Study on the variation in evapotranspiration in different period of the Genhe River Basin in China
Introduction
The evapotranspiration process is a key link in the hydrological cycle that links the atmospheric processes and land-surface processes of the climatic system. In contrast to precipitation, evapotranspiration is a process in which water vapor is transported from the surface to the atmosphere. As a core process of the climatic system, evapotranspiration closely links the hydrological cycle, the energy budget and the carbon cycle. Therefore, evapotranspiration studies are important to understand the changes in and effects of the climate and surface (Cammalleri et al., 2010; Vinukollu et al., 2011; Li, 2013). At the same time, the variation in and causes of evaporation have very important application value for the assessment of regional basin water resources, crop water requirements, production management, agricultural drought monitoring and ecological environmental problems (such as ecological water demand) (Liu et al., 2003).
Due to the special climate and environmental conditions in the cold temperate zone of high latitude, the region is less affected by human activities, and the eco-hydrological environment is relatively fragile. Evapotranspiration of water, soil and vegetation can reflect the climate change more truly (Li et al., 2019). Calanca et al. found that the actual evapotranspiration increased in the high altitude and the area south of the Alps but decreased in the low-altitude area in the northern foreland and the Alps (Calanca et al., 2006). Chen et al. analyzed multi-factor combinations that dominated the half-hour evapotranspiration of evergreen coniferous forests across three different climate regions in North America and found that temperature was the most critical to the change in evapotranspiration during the growing season (Chen et al., 2018). Findell et al. by developing and applying objective indicators based on physics, found that high evaporation increased the possibility of regional rainfall (Findell et al., 2011). The possibilities of experimentally determining evapotranspiration in the boreal forests of the permafrost zone are limited due to their inaccessibility; therefore, the determination of moisture consumption for evapotranspiration in these regions is performed by computational methods (Budagovsky, 1989; Bondarik et al., 1999; Karpechko et al., 2010). Previous studies on evapotranspiration mainly included studies on the composition and variation trend of global terrestrial evapotranspiration, the influence mechanism of evapotranspiration and its measurement (Jung et al., 2010; Zhang et al., 2016). However, the study area mainly focused on the basins of the warmer regions, such as the middle temperate zone, temperate zone and subtropical zone (Cammalleri et al., 2010). Little attention has been paid by scholars to the variation in and influencing factors of evapotranspiration in the basins of high-latitude and cold regions. In permafrost areas, evapotranspiration of soil, meadow, ice and snow and wetland water surface, etc., is an important factor involved in water circulation such as water vapor transport, precipitation, soil infiltration, surface runoff and underground runoff (Li et al., 2019). How meteorological factors affect evapotranspiration in permafrost areas, the variation trend of evapotranspiration in permafrost areas in different periods (growing season and freezing-thawing period) and the variation characteristics are all scientific questions to be solved. Due to the existence of complex eco-hydrological processes and fragile ecosystems, alpine regions are extremely vulnerable to damage and are difficult to repair when they are affected by regional climate change and human activities. Therefore, it is of great significance to study evapotranspiration in high latitude and cold regions in order to study the response of climate change to water cycle and the eco-hydrological process in permafrost regions.
The Genhe River Basin is located on the western slope of the northern part of the Greater Xingan Mountains (Fig. 1). It is located in the permafrost region. Most of the basin is within the temperate, cold and humid forest climatic zone of the Greater Xingan Mountains. The southwestern part of the Genhe River Basin is a temperate and semi-humid region with a combination of animal husbandry and agriculture. There are complex ecological and hydrological processes and fragile ecosystems in the Genhe River Basin. In recent years, under the influence of climate warming and human activities (He et al., 2014), ecological environmental changes have complicated evapotranspiration in the basin. From the south to the north, the Genhe River Basin is gradually transformed from medium-temperature grassland to coniferous forest. Therefore, considering the distribution of natural ecosystems and the uniqueness of geographical location, it is of great significance to study the regional water cycle in the Genhe River Basin in high-latitude and cold regions. By analyzing the variation characteristics of evapotranspiration in the freezing and thawing period and the growing season from 1980 to 2017 in the Genhe River Basin, this paper aims to explore the key factors affecting evapotranspiration and reveal the variation characteristics and influence mechanism of evapotranspiration.
Section snippets
Data sources
The time series of meteorological data are from 1980 to 2017, and the data are from the National Meteorological Information Center (Central Meteorological Administration, 1979) (http://data.cma.cn/). The meteorological data set was obtained from the informatized files of the monthly reports submitted by the Inner Mongolia Autonomous Region, and was compiled based on the relevant regulations of the “Specifications for Surface Meteorological Observations”. For details, please refer to the
Data processing
We used the tessellation polygon method (Burn et al., 2002) to calculate the meteorological data distributions throughout the river basin. We generated tessellation polygons based on the locations of the three weather stations and the boundaries of the Genhe River Basin (Fig. 1). We then used the area of each polygon as a weight and calculated the weighted average precipitation throughout the basin.
Multiple linear regression analysis
The basic task of the multiple regression equation is to calculate the regression coefficient
Characteristics of evapotranspiration during the freezing-thawing periods in the Genhe River Basin
The monthly average evapotranspiration in the freezing-thawing period in the Genhe River Basin presented a “low-high-low” pattern as a whole, and the variation range was larger than that of the growing season. From April to September, evapotranspiration continued to grow and peaked in September. From September to October, the evapotranspiration decreased continuously and reached a lower value in October.
The monthly average evapotranspiration during the freezing and thawing period was 28.29 mm,
Discussion and conclusions
In different climatic zones, the factors affecting forest evapotranspiration vary widely. For example, in the tropical, subtropical and most temperate regions, the main factors affecting forest evapotranspiration are precipitation, temperature and solar radiation (Smith et al., 2013; Cristiano et al., 2015). In cold and temperate regions, in addition to precipitation, temperature and solar radiation, the freezing and thawing of permafrost is also an important factor affecting forest
CRediT authorship contribution statement
Xinqing Lu: Investigation, Data curation, Software, Writing - original draft, Writing - review & editing, Visualization. Chuanfu Zang: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Data curation, Writing - original draft, Writing - review & editing, Supervision, Project administration. Tamara Burenina: Validation, Visualization, Supervision.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This research was funded by the National Natural Science Foundation of China (31660233), the Strategic Priority Research Program of the Chinese Academy of Sciences, Grant No. XDA20060402, and the Natural Science Foundation of Inner Mongolia Autonomous Region of China, China (2015BS0401). We thank the Inner Mongolia Agricultural University for its support and help with this research. We also thank my other colleagues' valuable comments and suggestions that have helped improve the manuscript.
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