Challenges in Reconciling Satellite-Based and Locally Reported Estimates of Wetland Change: A Case of Topographically Constrained Wetlands on the Eastern Tibetan Plateau

Jianing Fang,Benjamin Zaitchik

doi:10.3390/rs13081484

Abstract

The coupling of rapid warming and wetland degradation on the Tibetan Plateau has motivated studies of climate influence on wetland change in the region. These studies typically examine large, topographically homogeneous regions, whereas conservation efforts sometimes require fine-grained information in rugged terrain. This study addresses topographically constrained wetlands on the Eastern Tibetan, where herders report significant wetland degradation. We used Landsat images to examine changes in wetland areas and Sentinel-1 SAR images to investigate water level and vegetation structure. We also analyzed trends in precipitation, growing season length, and reference evapotranspiration in weather station records. Snow cover and the vegetation growing season were quantified using MODIS observations. We analyzed estimates of actual evapotranspiration using the Atmosphere-Land Exchange Inverse model (ALEXI) and the Simplified Surface Energy Balance model (SSEBop). Satellite-informed analyses failed to confirm herders’ accounts of reduced wetland function, as no coherent trends were found in wetland area, water content, or vegetation structure. An analysis of meteorological records did indicate a warming-induced increase in reference evapotranspiration, and both meteorological records and satellites suggest that the growing season had lengthened, potentially increasing water demand and driving wetland change. The discrepancies between the satellite data and local observations pointed to temporal, spatial, and epistemological gaps in combining scientific data with empirical evidence in understanding wetland change on the Tibetan Plateau.

Highlights

The alpine wetlands of the Eastern Tibetan Plateau are of high conservation value for multiple reasons
The hydrological cycles of alpine wetlands in the Eastern Tibetan Plateau affect water security in densely populated floodplains in East and Southeast Asia since the wetlands constitute the headwaters of the Yangtze, Mekong, and Yellow rivers [2]
We explored the use of publicly available satellite image and climate records to remotely assess temporal trends in small, fragmented wetlands in a rugged mountainous region of the Eastern Tibetan Plateau, where local herders have reported a widespread decline in wetlands and pasture over the past 30 years

Summary

Introduction

The alpine wetlands of the Eastern Tibetan Plateau are of high conservation value for multiple reasons. The Eastern Tibetan Plateau is one of China’s last places characterized by largely intact ecosystems [1], such that the wetlands of this region may harbor endemic species and characteristic ecosystems not found in other regions. The hydrological cycles of alpine wetlands in the Eastern Tibetan Plateau affect water security in densely populated floodplains in East and Southeast Asia since the wetlands constitute the headwaters of the Yangtze, Mekong, and Yellow rivers [2]. The coupling of rapid climate change and wetland degradation on the Tibetan Plateau since the 1970s has drawn attention from researchers and conservationists. Climate change is expected to be more significant in high altitude regions in general, and the Tibetan

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