How does temporal trend of reference evapotranspiration over the Tibetan Plateau change with elevation?

Abstract

Considerable efforts have been made to determine spatial and temporal patterns and the driving factors for reference evapotranspiration (RET) over the Tibetan Plateau (TP). Yet, how temporal trends of RET vary with respect to elevation is less clear. By using long-term daily meteorological records of 84 stations from 1971 to 2015, this study investigates the elevation dependence of RET trend over the TP. The results show that both increasing and decreasing trends of RET for the study period exist over the TP. The increasing and decreasing trends of RET have significant correlations with elevation, but the absolute changes become smaller in the higher elevation ranges at both the annual and seasonal scales. This is due to the elevation-dependent changes of climate factors, including vapour pressure deficit, mean air temperature, solar radiation, and wind speed, which demonstrate different relationships with elevation. A multivariate linear regression method was used to determine the contributions of the climate factors to RET changes, which indicates that vapour pressure deficit and solar radiation were the primary contributing factors to the increasing trend of RET and wind speed mainly influenced the decreasing trend. This elevation dependence of RET change-rate has important implications for water resources and ecosystems over the TP as well as other highelevation regions, where much of the globe's glacier and snow surfaces are stored. K E Y W O R D Sclimate change, Tibetan Plateau, elevation dependence, reference evapotranspiration

Drought characteristics and its elevation dependence in the Qinghai–Tibet plateau during the last half-century

“…All of them have caused the rapid wetter condition at highland regions. Together with global warming that glaciers in the QTP rapidly shrinks 43 , more streamflow was yielded in the region 25 . We concluded that the surrounding areas easily suffered from meteorological drought.…”

“…The Hurst index is used to predict the persistence of the time series. It can be computed by the method of rescaled range analysis (R/S) 25,26 . The following are the calculation steps:…”

“…In recent years, many scientists have focused on elevation-related climate change researches, confirming the evidences of the elevation-dependent warming 21 , 23 . Some have revealed that the warming trend displayed a slight decrease with elevation over 4,000 m 24 , Zhang et al 25 found smaller changes of PET in high-elevation areas at both annual and seasonal scales. Li et al 26 concluded an increasing tendency of the precipitation with increasing elevation in summer.…”

Effect of Elevation on Variation in Reference Evapotranspiration under Climate Change in Northwest China

“…The WS dominated the decrease in ET 0 at low elevations, while T dominated increasing ET 0 at high elevations. Zhang et al [46] found that increasing (decreasing) trends in ET 0 over the Tibetan Plateau and overall were negatively (positively) related to rising elevation over their study period , with the absolute trends in ET 0 becoming smaller along with rising elevation. Although there is growing evidence that the rate of warming is amplified with elevation, known as 'elevation-dependent warming' [47], especially in the Tibetan Plateau [25], elevation-dependent warming was insignificant in NWC; the relative contribution of warming to ET 0 variation was correlated to elevation (Figure 10).…”

Datasets of meteorological drought events and risks for the developing countries in Eurasia

“…The conditions of the reference evapotranspiration are unlikely to be met across large areas in some regions, such as the Tibetan Plateau (e.g. Zhang, Wang, & Chen, 2019), However, as was claimed by Allen et al (1998), the Penman-Monteith approach for estimating reference evapotranspiration does not fuel controversy and provides consistent and reliable information in different weather conditions and locations, which is why it is recommended by the Food and Agriculture Organization of the United Nations. Although the Penman-Monteith equation is more often recommended (Beguería et al, 2014) to estimate PET in the computation of SPEI, whether the Thornthwaite approach or Penman-Monteith equation is employed, similar estimates of PDSI seem to be produced (van der Schrier et al, 2011).…”