Evaluation of Global soil moisture products over the Tibetan Plateau in Humid and Semiarid Climates

Tangtang Zhang, Key laboratory of Land Surface Process and Climate Change in Cold and Arid Regions, Chinese Academy of Sciences, Lanzhou, China;Department of Civil and Environmental Engineering, University of California, Los Angeles, California, USA;Pingliang Land Surface Process & Severe Weather Research Station, CAS, Pingliang, Gansu, China

Mekonnen Gebremichael, Department of Civil and Environmental Engineering, University of California, Los Angeles, California, USA

Xin Ma, Key laboratory of Land Surface Process and Climate Change in Cold and Arid Regions, Chinese Academy of Sciences, Lanzhou, China

Qun Du, State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China

Jun Wen, Key Laboratory of Plateau Atmosphere and Environment, Sichuan Province, College of Atmospheric Sciences, Chengdu University of Information Technology, Chengdu, China

Abstract
Accurate soil moisture data products are essential for implementing the food, energy, and water nexus approach. This study evaluates the accuracy of three globally available soil moisture data products, namely, (1) the satellite-based remote sensing product known as the Essential Climate Variable (ECV) which is a new product combining passive and active microwave measurements, (2) the global land surface simulation known as the Global Land Data Assimilation System (GLDAS) driven by catchment model (referred to as “GLDAS1”), and (3) GLDAS driven by Noah model (referred to as “GLDAS2”). The study region is the Tibetan Plateau in China, characterized by high-elevation plateau and cold climate. The evaluation was made by comparison against a network of in-situ soil moisture measuring stations in two contrasting climates: the Maqu region (humid, elevation range 3430 – 3750 m.a.s.l), and the Naqu region (semiarid, elevation range 4100 – 6500 m.a.s.l). Results show that the observed soil moisture fields at both sites strong seasonal cycle. Both the ECV and GLDAS2 simulations capture well the temporal dynamics in observed soil moisture fields, at both sites. In terms of actual magnitudes, both ECV and GLDAS2 reproduced the average soil moisture at the Naqu site. However, they both underestimated the soil moisture at the Maqu site by 31% and 24%, at Naqu site by 20% and less than 5%. The GLDAS1 product, on the other hand, gives a constant value, and totally fails to capture the seasonal cycle at both sites. The performances of ECV and GLDAS2 is encouraging, however, the source of the bias at the humid site needs to be investigated further. The poor performance of GLDAS1 indicates that caution must be exercised in selecting appropriate land surface models.

Keywords
Soil moisture; ECV; GLDAS; Tibetan Plateau

Cite this paper
Tangtang Zhang, Mekonnen Gebremichael, Xin Ma, Qun Du, Jun Wen, Evaluation of Global soil moisture products over the Tibetan Plateau in Humid and Semiarid Climates , SCIREA Journal of Geosciences. Volume 6, Issue 3, June 2022 | PP. 69-81. 10.54647/geosciences17214

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