The ecohydrology of the soil-vegetation system restoration in arid zones: a review

Arid zones, which cover approximately 40 percent of the earth's land surface, support complicated and widely varied ecological systems. As such, arid zones are an important composition of the global terrestrial ecosystem, and water is the key and abiotic lim-ited factor in ecosystem-driven processes in these areas. Ecohydrology is a new cross discipline that provides, in an objective and comprehensive manner, novel ideas and approaches to the evaluation of the interaction and feedback mechanisms involved in the soil-vegetation systems in arid zones. In addition, ecohydrology provides a theoretical basis of ecological restoration that is cen-tered on vegetation construction. In this paper, long-term monitoring and local observations in the transitional belt between a de-sertified steppe and a steppified desert at the Shapotou Desert Research and Experiment Station, Tengger Desert, in northern China, were evaluated. The primary achievements and related research progress regarding ecohydrology in arid zones were analyzed and summarized, as a keystone, and the response of soil ecohydrological processes to the changes in the species composition, structure, and function of sandland vegetation was discussed. Meanwhile, the long-term ecological effects and mechanism of regulation of vegetation on soil habitat and on water-cycling were considered. As a vital participant in the ecohydrological processes of soil-vegetation systems, the studies on biological soil crusts was also summarized, and related theoretical models of restoration based on the water balance was reviewed.

Effects of soil-plant system change on ecohydrology during revegetation for mobile dune stabilization, Chinese arid desert

Soil-plant systems play an important role in sand fixing and surface protection in the arid desert of China. This study examines the ecohydrological responses after a soil-plant system change for mobile dune stabilization by using a series of soil hydrological experiments and ecological investigation. The study results showed that decades of succession of soil-plant system has endangered the stability of the protection system. With the accumulated water and nutrient, a bio-logical system develops in a thinner and thinner surface soil. Redistribution of precipitation has changed completely in the ecosystem. In 3-15 mm of soil, a high capacity of crust water retention ultimately limits most rainfall from infiltrating below 10-20 cm deep. When that takes place, lower plants begin to compete for water with grasses and shrubs. A drought horizon forms in 20-500 cm depth with shrub transpiration. Artificial shrubs with deep roots obtain hardly rainfall supply and are gradually eliminated from the protection system. All changes in water environment affect the structure and func-tion and stabilization of whole protection systems. It is necessary to establish a relatively stable water environment by managing the soil-plant system for constructing a sustainable protective system in arid desert.

Long Term Soil and Water Assessment Tool (SWAT) Calibration from an Ecohydrology Perspective

The performance on prediction by mathematical models which represent the conceived image of a system such as hydrology is oftentimes represented through calibration and verification processes. Oftentimes a best fit between observed and predicted flows is obtained through correlation coefficient (R2) and the Nash Sutcliffe model efficiency (NSE) by minimizing the average Root Mean Square Error (RMSE) of the observed versus simulated flows. However, these days, a new paradigm is emerging wherein accounting for the flow variability for the protection of freshwater biodiversity and maintenance of goods and services that rivers provide is paramount. Therefore, from an ecohydrology perspective, it is not clear if the existing method of model calibration meets the needs of the riverine ecosystem at its best. Thus, this study investigates and proposes a methodology using entropy theory to gage the calibration of Soil and Water Assessment Tool (SWAT) from an ecohydrology perspective characterized by the natural flow-regime paradigm: Indicators of Hydrologic Alteration.

Water yield and biomass production for on a eucalypt-dominated Mediterranean catchment under different climate scenarios

Worldwide,forests are vital in the regulation of the water cycle regulation and in water balance allocation.Knowledge of ecohydrological responses of production forests is essential to support management strategies,especially where water is already scarce.Shifting climatological patterns are expected to impact thermopluviometric regimes,water cycle components,hydrological responses,and plant physiology,evapotranspiration rates,crop productivity and land management operations.This work(1)assessed the impacts of different predicted climate conditions on water yield;(2)inferred the impacts of climate change on biomass production on eucalypt-to-eucalypt succes sion.To this end,the widely accepted Soil and Water Assessment Tool(SWAT)was run with the RCA,HIRHAM5 and RACMO climate models for two emission scenarios(RCP 4.5 and8.5).Three 12-year periods were considered to simulate tree growth under coppice regime.The results revealed an overall reduction in streamflow and water yield in the catchment in line with the projected reduction in total annual precipitation.Moreover,HIRHAM5 and RACMO models forecast a slight shift in seasonal streamflow of up to 2 months(for2024-2048)in line with the projected increase in precipitation from May to September.For biomass production,the extreme climate model(RCA)and severe emis sion scenario(RCP 8.5)predicted a decrease up to 46%.However,in the less extreme and more-correlated(with actual catchment climate conditions)climate models(RACMO and HIRHAM5)and in the less extreme emission scenario(RCP 4.5),biomass production increased(up to 20%),and the growth cycle was slightly reduced.SWAT was proven to be a valuable tool to assess climate change impacts on a eucalypt-dominated catchment and is a suitable decision-support tool for forest managers.

Effects of vegetation types on soil water dynamics during vegetation restoration in the Mu Us Sandy Land, northwestern China

The arid and semi-arid northwestern China has been undergoing ecological degradation and the efforts to reverse the ecological degradation have been undertaken for many years. Some shifting dunes have been fixed and the vegetation has been partially recovered in certain areas and the Mu Us Sandy Land in the Ordos Plateau is an example of the success. The present study attempts to reveal the relationships between the vegetation restoration and ecohydrology in the Mu Us Sandy Land. We continuously measured soil water content at 10-min intervals under three vegetation types(i.e., shifting dune, shrub-dominated community, and herb-dominated community) in the Mu Us Sandy Land from April 2012 to October 2013. The results show the infiltration coefficient increased with increased rainfall amount and eventually reached a stable value. Infiltration coefficients were 0.91, 0.64, and 0.74 in the shifting dune, in the shrub-dominated community, and in the herb-dominated community, respectively. Cumulative infiltration and soil texture are two vital factors affecting the depths of rainfall penetration. Only rainfall events larger than 35.0 mm could recharge soil water at the 60–80 cm layer in the herb-dominated community. Our results imply that the expected forward succession of restored vegetation may be destined to deterioration after reaching the climax simply because of following two facts:(1) soil water is mainly retained at shallower layer and(2) plant fine roots mainly distribute in deeper layer in the herb-dominated community.

Variations and controlling factors of vegetation dynamics on the Qingzang Plateau of China over the recent 20 years

The impacts of climate change and human activities on vegetation dynamics have attracted wide attention,espe-cially in sensitive and vulnerable areas such as the Qingzang Plateau of China.In this region,a series of ecological restoration projects have been launched while the effectiveness of these projects requires evaluation and further improvements.Remote sensing with high temporal resolution and spatial coverage is an effective way for the vegetation dynamics research in this region.In this study,the spatial and temporal distribution of climate factors and vegetation coverage as well as the influencing factors such as air temperature,precipitation,land use,slope,slope direction,soil and altitude were analyzed.The geographical detector was used to analyze the influence of climate factors on vegetation coverage and the interaction among factors in different eco-geographical regions.The results showed that:1)the average values from the 20 years of normalized difference vegetation index(NDVI)decreased gradually from southeast(>0.61)to northwest(0.12).The overall average of NDVI increased 0.02 per year from 1998 to 2018 and the impact factors varied among different eco-geographical regions;2)some con-trolling factors showed nonlinear enhancement such as altitude and slope;3)land use was an important factor affecting the distribution of vegetation especially in humid,semi-arid and arid areas,but the impacts of elevation and temperature were stronger than land use types in semi-humid and humid areas.The design and construc-tion of ecological protection and restoration projects on the Qingzang Plateau required scientific and detailed demonstration as well as monitoring and evaluation.In addition,new tools and theories were also needed in the selection of ecosystem restoration strategies.Based on the findings,this study also provides suggestions for the sustainable ecological restoration on the Qingzang Plateau.

Vegetation phenology and its ecohydrological implications from individual to global scales

The Earth is experiencing unprecedented climate change.Vegetation phenology has already showed strong response to the global warming,which alters mass and energy fluxes on terrestrial ecosystems.With technology and method developments in remote sensing,computer science and citizen science,many recent phenology-related studies have been focused on macrophenology.In this perspective,we 1)reviewed the responses of vegetation phenology to climate change and its impacts on carbon cycling,and reported that the effect of shifted phenology on the terrestrial carbon fluxes is substantially different between spring and autumn;2)elaborated how vegetation phenology affects ecohydrological processes at different scales,and further listed the key issues for each scale,i.e.,focusing on seasonal effect,local feedbacks and regional vapor transport for individual,watershed and global respectively);3)envisioned the potentials to improve current hydrological models by coupling vegetation phenology-related processes,in combining with machine learning,deep learning and scale transformation methods.We propose that comprehensive understanding of climate-macrophenology-hydrology interactions are essential and urgently needed for enhancing our understanding of the ecosystem response and its role in hydrological cycle under future climate change.

Changes in rainfall partitioning caused by the replacement of native dry forests of Lithraea molleoides by exotic plantations of Pinus elliottii in the dry Chaco mountain forests, central Argentina

The replacement of native dry forests by commercial(exotic)tree plantations could generate changes in rainfall partitioning,which further affects the water cycle.In this study,we determined(i)the rainfall partitioning into interception,throughfall and stemflow,(ii)the role of rainfall event size on rainfall partitioning,(iii)the pH of water channelized as throughfall and stemflow,and(iv)the runoff in Lithraea molleoides(a native species)and Pinus elliottii(an exotic species)stands in the dry Chaco mountain forests,central Argentina.On average,interception,throughfall and stemflow accounted for 19.3%,79.5%and 1.2%of the gross rainfall in L.molleoides stand,and 32.6%,66.7%and 0.7%of the gross rainfall in P.elliottii stand,respectively.Amounts of interception,throughfall and stemflow presented positive linear relationships with the increment of rainfall event size for both tree species(P<0.01 in all cases).Percentages of interception,throughfall and stemflow were all related to the increment of rainfall event size,showing different patterns.With increasing rainfall event size,interception exponentially decreased,throughfall asymptotically increased and stemflow linearly increased.Both P.elliottii and L.molleoides stands presented significant differences in the pH values of water channelized as throughfall(6.3 vs.6.7,respectively;P<0.01)and stemflow(4.5 vs.5.8,respectively;P<0.01).Runoff occupied only 0.3%of the gross rainfall in P.elliottii stand and was zero in L.molleoides stand.Our results showed that the native species L.molleoides presented 13.6%more water reaching the topsoil(i.e.,net rainfall;net rainfall=gross rainfall-interception-runoff)than the exotic species P.elliottii.This study improves our understanding of the effects of native vegetation replacement on the local water balance in the dry forest ecosystems.

Distribution Pattern of Trees in a Hydrological Gradient below the Paraná-Paraguay River Confluence

Riparian and riverine aquatic plant species have evolved within the context of flowing water habitats for which the flooding and droughts are the forcing factors that shape the community features, either through a positive or negative effect on the ecosystem’s function, according to the timing, frequency and magnitude of such events. In the Paraná floodplain landscape, topographic position is a crude indicator of the position along the complex gradient, but it also includes information about flood/drought periods and trees’ resilience to extreme hydrological phases. We present the occurrence of major tree species in riparian forests of the Paraná River on islands of different topographies in a section of the Paraná River downstream from the confluence with the Paraguay River. Our results suggest that each tree species had a preferred position in the topographic gradient, sites where the observed counts were more frequent. This trees species were more frequent between 2 and 8 m in the topographic position and were affected by 5 and 202 hydrosedimentologic pulses between 1949 and 1999. We suggest that knowledge of the distribution curves of the vegetation species present can help draw possible future scenarios of the river landscape. Future engineering works to alter the hydrological dynamics of Paraná should pay more attention to the distribution of riparian forests because they are indicators of changes at the landscape level and they are the support for the wildlife of the river.

Rainfall partitioning by desert shrubs in arid regions

We measured the rainfall partitioning among throughfall, stemflow, and interception by desert shrubs in an arid region of China, and analyzed the influence of rainfall and canopy characteristics on this partitioning and its ecohydrological effects. The percent-ages of total rainfall accounted for by throughfall, stemflow, and interception ranged from 78.85±2.78 percent to 86.29±5.07 per-cent, from 5.50±3.73 percent to 8.47±4.19 percent, and from 7.54±2.36 percent to 15.95±4.70 percent, respectively, for the four shrubs in our study (Haloxylon ammodendron, Elaeagnus angustifolia, Tamarix ramosissima, and Nitraria sphaerocarpa). Rain-fall was significantly linearly correlated with throughfall, stemflow, and interception (P < 0.0001). The throughfall, stemflow, and interception percentages were logarithmically related to total rainfall (P < 0.01), but were quadratically related to the maximum 1-hour rainfall intensity (P < 0.01). The throughfall and stemflow percentages increased significantly with increasing values of the rainfall characteristics, whereas the interception percentage generally decreased (except for average wind speed, air temperature, and canopy evaporation). Regression analysis suggested that the stemflow percentage increased significantly with increasing crown length, number of branches, and branch angle (R2 = 0.92, P < 0.001). The interception percentage increased significantly with increasing LAI (leaf area index) and crown length, but decreased with increasing branch angle (R2 = 0.96, P < 0.001). The mean funnelling percentages for the four shrubs ranged from 30.27±4.86 percent to 164.37±6.41 percent of the bulk precipitation. Much of the precipitation was funnelled toward the basal area of the stem, confirming that shrub stemflow conserved in deep soil layers may be an available moisture source to support plant survival and growth under arid conditions.

Hydrologic Monitoring Plan of the Brazilian Water Producer/PCJ Project

Both Ecosystem-based Adaptation (EbA) and Payment for Ecosystem Services (PES) have a wide range of strategies that include different economic instruments for nature conservation. Although the generation and maintenance of payment for hydrologic ecosystem services (Water-PES) is expanding in Brazil, there are difficulties in the implementation of projects. Due to the complexity and non-linearity of the hydrological processes, also affecting both EbA and Water-PES goals, monitoring quali-quantitative aspects of streams have been here addressed as a useful management tool. This study presents the Hydrological Monitoring Plan (HMP) of the Water Producer/PCJ project, operating between 2009-2014, in order to: 1) evaluate the impact of project actions under water quali-quantitative aspects;and 2) promote the incorporation of HMP’s elements in water resources management. HMP of the Water Producer/PCJ project has been implemented following the conditions for efficiency (baseline, long-term scale compatible with the actions of the project, in the experimental and reference watersheds). In addition, HMP is being implemented from upstream to downstream in catchments with areas ranging from 17 to 130 km2. This proposal favors the quantification and valuation of hydrologic services that could be assessed by ecohydrologic monitoring and modeling. Thus, we look forward to the consolidation of the Brazilian information system of water resources, the reduction of modeling uncertainties and integrated assessment of the consequences of land-use/land-cover change that strongly impact goals of EbA and Water-PES initiatives.

Nutrient enrichment driven by canopy rainfall redistribution:Mechanism,quantification,and pattern

Vegetation canopies intercept and redistribute rainfall into throughfall and stemflow,which transfer substantial amounts of elements into the soil,influencing soil microbial community,plant survival,and plant community succession.Despite advancements in ecohydrological research,the implication of nutrient enrichment resulting from this redistribution of rainfall by canopies remains largely unexplored.To address this gap,we conducted a systematic review of 1020 papers published between 2000 and 2022,gathering data on nutrient concentration and enrichment for critical ions(including K^(+),Na^(+),Ca^(2+),Mg^(2+),NH_(4)^(+),Cl^(-),NO_(3)^(-)and SO_(4)^(2-))from the Web of Science and Chinese Knowledge Infrastructure databases.We aimed to synthesize the mechanisms,quantify the enrichments,and identify global patterns of nutrient enrichment in stemflow and throughfall across climate zones,and vegetation types and ecosystems.The results of this study indicate that stemflow exhibits,on average,2.1times greater ion concentration(6.13 mg L^(-1))compared to throughfall.In particular,among the investigated ions,SO_(4)^(2-)(12.45and 6.32 mg L^(-1))for stemflow and throughfall,respectively,and Cl^(-)(9.21 and 4.81 mg L^(-1))exhibit the highest concentrations in both rainfall redistribution components,while K^(+)(13.7 and 5.8)and Mg^(2+)(5.6 and 2.8)have the highest enrichment factors.Across climate zones,throughfall and stemflow show the lowest ion concentrations but the highest enrichment factors in extremely humid regions.Along the temperature gradient,ion concentrations are the highest in cold climates with no clear patterns observed for enrichment factors with increasing temperature.In addition,shrubs,conifers,mixed forests,and artificial ecosystems demonstrate enrichment factors 1.1 to 3.0 times greater than those of trees,broad-leaved plants,pure forests,and natural ecosystems.These findings emphasize the need for increased attentions to artificial ecosystems,such as urban and agricultural ecosystems,which often received limited research focus,especially regarding shrubs and conifers exhibiting stronger nutrients enrichment capabilities.Future investigations should integrate soil moisture analysis to better understand the impact of rainfall redistribution on the nutrient enrichment processes,patterns,and nutrient balance in global terrestrial ecosystems.

Ecohydrological change mechanism of a rainfed revegetation ecosystem at southeastern edge of Tengger desert,Northwest China

Study is made on a 45 km-long artificial ecosystem without irrigation in Tengger desert on the basis of long-term ecological monitoring and ecohydrological fundamentals.Changes in water allocation, utilization, cycle and balance patterns in more than 40-year evolution of the soil-plant system are analyzed. The formation of a drought horizon in shrub rhizosphere and its effect, ecohydrological function of the crust and its effect on the soil-plant system change are discussed. Driven by water self-regulation and water stress, the soil-plant system is going to develop towards the steppe desert to ensure more effective use and optimum collocation of water resource.

Ecohydrological advances and applications in plant–water relations research:a review

Aims The field of ecohydrology is providing new theoretical frameworks and methodological approaches for understanding the complex interactions and feedbacks between vegetation and hydrologic flows at multiple scales.Here we review some of the major scientific and technological advances in ecohydrology as related to understanding the mechanisms by which plant–water relations influence water fluxes at ecosystem,watershed and landscape scales.Important Findings We identify several cross-cutting themes related to the role of plant–water relations in the ecohydrological literature,including the contrasting dynamics of water-limited and water-abundant ecosystems,transferring information about water fluxes across scales,understanding spatiotemporal heterogeneity and complexity,ecohydrological triggers associated with threshold behavior and shifts between alternative stable states and the need for long-term data sets at multiple scales.We then show how these themes are embedded within three key research areas where improved understanding of the linkages between plant–water relations and the hydrologic cycle have led to important advances in the field of ecohydrology:upscaling water fluxes from the leaf to the watershed and landscape,effects of plant–soil interactions on soil moisture dynamics and controls exerted by plant water use patterns and mechanisms on streamflow regime.In particular,we highlight several pressing environmental challenges facing society today where ecohydrology can contribute to the scientific knowledge for developing sound management and policy solutions.We conclude by identifying key challenges and opportunities for advancing contributions of plant–water relations research to ecohydrology in the future.

Effect of rainfall interannual variability on the biomass and soil water distribution in a semiarid shrub community

The dynamics of biomass and soil moisture in semiarid land is driven by both the current rainfall and the ecosystem memory.Based on a meta-analysis of existing experiments,an ecosystem model was used to calculate the effect of the rainfall interannual variability on the pattern of biomass and soil moisture in a shrub community.It was found that rainfall interannual variability enabled shrubs to be more competitive than grasses,and to maintain the dominant role over a longer time.The rainfall interannual variability resulted in complex soil moisture dynamics.The soil water recharge in wet years alternated with discharge in drought years.

Development of ecohydrological assessment tool and its application

The development of Hydro-Informatic Modelling System (HIMS) provides an integrated platform for hydrological simulation. To extend the application of HIMS, an ecohydrological modeling system named ecohydrological assessment tool (EcoHAT) has been developed. Integrating parameter-management tools, RS (remote sensing) inversion tools, module-design tools and GIS analysis tools, the EcoHAT provides an integrated tool to simulate ecohydrological processes on regional scale, which develops a new method on sustainable use of water. EcoHAT has been applied to several case studies, such as, the Yellow River Basin, the acid deposition area in Guizhou province and the riparian catchment of Guanting reservoir in Beijing. Results prove that EcoHAT can efficiently simulate and analysis the ecohydrological processes on regional scale and provide technical support to integrated water resources management on basin scale.

Feedbacks between vegetation restoration and local precipitation over the Loess Plateau in China

The implementation of large-scale vegetation restoration over the Chinese Loess Plateau has achieved clear improvements in vegetation fraction,as evidenced by large areas of slopes and plains being restored to grassland or forest.However,such large-scale vegetation restoration has altered land-atmosphere exchanges of water and energy,as the land surface characteristics have changed.These variations could affect regional climate,especially local precipitation.Quantitatively evaluating this feedback is an important scientific question in hydrometeorology.This study constructs a coupled land-atmosphere model incorporating vegetation dynamics,and analyzes the spatio-temporal changes of different land use types and land surface parameters over the Loess Plateau.By considering the impacts of vegetation restoration on the water-energy cycle and on land-atmosphere interactions,we quantified the feedback effect of vegetation restoration on local precipitation across the Loess Plateau,and discussed the important underlying processes.To achieve a quantitative evaluation,we designed two simulation experiments,comprising a real scenario with vegetation restoration and a hypothetical scenario without vegetation restoration.These enabled a comparison and analysis of the net impact of vegetation restoration on local precipitation.The results show that vegetation restoration had a positive effect on local precipitation over the Loess Plateau.Observations show that precipitation on the Loess Plateau increased significantly,at a rate of 7.84 mm yr^(-2),from 2000 to 2015.The simulations show that the contribution of large-scale vegetation restoration to the precipitation increase was about 37.4%,while external atmospheric circulation changes beyond the Loess Plateau contributed the other 62.6%.The average annual precipitation under the vegetation restoration scenario over the Loess Plateau was 12.4%higher than that under the scenario without vegetation restoration.The above research results have important theoretical and practical significance for the ecological protection and optimal development of the Loess Plateau,as well as the sustainable management of vegetation restoration.

中国生态水文学发展趋势与重点方向

In recent decades, the ecohydrology discipline was developed to provide theoretical and technical foundations for the protection and restoration of complex ecological systems(e.g., mountains, rivers, forests, farmlands, and lakes), and to further ecological civilization construction and green development in China. In this study, the progress and challenges of the ecohydrology discipline are elaborated, and the future development directions are proposed according to international scientific frontiers and national ecological civilization construction demands. Overall, the main discipline directions are to develop new ecohydrological monitoring methods, to comprehensively understand ecohydrological mechanisms and their basic theories, to promote integration of multi-scale and multi-variable models by considering both terrestrial and aquatic ecosystems, and to encourage multidisciplinary integration, particularly with the social sciences. Furthermore, the future research interests in China include: combining multi-source information, constructing comprehensive monitoring systems, studying spatiotemporal patterns of key ecohydrological variables and their variation characteristics, developing integrated models of ecological, hydrological, and economic processes, estimating their uncertainty;and conducting interdisciplinary studies that include the natural and social sciences. The application prospects in China are further explored for a variety of ecosystems, including forests, grasslands, rivers, lakes, wetlands, farmlands, and cities. This study will provide a reference to support the development of the ecohydrology discipline in China, and will provide a solid theoretical and technical foundation for the implementation of national ecological civilization construction.

Fingerprinting sediment sources in a typical karst catchment of southwest China

Due to the complex hydrogeological conditions in karst regions,it is difficult to measure sediment source contributions at a catchment scale directly.The objective of this study was to quantify the relative contributions of sediment sources and their temporal variability in a karst catchment in southwest China.Karst depressions can trap eroded sediment similar to a dam or reservoir and,thus,are representative and typical test beds for identifying sediment sources in karst regions.Three sediment cores were taken from a karst depression,58 soil samples from three potential sediment sources were collected,and 18 soil properties were analyzed.The relative contributions of cropland,forestland,and fissure or crack soils were calculated using a multivariate mixing model.The fingerprinting results demonstrated that the cropland was the main sediment source in karst catchment.Specifically,according to the mean sediment contributions of the three deposited sediment cores,the sediment contribution from cropland topsoil was 69.3%,varying from 46.9%to 92.3%,and forestland soil and crack soil accounted for 8.6%and 22.1%of the sediment yield,and varying from 2.8%to 16.5%and 4.8%-36.6%,respectively.This result indicated that great attention should be paid when using only a single core to quantify sediment provenance.Due to the deposited sediment was generally disturbed as cropland in the karst depression,the area that has not been disturbed in recent decades in depression was more appropriate to trace sediment sources in karst catchment.To the best of our knowledge,this study was the first to quantify the contributions of sediment sources in the karst catchment of southwest China.This study provides valuable information and a preliminary reference for applying a composite fingerprinting technique to quantify sediment sources in karst catchments.

Modeling the crop transpiration using an optimality-based approach

Evapotranspiration constitutes more than 80% of the long-term water balance in Northern China.In this area,crop transpiration due to large areas of agriculture and irrigation is responsible for the majority of evapotranspiration.A model for crop transpiration is therefore essential for estimating the agricultural water consumption and understanding its feedback to the environment.However,most existing hydrological models usually calculate transpiration by relying on parameter calibration against local observations,and do not take into account crop feedback to the ambient environment.This study presents an optimality-based ecohydrology model that couples an ecological hypothesis,the photosynthetic process,stomatal movement,water balance,root water uptake and crop senescence,with the aim of predicting crop characteristics,CO2 assimilation and water balance based only on given meteorological data.Field experiments were conducted in the Weishan Irrigation District of Northern China to evaluate performance of the model.Agreement between simulation and measurement was achieved for CO2 assimilation,evapotranspiration and soil moisture content.The vegetation optimality was proven valid for crops and the model was applicable for both C3 and C4 plants.Due to the simple scheme of the optimality-based approach as well as its capability for modeling dynamic interactions between crops and the water cycle without prior vegetation information,this methodology is potentially useful to couple with the distributed hydrological model for application at the watershed scale.