Kristen A. Bretz, Natalie N. Murphy, Erin R. Hotchkiss
Abstract Non‐perennial headwaters experience extremes in flow conditions that likely influence carbon fate. As surface waters contract through dry periods, reconnect during storms, and re‐expand or dry again, there is a great deal of variability in carbon emissions and export. We measured discharge, dissolved oxygen, carbon dioxide (CO 2 ), and dissolved organic carbon (DOC) continuously in a persistent pool at the base of a non‐perennial, forested headwater stream in the southeastern United States to characterize how flow changes affect carbon emissions and export as the stream expands and shrinks. We also compared carbon concentrations and export during different stream flow categories before and after fall wet‐up. CO 2 concentrations were high when discharge was lowest (median = 10.2 mg L −1 ) and low during high flows (3.2 mg L −1 ) and storms (1.1 mg L −1 ). High CO 2 concentrations led to high emissions on a per area basis during low flow times, but whole‐channel stream CO 2 emissions were limited by the small surface area of the stream during periods of surface water disconnection. DOC concentration varied by season (range = 0.1–16.2 mg L −1 ) with large pulses during smaller summer storms. We found that CO 2 and DOC concentrations differed among binned stages of stream flow. As non‐perennial streams become more prevalent across the southeastern United States due to shifts in climate, the relationships between flow and carbon movement into and out of stream networks will become increasingly critical to understanding stream carbon biogeochemistry.
{"title":"Carbon Biogeochemistry and Export Governed by Flow in a Non‐Perennial Stream","authors":"Kristen A. Bretz, Natalie N. Murphy, Erin R. Hotchkiss","doi":"10.1029/2022wr034004","DOIUrl":"https://doi.org/10.1029/2022wr034004","url":null,"abstract":"Abstract Non‐perennial headwaters experience extremes in flow conditions that likely influence carbon fate. As surface waters contract through dry periods, reconnect during storms, and re‐expand or dry again, there is a great deal of variability in carbon emissions and export. We measured discharge, dissolved oxygen, carbon dioxide (CO 2 ), and dissolved organic carbon (DOC) continuously in a persistent pool at the base of a non‐perennial, forested headwater stream in the southeastern United States to characterize how flow changes affect carbon emissions and export as the stream expands and shrinks. We also compared carbon concentrations and export during different stream flow categories before and after fall wet‐up. CO 2 concentrations were high when discharge was lowest (median = 10.2 mg L −1 ) and low during high flows (3.2 mg L −1 ) and storms (1.1 mg L −1 ). High CO 2 concentrations led to high emissions on a per area basis during low flow times, but whole‐channel stream CO 2 emissions were limited by the small surface area of the stream during periods of surface water disconnection. DOC concentration varied by season (range = 0.1–16.2 mg L −1 ) with large pulses during smaller summer storms. We found that CO 2 and DOC concentrations differed among binned stages of stream flow. As non‐perennial streams become more prevalent across the southeastern United States due to shifts in climate, the relationships between flow and carbon movement into and out of stream networks will become increasingly critical to understanding stream carbon biogeochemistry.","PeriodicalId":23799,"journal":{"name":"Water Resources Research","volume":"307 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135249084","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Meixian Liu, Alexander Y Sun, Kairong Lin, Wei Luo, Xinjun Tu, Xiaohong Chen
Abstract Non‐water‐limited canopy resistance ( r cs , also known as the bulk stomatal resistance or surface resistance) is a critical variable in estimating potential evapotranspiration (PET), which is widely used in ecohydrology related fields. However, quantifying r cs is a challenging work. Here we develop an approach for estimating r cs over the globe. Comparing results over the globe and across 10 ET data sets (used as inputs), which are based on diverse mechanisms and algorithms, we find that the approach can capture canopy resistance well (mean correlation of 0.84 ± 0.04, mean relative Root Mean Squared Error of 4.4% ± 1.0%, and mean relative Mean Absolute Error of 5.8% ± 1.4%), and the estimated r cs are very close to those estimated using another method ( R 2 = 0.92), which is based on a quite different hypothesis that is only suitable for saturated regions. Based on these, we find that the r cs shows an overall increasing trend (0.43 ± 0.13 s m −1 year −1 ) over the globe (at 77.6% ± 3.9% of the land grid cells) during 1982–2014, and the air temperature dominates the variabilities of r cs in regions with decreasing r cs (mean relative contribution of 57.9% ± 11.4%), while air CO 2 concentration controls the changes in r cs in regions with increasing r cs (mean relative contribution of 47.3% ± 8.0%). Moreover, we also find that the traditional PET estimator explicitly overestimates the increasing trends in PET, and tends to overestimate (underestimate) the increasing (decreasing) trends in regions with increasing (decreasing) PET. These findings can improve our knowledge on the complex water‐vegetation‐environment interactions and would be helpful for developing more accurate models for quantifying the impacts of global change on water resources.
非限水冠层阻力(rcs)，又称体积气孔阻力或表面阻力，是估算潜在蒸散发(PET)的关键变量，在生态水文相关领域得到广泛应用。然而，量化碳排放是一项具有挑战性的工作。在这里，我们开发了一种估算全球r cs的方法。对比基于不同机制和算法的全球和10个ET数据集(作为输入)的结果，我们发现该方法可以很好地捕获冠层阻力(平均相关系数为0.84±0.04，平均相对均方根误差为4.4%±1.0%，平均相对平均绝对误差为5.8%±1.4%)，估计的r cs与使用另一种方法估计的r cs非常接近(r2 = 0.92)。这是基于一个完全不同的假设，只适用于饱和区域。在此基础上,我们发现r cs显示了一个总体增加的趋势(0.43±0.13 s m 1年−−1)在世界各地(在77.6%±3.9%的土地网格细胞)在1982 - 2014年期间,和空气温度的主导着可变性r cs与减少区域r cs(平均57.9%±11.4%)的相对贡献,而空气CO 2浓度控制地区r cs的变化随着r cs(平均47.3%±8.0%)的相对贡献。此外，我们还发现传统的PET估计器明显高估了PET的增加趋势，并且倾向于高估(低估)PET增加(减少)区域的增加(减少)趋势。这些发现可以提高我们对水-植被-环境复杂相互作用的认识，并有助于开发更准确的模型来量化全球变化对水资源的影响。
{"title":"Estimating dynamic non‐water‐limited canopy resistance over the globe: Changes, contributors and implications","authors":"Meixian Liu, Alexander Y Sun, Kairong Lin, Wei Luo, Xinjun Tu, Xiaohong Chen","doi":"10.1029/2022wr034209","DOIUrl":"https://doi.org/10.1029/2022wr034209","url":null,"abstract":"Abstract Non‐water‐limited canopy resistance ( r cs , also known as the bulk stomatal resistance or surface resistance) is a critical variable in estimating potential evapotranspiration (PET), which is widely used in ecohydrology related fields. However, quantifying r cs is a challenging work. Here we develop an approach for estimating r cs over the globe. Comparing results over the globe and across 10 ET data sets (used as inputs), which are based on diverse mechanisms and algorithms, we find that the approach can capture canopy resistance well (mean correlation of 0.84 ± 0.04, mean relative Root Mean Squared Error of 4.4% ± 1.0%, and mean relative Mean Absolute Error of 5.8% ± 1.4%), and the estimated r cs are very close to those estimated using another method ( R 2 = 0.92), which is based on a quite different hypothesis that is only suitable for saturated regions. Based on these, we find that the r cs shows an overall increasing trend (0.43 ± 0.13 s m −1 year −1 ) over the globe (at 77.6% ± 3.9% of the land grid cells) during 1982–2014, and the air temperature dominates the variabilities of r cs in regions with decreasing r cs (mean relative contribution of 57.9% ± 11.4%), while air CO 2 concentration controls the changes in r cs in regions with increasing r cs (mean relative contribution of 47.3% ± 8.0%). Moreover, we also find that the traditional PET estimator explicitly overestimates the increasing trends in PET, and tends to overestimate (underestimate) the increasing (decreasing) trends in regions with increasing (decreasing) PET. These findings can improve our knowledge on the complex water‐vegetation‐environment interactions and would be helpful for developing more accurate models for quantifying the impacts of global change on water resources.","PeriodicalId":23799,"journal":{"name":"Water Resources Research","volume":"46 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135304910","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The clarification of freezing in a soil‐water system is critical for assessing the formation of a freezing zone and liquid water flow. The supercooling phenomenon of soil pore solutions has been found during the freezing process, but the mechanism remains poorly understood. In this study, we propose a free energy function of soil‐water systems based on the Classical Nucleation Theory. The analytical solution of the critical nucleation problem of saline soil‐water system is obtained by combining the initial freezing temperature model and Pitzer activity coefficients model in electrolyte solutions. Then, the freezing‐thawing experiments of saline soil with various salt contents were conducted for verifying the analytical solution. The derived boundary nucleation rate is the quantitative solution of the critical condition for the supercooling. The findings suggested that the theory results agreed well with the experiment results. For the salt‐free soil‐water system, the critical maximum radius of supercooling was 7.15 nm. We compared eight classical ice‐water interfacial tension models, and the “Reinhardt & Doye” and “DeMott & Rogers” models showed excellent performance when using the new free energy theoretical framework to predict the crystallization nucleation rate of soil‐water systems. A positive correlation between the boundary nucleation rate and soil‐water potential is detected. According to the influencing factors, the boundary nucleation rate of soil‐water system can be divided into three zones: salt nature control zone (R > 100 μm), salt‐pore mixed control zone (100 μm > R > 100 nm), and pore size control zone (R < 100 nm).
{"title":"Study on the Supercooling Characteristics of Freezing Soil Based On Nucleation Theory","authors":"Chong Wang, Kunyu Li, Zhikun Lin, Zhijie Yang, Honghong Cai, Yuanming Lai, Shuangyang Li","doi":"10.1029/2023WR034800","DOIUrl":"https://doi.org/10.1029/2023WR034800","url":null,"abstract":"The clarification of freezing in a soil‐water system is critical for assessing the formation of a freezing zone and liquid water flow. The supercooling phenomenon of soil pore solutions has been found during the freezing process, but the mechanism remains poorly understood. In this study, we propose a free energy function of soil‐water systems based on the Classical Nucleation Theory. The analytical solution of the critical nucleation problem of saline soil‐water system is obtained by combining the initial freezing temperature model and Pitzer activity coefficients model in electrolyte solutions. Then, the freezing‐thawing experiments of saline soil with various salt contents were conducted for verifying the analytical solution. The derived boundary nucleation rate is the quantitative solution of the critical condition for the supercooling. The findings suggested that the theory results agreed well with the experiment results. For the salt‐free soil‐water system, the critical maximum radius of supercooling was 7.15 nm. We compared eight classical ice‐water interfacial tension models, and the “Reinhardt & Doye” and “DeMott & Rogers” models showed excellent performance when using the new free energy theoretical framework to predict the crystallization nucleation rate of soil‐water systems. A positive correlation between the boundary nucleation rate and soil‐water potential is detected. According to the influencing factors, the boundary nucleation rate of soil‐water system can be divided into three zones: salt nature control zone (R > 100 μm), salt‐pore mixed control zone (100 μm > R > 100 nm), and pore size control zone (R < 100 nm).","PeriodicalId":23799,"journal":{"name":"Water Resources Research","volume":" ","pages":""},"PeriodicalIF":5.4,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46367554","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Highly accurate soil moisture information is necessary to understand land surface processes. However, observational techniques do not produce adequately accurate spatial‐temporal continuous regional soil moisture data. The data assimilation method can be used to improve the soil moisture estimations by merging multi‐source observed data, but its performance is affected by error covariance and the quality of assimilated data. We designed eight numerical experiments to analyze how to improve the filter performance through soil moisture assimilation using the unscented weighted ensemble Kalman filter (UWEnKF) and 1‐D Richards equation at Maqu and Erlinghu (ELH) observational sites in the source region of Yellow River (SRYR), China. The experimental results show that the filter performance improves as the quality of assimilated data increases in the soil moisture assimilation experiment when assimilating in‐situ surface soil moisture (SSM) observations, SMAP SSM data and downscaled SMAP SSM data. In other aspects, filter performance is readily affected by model and observation error covariances in soil moisture assimilation. If the SMAP SSM data are taken to be perfect (i.e., small bias), UWEnKF performs differently between different sites because of the underestimation or overestimation of SMAP SSM and model simulations compared to the in‐situ observations. Additionally, different soil moisture assimilation results can be obtained with different initial values at the beginning of the assimilation period. Overall, filter performance can be improved primarily by improving the quality of assimilated data (e.g., downscaling the remote sensing data), and by creating a reasonable and effective method for determining error covariance.
{"title":"Soil Moisture Estimation by Assimilating In‐Situ and SMAP Surface Soil Moisture Using Unscented Weighted Ensemble Kalman Filter","authors":"Xiaolei Fu, Yuchen Zhang, Qi Zhong, Haishen Lü, Yongjian Ding, Zhaoguo Li, Zhongbo Yu, Xiaolei Jiang","doi":"10.1029/2023WR034506","DOIUrl":"https://doi.org/10.1029/2023WR034506","url":null,"abstract":"Highly accurate soil moisture information is necessary to understand land surface processes. However, observational techniques do not produce adequately accurate spatial‐temporal continuous regional soil moisture data. The data assimilation method can be used to improve the soil moisture estimations by merging multi‐source observed data, but its performance is affected by error covariance and the quality of assimilated data. We designed eight numerical experiments to analyze how to improve the filter performance through soil moisture assimilation using the unscented weighted ensemble Kalman filter (UWEnKF) and 1‐D Richards equation at Maqu and Erlinghu (ELH) observational sites in the source region of Yellow River (SRYR), China. The experimental results show that the filter performance improves as the quality of assimilated data increases in the soil moisture assimilation experiment when assimilating in‐situ surface soil moisture (SSM) observations, SMAP SSM data and downscaled SMAP SSM data. In other aspects, filter performance is readily affected by model and observation error covariances in soil moisture assimilation. If the SMAP SSM data are taken to be perfect (i.e., small bias), UWEnKF performs differently between different sites because of the underestimation or overestimation of SMAP SSM and model simulations compared to the in‐situ observations. Additionally, different soil moisture assimilation results can be obtained with different initial values at the beginning of the assimilation period. Overall, filter performance can be improved primarily by improving the quality of assimilated data (e.g., downscaling the remote sensing data), and by creating a reasonable and effective method for determining error covariance.","PeriodicalId":23799,"journal":{"name":"Water Resources Research","volume":" ","pages":""},"PeriodicalIF":5.4,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48713944","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Since its passage in 1974, the U.S. Safe Drinking Water Act (SDWA) has become a pillar of water resources engineering, utility management, and public health policy. Complementing other environmental legislation from the same period, SDWA set standards for drinking water suppliers, service, and quality and has made an unmistakable positive impact on U.S. communities for the past 50 years. While drinking water faces different specific challenges today, the general principles established by SDWA are the same. Its success may be attributed to its broad political commitment at the federal level, firm enforcement at the state level, and dutiful execution at the local (public water supplier) level—all while customers know exactly what to expect—thus creating clear accountability for safe water. Just as SDWA helped resolve last century's drinking water problems, it can serve as a policy model for addressing this century's grand challenges.
{"title":"The Safe Drinking Water Act at 50: A Policy Model for Grand Challenges","authors":"Robert B. Sowby","doi":"10.1029/2023wr035172","DOIUrl":"https://doi.org/10.1029/2023wr035172","url":null,"abstract":"Since its passage in 1974, the U.S. Safe Drinking Water Act (SDWA) has become a pillar of water resources engineering, utility management, and public health policy. Complementing other environmental legislation from the same period, SDWA set standards for drinking water suppliers, service, and quality and has made an unmistakable positive impact on U.S. communities for the past 50 years. While drinking water faces different specific challenges today, the general principles established by SDWA are the same. Its success may be attributed to its broad political commitment at the federal level, firm enforcement at the state level, and dutiful execution at the local (public water supplier) level—all while customers know exactly what to expect—thus creating clear accountability for safe water. Just as SDWA helped resolve last century's drinking water problems, it can serve as a policy model for addressing this century's grand challenges.","PeriodicalId":23799,"journal":{"name":"Water Resources Research","volume":" ","pages":""},"PeriodicalIF":5.4,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48419809","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Le Zhang, Zhibing Yang, Y. Méheust, I. Neuweiler, R. Hu, Yi‐Feng Chen
Two‐phase flow involving non‐Newtonian fluids in fractured media is of vital importance in many natural processes and subsurface engineering applications, such as rock grouting, groundwater remediation, and enhanced oil recovery. Yet, how the displacement dynamics is impacted by the non‐Newtonian rheology remains an open question. Here, we conduct primary drainage experiments in which a shear‐thinning Xanthan gum solution displaces a silicone oil in a transparent rough fracture for a wide range of shear‐thinning property (controlled by polymer concentration) and flow rates. We first evaluate the effects of shear‐thinning property on displacement efficiency. Based on qualitative and quantitative analyses of the observed fluid morphologies, we present an experimental phase diagram of the obtained displacement patterns. We characterize a novel displacement pattern where the fluid‐fluid interface changes from stable (plug flow) to unstable (fingering) as the fracture aperture, averaged over the transverse direction, varies along the mean flow direction. We demonstrate that the existence of this mixed displacement pattern can be explained by local viscosity heterogeneity induced by the coupling of the shear‐thinning behavior and the spatial variability of apertures. Finally, we propose a theoretical model elucidating the mechanisms behind the flow regime transitions. The interface stability criterion predicted by this model exhibits good agreement with the experimental measurements, and stresses the potentially important role of fluid rheology, coupled to aperture variability, in immiscible displacements in rough fractures. These findings provide new insights into the dynamics of immiscible two‐phase flows with non‐Newtonian effects, and has potential implications for the aforementioned engineering applications.
{"title":"Displacement Patterns of a Newtonian Fluid by a Shear‐Thinning Fluid in a Rough Fracture","authors":"Le Zhang, Zhibing Yang, Y. Méheust, I. Neuweiler, R. Hu, Yi‐Feng Chen","doi":"10.1029/2023WR034958","DOIUrl":"https://doi.org/10.1029/2023WR034958","url":null,"abstract":"Two‐phase flow involving non‐Newtonian fluids in fractured media is of vital importance in many natural processes and subsurface engineering applications, such as rock grouting, groundwater remediation, and enhanced oil recovery. Yet, how the displacement dynamics is impacted by the non‐Newtonian rheology remains an open question. Here, we conduct primary drainage experiments in which a shear‐thinning Xanthan gum solution displaces a silicone oil in a transparent rough fracture for a wide range of shear‐thinning property (controlled by polymer concentration) and flow rates. We first evaluate the effects of shear‐thinning property on displacement efficiency. Based on qualitative and quantitative analyses of the observed fluid morphologies, we present an experimental phase diagram of the obtained displacement patterns. We characterize a novel displacement pattern where the fluid‐fluid interface changes from stable (plug flow) to unstable (fingering) as the fracture aperture, averaged over the transverse direction, varies along the mean flow direction. We demonstrate that the existence of this mixed displacement pattern can be explained by local viscosity heterogeneity induced by the coupling of the shear‐thinning behavior and the spatial variability of apertures. Finally, we propose a theoretical model elucidating the mechanisms behind the flow regime transitions. The interface stability criterion predicted by this model exhibits good agreement with the experimental measurements, and stresses the potentially important role of fluid rheology, coupled to aperture variability, in immiscible displacements in rough fractures. These findings provide new insights into the dynamics of immiscible two‐phase flows with non‐Newtonian effects, and has potential implications for the aforementioned engineering applications.","PeriodicalId":23799,"journal":{"name":"Water Resources Research","volume":" ","pages":""},"PeriodicalIF":5.4,"publicationDate":"2023-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46837065","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The wetting front dynamics during water imbibition in dry porous media affect the ultimate water distribution pattern. In this study, we investigate the impact of pressure pulses that emit waves in the water phase on the water distribution and imbibition patterns in porous media. We present experimental results of water spatial distribution in sand columns following infiltration under abrupt pressured‐water pulses and compare them with those of continuous inflow. Applying pressure waves during infiltration increases pressure gradients behind the wetting front, which can overcome capillary and gravitational forces, leading to uniform imbibition. To simulate the process, we developed a pore‐network model incorporating an analytical solution of pressure wave attenuation to predict the imbibition pattern. Our results demonstrate that the amplitude of the pressure wave is associated with a sharp wetting front, resulting in higher water content compared to Darcy‐type continuous flow. The findings suggest that pressure waves have the potential to achieve high water content in unsaturated media and provide insights into the spatial extent of their impact on water distribution.
{"title":"Impact of Pressure Waves on Water Imbibition and Flow in Unsaturated Porous Media","authors":"Doron Kalisman, A. Yakirevich, S. Sorek, T. Kamai","doi":"10.1029/2023WR034461","DOIUrl":"https://doi.org/10.1029/2023WR034461","url":null,"abstract":"The wetting front dynamics during water imbibition in dry porous media affect the ultimate water distribution pattern. In this study, we investigate the impact of pressure pulses that emit waves in the water phase on the water distribution and imbibition patterns in porous media. We present experimental results of water spatial distribution in sand columns following infiltration under abrupt pressured‐water pulses and compare them with those of continuous inflow. Applying pressure waves during infiltration increases pressure gradients behind the wetting front, which can overcome capillary and gravitational forces, leading to uniform imbibition. To simulate the process, we developed a pore‐network model incorporating an analytical solution of pressure wave attenuation to predict the imbibition pattern. Our results demonstrate that the amplitude of the pressure wave is associated with a sharp wetting front, resulting in higher water content compared to Darcy‐type continuous flow. The findings suggest that pressure waves have the potential to achieve high water content in unsaturated media and provide insights into the spatial extent of their impact on water distribution.","PeriodicalId":23799,"journal":{"name":"Water Resources Research","volume":" ","pages":""},"PeriodicalIF":5.4,"publicationDate":"2023-08-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43322354","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
As drought and wildfire frequency increase across the western United States, our ability to predict how water resources will respond to these disturbances depends on our understanding of the feedbacks that maintain watershed function and streamflow. Previous studies of non‐perennial headwater streams have ranked drivers of low‐flow conditions; however, there is a limited understanding of the interactions between these drivers and the processes through which these interactions affect streamflow. Here, we use stream water level, soil moisture, sap flow, and vapor pressure deficit data to investigate eco‐hydrological interactions along a mountainous headwater stream. Correlation and cross‐correlation analyses of these variables show that ecohydrological interactions are (1) nonlinear and (2) interconnected, suggesting that analyses assuming linearity and independence of each driver are inadequate for quantifying these interactions. To account for these issues and investigate causal linkages, we use convergent cross‐mapping (CCM) to characterize the feedbacks that influence non‐perennial streamflow. CCM is a nonlinear, dynamic method that has only recently been applied to hydrologic systems. CCM results reveal that atmospheric losses associated with local sap flow and vapor pressure deficit are driving changes in soil moisture and streamflow (p < 0.01) and that atmospheric losses influence stream water more directly than shallow soil moisture. These results also demonstrate that riparian processes continue to affect subsurface flows in the channel corridor even after stream drying. This study proposes a nonlinear framework for quantifying the ecohydrologic interactions that may determine how headwater streams respond to disturbance.
{"title":"Nonlinear Riparian Interactions Drive Changes in Headwater Streamflow","authors":"Sarah K. Newcomb, S. Godsey","doi":"10.1029/2023wr034870","DOIUrl":"https://doi.org/10.1029/2023wr034870","url":null,"abstract":"As drought and wildfire frequency increase across the western United States, our ability to predict how water resources will respond to these disturbances depends on our understanding of the feedbacks that maintain watershed function and streamflow. Previous studies of non‐perennial headwater streams have ranked drivers of low‐flow conditions; however, there is a limited understanding of the interactions between these drivers and the processes through which these interactions affect streamflow. Here, we use stream water level, soil moisture, sap flow, and vapor pressure deficit data to investigate eco‐hydrological interactions along a mountainous headwater stream. Correlation and cross‐correlation analyses of these variables show that ecohydrological interactions are (1) nonlinear and (2) interconnected, suggesting that analyses assuming linearity and independence of each driver are inadequate for quantifying these interactions. To account for these issues and investigate causal linkages, we use convergent cross‐mapping (CCM) to characterize the feedbacks that influence non‐perennial streamflow. CCM is a nonlinear, dynamic method that has only recently been applied to hydrologic systems. CCM results reveal that atmospheric losses associated with local sap flow and vapor pressure deficit are driving changes in soil moisture and streamflow (p < 0.01) and that atmospheric losses influence stream water more directly than shallow soil moisture. These results also demonstrate that riparian processes continue to affect subsurface flows in the channel corridor even after stream drying. This study proposes a nonlinear framework for quantifying the ecohydrologic interactions that may determine how headwater streams respond to disturbance.","PeriodicalId":23799,"journal":{"name":"Water Resources Research","volume":" ","pages":""},"PeriodicalIF":5.4,"publicationDate":"2023-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43714022","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We present the satellite vegetation index time series model for detecting historical floods in ungauged hyperarid regions (SatVITS‐Flood). SatVITS‐Flood is based on observations that floods are the primary cause of local vegetation expansion in hyperarid regions. To detect such expansion, we used two time‐series metrics: (a) trend change detection from the Breaks For Additive Season and Trend and (b) a newly developed seasonal change metric based on Temporal Fourier Analysis (TFA) and the growing‐season integral anomaly (TFA‐GSIanom). The two metrics complement each other by capturing changes in perennial plant species following extreme, rare floods and ephemeral vegetation changes following more frequent floods. Metrics were derived from the time series of the normalized difference vegetation index, the modified soil‐adjusted vegetation index, and the normalized difference water index, acquired from MODIS, Landsat, and Advanced Very High‐Resolution Radiometer. The timing of the change was compared with the date of the flood and the magnitude of change with its volume and duration. We tested SatVITS‐Flood in three regions on different continents with 40‐year‐long, systematic, reliable gauge data. Our results indicate that SatVITS‐Flood can predict flood occurrence with an accuracy of 78% and precision of 67% (Recall = 0.69 and F1 = 0.68; p < 0.01), and the flood volume and duration with NSE of 0.79 (RMSE = 15.4 × 106 m3 event−1), and R2 of 0.69 (RMSE = 5.7 days), respectively. SatVITS‐Flood proved useful for detecting historical floods and may provide valuable long‐term hydrological information in poorly documented areas, which can help understand the impacts of climate change on the hydrology of hyperarid regions.
我们提出了卫星植被指数时间序列模型，用于检测未接种疫苗的超干旱地区的历史洪水（SatVITS‐Flood）。SatVITS‐洪水是基于洪水是超干旱地区当地植被扩张的主要原因的观测结果。为了检测这种扩展，我们使用了两个时间序列度量：（a）从加性季节和趋势的中断中检测趋势变化，以及（b）基于时间傅立叶分析（TFA）和生长季节积分异常（TFA-GSIanom）的新开发的季节变化度量。这两个指标通过捕捉极端罕见洪水后多年生植物物种的变化和更频繁洪水后短暂植被的变化来相互补充。从MODIS、Landsat和Advanced Very High Resolution Radiometer获得的归一化差异植被指数、改良土壤调整植被指数和归一化差异水分指数的时间序列中得出指标。将变化的时间与洪水发生的日期进行了比较，并将变化的幅度与洪水的水量和持续时间进行了比较。我们用40年的系统可靠的测量数据在不同大陆的三个地区测试了SatVITS洪水。我们的结果表明，SatVITS‐Flood可以预测洪水发生的准确率为78%，准确率为67%（Recall=0.69和F1=0.68；p<0.01），NSE的洪水量和持续时间分别为0.79（RMSE=15.4×106 m3事件−1）和0.69（RMSE=5.7天）。SatVITS‐Flood被证明可用于探测历史洪水，并可能在记录不足的地区提供有价值的长期水文信息，这有助于了解气候变化对超干旱地区水文的影响。
{"title":"SatVITS‐Flood: Satellite Vegetation Index Time Series Flood Detection Model for Hyperarid Regions","authors":"Omer Burstein, T. Grodek, Y. Enzel, D. Helman","doi":"10.1029/2023WR035164","DOIUrl":"https://doi.org/10.1029/2023WR035164","url":null,"abstract":"We present the satellite vegetation index time series model for detecting historical floods in ungauged hyperarid regions (SatVITS‐Flood). SatVITS‐Flood is based on observations that floods are the primary cause of local vegetation expansion in hyperarid regions. To detect such expansion, we used two time‐series metrics: (a) trend change detection from the Breaks For Additive Season and Trend and (b) a newly developed seasonal change metric based on Temporal Fourier Analysis (TFA) and the growing‐season integral anomaly (TFA‐GSIanom). The two metrics complement each other by capturing changes in perennial plant species following extreme, rare floods and ephemeral vegetation changes following more frequent floods. Metrics were derived from the time series of the normalized difference vegetation index, the modified soil‐adjusted vegetation index, and the normalized difference water index, acquired from MODIS, Landsat, and Advanced Very High‐Resolution Radiometer. The timing of the change was compared with the date of the flood and the magnitude of change with its volume and duration. We tested SatVITS‐Flood in three regions on different continents with 40‐year‐long, systematic, reliable gauge data. Our results indicate that SatVITS‐Flood can predict flood occurrence with an accuracy of 78% and precision of 67% (Recall = 0.69 and F1 = 0.68; p < 0.01), and the flood volume and duration with NSE of 0.79 (RMSE = 15.4 × 106 m3 event−1), and R2 of 0.69 (RMSE = 5.7 days), respectively. SatVITS‐Flood proved useful for detecting historical floods and may provide valuable long‐term hydrological information in poorly documented areas, which can help understand the impacts of climate change on the hydrology of hyperarid regions.","PeriodicalId":23799,"journal":{"name":"Water Resources Research","volume":" ","pages":""},"PeriodicalIF":5.4,"publicationDate":"2023-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49523945","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Reducing flood risk through disaster planning and risk management requires accurate estimates of exposure, damage, casualties, and environmental impacts. Models can provide such information; however, computational or data constraints often lead to the construction of such models by aggregating high‐resolution flood hazard grids to a coarser resolution, the effect of which is poorly understood. Through the application of a novel spatial classification framework, we derive closed‐form solutions for the location (e.g., flood margins) and direction of bias from flood grid aggregation independent of any study region. These solutions show bias of some key metric will always be present in regions with marginal inundation; for example, inundation area will be positively biased when water depth grids are aggregated and volume will be negatively biased when water surface elevation grids are aggregated through averaging. In a separate computational analysis, we employ the same framework to a 2018 flood and successfully reproduce the findings of our study‐region‐independent derivation. Extending the investigation to the exposure of buildings, we find regions with marginal inundation are an order of magnitude more sensitive to aggregation errors, highlighting the importance of understanding such artifacts for flood risk modelers. Of the two aggregation routines considered, averaging water surface elevation grids better preserved flood depths at buildings than averaging of water depth grids. This work provides insight into, and recommendations for, aggregating grids used by flood risk models.
{"title":"Bias in Flood Hazard Grid Aggregation","authors":"Seth Bryant, H. Kreibich, B. Merz","doi":"10.1029/2023WR035100","DOIUrl":"https://doi.org/10.1029/2023WR035100","url":null,"abstract":"Reducing flood risk through disaster planning and risk management requires accurate estimates of exposure, damage, casualties, and environmental impacts. Models can provide such information; however, computational or data constraints often lead to the construction of such models by aggregating high‐resolution flood hazard grids to a coarser resolution, the effect of which is poorly understood. Through the application of a novel spatial classification framework, we derive closed‐form solutions for the location (e.g., flood margins) and direction of bias from flood grid aggregation independent of any study region. These solutions show bias of some key metric will always be present in regions with marginal inundation; for example, inundation area will be positively biased when water depth grids are aggregated and volume will be negatively biased when water surface elevation grids are aggregated through averaging. In a separate computational analysis, we employ the same framework to a 2018 flood and successfully reproduce the findings of our study‐region‐independent derivation. Extending the investigation to the exposure of buildings, we find regions with marginal inundation are an order of magnitude more sensitive to aggregation errors, highlighting the importance of understanding such artifacts for flood risk modelers. Of the two aggregation routines considered, averaging water surface elevation grids better preserved flood depths at buildings than averaging of water depth grids. This work provides insight into, and recommendations for, aggregating grids used by flood risk models.","PeriodicalId":23799,"journal":{"name":"Water Resources Research","volume":" ","pages":""},"PeriodicalIF":5.4,"publicationDate":"2023-08-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47989932","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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