Local Water Cycle Research Articles

Physical Explanation for Paradoxical Climate Change in Semi-Arid Inland Eurasia Based on a Remodeled Precipitation Recycling Ratio and Clausius–Clapeyron Equation

Under global warming, the climate in semi-arid inland Eurasia (SAIE) has changed in an opposite manner, thereby seriously impacting the local ecological environment. However, the key influencing factors and physical mechanism remain inconclusive. In this paper, we remodel the precipitation recycling ratio (PRR) model to assess the contributions of moisture from different water vapor sources to local precipitation, analyze the characteristics of the PRR and precipitation in SAIE, and provide possible physical reasons based on the Clausius–Clapeyron equation. It is found that the PRR increased from 1970 to 2017 as the result of linear trend analysis, with obvious seasonality. Moreover, the component of precipitation contributed by locally evaporated moisture (Pl), and that contributed by advected moisture (Pa) as well as the total precipitation (P), increased during the past 48 years. In particular, the Pa, Pl, and P in autumn and winter all increased obviously during the past 20 years from the interdecadal change trend, as well as the PRR (Pl/P), which was opposite to the decrease in the total water vapor input I(Ω) in the horizontal direction. According to the Clausius–Clapeyron equation, one of the causes might be that global warming has accelerated the local water cycle and driven the increase in Pa, and the increase in atmospheric water holding capacity caused by global warming provides the power source. We suggest that the climate’s transformation from dry to wet in SAIE can only be temporary since SAIE is an inland area and the adjustment of atmospheric circulation did not lead to the increase in external water vapor.

Understanding Meteorological Changes Following Severe Defoliation during a Strong Hurricane Landfall: Insights from Hurricane Michael (2018)

Abstract Despite prompting persistent meteorological changes, severe defoliation following a tropical cyclone (TC) landfall has received relatively little attention and is largely overlooked within hurricane preparedness and recovery planning. Changes to near-track vegetation can modify evapotranspiration for months after tropical cyclone passage, thereby altering boundary layer moisture and energy fluxes that drive the local water cycle. This study seeks to understand potential spatial and temporal changes in defoliation-driven meteorological conditions using Hurricane Michael (2018) as a testbed. In this sensitivity study, two Weather Research and Forecasting (WRF) Model simulations, a normal-landscape and a post-TC scenario, are compared to determine how a defoliation scar placed along Michael’s path alters surface heat fluxes, temperature, relative humidity, and precipitation near the storm’s track. In the month following the foliage reduction, WRF resolves a 0.7°C 2-m temperature increase, with the greatest changes occurring at night. Meanwhile, the simulations produce changes to the sensible and latent heat fluxes of +8.3 and −13.9 W m−2, respectively, while average relative humidity decreases from 73% to 70.1%. Although the accumulated precipitation in the defoliated simulation was larger along a narrow corridor paralleling and downwind of the hurricane track, neither simulation satisfactorily replicated post-Michael precipitation patterns as recorded by NCEP Stage IV QPE, casting doubt as to whether the downwind enhancement was exclusively due to the defoliation scar. This sensitivity analysis provides insight into the types of changes that may be possible following rapid and widespread defoliation during a TC landfall.

Application of a Machine Learning Algorithm in Generating an Evapotranspiration Data Product From Coupled Thermal Infrared and Microwave Satellite Observations.

Land surface evapotranspiration (ET) is one of the main energy sources for atmospheric dynamics and a critical component of the local, regional, and global water cycles. Consequently, accurate measurement or estimation of ET is one of the most active topics in hydro-climatology research. With massive and spatially distributed observational data sets of land surface properties and environmental conditions being collected from the ground, airborne or space-borne platforms daily over the past few decades, many research teams have started to use big data science to advance the ET estimation methods. The Geostationary satellite Evapotranspiration and Drought (GET-D) product system was developed at the National Oceanic and Atmospheric Administration (NOAA) in 2016 to generate daily ET and drought maps operationally. The primary inputs of the current GET-D system are the thermal infrared (TIR) observations from NOAA GOES satellite series. Because of the cloud contamination to the TIR observations, the spatial coverage of the daily GET-D ET product has been severely impacted. Based on the most recent advances, we have tested a machine learning algorithm to estimate all-weather land surface temperature (LST) from TIR and microwave (MW) combined satellite observations. With the regression tree machine learning approach, we can combine the high accuracy and high spatial resolution of GOES TIR data with the better spatial coverage of passive microwave observations and LST simulations from a land surface model (LSM). The regression tree model combines the three LST data sources for both clear and cloudy days, which enables the GET-D system to derive an all-weather ET product. This paper reports how the all-weather LST and ET are generated in the upgraded GET-D system and provides an evaluation of these LST and ET estimates with ground measurements. The results demonstrate that the regression tree machine learning method is feasible and effective for generating daily ET under all weather conditions with satisfactory accuracy from the big volume of satellite observations.

Mechanisms of Reduced Mid‐Holocene Precipitation in Arid Central Asia as Simulated by PMIP3/4 Models

AbstractWe investigated the precipitation changes in mid‐latitude arid central Asia (ACA, including Central Asia and Xinjiang) and the related mechanisms in the mid‐Holocene using the output from the Paleoclimate Modeling Intercomparison Project phases 3 and 4 (PMIP3/4). The annual precipitation in ACA was decreased in the mid‐Holocene compared with the preindustrial period, consistent in direction with reconstruction records. Such change was mainly due to deficient winter and spring (December‐May) precipitation in the mid‐Holocene. The decrease in incoming solar radiation in the mid‐Holocene winter and spring caused stronger surface and tropospheric cooling in the northern low latitudes. It reduced the meridional temperature gradient in the troposphere, thereby weakening the westerly winds and related transport of water vapor. More importantly, the cooling weakened the local water cycle in ACA. Finally, the precipitation decreased over almost all of ACA. In the mid‐Holocene summer (June‐August), the meridional temperature gradient and related westerly winds were also reduced. It was mainly caused by stronger surface and tropospheric warming in the northern mid‐ to high latitudes. The stronger warming was due to increased summer incoming solar radiation in the mid‐Holocene. This process differed from that occurred in winter and spring. Therefore, the water vapor transport was weakened, and the summer precipitation was deficient in northern ACA. At the same time, strengthened descending motions contributed to the decrease in summer precipitation in most parts of Central Asia. On the contrary, intensified ascending motions increased summer precipitation in southeastern Xinjiang.

Informing Nature-based Climate Solutions for the United States with the best-available science.

Nature-based Climate Solutions (NbCS) are managed alterations to ecosystems designed to increase carbon sequestration or reduce greenhouse gas emissions. While they have growing public and private support, the realizable benefits and unintended consequences of NbCS are not well understood. At regional scales where policy decisions are often made, NbCS benefits are estimated from soil and tree survey data that can miss important carbon sources and sinks within an ecosystem, and do not reveal the biophysical impacts of NbCS for local water and energy cycles. The only direct observations of ecosystem-scale carbon fluxes, for example, by eddy covariance flux towers, have not yet been systematically assessed for what they can tell us about NbCS potentials, and state-of-the-art remote sensing products and land-surface models are not yet being widely used to inform NbCS policymaking or implementation. As a result, there is a critical mismatch between the point- and tree-scale data most often used to assess NbCS benefits and impacts, the ecosystem and landscape scales where NbCS projects are implemented, and the regional to continental scales most relevant to policymaking. Here, we propose a research agenda to confront these gaps using data and tools that have long been used to understand the mechanisms driving ecosystem carbon and energy cycling, but have not yet been widely applied to NbCS. We outline steps for creating robust NbCS assessments at both local to regional scales that are informed by ecosystem-scale observations, and which consider concurrent biophysical impacts, future climate feedbacks, and the need for equitable and inclusive NbCS implementation strategies. We contend that these research goals can largely be accomplished by shifting the scales at which pre-existing tools are applied and blended together, although we also highlight some opportunities for more radical shifts in approach.

Species and spatial differences in vegetation rainfall interception capacity: A synthesis and meta-analysis in China

Canopy interception is an important part of the water cycle, which ultimately affects the water budget by dissipating in the form of evaporation. The canopy interception rate (I) is a commonly used index to describe interception but is dynamic with rainfall conditions, which reduces comparability of results among different sites or vegetation types. While canopy storage capacity (I0) is relatively stable but is rarely used in previous studies. This study analyzed data from the existing literature to obtain an understanding of the measured and modeled values of I0 for the main vegetation types in China, then comprehensively assess the species and spatial differences of canopy interception capacity. The results showed that trees dominate intercepted precipitation in the southern region, while shrubs dominate intercepted precipitation in the north. The comprehensive interception capacity of vegetation in the southern region was generally higher than that in the north; however, changes in interception related to regional forestation policies may reverse this trend. The I value of single-species forest stand canopies, located primarily in southern humid regions, is generally larger than that of shrubs, which are generally located in northern arid regions. Within a given area, the actual I value of shrubs was greater than that of single-species forest stand, indicating shrubs have a greater influence on the local water cycle than trees where both exist. Variations in I and I0 were sensitive to meteorological factors and stand structure, which led to inconsistent results when evaluating vegetation canopy interception. Overall, this study quantifies and reviews studies on vegetation canopy interception in China and suggests that the current structural characteristics of the northern shrub land may be unfavorable for water conservation in the northern arid region. How to adjust vegetation to maintain regional water supply and demand balance is a problem that needs to be solved in the future.

Determination of impervious area of Saroor Nagar Watershed of Telangana using spectral indices, MLC, and machine learning (SVM) techniques.

Urbanization affects the local wind and water cycle by changing the natural surface and atmospheric conditions, which further changes the local climate and climate system. Assessment of built-up-area changes in a rapidly growing urban area within a short time is a prime factor for administrators for better environmental assessment and sustainable development of urban areas. Traditional survey approaches, on the other hand, are unable to meet the demand for rapid urban land management development, and there is a pressing need to develop new methods to address the limitations of existing ones. This study compares various urban spectral indices to other existing approaches in order to determine which index provides a better representation of the impervious area in the urban watershed. Landsat 8 OLI (Operational Land Imager) satellite images acquired on 15 March 2014 and 31 March 2020 are used in the present study. Indices, namely Modified Built-up Index (MBUI), SwiRed Index (SwiRed), and Enhanced Built-up and Bareness Index (EBBI), were utilized to extract impervious areas. Thresholding of indices is done by comparing them with 1000 reference points taken from Google Earth imagery of the respective years. The accuracy of the urban indices is assessed by comparing the results with high-resolution Google Earth Satellite Images. The impervious area is extracted from spectral indices and other remote sensing techniques such as maximum likelihood classification and support vector machine classification techniques. The overall accuracy of SVM, MLC, MBUI, EBBI, and SwiRed for the 2014 dataset was found to be 95.1%, 90.8%, 83.9%, 78.9%, and 87.3%, respectively, and the overall accuracy of SVM, MLC, MBUI, EBBI, and SwiRed was found to be 96%, 89.2%, 89.1%, 85.5%, and 92.6%, respectively. Impervious areas in the heterogeneous urban environment can be monitored in a better way and within lesser time by using spectral indices generated using Landsat 8 OLI (Operational Land Imager) satellite data.

What roles do architectural design and on-site water servicing technologies play in the water performance of residential infill?

More than half of new urban residential developments are planned as infill in Australia's major cities. This provides an unprecedented opportunity to use innovative design and technology to address urban water challenges such as flooding, reduced water security and related infrastructure and urban heat island issues. However, infill can have positive or negative water impacts, depending on architectural design and on-site water servicing technologies implemented. In this study we asked, “What influence does residential infill development have on the local urban water cycle?” and “What roles do architectural design and technologies play?” To answer these questions, a set of 196 design-technology configurations were developed by combining 28 architectural designs and 7 on-site water-servicing technology options. The configurations represent three cases: (i) existing (EX) or before infill, (ii) business-as-usual development (BAU), and (iii) alternative development (ALT). Using the Site-scale Urban Water Mass Balance Assessment (SUWMBA) model and a set of water performance indicators, the impact of configurations on the urban water cycle was quantified. The results showed BAU, on average, increases population density, stormwater discharge, and imported water by 98%, 44% and 85%, and decreases evapotranspiration and infiltration by 53% and 34%, compared to the EX conditions. More population density (141%) with lower impacts on the urban water cycle (21% and 64% increase for stormwater discharge and imported water, and 29% and 17% reduction in evapotranspiration and infiltration) can be achieved by appropriate integration of ALT designs and technologies. Architectural design has a greater influence on urban water flows than the implementation of on-site water servicing technologies. The results have a great implication for sustainable urban water management for managing the risks associated with pluvial flooding, water insecurity, and urban heat. It also highlights the underutilised role of architects and urban planners to address urban water issues.

Integrating Ecosystem Services Into Water Resource Management: An Indicator-Based Approach

Natural ecosystems are fundamental to local water cycles and the water ecosystem services that humans enjoy, such as water provision, outdoor recreation, and flood protection. However, integrating ecosystem services into water resources management requires that they be acknowledged, quantified, and communicated to decision-makers. We present an indicator framework that incorporates the supply of, and demand for, water ecosystem services. This provides an initial diagnostic for water resource managers and a mechanism for evaluating tradeoffs through future scenarios. Building on a risk assessment framework, we present a three-tiered indicator for measuring where demand exceeds the supply of services, addressing the scope (spatial extent), frequency, and amplitude for which objectives (service delivery) are not met. The Ecosystem Service Indicator is measured on a 0–100 scale, which encompasses none to total service delivery. We demonstrate the framework and its applicability to a variety of services and data sources (e.g., monitoring stations, statistical yearbooks, modeled datasets) from case studies in China and Southeast Asia. We evaluate the sensitivity of the indicator scores to varying levels data and three methods of calculation using a simulated test dataset. Our indicator framework is conceptually simple, robust, and flexible enough to offer a starting point for decision-makers and to accommodate the evolution and expansion of tools, models and data sources used to measure and evaluate the value of water ecosystem services.

Impact of landscape dams on river water cycle in urban and peri-urban areas in the Shiyang River Basin: Evidence obtained from hydrogen and oxygen isotopes

To meet the needs of human recreation and provide community amenities, landscape dams (i.e., water retaining structures for intercepting river water in cities and surrounding areas, which are mainly used to create an urban landscape environment) are built in urban and peri-urban areas worldwide. The construction of these dams, however, may adversely affect the local and regional water cycle. We collected water samples from 2015 to 2019 from different water bodies in urban and peri-urban areas traversing the middle and upper reaches of Shiyang River Basin in the arid area of Central Asia to analyze their isotopic characteristics. Meanwhile, field surveys as well as meteorological, hydrological, and remote-sensing data were added to evaluate the hydrologic effects of urban landscape dams on a watershed scale in an arid region with scarce water resources and fragile ecosystems. Isotopic values of landscape water were more enriched than that of natural river. The result of the evaporation loss ratio showed that the landscape water was 0–5% higher. Moreover, the cumulative effect of multiple landscape dams leads to a great loss of water resources in arid areas. The study also demonstrated that evaporation is a vital factor in causing change in the isotope composition of the landscape water in the Shiyang River Basin. The interaction between surface water and groundwater was frequent within the landscape dam area wherein groundwater was mainly recharged by surface water leakage. Sufficient attention should be given to the evaporation, leakage, local precipitation, and groundwater changes caused by the impoundment of landscape dams. Thus, the potentially adverse effects of urban landscape dams in arid regions should be highly considered in long-term water-resources sustainability planning.

Temporal variability in evapotranspiration and energy partitioning over a seasonally flooded scrub forest of the Brazilian Pantanal

Brazilian Pantanal is the largest seasonal wetland in the world and it plays an important role in regulating the local and global water cycle and energy balance. The Pantanal landscape consists of a mosaic of temporary and permanent aquatic habitats, floodable and non-floodable pastures, and forests; however, patterns of energy exchange are poorly understood, especially for seasonally flooded forests. Thus, the main objective of this research was to assess the variability of evapotranspiration (ET) and to evaluate biophysical controls on ET for a seasonally flooded scrub-forest. We used eddy covariance to measure latent (LE) and sensible (H) heat fluxes and linked both micrometeorological and remote sensing data to assess the connection between water dynamics and phenology. Our data suggest that 72% of the net radiation (Rn) was consumed by LE + H, even during the dry season, indicating that trees can access deep water when surface water is limiting. The decoupling factor (0.63 ± 0.08) suggests that the canopy is decoupled from the atmosphere and ET is essentially sensitive to Rn. The patterns of ET and vapor pressure deficit suggest that ET was more dependent on the Rn received and less dependent on stomatal control, but still exhibited a strong relationship with biotic factors such as enhanced vegetation index (EVI), which is sensitive to seasonal variations in leaf area index and canopy cover. Stomatal limitations of this seasonally flooded forest appear to be minimal, even in the dry season, presumably due to the relatively high-water table, the ability of trees to acquire subsurface water, and the predominance of secondary species with high rates of leaf gas exchange. These data indicate that seasonally flooded tropical forests of the Pantanal are consistent sources of water vapor to the atmosphere even during seasonal drought.

Development of Seawater Intrusion Vulnerability Assessment for Averaged Seasonality of Using Modified GALDIT Method

Climate change and anthropogenic activities are necessitating accurate diagnoses of seawater intrusion (SWI) to ensure the sustainable utilization of groundwater resources in coastal areas. Here, vulnerability to SWI was assessed by classifying the existing GALDIT into static parameters (groundwater occurrence (G), aquifer hydraulic conductivity (A), and distance from shore (D)) and dynamic parameters (height to groundwater-level above sea-level (L), impact of existing status of seawater intrusion (I), and aquifer thickness (T)). When assessing the vulnerability of SWI based on observational data (2010–2019), 10-year-averaged data of each month is used for GALDIT dynamic parameter for representing the seasonal characteristics of local water cycles. In addition, the parameter L is indicated by the data observed at the sea-level station adjacent to the groundwater level station. The existing GALDIT method has a range of scores that can be divided into quartiles to express the observed values. To sensitively reflect monthly changes in values, the range of scores is divided into deciles. The calculated GALDIT index showed that the most vulnerable month is September, due to relatively low groundwater level. The proposed method can be used to apply countermeasures to vulnerable coastal areas and build water resources management plan considering vulnerable seasons.

The role of dew and radiation fog inputs in the local water cycling of a temperate grassland during dry spells in central Europe

Abstract. During dry spells, non-rainfall water (hereafter NRW) mostly formed from dew and fog potentially plays an increasingly important role in temperate grassland ecosystems with ongoing global warming. Dew and radiation fog occur in combination during clear and calm nights, and both use ambient water vapor as a source. Research on the combined mechanisms involved in NRW inputs to ecosystems is rare, and distillation of water vapor from the soil as a NRW input pathway for dew formation has hardly been studied. Furthermore, eddy covariance (EC) measurements are associated with large uncertainties on clear, calm nights when dew and radiation fog occur. The aim of this paper is thus to use stable isotopes as tracers to investigate the different NRW input pathways into a temperate Swiss grassland at Chamau during dry spells in summer 2018. Stable isotopes provide additional information on the pathways from water vapor to liquid water (dew and fog) that cannot be measured otherwise. We measured the isotopic composition (δ18O, δ2H, and d=δ2H-8⋅δ18O) of ambient water vapor, NRW droplets on leaf surfaces, and soil moisture and combined them with EC and meteorological observations during one dew-only and two combined dew and radiation fog events. The ambient water vapor d was found to be strongly linked with local surface relative humidity (r=-0.94), highlighting the dominant role of local moisture as a source for ambient water vapor in the synoptic context of the studied dry spells. Detailed observations of the temporal evolution of the ambient water vapor and foliage NRW isotopic signals suggest two different NRW input pathways: (1) the downward pathway through the condensation of ambient water vapor and (2) the upward pathway through the distillation of water vapor from soil onto foliage. We employed a simple two-end-member mixing model using δ18O and δ2H to quantify the NRW inputs from these two different sources. With this approach, we found that distillation contributed 9 %–42 % to the total foliage NRW, which compares well with estimates derived from a near-surface vertical temperature gradient method proposed by Monteith in 1957. The dew and radiation fog potentially produced 0.17–0.54 mm d−1 NRW gain on foliage, thereby constituting a non-negligible water flux to the canopy, as compared to the evapotranspiration of 2.7 mm d−1. Our results thus underline the importance of NRW inputs to temperate grasslands during dry spells and reveal the complexity of the local water cycle in such conditions, including different pathways of dew and radiation fog water inputs.

Determining the Isotopic Composition of Surface Water Vapor Flux From High‐Frequency Observations Using Flux‐Gradient and Keeling Plot Methods

AbstractThe isotopic composition of surface water vapor flux (δE) is a quantity frequently used to investigate the local and regional water cycle. This study reports the results of a comparative evaluation of δE determined with the Keeling plot and the flux‐gradient methods using high‐frequency data collected at a cropland site and a lake site. Three regression models, ordinary least squares (OLS), York's solution (YS), and geometric mean regression, were tested with the Keeling plot method. Results show that concentration‐dependent field characterization of measurement errors can improve the estimation of the YS regression. For both sites, broad agreement was achieved among the Keeling plot method with YS regression, the Keeling plot method with OLS regression and the flux‐gradient method. For the lake site, OLS was the least biased of the three regression models in reference to the δE calculated by the Craig‐Gordon (CG) model of isotopic evaporation of open water. Good agreement was aslo achieved between the flux‐gradient method and the CG model at the lake site under open‐fetch conditions. A footprint analysis suggests that the Keeling method with OLS regression may be less sensitive to fetch than the flux‐gradient method.

Experimenting Transition to Sustainable Urban Drainage Systems—Identifying Constraints and Unintended Processes in a Tropical Highly Urbanized Watershed

Green Infrastructure promotes the use of natural functions and processes as potential solutions to reduce negative effects derived from anthropocentric interventions such as urbanization. In cities of Latin America, for example, the need for more nature-based infrastructure is evident due to its degree of urbanization and degradation of ecosystems, as well as the alteration of the local water cycle. In this study, an experimental approach for the implementation of a prototype is presented. The prototype consists of a gray-hybrid element for first flush bio-treatment and runoff detention, adapted to the existing stormwater sewer. The experiment took place in a highly urbanized watershed located in the Metropolitan Area of Costa Rica. The characteristics of the existing infrastructure in the study area at different scales were mapped and compared using the Urban Water System Transition Framework. Subsequently, preferences related to spatial locations and technologies were identified from different local decision-makers. Those insights were adopted to identify a potential area for the implementation of the prototype. The experiment consisted of the adaptation of the local sewer to act as a temporal reservoir to reduce the effects derived from rapid generation of stormwater runoff. Unexpected events, not considered initially in the design, are reported in this study as a means to identify the necessary adaptations of the methodology. Our study shows from an experimental learning-experience that the relation between different actors advocating for such technologies influences the implementation and operation of non-conventional technologies. Furthermore, the willingness of residents to modify their urban environments was found to be associated to their own perceptions about security and vandalism occurring in green spaces. The implementation of the prototype showed that both the hydraulic performance is relevant for considering it as a success, as well as the dynamics of the adapted element with the existing urban conditions. In consequence, those aspects should be carefully considered as the design factors of engineering elements when they are related to complex socio-ecological urban systems.

Constraining the Water Cycle Model of an Important Karstic Catchment in Southeast Tibetan Plateau Using Isotopic Tracers (2H, 18O, 3H, 222Rn)

Understanding the connectivity between surface water and groundwater is key to sound geo-hazard prevention and mitigation in a waterscape such as the Jiuzhaigou Natural World Heritage Site in the southeast Tibetan Plateau, China. In this study, we used environmental isotope tracers (2H, 18O 3H, and 222Rn) to constrain a water cycle model including confirming hydrological pathways, connectivity, and water source identification in the Jiuzhaigou catchments. We established the local meteoric water line (LMWL) based on the weekly precipitation isotope sampling of a precipitation station. We systematically collected water samples from various water bodies in the study area to design the local water cycle model. The regional water level and discharge changes at one month after the earthquake indicated that there was a hydraulic connection underground across the local water divide between the Rize (RZ) river in the west and Zechawa (ZCW) lake in the east by the δ18O and δ2H measurements. We employed an end-member mixing model to identify and quantify Jiuzhaigou runoff-generating sources and their contributions, and we found that the average contributions of precipitation and groundwater to the surface runoff in the catchments are about 30% and 70%, respectively. The two branches of the Shuzheng (SZ) trunk were recharged by 62 ± 19% from the ZCW lake and 38 ± 19% from the RZ river, which was consistent with the fractions calculated by the actual discharge volume. 222Rn mass balance analyses were employed to estimate the water exchange between groundwater and river, which further confirmed this estimate. 222Rn concentrations and 3H contents showed that the groundwater had a short residence time and it was moderate precipitation, thought the contribution of groundwater to the river was 70%, according to the different tracers. A three-dimensional conceptual model of the water cycle that integrated the regional hydrological and geological conditions was established for the catchments.

Influence of wetland reclamation on land-surface energy exchange and evapotranspiration in the Sanjiang plain, Northeast China

Sustained, large-scale wetland reclamation of paddy fields has been implemented since the 1960s in the Sanjiang Plain, northeast China. The investigation of the effect of this reclamation on land-surface energy exchange and the local water cycle is important for evaluating the stability of regional water resources for future agriculture development and ecological conservation. This study used the eddy covariance method to measure evapotranspiration (ET) and dominant energy transport fluxes for two sites, a typical natural marsh and a paddy field, during the growing seasons of 2017–2018. The two sites showed similar total available energy, whereas the ratio of the latent to net radiative energy (LE/Rn) was substantially lower in the marsh (0.49) compared to the paddy field (0.81), indicating a considerable increase in ET energy consumption after wetland reclamation. The average ET rates of the marsh and paddy field were 2.3 mm d−1 and 3.6 mm d−1, respectively, throughout the growing season. Both the high Priestley-Taylor coefficient (αeq, 1.21 ± 0.20) and the decoupling factor (Ω) suggested Rn-limited conditions in the paddy field, whereas the controlling factor in the marsh changed from vapor pressure deficit (VPD) to radiation energy over the season. The greatest difference in ET occurred in spring due to the alteration in the hydrological environment, including a lowered standing water table and elevated water temperature in the paddy site. The differences in physiology and canopy shape between the paddy and marsh plants contributed largely to enhanced ET during the summer months. In total, alterations in the hydrological environment, canopy structure and plant physiology contributed to the increase in ET, suggesting a synthetic influence of marsh reclamation on surface energy and ET processes. Wetland reclamation increased water consumption through ET and altered the seasonal pattern of the energy balance. This process will inevitably result in increased deficits in regional water resources in the Sanjiang Plain.

Effects of vegetation restoration on groundwater drought in the Loess Plateau, China

The Loess Plateau (LP) is a typical water-limited area. Since the revegetation plan started in 1999, the rapid growth of vegetation has not only significantly changed the local water cycle, but also probably affected regional groundwater drought. However, the effect of revegetation on groundwater drought remains largely unexplored. To this end, we isolated the groundwater anomalies from terrestrial water storage of the Gravity Recovery and Climate Experiment satellites and soil moisture of the Global Land Data Assimilation System, and further used the drought severity index to characterize groundwater drought. The evolution characteristics of groundwater drought in the LP were analyzed, and the effect of revegetation plan on groundwater drought were explored. Results indicated that: (1) Normalized Difference Vegetation Index (NDVI) during 2003 ~ 2015 in the LP was growing rapidly, meanwhile, groundwater storage significantly decreased (p < 0.01) and groundwater drought intensified in terms of its area and intensity; (2) compared with meteorological factors, NDVI is more strikingly correlated (p < 0.05) with groundwater drought on annual, seasonal and monthly scales, especially near the key areas of vegetation restoration; (3) the growth rate of vegetation is a dominant factor affecting groundwater drought in the LP, in which the groundwater consumption rate caused by vegetation dynamics in the significant area is higher than non-significant area. Our research results provide guidance for formulation scientific and sustainable ecological restoration policies in the LP, and also offer new ideas for the study of the relationship between vegetation and groundwater drought.

Water Quality of Freshwater Ecosystems in a Temperate Climate

Water is the substance that made life on Earth possible. It plays a key role in both the individual and population development of all species. Water is also a critical resource for humans as populations continue to grow and climate change affects global and local water cycles. Water is a factor limiting economic development in many regions of the world. Under these conditions, good water quality becomes an extremely important factor that determines its economic utility, including water supply, recreation, and agriculture. Proper water quality maintenance of freshwater ecosystems is also very important for preserving biodiversity. The quality of water depends on many factors, the most important of which are related to human impact on water ecosystems, especially the impact of various pollutants from municipal economy, industry and agriculture. Hydrotechnical changes, such as river damming, drainage processes and water transport between catchments also have a significant impact. Water quality is also dependent on the impact of natural conditions connected, e.g., with climate, catchment, water organisms and their interactions within the food-webs, etc. This Special Issue consists of fourteen original scientific papers concerning different problems associated with the water quality of freshwater ecosystems in a temperate climate. Most of the articles deal with the relations between water quality and the structure of ecosystem biocenoses. The conclusion of these articles confirms the fact that the deterioration of water quality has a direct impact on the quantitative and qualitative structure of biocenoses. This is accompanied by a decline in biodiversity and the disappearance of rare plant and animal species. They also draw attention to the particular importance of internal physical and chemical differentiation within the aquatic ecosystem, both in horizontal and vertical dimensions. The problem of ensuring proper ecological conditions and good quality of water in freshwater aquatic ecosystems is also raised, and methods for the restoration of water bodies are presented. The majority of the research presented in this Special Issue was carried out in Central Europe, and one of the papers concerns the area of West Africa—the edge of temperate climate zone.

An isotopic approach to partition evapotranspiration in a mixed deciduous forest

AbstractTranspiration (T) is perhaps the largest fluxes of water from the land surface to the atmosphere and is susceptible to changes in climate, land use and vegetation structure. However, predictions of future transpiration fluxes vary widely and are poorly constrained. Stable water isotopes can help expand our understanding of land–atmosphere water fluxes but are limited by a lack of observations and a poor understanding of how the isotopic composition of transpired vapour (δT) varies. Here, we present isotopic data of water vapour, terrestrial water and plant water from a deciduous forest to understand how vegetation affects water budgets and land–atmosphere water fluxes. We measured subdiurnal variations of δ18OT from three tree species and used water isotopes to partition T from evapotranspiration (ET) to quantify the role of vegetation in the local water cycle. We find that δ18OT deviated from isotopic steady‐state during the day but find no species‐specific patterns. The ratio of T to ET varied from 53% to 61% and was generally invariant during the day, indicating that diurnal evaporation and transpiration fluxes respond to similar atmospheric and micrometeorological conditions at this site. Finally, we compared the isotope‐inferred ratio of T to ET with results from another ET partitioning approach that uses eddy covariance and sap flux data. We find broad midday agreement between these two partitioning techniques, in particular, the absence of a diurnal cycle, which should encourage future ecohydrological isotope studies. Isotope‐inferred estimates of transpiration can inform land surface models and improve our understanding of land–atmosphere water fluxes.