Spatiotemporal Changes of Reference Evapotranspiration in Mongolia during 1980–2006

Wenjun Yu,Ren Li,Tonghua Wu,Yanhui Qin,Tianye Wang,Weizhen Wang,Xiaofan Zhu,Weihua Wang

doi:10.1155/2016/9586896

Abstract

Reference evapotranspiration (RET) plays an important role in the terrestrial hydrological cycle. Applying the Penman-Monteith method, the RET over Mongolia was estimated from 1980 to 2006. The changing trends and magnitude of RET were detected by the Mann-Kendall test and Theil-Sen’s slope methods. Meanwhile, aridity indices were estimated using two different indices. The impacts of meteorological variables on RET were assessed through sensitive analysis by comparing the resulting RETs from artificially disturbed meteorological variables. The results indicated that the RET for 16 stations in Mongolia showed an increasing trend, particularly in the center and south. The calculated RET was higher than precipitation, which means severe droughts in Mongolia. The spatial patterns of RET are significantly influenced by climatic conditions as well as characteristics of the underlying surface (e.g., elevation and vegetation). The mean annual RET decreased from the south to the north, owing to sparse vegetation in the south of Mongolia. The sensitivity analysis revealed that the changes of RET were strongly affected by air temperature and relative humidity.

Highlights

Evapotranspiration is used to describe the water cycle part of water loss from land surface into the atmosphere by the processes of both transpiration and evaporation, which plays an important role in the energy exchange processes between land and atmosphere
The Reference evapotranspiration (RET) was calculated by the FAO P-M method in Mongolia from 1980 to 2006
The trend changes of RET for 16 stations on annual and seasonal scales were detected by nonparametric Mann-Kendall trend test and Theil-Sen’s slope, respectively

Summary

Introduction

Evapotranspiration is used to describe the water cycle part of water loss from land surface into the atmosphere by the processes of both transpiration and evaporation, which plays an important role in the energy exchange processes between land and atmosphere. Reference evapotranspiration (RET) is defined as the atmospheric evaporation demand on a reference surface, which is a hypothetical grass reference crop with a height of 0.12 m, fixed surface resistance of 70 s/m, and an albedo of 0.23 [1]. The RET assessment is the effective basis for estimating water demands of agricultural irrigation. As reported in previous studies [2, 3], there is a complementary relationship between RET and actual evapotranspiration. It is necessary to provide accurate determination of RET for agricultural water management

Methods

Results

Conclusion