Changes In ET Research Articles

Vegetation Restoration Enhanced Canopy Interception and Soil Evaporation but Constrained Transpiration in Hekou–Longmen Section During 2000–2018

The quantitative assessment of the impact of vegetation restoration on evapotranspiration and its components is of great significance in developing sustainable ecological restoration strategies for water resources in a given region. In this study, we used the Priestley-Taylor Jet Pro-pulsion Laboratory (PT-JPL) to simulate the ET components in the Helong section (HLS) of the Yellow River basin. The effects of vegetation restoration on ET and its components, vegetation transpiration (Et), soil evaporation (Es), and canopy interception evaporation (Ei) were separated by manipulating model variables. Our findings are as follows: (1) The simulation results are compared with the ET calculated by water balance and the annual average ET of MODIS products. The R2 of the validation results are 0.61 and 0.78, respectively. The results show that the PT-JPL model tracks the change in ET in the HLS well. During 2000–2018, the ET, Ei, and Es increased at a rate of 1.33, 0.87, and 2.99 mm/a, respectively, while the Et decreased at a rate of 2.52 mm/a. (2) Vegetation restoration increased the annual ET in the region from 331.26 mm (vegetation-unchanged scenario) to 338.85 mm (vegetation change scenario) during the study period, an increase of 2.3%. (3) TMP (temperature) and VPD (vapor pressure deficit) were the dominant factors affecting ET changes in most areas of the HLS. In more than 37.2% of the HLS, TMP dominated the change affecting ET, and vapor pressure difference (VPD) dominated the area affecting ET in 30.5% of the HLS. Overall, the precipitation (PRE) and VPD were the main factors affecting ET changes. Compared with previous studies that directly explore the relationship between many influencing factors and ET results through correlation research methods, our study uses control variables to obtain results under two different scenarios and then performs difference analysis. This method can reduce the excessive interference of influencing factors other than vegetation changes on the research results. Our findings can provide strategic support for future water resource management and sustainable vegetation restoration in the HLS region.

A Distinct Role for Aerosol and GHG Forcing in Historical CMIP6 Evapotranspiration Trends

AbstractEvapotranspiration (ET) is crucial for the global water balance, plant growth, and freshwater availability. It connects the surface water balance with surface energy fluxes, making its accurate representation vital for climate projections. However, global climate models (GCMs) struggle with ET representation due to resolution limitations and simplified depictions of soil, plant, and atmosphere interactions. Simulated future changes in ET are uncertain, and the role of driving processes remain unclear. Here, we explore the utility of a simple and interpretable method to disentangle these varying drivers. We investigate the sensitivity of JJA ET to different atmospheric variables through simple linear models predicting ET from atmospheric variables only. The model consistently yields good results across GCMs or forcing scenarios. We find that GCMs have shown strong decreases and subsequent increases in ET over the historical period, related to changes in net surface radiation. For future climate projections, decreases in water availability compete with higher available surface radiation, making future projections uncertain. Single forcing GCM realizations show that historical ET trends in densely populated regions have been more influenced by aerosol emissions than greenhouse gases. Finally, we investigate which atmospheric variables explain most short‐term (year‐to‐year) and long‐term (decadal) changes. While water availability may be the most important driver of short‐term variability, for certain regions, radiation trends dominate long‐term forcing. This paper leverages a simple approach to provide a comprehensive and understandable view into recent and future changes in ET, reconciling the evidence provided by more complex case studies.

Abstract P146: Sex-Dependent Regulation of the Endothelin System in Multi-End Organ Inflammation in Lupus-Associated Cardiovascular Disease

Lupus is a chronic autoimmune disease characterized by IgG deposition, Toll-like receptor 7 (TLR7) overactivation, and autoantibody production resulting in end organ inflammation. SLE disproportionally affects women, SLE disproportionally affects women to men (9:1 ratio), with a high prevalence in African American women. Highly vascularized organs are severely impacted by lupus, specifically the kidneys and brain. Recent literature has shown that cardiovascular disease (CVD) has significant detrimental impacts on organ crosstalk. Endothelin-1 (ET-1), a potent vasoconstricting peptide, has been shown elevated in patients with CVD and in patients with lupus independent of disease severity. However, the extent to which ET-1 promotes lupus-associated CVD and end organ cross talk remains to be elucidated. Therefore, we hypothesized that TLR7 overactivation in a murine model of SLE-associated CVD would lead to a sex-dependent regulation of the renal and cerebral ET systems. Female and male lupus-prone B6.Nba2 mice were subjected to bi-weekly treatment with the Resiquimod (R848; TLR7/8 agonist; 100ug/30ul) or vehicle control (Acetone) for one month and subsequently studied for 12 weeks. At 16 weeks, the kidneys and brains were collected for histology and ET system (ET-1, ET A, and ET B ) analysis. Exploration of specific end organ damage demonstrates a profound increase in renal and cerebral IgG complex deposition as well as renal macrophages and T cells in both females and males receiving R848. Renal ET-1 levels displayed no time nor treatment-dependent effects in females, while males exhibited a significant time-dependent increase in expression at the 4 and 16-week timepoints. Interestingly, at the receptor level, neither sex demonstrated differences in ET A nor ET B levels in the kidney. While renal ET-1 level did not change, females demonstrated a significant increase in cerebral ET-1 at the 16-week timepoint, while males trended for increased cerebral ET-1. At the receptor level, females had a trend for increased cerebral ET A expression, while there was no change in males, and neither sex displayed a change in ET B receptor expression. These findings suggest a potential shift towards a pro-inflammatory state via the cerebral ET-1/ET A signaling axis in the R848-treated females. These findings warrant further exploration into the end-organ specific pathophysiological role ET-1/ET A signaling in multiorgan crosstalk in lupus-associated CVD.

Climate Change and Vegetation Greening Jointly Promote the Increase in Evapotranspiration in the Jing River Basin

Within the Earth’s terrestrial environment, evapotranspiration significantly contributes to the hydrological cycle, accounting for around 80% of the precipitation on landmasses to be reintroduced into the atmosphere. This mechanism profoundly affects the distribution and availability of surface water resources throughout the ecosystem. Gaining insight into the factors influencing local evapotranspiration fluctuations in response to varying climatic and vegetative scenarios is crucial for effective water management strategies and rehabilitating ecosystem resilience. To this end, our study focuses on the Jing River Basin in the Loess Plateau, utilizing multi-source remote sensing data and climatic information to investigate the spatiotemporal dynamics of evapotranspiration from 1984 to 2018 through the application of the Priestley–Taylor Jet Propulsion Laboratory (PT-JPL) model. Our research results indicate a general ascending tendency in evapotranspiration across the investigated region, demonstrating a notably discernible escalation at a pace of approximately 3.11 mm/year (p < 0.01), with an annual vegetation ET volume reaching 533.88 mm. Across different vegetation types in the Jing River Basin between 1984 and 2018, the mean yearly ET was observed to be highest in forests (572.88 mm), followed by croplands (564.74 mm), shrublands (536.43 mm), and grasslands (503.42 mm). The leaf area index (LAI) demonstrated the strongest partial correlation with ET (r = 0.35) and contributed the most significantly to the variation in ET within the Jing River Basin (0.41 mm/year). Additionally, LAI indirectly influences ET through its impact on vapor pressure deficit (VPD), precipitation (Pre), and temperature (Temp). Radiation is found to govern most ET changes across the region, while radiation and precipitation notably affected ET by modulating air temperature. In summary, these radiant energy changes directly affect the evaporation rate and total evapotranspiration of surface water. It provides important support for understanding how evapotranspiration in the Jing River Basin is adjusting to climate change and increased vegetation cover. These findings serve as a theoretical foundation for devising sustainable vegetation restoration strategies to optimize water resource utilization within the region.

Interannual variation in gross ecosystem production and evapotranspiration in a temperate semiarid grassland undergoing vegetation recovery

Carbon gains (gross ecosystem production, GEP) and water losses (evapotranspiration, ET) are critical for assessing vegetation recovery potential in drylands. However, large uncertainties remain regarding the controlling factors that regulate GEP and ET in semiarid grasslands, especially during periods of vegetation re-establishment and succession. Using the eddy-covariance technique, we assessed the interannual variability and key biophysical controls of carbon (C) and water vapor (H2O) fluxes in a semiarid grassland ecosystem in northern China from 2012 to 2020. After years of being subjected to heavy grazing and with a recent ban, the shrub-to-herb ratio at the site increased from 0.5 in 2014 to 0.63 in 2020. Associated with decreasing soil water availability (∼4.0% year−1), canopy transpiration and light use efficiency also decreased at rates of about 3.3% and 6.2% year−1, respectively. Multi-year means of GEP and ET were 166.6 ± 20.1 g C m−2 (mean ± SD) and 190.2 ± 21.8 mm, respectively. Interannual variability in GEP was mostly driven by variation in summer GEP, which for the most part was limited by mid-summer air temperature (Ta), particularly when exceeding the plants’ optimal temperature for photosynthesis. Interannual variability in ET was predominantly caused by variation in spring ET, which was mostly affected by spring vapor pressure deficit (VPD) and associated reductions in canopy stomatal conductance. Synchronous changes in GEP and ET resulted in a relatively stable annual water use efficiency (WUE) of 0.97 ± 0.13 g C kg−1 H2O. This stability is indicative of the shrubs’ capabilities to acclimate to arid conditions. Our results suggest that temperature and atmospheric aridity have important roles in regulating C gains and H2O losses in recovering dryland vegetation, respectively. Future increases in climatic variability anticipated with global climate change may augment the regional transition from grass to shrub cover.

Soil Moisture and Atmospheric Aridity Impact Spatio‐Temporal Changes in Evapotranspiration at a Global Scale

AbstractEvapotranspiration (ET) constitutes the water exchange from land to the atmosphere, which in turn modulates precipitation and soil moisture (SM). Multiple lines of evidence document complex feedbacks between changes in ET and temperature, atmospheric CO2 and vegetation greening. However, the existing analyses on global changes in ET do not account for the direct effects of SM supply and atmospheric water demand, expressed by vapor pressure deficit (VPD), while considering multiple environmental variables. Here we evaluated the performance of ET products using 140 flux towers included in the FLUXNET database. All ET products show reasonable performance, with an overall correlation higher than 0.7 and better performance at a higher latitude. From analysis of the ensemble mean of annual ET, we show insignificant (P = 0.06) trends in global ET during 1982–2020 and a significantly (P < 0.01) increasing trend during 2002–2020. Changes in GLEAM ET generally exert a positive response to changes in SM and a negative response to changes in VPD. Yet, these effects are not globally consistent and are largely determined by changes in vegetation transpiration. Using our finding as a benchmark, Earth System Models mostly reproduce the positive response of ET to SM with less coupling strength, while showing negative effects of VPD on ET with stronger coupling strength. Our study highlights that concurrent soil drying and atmospheric aridity could intensify water exchanges and the importance of realistically representing SM‐VPD‐ET interactions in models for accurate predictions of the hydrological cycle.

Hydrological response to climate change in the Deme watershed, Omo-Gibe Basin, Ethiopia

Abstract Climate change is believed to have led to changes in global patterns. This study evaluated the hydrological responses to climate change in the Deme watershed using the Soil and Water Assessment Tool (SWAT) for two consecutive periods of 2031–2050 and 2051–2070. Climate variables were downscaled from RACMO22T, under RCP4.5 and RCP8.5 scenarios from CORDEX-Africa. Distribution mapping and variance scaling methods were used for bias correction of precipitation and temperatures, respectively, and for further analysis. The SWAT model was calibrated (and validated) for the 1989–2000 (2001–2010) period, and the hydrological model showed a reasonably good agreement. The result shows that the rainfall and streamflow show a decreasing signal in the wet season. The maximum projected change in annual temperature, PET, and ET was 2.15 °C, 10.89, and 9.24%, respectively, in the far future period under the RCP8.5 scenario. These incremental changes have an impact on declining annual rainfall and streamflow up to 27.6 and 26.2%, respectively, under the RCP8.5 scenario in 2031–2050. The subsequent results were the maximum decline of surface runoff by 15.10%, groundwater by 14.78%, and total water yield by 26.10% in 2031–2050 under the RCP8.5 scenario. Thus, the concerned body integrates its duties with climate change.

Climate-driven vegetation greening further reduces water availability in drylands.

Climate change alters surface water availability (WA; precipitation minus evapotranspiration, P - ET) and consequently impacts agricultural production and societal water needs, leading to increasing concerns on the sustainability of water use. Although the direct effects of climate change on WA have long been recognized and assessed, indirect climate effects occurring through adjustments in terrestrial vegetation are more subtle and not yet fully quantified. To address this knowledge gap, here we investigate the interplay between climate-induced changes in leaf area index (LAI) and ET and quantify its ultimate effect on WA during the period 1982-2016 at the global scale, using an ensemble of data-driven products and land surface models. We show that ~44% of the global vegetated land has experienced a significant increase in growing season-averaged LAI and climate change explains 33.5% of this greening signal. Such climate-induced greening has enhanced ET of 0.051 ± 0.067 mm year-2 (mean ± SD), further amplifying the ongoing increase in ET directly driven by variations in climatic factors over 36.8% of the globe, and thus exacerbating the decline in WA prominently in drylands. These findings highlight the indirect impact of positive feedbacks in the land-climate system on the decline of WA, and call for an in-depth evaluation of these phenomena in the design of local mitigation and adaptation plans.

Combined brain network topological metrics with machine learning algorithms to identify essential tremor.

Essential tremor (ET) is a common movement syndrome, and the pathogenesis mechanisms, especially the brain network topological changes in ET are still unclear. The combination of graph theory (GT) analysis with machine learning (ML) algorithms provides a promising way to identify ET from healthy controls (HCs) at the individual level, and further help to reveal the topological pathogenesis in ET. Resting-state functional magnetic resonance imaging (fMRI) data were obtained from 101 ET and 105 HCs. The topological properties were analyzed by using GT analysis, and the topological metrics under every single threshold and the area under the curve (AUC) of all thresholds were used as features. Then a Mann-Whitney U-test and least absolute shrinkage and selection operator (LASSO) were conducted to feature dimensionality reduction. Four ML algorithms were adopted to identify ET from HCs. The mean accuracy, mean balanced accuracy, mean sensitivity, mean specificity, and mean AUC were used to evaluate the classification performance. In addition, correlation analysis was carried out between selected topological features and clinical tremor characteristics. All classifiers achieved good classification performance. The mean accuracy of Support vector machine (SVM), logistic regression (LR), random forest (RF), and naïve bayes (NB) was 84.65, 85.03, 84.85, and 76.31%, respectively. LR classifier achieved the best classification performance with 85.03% mean accuracy, 83.97% sensitivity, and an AUC of 0.924. Correlation analysis results showed that 2 topological features negatively and 1 positively correlated with tremor severity. These results demonstrated that combining topological metrics with ML algorithms could not only achieve high classification accuracy for discrimination ET from HCs but also help us to reveal the potential topological pathogenesis of ET.

Evapotranspiration of Irrigated Crops under Warming and Elevated Atmospheric CO2: What Is the Direction of Change?

Future changes in crop evapotranspiration (ETc) are of interest to water management stakeholders. However, long-term projections are complex and merit further investigation due to uncertainties in climate data, differential responses of crops to climate and elevated atmospheric CO2, and adaptive agricultural management. We conducted factor-control simulation experiments using the process-based CropSyst model and investigated the contribution of each of these factors. Five major irrigated crops in the Columbia Basin Project area of the USA Pacific Northwest were selected as a case study and fifteen general circulation models (GCM) under two representative concentration pathways (RCP) were used as the climate forcing. Results indicated a wide range in ETc change, depending on the time frame, crop type, planting dates, and CO2 assumptions. Under the 2090s RCP8.5 scenario, ETc changes were crop-specific: +14.3% (alfalfa), +8.1% (potato), −5.1% (dry bean), −8.1% (corn), and −12.5% (spring wheat). Future elevated CO2 concentrations decreased ETc for all crops while earlier planting increased ETc for all crops except spring wheat. Changes in reference ET (ETo) only partially explains changes in ETc because crop responses are an important modulating factor; therefore, caution must be exercised in interpreting ETo changes as a proxy for ETc changes.

The Influence of Landcover and Climate Change on the Hydrology of the Minjiang River Watershed

Changes in the climate and landcover are the two most important factors that influence terrestrial hydrological systems. Today, watershed-scale hydrological models are widely used to estimate the individual impacts of changes in the climate and landcover on watershed hydrology. The Minjiang river watershed is an ecologically and economically important, humid, subtropical watershed, located in south-eastern China. Several studies are available on the impacts of recent climate change on the watershed; however, no efforts have been made to separate the individual contributions of climate and landcover changes. This study is an attempt to separate the individual impacts of recent (1989–2018) climate and landcover changes on some of the important hydrological components of the watershed, and highlight the most influential changes in climate parameters and landcover classes. A calibrated soil and water assessment tool (SWAT) was employed for the study. The outcomes revealed that, during the study period, water yield decreased by 6.76%, while evapotranspiration, surface runoff and sediment yield increased by 1.08%, 24.11% and 33.85% respectively. The relative contribution of climate change to landcover change for the decrease in the water yield was 95%, while its contribution to the increases in evapotranspiration, surface runoff and sediment yield was 56%, 77% and 51%, respectively. The changes in climate parameters that were most likely responsible for changes in ET were increasing solar radiation and temperature and decreasing wind speed, those for changes in the water yield were decreasing autumn precipitation and increasing solar radiation and temperature, those for the increase in surface runoff were increasing summer and one-day maximum precipitation, while those for the increasing sediment yield were increasing winter and one-day maximum precipitation. Similarly, an increase in the croplands at the expense of needle-leaved forests was the landcover change that was most likely responsible for a decrease in the water yield and an increase in ET and sediment yield, while an increase in the amount of urban land at the expense of broadleaved forests and wetlands was the landcover change that was most likely responsible for increasing surface runoff. The findings of the study can provide support for improving management and protection of the watershed in the context of landcover and climate change.

After-discharge in the upper airway muscle genioglossus following brief hypoxia.

Genioglossus (GG) after-discharge is thought to protect against pharyngeal collapse by minimizing periods of low upper airway muscle activity. How GG after-discharge occurs and which single motor units (SMUs) are responsible for the phenomenon are unknown. The aim of this study was to investigate genioglossal after-discharge. During wakefulness, after-discharge was elicited 8-12 times in healthy individuals with brief isocapnic hypoxia (45-60 s of 10% O2 in N2) terminated by a single breath of 100% O2. GG SMUs were designated as firing solely, or at increased rate, during inspiration (Inspiratory phasic [IP] and inspiratory tonic [IT], respectively); solely, or at increased rate, during expiration (Expiratory phasic [EP] or expiratory tonic [ET], respectively) or firing constantly without respiratory modulation (Tonic). SMUs were quantified at baseline, the end of hypoxia, the hyperoxic breath, and the following eight normoxic breaths. A total of 210 SMUs were identified in 17 participants. GG muscle activity was elevated above baseline for seven breaths after hyperoxia (p < 0.001), indicating a strong after-discharge effect. After-discharge occurred due to persistent firing of IP and IT units that were recruited during hypoxia, with minimal changes in ET, EP, or Tonic SMUs. The firing frequency of units that were already active changed minimally during hypoxia or the afterdischarge period (p > 0.05). That genioglossal after-discharge is almost entirely due to persistent firing of previously silent inspiratory SMUs provides insight into the mechanisms responsible for the phenomenon and supports the hypothesis that the inspiratory and expiratory/tonic motor units within the muscle have idiosyncratic functions.

Symptom Burden and Quality of Life in High-Risk Essential Thrombocythemia and Polycythemia Vera Patients Receiving Hydroxyurea or Pegylated Interferon Alfa-2a: Results of Myeloproliferative Neoplasms Research Consortium (MPN-RC) 111 and 112 Trials

Symptom Burden and Quality of Life in High-Risk Essential Thrombocythemia and Polycythemia Vera Patients Receiving Hydroxyurea or Pegylated Interferon Alfa-2a: Results of Myeloproliferative Neoplasms Research Consortium (MPN-RC) 111 and 112 Trials

Resolving Drivers of a Spatial Gradient in Evapotranspiration Through the Simulated Translocation of Landscape Factors

AbstractA number of studies using the so‐called space‐for‐time substitution (STS) approach have predicted that climate warming of snow‐influenced watersheds would result in alarming increases in long‐term ET and concurrent decreases in runoff. This empirical approach implicitly assumes that any spatial covariation of factors across the landscape would remain fixed in time, that is, the “covariance‐stationarity” assumption. A better understanding of this assumption, in terms of what it means and how it affects predictions, is needed to assess the implications of STS predictions. To address this, we examined the influence of the covariance‐stationarity assumption on STS predictions of long‐term ET in response to warming. We did this by simulating changes in ET resulting from elevational transfers of factors in ways that emulate STS. This approach was applied to the upper San Joaquin River, a snow‐influenced watershed in the Sierra Nevada, USA. Predicted increases in ET from STS including the covariance‐stationarity assumption were 3–7 times greater than STS treating air temperature as an independent factor, over most of the higher elevations. Based on results from a factorial analysis, these differences were attributed primarily to the pedologic gradient across elevation, which transitions from loamy Alfisol soils at lower elevations to sandy Entisol/Inceptisol soils and exposed bedrock at upper elevations. The covariance‐stationarity assumption does not seem realistic for soil and air temperature over timescales of projected climate. Therefore, the confounding of these factors in the STS approach can substantially overestimate the sensitivity of long‐term ET to air temperature.

Improving Representation of Deforestation Effects on Evapotranspiration in the E3SM Land Model

AbstractEvapotranspiration (ET) plays an important role in land‐atmosphere coupling of energy, water, and carbon cycles. Following deforestation, ET is typically observed to decrease substantially as a consequence of decreases in leaf area and roots and increases in runoff. Changes in ET (latent heat flux) revise the surface energy and water budgets, which further affects large‐scale atmospheric dynamics and feeds back positively or negatively to long‐term forest sustainability. In this study, we used observations from a recent synthesis of 29 pairs of adjacent intact and deforested FLUXNET sites to improve model parameterization of stomatal characteristics, photosynthesis, and soil water dynamics in version 1 of the Energy Exascale Earth System Model (E3SM) Land Model (ELMv1). We found that default ELMv1 predicts an increase in ET after deforestation, likely leading to incorrect estimates of the effects of deforestation on land‐atmosphere coupling. The calibrated model accurately represented the FLUXNET observed deforestation effects on ET. Importantly, the search for global optimal parameters converged at values consistent with recent observational syntheses, confirming the reliability of the calibrated physical parameters. Applying this improved model parameterization to the globe scale reduced the bias of annual ET simulation by up to ~600 mm/year. Analysis on the roles of parameters suggested that future model development to improve ET simulation should focus on stomatal resistance and soil water‐related parameterizations. Finally, our predicted differences in seasonal ET changes from deforestation are large enough to substantially affect land‐atmosphere coupling and should be considered in such studies.

Correction to “Ecohydrological responses to rewetting of a highly impacted raised bog ecosystem”

We are providing this correction to clarify and correct several details as originally presented in D'Acunha, Lee, and Johnson (2018). Figure A in D'Acunha et al. (2018) incorrectly presented the locations of the wells and piezometers monitored for groundwater level by the City of Delta. While the geographic coordinates given in Table A of D'Acunha et al. (2018) correctly correspond to the groundwater level measurement locations, the markers in Figure A of D'Acunha et al. (2018) are shifted from their correct placement. We provide an updated figure below (Figure A) to correct this issue. We also wish to highlight that water level monitoring was conducted by the City of Delta, as noted in the Methods section and the Acknowledgements of D'Acunha et al. (2018). The methodology described in section 2.2 should have been specifically attributed to Howie et al. (2009). Also, this information was not conveyed in the figure legends of Figures 2 and 4 in D'Acunha et al. (2018), and we wish to emphasize that the authors of D'Acunha et al. (2018) were not involved in water level monitoring. The statement in D'Acunha et al. (2018) that indicated all water level measurements began in September 2005 is incorrect. Of the 11 piezometers used in D'Acunha et al. (2018), 6 have readings beginning in September 2005, one began in October 2005, and five began in August 2006. We summarize the starting times for each location in Table A of this Correction. We also note that the location identification nomenclature used for groundwater level measurements used by the City of Delta differs from that used in D'Acunha et al. (2018). Table A in this Correction provides a one-to-one correspondence of location codes used in D'Acunha et al. (2018) to the nomenclature used by the City of Delta and other agencies engaged in water level measurements. Location code D'Acunha et al. (2018) The statement in D'Acunha et al. (2018) that “Transects B and E were harvested during World War II” is incorrect. The position of three groundwater monitoring locations along Transect B (B1, B2, and B3) are adjacent to, but outside of, areas that experienced peat harvesting (Hebda, Gustavson, Golinski, & Calder (2000); Figure A). As these locations are 35 m south of the polygonal perimeter of an area defined as experiencing peat harvesting, the remote sensing products with 1 km (MODIS ET) and 250 m (MODIS NDVI) pixel resolutions overlap with areas for which peat was harvested. However, the influence of legacy peat harvesting on groundwater levels is difficult to assess for locations outside of harvest areas. Transect E is located perpendicular to a blocked perimeter drainage ditch in an area which has never had peat harvesting with Locations E3 and E4 near this blocked drainage ditch (Howie et al., 2009). Tree and shrub regrowth has been reported following the 2005 fire, which could be a significant factor driving the ET trends observed for Transect B using the MODIS MOD16A2 product. While it is not possible from the satellite record to determine the relative strengths of regrowth vs. rewetting as potential causal (and interacting) mechanisms leading to changes in ET, vegetative regrowth should be recognized as a potentially important ET component. Future research could use an isotopic approach to segregate ET into evaporation (E) and transpiration (T), where rewetting would presumably increase E for areas more proximal to the blocked ditches, while more and larger trees and shrubs would likely lead to increased T. It should also be noted that vegetative communities in Burns Bog are highly complex and variable over short distances in relation to micro-topography and other features. Remote sensing imagery aggregates optical characteristics of the entire plant community that occurs within each pixel. As such, we recognize the difficulty of identifying changes in vegetative communities from remote sensing imagery, particularly at the 250 m MODIS NDVI pixel size. We acknowledged this difficulty in the Discussion section of D'Acunha et al. (2018) and indicated that we were unable to assess the abundance of mosses using remotely sensed data for the transects. Rather, surveys and an inventory of vegetation cover are needed to fully assess composition of and changes within vegetative communities. Remote sensing data can help to identify areas that may be experiencing changes as screening tool to help plan for field-based measurements. The statement in the Conclusion section of D'Acunha et al. (2018) that ditch blocking was part of the restoration efforts by Metro Vancouver is incorrect. Ditch blocking has been carried out by the City of Delta since 2001. Finally, “Set” in Figure 3 caption, should be “Sept”.

Investigating the temporal and spatial variations of water consumption in Urmia Lake River Basin considering the climate and anthropogenic effects on the agriculture in the basin

Urmia Lake River Basin (ULRB) is one of the most important habitats in the world and one of the major agricultural regions in Iran. On average, the ratio of irrigation to evapotranspiration in this basin is more than 73%. Investigating the irrigation water requirement pattern changes and the spatial distribution of evapotranspiration during the basin development period on a regional scale play important roles in understanding the basin situation. In this study, the actual evapotranspiration has been estimated by SEBAL model. By estimating the precipitation distribution in the basin, the agricultural irrigation water requirement pattern has been calculated using the land use map in 1995, 2010 and 2014 in the total agricultural lands and in its 7 major subbasins where ET changes from 369 to 1000 mm. The maximum irrigation water consumption were 535 million cubic meters in Urmia subbasin (2010) and then 469 million cubic meters in Miandoab Subbasin (2014), While its average was 2108 million cubic meters in the basin. Furthermore, the maximum and minimum levels of evapotranspiration pattern in the total agricultural lands were 765 and 555 mm in 2010 and 1995, respectively. This study included (1) a comparison between regional irrigation water requirement in the basin and (2) investigating the causes of (including natural and anthropogenic) changes in the amount of irrigation water consumption over the years. The study approach provided a simple but powerful assessment to describe the irrigation water consumption pattern in the subbasins using the minimum ground data and to identify the water management strategies in basin agriculture and climate changes.

Comparison of baseline period choices for separating climate and land use/land cover change impacts on watershed hydrology using distributed hydrological models

Separating impacts of land use/land cover change (LUCC) and climate change on hydrology is essential for watershed planning and management. This is typically done via hydrological modelling in combination with the one-factor-at-a-time analysis. However, it remains unclear how large the differences in isolated hydrological impacts would be when selecting different baseline periods. In this study, we compared baseline period choices for separating climate change and LUCC impacts on watershed hydrology in a typical inland river basin in northwest China, i.e. the Upper Heihe River Basin, with two hydrological models, i.e., Soil and Water Assessment Tool and Distributed Hydrology Soil Vegetation Model. In the real LUCC case which considers the actual land use changes between 2000 and 2011, the absolute contributions of LUCC to the variations in water yield and ET are slight and almost have the same magnitude for different baseline period choices, whereas those of climate change are substantial and with varying magnitudes. Compared with the absolute contributions, the relative contributions of climate change and LUCC seem less sensitive to the choices of baseline periods. In the hypothetical LUCC case which assumes an extreme land use conversion (i.e., grassland converts to farmland completely), both climate change and LUCC contribute to the changes in water yield and ET significantly. Moreover, both the absolute and relative contributions diverge noticeably between various baseline period choices. The influences of baseline period choices on the partitioning of hydrological impacts diverge significantly between different hydrological models. This study highlights that baseline period choice is an important source of uncertainty when disentangling the impacts of LUCC and climate change on hydrology. Some useful recommendations regarding baseline period selection have been proposed, which may help to reduce the uncertainties associated with baseline period choices.

Area-wide evapotranspiration monitoring at the crown level of a tropical mountain rain forest

Ecosystem water regulation couples energy and water balance, depends on the integrity of the ecosystem, and responds to changes in climate. Changes in tree-water relationships in the biodiversity hotspot of the tropical Andes in southern Ecuador might be potentially observed at the level of individual trees, thus providing an efficient ecosystem monitoring method with applications in forest management and conservation at the tree and landscape levels. In this study, we combine area-average measurements from a laser scintillometer above the forest with optical satellite data at high spatial resolution to obtain area-wide evapotranspiration data. The processing of field data includes the calculation of energy storage in forest biomass and the partitioning of evapotranspiration into transpiration and evaporation. Satellite-based estimates are calibrated by using tower flux measurements and meteorological data within periods of humid and less-humid atmosphere. The annual evapotranspiration was 1316mm, of which 1086mm per year corresponds to the forest transpiration at the study site. Average values of 4.7 and 4.1mm d−1 per tree crown are observed under humid and less-humid atmospheric conditions, respectively, when applying high-resolution area-wide evapotranspiration in individual crown analysis. Approximately 24% of the observed crowns show a positive monthly change in ET, and 51% of the crowns show a significant change in the daily ET, which can be considered sensitive individuals concerning water relationships. The limitations in the area-wide evapotranspiration at the crown level can be explained by considering the spectral responses of the crown individuals. The presented method can be robustly deployed in the ecological monitoring of mountain forests.

Asymmetric sensitivity of ecosystem carbon and water processes in response to precipitation change in a semi‐arid steppe

Summary Semi‐arid ecosystems play an important role in regulating the dynamics of the global terrestrial CO2 sink. These dynamics are mainly driven by increasing inter‐annual precipitation variability. However, how ecosystem carbon processes respond to changes in precipitation is not well understood, due to a lack of substantial experimental evidence that combines increased and decreased precipitation treatments. This study, a 3‐year field manipulation experiment with five precipitation levels conducted in a semi‐arid steppe, examined the impacts of increased and decreased precipitation on ecosystem CO2 (GEP: gross ecosystem photosynthesis; ER: ecosystem respiration; NEE: net ecosystem CO2 exchange), water exchange (ET: evapotranspiration), and resource use efficiency (CUE: carbon use efficiency; WUE: water use efficiency). We found that decreased precipitation reduced ecosystem CO2, water exchange and resource use efficiency significantly, while increased precipitation did not cause significant influence on them. That is, they responded more sensitively to decreased precipitation. Soil water availability was the most important driver determining changes in GEP, ER and ET. Changes in NEE, CUE and WUE were predominately regulated by soil temperature. Photosynthesis at leaf and ecosystem levels showed significantly greater sensitivity to changed precipitation than respiration and ET, and therefore determined the trends of net carbon uptake and resource use efficiency. This study highlighted an asymmetric response of ecosystem carbon and water processes to altered precipitation. This is potentially important for improving our understanding of how possible future changes in precipitation will affect the carbon cycle. Taking this asymmetric response into consideration will inevitably reduce uncertainties in predicting the dynamics of the global carbon cycle. A lay summary is available for this article.