Modelling the effects of climate change on transpiration and evaporation in natural and constructed grasslands in the semi-arid Loess Plateau, China
Introduction
Evapotranspiration (ET) is an essential component of the soil-plant-atmosphere continuum (SPAC) system (Sprenger et al., 2017; Tello-García et al., 2020), and plays a crucial role as the driving force for hydrological cycling and energy balance in terrestrial ecosystems (Fisher et al., 2017). ET consists of two parts, namely vegetation transpiration (T) and soil evaporation (E). T is an important part of soil water consumption, and is regarded as productive water loss, because it is involved in essential plant physiological processes, and is thus closely associated with biomass production. In contrast, E is generally considered as non-productive water loss, since it is lost directly from the soil (Aouade et al., 2016; Unkovich et al., 2018). Therefore, quantifying T and E, and subsequently promoting the transformation from E to T without increasing the total amount of ET, has become an important approach to improve water use efficiency, and has generated worldwide research interests, especially in arid and semi-arid ecosystems (Aouade et al., 2016; Graham et al., 2016).
Both T and E are controlled by the combined effects of multiple factors, such as climatic factors, topography characteristics, vegetation species, and anthropogenic management (Odongo et al., 2019; Sadeghi et al., 2017; Zhou et al., 2006). Of these, climate change is generally believed to significantly influence the total ET in terrestrial ecosystems, which has been widely investigated at large spatial scales, including global, regional, and catchment scales (Allen et al., 2015; Odongo et al., 2019; Tello-García et al., 2020). In addition, several studies have been conducted taking specific vegetation properties into account, to improve our understanding of the effects of climate change on ET dynamics under diverse vegetation conditions (Alemayehu et al., 2017; Siad et al., 2019), and have significantly enriched our knowledge in the field. However, ET partitioning is still not entirely understood, owing to the high heterogeneity of surface conditions (topographic characteristics, vegetation species, soil types, etc.) (Montaldo et al., 2020). In recent years, studies have also been conducted on the effects of climate change on ET at smaller scales, aiming to provide experimental data and theoretical guidance for accurate large-scale simulations, and to promote more effective vegetation management (Allen et al., 2015; Chebbi et al., 2018). Numerous studies, focused particularly on T processes, have consistently concluded that climate change-induced evaporative demand promotes T, and that their relationships can be expressed as linear or non-linear functions in different climatic areas (Ghimire et al., 2014; Grossiord et al., 2017). In contrast, limited research has been conducted on the effects of climate change on E (Chebbi et al., 2018; Montaldo et al., 2020), and consequently, different effects of climate change on T and E, remain poorly understood to date. In addition, the different changes of T and E will lead to different eco-hydrological effects (e.g., alterations in water use efficiency and soil water conditions). Therefore, the lack of systematic studies on E will also result in the inadequate understanding of them. Moreover, considering the manpower and time required for long-term field experiments, little research has been designed to systematically investigate the effects of climate in different hydrological years on T and E (Ferlan et al., 2016; Montaldo et al., 2020). However, such information provides the basis for developing policies for vegetation conservation and water resource management, which further necessitates in-depth research on T and E under changing climatic conditions.
The Loess Plateau (6.4 × 105 km2) situated in northwest China is well-known for its severe soil erosion, which is considered to be caused by the combined effects of loose soil, intensive rainfall, and low vegetation coverage (Feng et al., 2018; Li et al., 2016; Zheng, 2006). During the past decades, the soil erosion has caused serious land degradation, and therefore, greatly hindered the agricultural production and ecosystem restoration (Feng et al., 2018; Zhou et al., 2006). In order to mitigate the effects of soil erosion and land degradation, measures of the ‘Engineering construction’ (Li et al., 2016) and the ‘Comprehensive erosion control’ (Shi and Shao, 2000) have been implemented in 1950s and 1960s, respectively. Furthermore, the Chinese central government launched the 'Grain to Green' project in 1999 to improve the vegetation cover and remediate ecological functions (Liu et al., 2019; Liu and Liu, 2018). Constructed vegetation, including trees and grass, significantly altered hydrological processes through ET, and greatly alleviated soil loss, as expected (Liu and Liu, 2018). However, it also had some negative impacts on the local ecosystems and the environment, such as soil desiccation due to excessive water uptake from deep soil layers by the roots and low survival rate of vegetation due to water deficit (Feng et al., 2016). These effects, which appeared to be the result of an imbalance between vegetation water demand and soil water supply, have already seriously hindered sustainable development of local ecosystems (Liu et al., 2019; Feng et al., 2016). Furthermore, the climatic trend of lower precipitation and higher temperature in the Loess Plateau also exacerbates this imbalance, which is highly detrimental to vegetation growth (Chebbi et al., 2018; Unkovich et al., 2018), especially in conditions of extreme drought (Allen et al., 2015; Raz-Yaseef et al., 2010; Tello-García et al., 2020). Hence, there is an urgent need to identify and compare the responses of T and E to the changing climate, under natural and constructed vegetation conditions, which would be pivotal for the selection of constructed vegetation species, improvement of their survival rates, and ecosystem restoration (Chebbi et al., 2018; Unkovich et al., 2018).
Nowadays, several approaches including water or energy balance theories (Kool et al., 2014), sap flow technologies (Chebbi et al., 2018), eddy-covariance measurements (Aouade et al., 2016), remote sensing technologies (Liu et al., 2017), and modellings (Chattaraj et al., 2014; Nosetto et al., 2012) are available to investigate the response of T or E to changes in climate. Of them, modellings showed strong applicability and flexibility in producing T and E dynamics at diverse temporal and spatial scales for various vegetation types, and were thus widely used (Aggarwal et al., 2017; Chattaraj et al., 2014). These relevant studies have, as yet, mainly been conducted in farmlands (Chattaraj et al., 2014), whereas have seldom been performed in grasslands. Besides, research comparing natural and constructed grasslands is relatively lacking. However, because of the relatively lower water consumption than tree species and advantages in being used as feed for livestock, grasslands have been highly recommended and are thus widely distributed in the Loess Plateau. Therefore, the eco-hydrological effects caused by different responses of their T and E to diverse climatic conditions should also be paid full attention to.
The present study was undertaken taking these points into consideration. A two-year field experiment was conducted in a natural (Imperata cylindrica plot, natural restoration without any anthropogenic management) and two typical constructed grasslands (Pennisetum giganteum and Medicago sativa plots, which were harvested and stored as feed for livestock after the growing season), in the semi-arid Loess Plateau, to establish models for simulating their T and E processes under different climatic scenarios (a combination of climate characteristics in both future periods and different hydrological years). The main objectives of this study were to: (1) identify the different effects of climate change on T and E based on ET partitioning, (2) investigate the eco-hydrological effects (water consumption strategies and soil water conditions) resulting from the different responses of T and E to the changing climate, and (3) compare the above characteristics in natural and constructed grasslands. The results of this study will improve our understanding of the hydrological processes occurring in the grasslands and their responses to climate change, and provide theoretical and practical guidance for grass species selection, grassland ecosystem conservation, and water resource management in the Loess Plateau.
Section snippets
Site description and experimental plot selection
Field experiments were conducted in the Nanxiaohegou Basin (107°30′–107°37′E and 35°41′–35°44′N, 1058–1450 m a.s.l.), Qingyang city, Gansu province in central Loess Plateau of China (Fig. 1). The basin was selected as a typical small-scale basin (36.5 km2) by the Yellow River Conservancy Committee in 1951 because of its typicality and representativeness in terrain characteristics and vegetation types. This region has a warm temperate continental climate, with characteristic hot and rainy
Results of parameter sensitivity analysis and calibration
The modified Morris screen method was used to calculate the specific values of sensitivity indices for soil hydraulic and vegetation physiological parameters (Table 1), and the results showed that the pore size distribution parameter (0–40 cm) was the most sensitive among all parameters, presenting a high sensitivity. Soil saturated moisture contents (0–40 and 40–100 cm), parameter of pore size distribution (40–100 cm), field water capacity, and all vegetation parameters were sensitive,
Reasons for the different responses of the grass species to climate change
Previous studies conducted worldwide have shown that natural and constructed grasslands have different ET characteristics (Gu et al., 2018; Huang et al., 2019; Li et al., 2019). An important reason was that T and E responded differently to their environmental controlling elements (Li et al., 2019), namely evaporative demand and water supply (Jiao et al., 2018; Montaldo et al., 2020). In reality, both T and E in many semi-arid areas have experienced a suppression due to the increasingly warm and
Conclusion
In this study, the effects of climate change on transpiration and evaporation of a natural (Imperata cylindrica plot) and two constructed grasslands (Pennisetum giganteum and Medicago sativa plots) in the Loess Plateau were investigated using the Hydrus-1D model based on pre-set climate scenarios. The results revealed that transpiration responses in all three grasslands were greater than that of evaporation under changing climate, and their transpiration response degrees could be ranked from
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.
Acknowledgments
We sincerely thank the academic editor and anonymous reviewers for their insightful and constructive comments. We also thank the staff at Xifeng Experiment Station of Soil and Water Conservation as well as Xianghua Feng, Ling Zhang, Zhixu Zhang, Chong Fu, and Shaona Wang from Xi’an University of Technology, China, and instructor Sun, Mingming Guo, Hongliang Kang, and Qianhua Shi from Northwest A&F University, China, and Guangchen Chu from the Institute of Earth Environment, Chinese Academy of
References (81)
- et al.
Modelling soil water balance and root water uptake in cotton grown under different soil conservation practices in the Indo-Gangetic Plain
Agric. Ecosyst. Environ.
(2017) - et al.
Combining stable isotopes, Eddy Covariance system and meteorological measurements for partitioning evapotranspiration, of winter wheat, into soil evaporation and plant transpiration in a semi-arid region
Agric. Water Manag.
(2016) - et al.
How climate and vegetation type influence evapotranspiration and water use efficiency in Canadian forest, peatland and grassland ecosystems
Agric. For. Meteorol.
(2012) - et al.
Predicting the impact of climate change on water requirement of wheat in the semi-arid Indo-Gangetic Plains of India
Agric. Ecosyst. Environ.
(2014) - et al.
Analysis of evapotranspiration components of a rainfed olive orchard during three contrasting years in a semi-arid climate
Agric. For. Meteorol.
(2018) - et al.
Effects of landscape restoration on soil water storage and water use in the Loess Plateau Region, China
For. Ecol. Manage.
(2010) - et al.
The differences of water balance components of caragana korshinkii grown in homogeneous and layered soils in the desert-loess plateau transition zone
J. Arid Environ.
(2013) - et al.
Carbon and water flux patterns of a drought-prone mid-succession ecosystem developed on abandoned karst grassland
Agric. Ecosyst. Environ.
(2016) - et al.
Transpiration and canopy conductance of two contrasting forest types in the Lesser Himalaya of Central Nepal
Agric. For. Meteorol.
(2014) - et al.
Effects of agricultural management on measurements, prediction, and partitioning of evapotranspiration in irrigated grasslands
Agric. Water Manag.
(2016)
Partitioning evapotranspiration using an optimized satellite-based ET model across biomes
Agric. For. Meteorol.
Hydroclimatic response of evapotranspiration partitioning to prolonged droughts in semiarid grassland
J. Hydrol.
Natural grasslands maintain soil water sustainability better than planted grasslands in arid areas
Agric. Ecosyst. Environ.
Spatial variations in soil-water carrying capacity of three typical revegetation species on the Loess Plateau
China. Agric. Ecosyst. Environ.
Evapotranspiration partitioning and its implications for plant water use strategy: evidence from a black locust plantation in the semi-arid Loess Plateau, China
For. Ecol. Manage.
A review of approaches for evapotranspiration partitioning
Agric. For. Meteorol.
A simple and objective method to partition evapotranspiration into transpiration and evaporation at eddy-covariance sites
Agric. For. Meteorol.
Modeling the effects of parameter optimization on three bioretention tanks using the HYDRUS-1D model
J. Environ. Manage.
Biophysical effect of conversion from croplands to grasslands in water-limited temperate regions of China
Sci. Total Environ.
Seasonal groundwater contribution to crop-water use assessed with lysimeter observations and model simulations
J. Hydrol.
Fixed and variable components of evapotranspiration in a Mediterranean wild-olive - grass landscape mosaic
Agric. For. Meteorol.
River flow forecasting through conceptual models part I - a discussion of principles
J. Hydrol.
The hydrologic consequences of land cover change in central Argentina
Agric. Ecosyst. Environ.
Impact of land use and land cover transitions and climate on evapotranspiration in the Lake Naivasha Basin, Kenya
Sci. Total Environ.
Comparison of hourly and daily reference crop evapotranspiration equations across seasons and climate zones in Australia
Agric. Water Manag.
Experimental studies on the effects of the “Conversion of Cropland to Grassland Program” on the water budget and evapotranspiration in a semi-arid steppe in Inner Mongolia
China. J. Hydrol.
Characteristics of soil evaporation, plant transpiration and water budget of Nitraria dune in the arid Northwest China
Agric. For. Meteorol.
Effects of spatial variations in soil evaporation caused by tree shading on water flux partitioning in a semi-arid pine forest
Agric. For. Meteorol.
Vulnerability of crops and native grasses to summer drying in the U.S. Southern Great Plains
Agric. Ecosyst. Environ.
Rosetta v1.2: A computer program for estimating soil hydraulic parameters with hierarchical pedotransfer functions
J. Hydrol.
Soil and water loss from the Loess Plateau in China
J. Arid Environ.
A review of coupled hydrologic and crop growth models
Agric. Water Manag.
Drought- and heat-induced shifts in vegetation composition impact biomass production and water use of alpine grasslands
Environ. Exp. Bot.
Seasonal evapotranspiration, energy fluxes and turbulence variance characteristics of a Mediterranean coastal grassland
Agric. For. Meteorol.
Field measurements of bare soil evaporation and crop transpiration, and transpiration efficiency, for rainfed grain crops in Australia – a review
Agric. Water Manag.
Modelling the effects of land cover and climate change on soil water partitioning in a boreal headwater catchment
J. Hydrol.
Characteristics of fine root system and water uptake in a triploid Populus tomentosa plantation in the North China Plain: implications for irrigation water management
Agric. Water Manag.
Comparison of three methods to develop pedotransfer functions for the saturated water content and field water capacity in permafrost region
Cold Reg. Sci. Technol.
Interannual variation of evapotranspiration from forest and grassland ecosystems in western canada in relation to drought
Agric. For. Meteorol.
Effect of vegetation changes on soil Erosion on the Loess Plateau
Pedosphere
Cited by (31)
Partitioning and controlling factors of evapotranspiration: 1. Hydrological modeling constrained with isotope-based water balance decoupling
2024, Agriculture, Ecosystems and EnvironmentEstimation of water budget components and its driving factors analysis in arid grassland
2024, Science of the Total Environment