Interdependent Dynamics of LAI-Albedo across the Roofing Landscapes: Mongolian and Tibetan Plateaus

Li Tian,Jiquan Chen,Changliang Shao

doi:10.3390/rs10071159

Abstract

The Mongolian Plateau (MP) and Tibetan Plateau (TP) have experienced higher-than-global average warming in recent decades, resulting in many significant changes in ecosystem structure and function. Among them are the leaf area index (LAI) and albedo, which play a fundamental role in understanding many causes and consequences of land surface processes and climate. Here, we focused on the spatiotemporal changes of LAI, albedo, and their spatiotemporal relationships on the two roofing landscapes in Eurasia. Based on the MODIS products, we investigated the spatiotemporal changes of albedo(VIS, NIR and SHO) and LAI from 2000 through 2016. We found that there existed a general negative logarithmic relationship between LAI and three measures of albedo on both plateaus. No significant relationship was found for LAI-albedoNIR on the TP, due to more complex land surface canopy characteristics affected by the NIR reflection there. During 2000–2016, overall, annual mean LAI increased significantly by 119.40 × 103 km2 on the MP and by 28.35 × 103 km2 on the TP, while the decreased areas for annual mean albedoVIS were 585.59 × 103 km2 and 235.73 × 103 km2 on the MP and TP, respectively. More importantly, the LAI-albedo relationships varied substantially across the space and over time, with mismatches found in some parts of the landscapes. Substantial additional efforts with observational and/or experimental investigations are needed to explore the underlying mechanisms responsible for these relationships, including the influences of vegetation characteristics and disturbances.

Highlights

Vegetation greening up across global terrestrial surfaces has been widely recognized as a sound indicator for understanding fundamental changes in ecosystem functions and their feedback to the regional/global climate [1,2]
On the Mongolian Plateau (MP), the Eurasian steppe includes meadow, meadow steppe, typical steppe, desert steppe, and desert from the southeast (i.e., Inner Mongolia) to the north (Mongolia) before it reaches the desert (Figure 1a), which is coupled with a decrease in leaf area index (LAI) (Figure 1b) and increasing albedoSHO (Figure 1c) along the same gradient
Because we focused on the changes in grassland vegetation type for the two plateaus, the value of LAI focused on a very narrow frequency range for both plateaus; comparing two plateaus, the Tibetan Plateau (TP) showed a stronger level of skewedness for annual LAI and albedoSHO (Figure 1d,e)

Summary

Introduction

Vegetation greening up across global terrestrial surfaces has been widely recognized as a sound indicator for understanding fundamental changes in ecosystem functions and their feedback to the regional/global climate [1,2]. Recent studies have suggested positive albedo feedbacks with increased cooling of the atmosphere due to higher evapotranspiration that is associated with the changes in leaf area and temperature differences between the land surface and the atmosphere [9,13,14] It appears that the changes in leaf area, its spatiotemporal distributions, and the warming/cooling of the atmosphere are key processes for understanding the significance of albedo in time and space, including its role in modeling biophysical processes such as the thawing of frozen soil, deforestation, and vegetation cover that are crucial for modeling ecosystem dynamics at landscape, regional, and global scales [12]

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