Study on the Variation Trend of Potential Evapotranspiration in the Three-River Headwaters Region in China Over the Past 20 years

Xiaohang Wen,Yuqing Ruan,Bin Xie,Siqiong Luo,Chao Wang,Shaobo Zhang,Xiaoguang Sun,Linxi Meng,Wenqi Pan,Bangjun Cao,Maoshan Li,Zihan Zhang

doi:10.3389/feart.2020.582742

Abstract

To study the variation trend of potential evapotranspiration (PET) in the Three-River Headwaters (TRH) region of the Qinghai-Tibet Plateau in China, we use 2-m temperature and surface pressure observation data from 14 meteorological weather stations in the TRH region, and the surface PET is calculated by the Penman-Monteith formula. The global land surface data assimilation system (GLDAS) from 2000 to 2018 were used to compare and verify the accuracy and applicability of the calculated PET in the THR region. The results show that in the past 20 years, the PET of 14 weather stations in the TRH region has shown an increasing trend, with annual averaged growth rate of 1.4±1.2 mm·a-1, and the spatial distribution of the annual variation rate of PET has obvious difference. PET is higher in the eastern area of TRH region, and lower in the western area. The drought in this area increased from southeast to northwest, which was consistent with the spatial distribution of precipitation. The aridity index K has fluctuated and increased begore 2015, but there was a sudden change in 2018, and the aridity index K in the TRH began to decline after 2018, and the climate changed from dry to wet.

Highlights

The Qinghai-Tibetan Plateau (QTP) and the adjacent high mountain regions of the Himalayas play an important role in the global climate dynamic through its impact on the Asian monsoon system, which in turn is impacting the water resources of this extremely vulnerable region (Krause et al, 2010)
The wind speed of Global Land Data Assimilation System (GLDAS) is above 4 m·s−1 in all stations, while the most observation of wind speed is below 2.5 m·s−1, except WDL, XH, TTH, and MD (4.1, 3.6, 3.6, and 2.9 m·s−1, respectively)
Due to the lack of observed solar radiation data, it is difficult to analyze the changes of potential evapotranspiration (PET) caused by the radiation changes in the Three-River Headwaters (TRH) region

Summary

INTRODUCTION

The Qinghai-Tibetan Plateau (QTP) and the adjacent high mountain regions of the Himalayas play an important role in the global climate dynamic through its impact on the Asian monsoon system, which in turn is impacting the water resources of this extremely vulnerable region (Krause et al, 2010). Many researchers focus on the characteristics of climate change in the TRH Region, and found that the near surface temperature from meteorological stations has gradually increased in recent decades. Li et al (2012) used the evapotranspiration model to evaluate the annual average PET in alpine regions, analyzed the response of annual evapotranspiration to land use changes, and used the Vegetation Temperature Condition Index to modify the plant effective water coefficient (w). We use the precipitation and latent heat flux data of GLDAS to analyze the regional distribution characteristics of precipitation and PET in the TRH region from 2000 to 2018, and use the Manner-Kendall nonparametric test method (Libiseller and Grimvall, 2002; Yue and Wang, 2004) to evaluate the variation trend of PET, precipitation, and aridity index K. We use this empirical coefficient making the calculation results more applicable in the TRH region. n is the actual sunshine duration (h), and N is the maximum possible sunshine duration (h). σ is Stefan-Boltzmann constant for a day (4.903 × 10−9 MJ·K−4·m−2·d−1), Tmax,K and Tmin,K are the maximum and minimum 2-m air temperature (K)

RESULT

Findings

CONCLUSION AND DISCUSSION