查看更多>>摘要：Recent increases in the incidences of wildfires have necessitated the development of methodologies to quantify the effect of these fires on streamflows. Climate variability has been cited as a major challenge in revealing the true contribution of disturbance to streamflow changes. To address this, we developed an annual Budyko "decomposition" method for (1) statistical change detection of hydrologic signatures post-fire, (2) separating climate-driven and fire-driven changes in streamflow, and (3) estimating hydrologic recovery timescales after fire. We demonstrate the use of this methodology for 17 watersheds in Southern California with high interannual variability in precipitation. We show that while traditional metrics like changes in flow or runoff ratio might not detect a disturbance effect due to confounding climate signals, the Budyko framework can be used successfully for statistical change detection. The Budyko approach was also found to be robust in detecting changes in 5 highly burned catchments (>40% burned area ratio), while changes in less burned (2) and unburned catchments (10) were insignificant. We further used the Budyko approach to quantify the contribution of fire-driven versus climate driven changes in streamflow and found that fire contributed to an average increase in streamflow on the order of 80 mm yr 1, though the effect varied greatly between years. Finally, we estimated hydrologic recovery timescales that varied between 5 and 45 years for four burned catchments. We found a significant linear relationship between recovery time and burned area at medium and high severity for our study catchments, with about 4 years of recovery time per 10% of the watershed burned.
查看更多>>摘要：Water-rock interaction (WRI) and prior calcite precipitation (PCP) are often employed to interpret the variation in the trace elements present in speleothems and are assumed to be strengthened under drier climates. However, this interpretation is sometimes not consistent with speleothem records in monsoonal China (Zhou et al., 2011; Ban et al., 2018). In this study, a three-year monitoring program was carried out from 2012 to 2014 at Kaiyuan Cave on Shandong Peninsula, coastal North China to investigate how the element geochemistry of drip-water responds to changes in hydroclimate. It was found that trace elements and their ratios to Ca (X/Ca ratio) responded differently to hydroclimatic change at Kaiyuan Cave during the period from 2012 to 2014. Sr and Ba, which are controlled by incongruent dissolution of the host-rock and are sensitive to residence time, show a long -term increasing trend from 2012 to 2014, while Mg and U illustrate a long-term decreasing trend possibly due to reduced dissolution of the host-rock and less input from the soil layer. All the X/Ca ratios are affected by WRI, but the soil layer may have played a role to some extent on the Sr/Ca, Ba/Ca and U/Ca ratios. These findings indicate that trace elements (and X/Ca ratios) of karstic drip-water and speleothems do not respond in the same direction to hydroclimate change as is often suggested in previous publications. Caution is advised when these geochemical proxies are applied to interpret changes in precipitation and/or summer monsoon intensity in China.
Baek, Ji-YoungPark, Byeong-HakRau, Gabriel C.Lee, Kang-Kun...
12页
查看更多>>摘要：When modelling heat transport in hydrogeological systems, a standard assumption is local thermal equilibrium (LTE), which implies that the porous medium temperature at the interface between the solid and fluid instantaneously reaches equilibrium. Few studies have investigated the validity of the LTE assumption and its violation, also known as local thermal non-equilibrium (LTNE), as well as its impact on the accuracy of heat transport models. While the theoretical conditions under which LTNE occurs in natural groundwater flow have recently been revealed, these have not yet been experimentally verified. We examined the applicability of the LTE assumption by conducting systematic laboratory experiments using eight distinct flow velocities (Reynolds number, Re < 0.37) through sand (0.76 mm grain size), injecting both heat and solute as tracers and observing the response at multiple points downstream. Theoretical heat transport parameters were calculated from solute tracer experiments by applying a retardation factor, and the results were subsequently compared to the actual parameters estimated from heat tracing. Our experimental results confirm that the LTE assumption can be violated under natural groundwater flow conditions, and that LTNE impacts thermal dispersion coefficients more significantly than thermal front velocities. The largest differences between the predicted and estimated thermal transport parameters were 112% and 13% for the dispersion coefficients and velocities, respectively. Our results demonstrate that LTNE effects need to be considered in heat transport modelling especially when analyzing thermal dispersion coefficients.
查看更多>>摘要：Quantifying the regional evapotranspiration is critical in terrestrial water balance and global water cycle, while partitioning of evapotranspiration is challenging but fundamental to predict the fate of terrestrial ecosystems under climate changes. Here, we performed in-situ measurements of water isotopes in atmospheric vapor, plant tissues and soil pools in a Pinus yunnanensis forest ecosystem in southwest China, aiming to partitioning ET by estimating the stable isotopic compositions of ET and that of its two components, i.e., plant transpiration and soil water evaporation. We used combined high-frequency laser spectroscopy and chamber methods, to constrain the estimates of T/ET. We first found that the estimated daily T/ET ratio ranges from 0.59 to 0.81, with an apparent increasing shift in the early growing season and maintaining a plateau level of over 0.75 during the peak growing season. This higher averaged T/ET of 0.73 +/- 0.06 indicates that plant transpiration is the main component of evapotranspiration. The estimated dE and dT are in agreement with result from customized chamber method. We also found that in monsoon season (in June-September), soil water content is the main control of T/ET variations, with leaf area index playing only a partial role. Our study confirms the critical impact of soil water on the seasonal change of T/ET in Pinus yunnanensis ecosystem such as the SW China. However, we are also aware the sensitivity of controls on estimated T/ET at different time scale interested. Our results here provide insight into the regional hydrological cycle in alpine forest ecosystem and potentially benefits many applications from forest ecosystem protection to paleo isotope archives.
查看更多>>摘要：To quantify the hydrological effects of disconnected impervious area is significant for urban planning and storm water management. Most relevant studies were event-based analysis and only focused on surface runoff. The accumulated impacts of disconnected imperviousness on both surface and subsurface runoff have not been fully understood yet. In this study, a physically based model coupling surface runoff, subsurface runoff and evapotranspiration was constructed for continuous simulation of the hydrological processes in an RPA (receiving pervious area)-DIA (disconnected impervious area) system at street block scale. Five RPA types with natural clay loam, compacted clay loam, natural sandy clay loam and depressed clay loam were considered. For each RPA type, urban development scenarios with varying disconnected impervious area ratios (DIRs) were designed. The results presented that both the annual total and averaged event-based surface runoff followed a generally Power form relationship with DIR for all the RPA types, which can be satisfactorily described by a concise and meaningful formula. Disconnected impervious surface can lead to higher event-based initial soil moistures, and it is much more significant when during dry months (autumn and winter) with less potential evapotranspiration intensity than during wet months (spring and summer). This results imply the importance to take the potential increased initial soil moisture of RPA and the corresponded increased runoff generation into consideration of storm water management when imperviousness disconnection is applied. At last, with the increase of DIR, the annual total groundwater recharge had a tendency to rise first and then decrease. This proves the possibility of improving underground water resource storage or maintain the groundwater recharge to the predeveloped level in the process of urban imperviousness expanding. Since this simulation work lacks on-ground validation, further studies based on the conclusions are still needed from the perspective of measured data analysis in urban RPADIA system.
查看更多>>摘要：Increasing legal requirements by local and regional governments to protect hydrosystems and maintain their hydrological services require nowadays the identification of wetlands of particular interest for conservation. Individual wetlands, however, have a limited effect on these services, especially on stream flow at the watershed scale in general. On the other hand, the compound effect of all wetlands does not allow for the identification of wetlands with substantial effects. Building on previous hydrological modelling development and seeking for a compromise between assessing the impact of individual wetlands and all wetlands, we propose the creation of wetland networks (i.e., wetlandscapes) based on: (i) geographic location, (ii) typology, (iii) wetland area, and (iv) contributing area. Thus, we tested the relevance of different ways of building wetland networks using the semi-distributed hydrological model HYDROTEL with a case study, that of the St. Charles River watershed, Quebec, Canada. We defined 48 wetland networks and assessed their capacity to attenuate peak flows and support low flows using 47 years of meteorological data, at both the sub-watershed scale and the watershed scale. Our results clearly demonstrate differences in the networks effect, confirming the relevance of the proposed framework. Although large wetlands with large contributing areas tend to have the strongest effect on high and low flows, we illustrate that small wetlands with large contributing areas can have a significant effect on extreme stream flows. This study also suggests that riparian wetlands might amplify peak flows as well as low flows. The application of the proposed modelling framework to various climates and geological contexts has the potential to be useful to support the design of wetland conservation programs and to meet some legal requirements based on the protection of wetland networks.
查看更多>>摘要：Assessment of the accuracy of satellite-based precipitation products (SPPs) is essential prior to their use in formal applications. However, thorough assessments of SPPs by traditional approaches are typically not practical when gauge observations are sparse. The triple collocation (TC) approach can be used to perform spatially continuous assessments, but TC is affected by error and bias. In this study, a novel approach for the spatially continuous assessment of SPPs that integrates TC and the traditional discrete gauge-based approach via geographically weighted regression (GWR) was developed. This approach, referred to as TC-GWR, allows SPPs to be assessed in areas with limited gauge observations. The TC-GWR was tested comprehensively through using four widely-used SPPs over mainland China. The TC-GWR generates spatially continuous assessment results for SPPs and outperforms significantly the original TC approach in assessing the accuracy of SPPs quantitatively. The performance of TC-GWR was generally robust to variation in the density of gauge stations (50, 100, 200, 400, and 800 gauge stations) and showed acceptable performance when gauge data are relatively sparse, except for the extremely sparse gauge cases (only 10 stations over mainland China). Overall, TC-GWR integrates the advantages of the traditional approach (higher reliability) and the TC approach (spatial continuity) and provides a valuable alternative for assessing SPPs in areas with limited gauge observations, such as remote mountainous areas and developing countries.
查看更多>>摘要：ABSTR A C T The complexity of rainfall-canopy interactions is likely to increase under extreme weather events. Extreme conditions may affect forest structure and change the throughfall (TF) spatial distribution over time. Mistakenly claiming the time stability of TF spatial variability can lead to misunderstanding the rainfall-canopy interactions, obscuring the relationships between weather, forests, and hydrology. Herein we rely on an unprecedented six-hydrological-year event-based dataset from the Brazilian Atlantic Forest, spanning from 2013 to 2019 (summing up 427 rainfall events) to assess: (i) the effects of a prolonged drought period on the TF time stability; and (ii) the importance of forest structure for the TF time stability. The mean relative difference and time stability index were applied for different period lengths and related to forest structure, gross rainfall amount (GR), maximum rainfall intensity, and drought occurrence to assess whether they affect the TF spatial variability. The results indicated that the throughfall spatial variability is less time stable during droughts due to a combination of more light intensity events with some extreme intensities (> 20 mm h(-1)), which were not observed in the non-drought period. Changes in forest structure became evident after drought conditions and could not be tracked in studies with short monitoring periods. Since throughfall spatial distribution is driven by forest structure (e.g., tree density, species dominance, and biomass), such dynamics affected the time stability of the spatial variability. The time instability was even greater for GR < 10 mm because of the greater rainfall-canopy interactions prior to canopy saturation. Therefore, not accounting for forest dynamics and drought effects on the TF spatial variability lead to misinterpreting time stability.
查看更多>>摘要：Pan evaporation (Epan) reflects the evaporation potential of surface water and is a key indicator of atmospheric evaporative demand. Previous studies have found a substantial decrease in Epan across China, dominated by declining wind speed and solar radiation before the late 2000 s. However, how Epan responds to the recovery of wind speed and solar radiation since the late 2000 s remains unclear. Here, we investigate the spatial and temporal patterns of Epan and analyze its controlling factors, based on the daily meteorological observations during 1965-2018 at 2,018 stations over China. We find that the annual Epan in the northwest and south of China is higher than that in the northeast and central parts of China. The national mean Epan decreases significantly during 1965-1989 at a rate of-6.57 mm yr(-2), then reverses at a rate of 4.58 mm yr(-2). Distinct seasonal discrepancies and geographical heterogeneities in Epan trends are observed. Declining wind speed mainly contributes to the decrease in Epan before 1989, while relative humidity is shown as the dominant factor that drives the growth of Epan after the turning point. The recovery of wind speed still has significant impact on Epan variation in parts of China, while Epan is only mainly affected by solar radiation in parts of central China in autumn. Our findings highlight the importance of understanding Epan variations and driving factors, and call for precautions and adaptation actions to combat and prevent flash droughts over China, especially in the south of China.
查看更多>>摘要：Blue water (irrigation water) and green water (rainwater) constitute the indispensable inputs in crop production, and they virtually flow through crop trade. The valuation of water for crops is becoming essential for providing not only guidance in measuring both the biophysical and economic sustainability of agricultural water resources but also crucial information for investors and authorities engaged in water allocations. However, valuation of green water has been severely disregarded. Here, taking the Yellow River Basin as the study case, we show the feasibility of estimating the value of green water for crop production considering the costs in production processes in addition to blue water valuation. Thus, the volume versus value of blue and green water consumed in crop production as well as that of corresponding virtual water (VW) flows related to crop transfers within the basin are comparable. Fourteen major crops in current three typical years and four scenarios for the year 2050 under climate-socio-economic changes are examined. Results show that value of blue water was approximately 3 times that of green water for irrigated crops, whereas at similar level to the value of green water for rain-fed crops. Visible trade-offs between the regional volume and value of water used in crop production and that of the intra-national VW flows exist in terms of magnitude in time and space, as well as the structure by crops. The total volumes of the water footprint (WF), i.e., water consumption, in crop production and VW exports changed little over years, however the corresponding total water values was tripled and seven-folded, respectively, due to apple production expansions. Wheat was the biggest contributor in volume of VW export while apple accounted the most in value of VW export of the basin. The considered scenarios for 2050 suggested that the reduced values of crop-related WF and VW flows were more sensitive than the corresponding water quantity. This study implies the importance of managing the internal trade-offs or mutual effects between water resources and economic returns.
NSTL
Elsevier