cold humid island hypothesis means EO products (albedo, enhanced vegetation index – EVI, daytime land surface temperature, night-time land surface temperature, and the diurnal amplitude in the land surface temperature) can be used to directly assess peatlands without further calibration or correlation to other ecosystem variables. Knowledge of specific sites within a target region means it is possible to use controls to assess absolute and relative status. By considering the state and expected trajectory of the five EO products over British peatlands it was possible to combine the five EO products into a peat health index. When compared to control locations the majority (69 %) of British peatlands showed that they were on a downward trajectory. This downward trajectory was primarily driven by changes in Land Surface Temperature (LST) and, crucially, by deviations from expected trends, as indicated by control variables.