Synthesizing a Regional Territorial Evapotranspiration Dataset for Northern China

Weiwei Zhu,Nana Yan,Abdelrazek Elnashar,Linjiang Wang,Hongwei Zeng,Bingfang Wu

doi:10.3390/rs13061076

Abstract

As a vital role in the processes of the energy balance and hydrological cycles, actual evapotranspiration (ET) is relevant to many agricultural, ecological and water resource management studies. The available global or regional ET products provide ET estimations with various temporal ranges, spatial resolutions and calculation methods (algorithms, inputs and parameterization, etc.), leading to varying degrees of introduced uncertainty. Northern China is the main agriculturally productive region supporting the whole country; thus, understanding the spatial and temporal changes in ET is essential to ensure water resource and food security. We developed a synthesis ET dataset for Northern China at a 1000 m spatial resolution, with a monthly temporal resolution covering a period ranging from 1982 to 2017, using an in-depth assessment of several ET products. Specifically, assessments were performed using in situ measured ET from eddy covariance (EC) observation towers at the site-pixel scale over interannual months under the conditions of different land cover types, climatic zones and elevation levels to select the most optimally performing ET products to be used in the synthesized ET dataset. Eight indicators under 21 conditions were involved in the assessment sheet, while the statistics of the different ET product occurrences and corresponding ratios were analyzed to select the best-performing ET products to build the synthesis ET dataset using the weighted mean method. The weights were determined by the Taylor skill score (TSS), calculated with ET products and EC ET observation data. Based on the assessment results, the Penman–Monteith–Leuning (PML_v2), ETWatch and Operational Simplified Surface Energy Balance (SSEBop) datasets were selected for implementation in the synthesis ET dataset from 2003 to 2017, while Global Land Evaporation Amsterdam Model (GLEAM) v3.3a, complementary relationship (CR) ET, and Numerical Terradynamic Simulation Group (NTSG) datasets were chosen for the synthesis ET dataset from 1982 to 2002. The weighted mean synthesized results from 2003 to 2017 performed well when compared to the in situ measured EC ET values produced under all of the above conditions, while the synthesized results from 1982 to 2002 performed well through the water balance method in Heihe River Basin. These results can provide more stable ET estimations for Northern China, which can contribute to relevant agricultural, ecological and hydrological studies.

Highlights

Evapotranspiration (ET) is a process in which liquid or solid water is converted into water vapor after precipitation reaches the ground during the hydrological cycle and returns to the atmosphere [1,2,3]; it mainly involves surface water, soil water evaporation and vegetation canopy transpiration [4,5]
This study provided an effective method for assessing ET products with in situ measured flux eddy covariance (EC) ET across different months and various underlying surface types to develop a long-term synthesis ET dataset for Northern China
The comprehensive assessment was carried out under different conditions, namely, over interannual months and across different land cover types, climatic zones and elevation levels, and the latter three conditions were stratified into three classes

Summary

Introduction

Evapotranspiration (ET) is a process in which liquid or solid water is converted into water vapor after precipitation reaches the ground during the hydrological cycle and returns to the atmosphere [1,2,3]; it mainly involves surface water, soil water evaporation and vegetation canopy transpiration [4,5]. Northern China has a complicated terrain and a large east–west span and is the country’s main wheat and corn production area [31]. Food security in this region is primarily dependent on water resource security, because most of the cultivated land is irrigated [32]. In situ ground measurement methods of ET using observational instruments, such as Bowen ratio (BR) systems [34], eddy covariance (EC) systems [35] and lysimeters [36], are widely applied across relevant research areas

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Discussion

Conclusion