Net Rainfall Research Articles

Applicability of a Modified Gash Model for Artificial Forests in the Transitional Zone between the Loess Hilly Region and the Mu Us Sandy Land, China

Afforestation in the transitional zone between the loess hilly area and the Mu Us Sandy Land of China has reshaped the landscape and greatly affected eco-hydrological processes. Plantations are crucial for regulating local net rainfall inputs, thus making it necessary to quantify the closure loss of plantation species in drought and semi-arid areas. To quantify and model the canopy interception of these plantations, we conducted rainfall redistribution measurement experiments. Based on this, we used the modified Gash model to simulate their interception losses, and the model applicability across varying rainfall types was further compared and verified. Herein, Caragana korshinskii, Salix psammophila, and Pinus sylvestris plantations in the Kuye River mountain tract were chosen to measure the precipitation distribution from May to October (growing season). The applicability of a modified Gash model for different stands was then evaluated using the assessed data. The results showed that the canopy interception characteristics of each typical plantation were throughfall, interception, and stemflow. The relative error of canopy interception of C. korshinskii simulated by the modified Gash model was 8.79%. The relative error of simulated canopy interception of S. psammophila was 4.19%. The relative error of canopy interception simulation of P. sylvestris was 13.28%, and the modified Gash model had good applicability in the Kuye River Basin. The modified Gash model has the greatest sensitivity to rainfall intensity among the parameters of the C. korshinskii and S. psammophila forest. The sensitivity of P. sylvestris in the modified Gash model is that the canopy cover has the greatest influence, followed by the mean rainfall intensity. Our results provide a scientific basis for the rational use of water resources and vegetation restoration in the transitional zone between the loess hilly region and the Mu Us Sandy Land. This study is of import for the restoration and sustainability of fragile ecosystems in the region.

Research on the distributed Clark confluence model based on basic watershed units

Abstract Based on the confluence principle, the confluence should represent the aggregate of net rainfall confluences within each distinct basic watershed unit (BWU) of a basin. The BWUs are categorized as V-type and Horseshoe-type based on their shape characteristics and two types of time–area curves of slope convergence have been derived separately. The cascade river convergence is modeled using a lagged linear reservoir, resulting in the development of a distributed CLARK convergence model based on the BWUs of a basin (BWU-DCLARK). The key findings are as follows: (1) The BWU-DCLARK model effectively captures the runoff convergence process and has been successfully applied in the Yanduhe River basin. Modeling results demonstrate high simulation accuracy. (2) The time of slope convergence indicates that the regulatory and storage effects on runoff of BWUs cannot be overlooked. (3) The BWU-DCLARK confluence model not only enables the calculation of flow at the basin outlet but also facilitates the computation of flow at any node along the river chain which is of great significance for hydrological forecasting in un-gauged basins but the application effect will need further verification.

Development of low-cost rainwater harvesting to support on-site water supply in rural Tajikistan

Farmers in remote, arid areas, far from available water sources, need affordable water solutions for household and livestock use. In this study, the water needs and potential for rainwater harvesting (RWH) in the Kysylsu River Basin are estimated at different altitudes. The mean annual net rainfall depth varied from 545 to 900 mm. With an average roof area of 550 m2, 211 m3 to 344 m3 rainwater can be harvested for dry and wet years respectively. Based on the estimated water demand and rainfall deficit, the average household need was estimated to be 100 m3. For a low-cost water storage solution, we tested different types of waterproof materials to replace smaller 12-18 m3 concrete tanks commonly used in the region. Soil pits lined with 0.3 mm double layer polyethene (0.6 mm in total) was the best solution for 5 m3 volume tanks in terms of the costs and durability and 0.8 mm double layer polyethene (1.6 mm in total) was ideal for sealing 10 m3 volume tanks. This study demonstrates the efficiency of the system for improved livelihood of the families through rain harvesting.

Dam periodic storage drives the spatial pattern of vegetation towards banded evolution

Emerging and fragile ecosystems such as reservoir riparian zones are of increasing concern with the increasing number of damming projects worldwide. Current knowledge of riparian vegetation in reservoirs focuses on the individual and community level, with little understanding of spatial patterns and ecological processes at the landscape level. Here, we demonstrate the evolution process, evolution direction, and evolution mechanism of vegetation spatial patterns under persistent and periodic inundation disturbances in the reservoir riparian zone, through coupled analyses of landscape evolution and ecological processes, using continuous years of drone observation data in the riparian zones of two major reservoirs, Xiaowan and Nuozhadu of the Lancang River. We found that vegetation landscape evolution is driven by seed dispersal, environmental factors fluctuations, species tolerance differences, and competition for resource availability, showing a clear trend towards banded evolution. Ecological niche processes such as periodic wet-dry environmental filtering and interspecific competition dominated the formation of vegetation banding patches, and neutral processes of random seed dispersal dominated the areas where banding patches were formed. The water requirements of plants during the exposing period lead to a greater influence of environmental factors that are closely related to water, such as net rainfall, sunshine hours, groundwater storage, and soil moisture. Water redistribution between vegetated and bare ground patches is key to their formation and stability in the upper part of the riparian zone, where drought stress is severe, while in the lower part, vegetation is mainly affected by inundation stress during flooding periods. Therefore, riparian vegetation restoration is critical to maintain a certain area of bare ground patches for drought areas in the exposing period, in contrast to the emphasis on vegetation patch coverage. And it is possible to carry out spatial planning based on the development trend of the belt distribution, taking into account the flood and drought tolerance of the species as well as the fluctuating rhythms of the main factors, such as the rainfall, which is worth exploring further.

Evaporation of intercepted rainfall–Comparing canopy water budget and energy balance related long term measurements at a Norway spruce site

Rain interception of a Norway spruce stand was analyzed based on canopy water balance measurements Emass and for two eddy covariance (EC) related methods covering a long period (2008–2018). Emass was calculated as residual between gross rainfall above and net rainfall below the canopy. EC related observations are based on the water equivalent either (i) directly measured by eddy covariance (ETEC) or (ii) as residual in the Energy Balance equation (ETEB). To relate the different methods to wet canopy conditions, the Rutter model was used to dynamically calculate water storage in the canopy. Finally, the different time series were integrated over the duration of modeled interception events.The canopy water balance shows a mean annual gross precipitation of 936 ± 173 mm/year of which 376 ± 56 mm/year evaporated due to interception. The majority of rainfall events (81%) is characterized by a depth <5 mm, which leads to a high fraction of annual precipitation being captured by the canopy surface (0.41). The application of the Rutter model yielded good agreement between observed and modeled throughfall and served as a reasonable standard to define interception events. Wet canopy evaporation as the residual of the energy balance ETEB and from gas analyzer measurements ETEC are both systematically underestimating Emass. The mean annual underestimation of Emass is 145 mm/year for ETEB and 288 mm/year for ETEC. Most of the discrepancy can be mainly explained by an underestimation of turbulent fluxes, at which data is most affected during raining conditions. An analysis of the linear relation between the annual sum of turbulent fluxes and available energy shows the lowest slope (0.57 ± 0.15) for measurements during rainfall, while the highest slope (0.76 ± 0.03) occurs under completely dry conditions. Both fluxes should be gap-filled and corrected separately for dry (transpiration) and wet (interception) conditions in order to determine proper amounts of evapotranspiration with the eddy covariance method.

Modelling the influence of mechanical-ecohydrological feedback on the nonlinear dynamics of peatlands

Peatlands are complex systems that exhibit nonlinear dynamics due to internal and external feedback mechanisms. However, the feedback of vegetation on peat volume changes that potentially affect peatland dynamics is not well understood. Here, we analyse the consequences of coupling between plant functional types with peat stiffness on a nonequilibrium model of a peatland by developing MPeat model. In this formulation, the peat systems prefer to exist in two possible states defined by two limit cycles, one corresponding to a wet and the other to a dry attractor. These states can also coexist under the same net rainfall indicating bistability in which a crucial drying threshold leads to a tipping point and associated regime shift from soft-wet to stiff-dry states with related changes in rates of carbon storage. While the shift from wet to dry states constitutes a tipping point, to shift from the dry to wet states requires more sustained increases in net rainfall, indicating that dry state is the more stable attractor as the peatland grows. As the model peatland evolves, the response of surface motion, carbon accumulation, and water table depth to the same external forcing becomes increasingly higher amplitude indicating that a degree of caution may be required when interpreting the paleorecord. Investigation of the behaviour of these states in response to seasonal variations in water budget suggests that the wet state will display high amplitude and later peak timing when compared to the dry state, a phenomenon that is observed in measures of surface motion. Our study highlights the possible importance of mechanical-ecohydrological feedback and, in particular, the role of the coupling between the proportion of plant functional types, peat Young's modulus, plant weight, and water table position in influencing peatland regime shifts, critical thresholds or tipping points, and both short- and long-term peatland dynamical behaviour.

A research agenda for nonvascular photoautotrophs under climate change.

Nonvascular photoautotrophs (NVP), including bryophytes, lichens, terrestrial algae, and cyanobacteria, are increasingly recognized as being essential to ecosystem functioning in many regions of the world. Current research suggests that climate change may pose a substantial threat to NVP, but the extent to which this will affect the associated ecosystem functions and services is highly uncertain. Here, we propose a research agenda to address this urgent question, focusing on physiological and ecological processes that link NVP to ecosystem functions while also taking into account the substantial taxonomic diversity across multiple ecosystem types. Accordingly, we developed a new categorization scheme, based on microclimatic gradients, which simplifies the high physiological and morphological diversity of NVP and world-wide distribution with respect to several broad habitat types. We found that habitat-specific ecosystem functions of NVP will likely be substantially affected by climate change, and more quantitative process understanding is required on (1) potential for acclimation, (2) response to elevated CO2 , (3) role of the microbiome, and (4) feedback to (micro)climate. We suggest an integrative approach of innovative, multimethod laboratory and field experiments and ecophysiological modelling, for which sustained scientific collaboration on NVP research will be essential.

Experimental partitioning of rainfall into throughfall, stemflow and interception loss by Haloxylon ammodendron, a dominant sand-stabilizing shrub in northwestern China

Rainfall partitioning by the vegetation canopy represents a significant component of the local hydrological cycle by reshaping the amount and spatial distribution of rainfall. Measuring the components of rainfall partitioning, however, has been a challenging task due to laborious- and time-consuming field experiments. In this study, to probe the influences of long-term afforestation on dynamic patterns of rainfall partitioning, the dominant sand-stabilizing shrub Haloxylon ammodendron at three different ages was selected for field measurements during the 2020–2021 growing season. The throughfall percentage for young H. ammodendron (YH, 75.9 %) was significantly higher than that for middle-aged H. ammodendron (MAH, 63.4 %) and mature H. ammodendron (MH, 62.4 %) (p < 0.05 for all cases). However, the interception loss percentage of YH (22.3 %) was significantly lower than that for MAH (35.0 %) and MH (36.5 %) (p < 0.05 for all cases). No significant difference was found for stemflow percentage among YH (1.8 %), MAH (1.5 %) and MH (1.1 %). Smaller rainfall events contributed to a higher interception loss percentage and a lower net rainfall percentage for all ages. Both throughfall and stemflow percentage first showed increasing trends and then tended to be stable with increasing rainfall amount and duration, whereas interception loss percentage showed the opposite patterns. Rainfall partitioning was significantly correlated with the plant area index, stem basal area and canopy height (p < 0.05 for all cases), which may account for significant differences in rainfall partitioning patterns, as all shrubs experienced the same weather conditions. The average funneling ratio was 56.6, 26.7 and 17.9 for YH, MAH and MH, respectively. These results suggested that H. ammodendron afforestation can have a significant impact on rainfall partitioning by reducing net rainfall reaching the soil and may have some implications for local water budget and ecosystem management in oasis–desert ecotones.

The transfR toolbox for transferring observed streamflow series to ungauged basins based on their hydrogeomorphology

This R package technically gathers the methods developed and lessons learnt over recent years for estimating discharge of ungauged outlets, in a runoff–runoff type approach (discharge is both the input and output). It uses the observed discharge of neighbouring gauged basins and a geomorphology-based deconvolution–convolution modelling approach. The continuous hydrological modelling is based on the description of the hydro-geomorphometry of the river drainage network that can be easily described for any outlet considered. An inversion of this model allows us to deconvolute the observed discharge series and to estimate the signal of the water flowing into rivers from the hillslope, namely the net rainfall. The transfer of this net rainfall to a targeted ungauged basin enables the simulation of the discharge series there. The methodology has been tested in several hydro-climatic contexts, and with this package we aim to encourage further evaluation and improvement as well as subsequent operational applications.

Flood patterns in a catchment with mixed bedrock geology and a hilly landscape: identification of flashy runoff contributions during storm events

Abstract. With flash flood events having been repeatedly observed in Central and Western Europe in recent years, there is a growing interest in how catchment physiographic properties and hydrological conditions are eventually controlling rapid and concentrated hydrological responses. Here we focus on a set of two nested catchments in Luxembourg (Europe) that have been exposed in 2016 and 2018 to flash flood events and study their seasonal runoff time transfer distributions. Both catchments are of similar size (∼ 30 km2) and have analogous hydrological distance distributions, but their geological bedrock and landscape features are notably different. The upper catchment (KOE) is dominated by a low land area (38 % of the catchment is located less than 30 m above the river network) consisting of variegated marly bedrock (middle Keuper Km3) and moderately steep Luxembourg sandstone outcrops (lower Liassic Li2). The lower catchment (HM) has its drainage network deeply cut into the Luxembourg sandstone, with half of it being covered by marly plateaus (Lower Liassic Li3, located between 80 and 100 m above the river network) featuring heavy clay soil. Based on data generated from a dedicated hydro-meteorological monitoring network, we calculated for 40 rainfall–runoff events observed between August 2019 and July 2021 the corresponding net rainfall transfer time distributions (TTDs) from the hillslopes to the catchment outlet. We then compared the TTD properties and related them to the catchment's hydrological state and rainfall properties. We observed a marked seasonality in TTDs for both catchments. The KOE catchment reacts fastest during the winter period (December–February), while its response time is most delayed and spread out during periods of catchment recharging (October–November) and drying (March–May). The HM catchment exhibits similar TTDs during the mid-October to mid-April period, but they diverge markedly during the remaining part of the year, with opposite variations. During the mid-April to mid-October period, the average response time increases progressively in the KOE catchment. This behavior is in stark contrast to the HM catchment, where response times are significantly shorter (peak discharge delay time decreases by −70 % ± 28 %) and more concentrated (runoff volume occurring in 1 h increases by +48 % ± 87 %) during the mid-April to mid-October, in comparison to the extended winter period. This opposite seasonality leads us to consider different control factors of the runoff transfer processes in relation with the topographic and geological layout of the catchment areas. In the KOE catchment, we found the TTD to be essentially driven by onset and cessation of hydrological connectivity on the flat marly terrain – the latter operating like a variable contributing area in terms of deep soil storage dynamics (except for one summer event). The HM section exhibits contrasted TTDs throughout the year, suggesting threshold-dependent hydrological processes. More specifically, particularly quick runoff transfers seem to dominate under dry conditions (mid-April to mid-October). Correlation analyses compared to the literature on runoff generation on the one hand and our descriptive knowledge of the catchments on the other hand suggest multiple causes for the triggering of these rapid flows. The fractured marly plateaus, but also the hydrophobic forest litter forming during dry conditions on steep slopes, stand as our main hypotheses in this respect. Moreover, the absence of a riparian zone, preventing any dampening of (observed) abrupt and massive flows during extreme precipitation events, also seems to be a key feature of the rapid runoff transfer. For improving our understanding and forecasting capabilities in Luxembourg (and more broadly in the nearby regions of Germany, Belgium, and France with similar physiographic and climate conditions), we recommend further studies focusing on catchments with fractured bedrock and limited riparian zones. Special attention may equally be given to the hypothesized responses of hydrophobic soil surfaces on steep hillslopes and marly soils to heavy precipitation events occurring after extended dry spells.

Effect of dust on rainfall over the Red Sea coast based on WRF-Chem model simulations

Abstract. Water is the single most important element of life. Rainfall plays an important role in the spatial and temporal distribution of this precious natural resource, and it has a direct impact on agricultural production, daily life activities, and human health. One of the important elements that govern rainfall formation and distribution is atmospheric aerosol, which also affects the Earth's radiation balance and climate. Therefore, understanding how dust compositions and distributions affect the regional rainfall pattern is crucial, particularly in regions with high atmospheric dust loads such as the Middle East. Although aerosol and rainfall research has garnered increasing attention as both an independent and interdisciplinary topic in the last few decades, the details of various direct and indirect pathways by which dust affects rainfall are not yet fully understood. Here, we explored the effects of dust on rainfall formation and distribution as well as the physical mechanisms that govern these phenomena, using high-resolution WRF-Chem simulations (∼ 1.5 km × 1.5 km) configured with an advanced double-moment cloud microphysics scheme coupled with a sectional eight-bin aerosol scheme. Our model-simulated results were realistic, as evaluated from multiple perspectives including vertical profiles of aerosol concentrations, aerosol size distributions, vertical profiles of air temperature, diurnal wind cycles, and spatio-temporal rainfall patterns. Rainfall over the Red Sea coast is mainly caused by warm rain processes, which are typically confined within a height of ∼ 6 km over the Sarawat mountains and exhibit a strong diurnal cycle that peaks in the evening at approximately 18:00 local time under the influence of sea breezes. Numerical experiments indicated that dust could both suppress or enhance rainfall. The effect of dust on rainfall was calculated as total, indirect, and direct effects, based on 10-year August-average daily-accumulated rainfall over the study domain covering the eastern Red Sea coast. For extreme rainfall events (domain-average daily-accumulated rainfall of ≥ 1.33 mm), the net effect of dust on rainfall was positive or enhancement (6.05 %), with the indirect effect (4.54 %) and direct effect (1.51 %) both causing rainfall increase. At a 5 % significance level, the total and indirect effects were statistically significant whereas the direct effect was not. For normal rainfall events (domain-average daily-accumulated rainfall &lt; 1.33 mm), the indirect effect enhanced rainfall (4.76 %) whereas the direct effect suppressed rainfall (−5.78 %), resulting in a negative net suppressing effect (−1.02 %), all of which were statistically significant. We investigated the possible physical mechanisms of the effects and found that the rainfall suppression by dust direct effects was mainly caused by the scattering of solar radiation by dust. The surface cooling induced by dust weakens the sea breeze circulation, which decreases the associated landward moisture transport, ultimately suppressing rainfall. For extreme rainfall events, dust causes net rainfall enhancement through indirect effects as the high dust concentration facilitates raindrops to grow when the water vapor is sufficiently available. Our results have broader scientific and environmental implications. Specifically, although dust is considered a problem from an air quality perspective, our results highlight the important role of dust on sea breeze circulation and associated rainfall over the Red Sea coastal regions. Our results also have implications for cloud seeding and water resource management.

A New Urban Waterlogging Simulation Method Based on Multi-Factor Correlation

Waterlogging simulation is a key technology for solving urban waterlogging problems. The current waterlogging modeling process is relatively complex and requires high basic data, which is not conducive to rapid modeling and popularization. In this study, we evaluated the correlation between rainfall and waterlogging water using the following factors: terrain, evaporation, infiltration, pipe drainage capacity, and river flood water level. By quantifying the influence value of each factor on rainfall, we established a simplified model for fast calculation of waterlogging depth through input rainfall. Waterlogging data was collected from Guangzhou, China to set up the multi-factor correlation model, and verify the simulation results of the model. After the original rainfall is added/deducted, the added/loss value, the relationship between net rainfall, and maximum water depth is better than that between original rainfall and maximum water depth. Establishing a stable multi-factor correlation model for a waterlogging point requires at least three historical waterlogging event data for parameter calibration by sensitivity analysis. Comparing the simulation of four waterlogging points, the multi-factor correlation model (error = −13%) presented the least error in simulating the maximum water volume, followed by the Mike Urban model (error = −19%), and finally the SWMM model (error = 20%). Furthermore, the multi-factor correlation model and SWMM model required the least calculation time (less than 1 s), followed by the Mike Urban model (About half a minute). By analyzing the waterlogging data of Guangzhou, 42 waterlogging points with modeling conditions were screened out to further validate the multi-factor correlation model. Each waterlogging point was modeled based on the historical field, and the last rainstorm was used for model verification. The mean error of the comparison between the simulated maximum waterlogging and the measured maximum waterlogging was 3%, and the R2 value was 0.718. In summary, the multi-factor correlation model requires fewer basic data, has a simple modeling process and wide applicability, and makes it easy to realize the intelligent parameter adjustment, which is more suitable for the urgent requirements of current urban waterlogging prediction. The model results may prove accurate and provide scientific decision support for the prevention and control of urban waterlogging.

Rainfall partitioning and associated chemical alteration in three subtropical urban tree species

Rainwater is altered hydrologically and chemically as it passes through tree canopies to reach the soil surface, but this aspect of urban forest ecosystems has received less attention than that of natural ecosystems. Hydrological partitioning and changes in solute composition of rainfall were examined in an urban forest within Guangzhou city, in southern China, with reference to three typical subtropical urban tree species (Roystonea regia, Ficus microcarpa, and Lagerstroemia speciosa) with large but morphologically distinct canopies. Three components of rainfall, namely throughfall, stemflow, and interception, were measured and sampled from September 2018 to September 2019. A canopy budget model was used for estimating the contribution of canopy exchange and dry deposition to net rainfall (throughfall + stemflow) solute flux. Being a palm, R. regia recorded the highest percentages of throughfall (72.60%) and stemflow (8.68%) whereas interception was higher in F. microcarpa (33.48%) and L. speciosa (30.54%). The concentrations of almost all the solutes (Ca2+, K+, Na+, Mg2+, Cl−, NO3−, and SO42−) in throughfall and stemflow were higher than those in rainfall, suggesting that water was enriched with these solutes as a result of passing through the canopy. The model of canopy budget also showed that whereas all the three species were similar in terms of the leaching of macronutrient cations, the species differed in term of anions: whereas R. regia and L. speciosa generally absorbed or retained anions on foliage, twigs, or trunks, F. microcarpa leached Cl− and NO3− (presumably because of its unique aerial root). These results can inform the design of urban forests. For example, the lack of NO3− uptake by F. microcarpa suggests that it would be less suitable for mitigating the problems of N deposition which are significant in southern China than the other two species; on other hand, the rainfall partitioning and canopy exchange characteristics of L. speciosa make it more suitable for intercepting rainwater as well as for alleviating the problem of N deposition. The findings of this study therefore have significant implications for the selection of urban tree species in similar subtropical regions worldwide.

River Buffer Effectiveness in Controlling Surface Runoff Based on Saturated Soil Hydraulic Conductivity

In tropical Indonesia, rainforests are managed by an intensive forest management system (IFMS). The IFMS has promoted selective logging for timber harvesting and intensive line planting to enrich the standing stock. The implementation of the IFMS has reduced the forest canopy cover, disturbed the surface soil, changed the soil hydraulic properties, and increased direct runoff and soil erosion. Investigation of the IFMS impact on soil hydraulic properties and the generation of surface runoff using a saturated hydraulic conductivity model is needed. Soil hydraulic properties were investigated on 11 plots, including one virgin forest plot and 10 plots at different operational periods of the IFMS. A two-dimensional saturated soil water flow simulation was applied to generate surface runoff from different periods of the IFMS. The main parameters of canopy cover, net rainfall, and saturated hydraulic conductivity were used in the simulations. A simulation scenario of a surface runoff hydrograph in different forest operations was used to analyze the river buffer effectiveness. The results showed that fundamental IFMS activities associated with mechanized selective logging and intensive line planting have reduced the soil hydraulic conductivity within the near-surface profile. The recovery time for near-surface Ks on non-skidder tracks was between 10 and 15 years, whereas on the skidder tracks it was more than 20 years. Forest disturbances have altered the typical surface hydrological pathways, thereby creating the conditions for more surface runoff on disturbed surfaces than on undisturbed surfaces. Maintaining the buffer area is an effective means to reduce the peak discharge and surface runoff in the stream channel.

Delayed Collapse of the North Pacific Intermediate Water After the Glacial Termination

AbstractCarbon release from the North Pacific in glacial‐interglacial cycles has been mainly linked to the North Pacific Intermediate Water (NPIW) formation and associated carbon/nutrient water upwelling and biological productivity changes. However, relationship between NPIW and atmospheric CO2 change in the early interglacial remains unclear. Here we report a high‐resolution sediment record of NPIW evolution based on paleo‐redox changes in the Western North Pacific during the last 400 ka. Our proxy and model results reveal a delayed collapse of NPIW after the glacial termination was coeval with decreased salinity of intermediate water and increased net rainfall in the North Pacific. Such weakened NPIW formation in the North Pacific probably make a contribution to maintain high atmospheric CO2 concentrations through weakened intermediate‐to‐deep ocean stratification and reduced subsurface biological pump net efficiency, countering the return to more stratified conditions in the Southern Ocean, which should drive down atmospheric CO2 during the early interglacial.

Rainfall partitioning in the Cerrado and its influence on net rainfall nutrient fluxes

Quantitative studies on the water and nutrient enrichment of throughfall and stemflow in the Cerrado are lacking, especially among tree species. This work tested the hypothesis that the chemistry of rainfall fractions is altered after passing through the canopy and that the chemistry of stemflow can substantially change among tree species. We compared the nutrient concentrations in rainfall, throughfall and stemflow, dry deposition and canopy exchange among eight Cerrado species in Brazil. Rainfall, throughfall and stemflow were monitored from April 2018 to March 2019. The following chemical factors were determined using a Metrohm liquid chromatograph ECO IC: Na2+, K+, Ca2+, Mg2+, Br−, Cl−, NO3−,SO42−and PO43−. The enrichment ratio, depositions of rainfall, throughfall and stemflow and canopy budget of different nutrients were calculated for the stand and species. A comparison between the mean concentrations showed that most of the elements and compounds were relatively more concentrated in the throughfall and stemflow, except for Na2+and Ca2+, which were more concentrated in the rainfall (p<0.05). We noted that each species had a specific contribution to the stemflow nutrients. The different components and canopy geometry, as well as the bark morphology of the studied species, contributed varying proportions to the nutrient fluxes. The stemflow deposition of most nutrients was significantly higher in Xylopia aromatica. The highest nutrient input by stemflow was observed for K+, which ranged from 2.13 (A. peregrina) to 77.36 (X. aromatica) kg ha−1y − 1. A canopy budget model indicated that canopy exchange was often more dominant than dry deposition. Unlike the other nutrients, Cl− and PO43− were taken up by the canopy. Given the variation in the nutrient input, these results highlight the importance of investigating the individual contribution of the stemflow of each species in the Cerrado forest and provide a potential strategy for adapting the species to soil recovery.

Parameter regionalization of the FLEX-Global hydrological model

Global hydrological models (GHMs) are important tools for addressing worldwide change-related water resource problems from a global perspective. However, the development of these models has long been hindered by their low accuracy. In order to improve the streamflow simulation accuracy of GHMs, we developed a GHM—the FLEX-Global—based on the regionalization of hydrological model parameters. The FLEX-Global model is primarily based on the framework of the FLEX hydrological model coupled with the HAND-based Storage Capacity curve (HSC) runoff generation module to calculate net rainfall, and uses the global river-routing CaMa-Flood model to calculate river network routing. This new model allows for streamflow simulation at a spatial resolution of 0.5°×0.5° and a temporal resolution of 1 day in global catchments. To validate FLEX-Global accuracy, the FLEX-Global-simulated streamflow of 26 major rivers distributed in five different climate zones was compared with the observed data from the Global Runoff Data Center (GRDC). Next, the model performance of FLEX-Global was further verified by comparing it with that of seven existing GHMs with varying accuracy in the five climate zones. Multi-metric evaluation indicated that the streamflow simulation accuracy was improved by the FLEX-Global model with regionalized parameters, especially in the tropical and dry climate zones. This newly-developed GHM with regionalized parameters can provide scientific support for the assessment of climate change impact, optimization of global water resource mangement, simulation of Earth’s multi-sphere coupling, and implementation of the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP).

Analysis of the specific water level of flood control and the threshold value of rainfall warning for small and medium rivers

Abstract. In order to fully use the newly-built hydrologic stations in small and medium rivers for flood warning and prevention, based on the technical line of the investigation and evaluation of flash flood disasters, different historical flood information of the warning river section was investigated, while the elevations of riverain houses were measured. The relationship between the stations and affected population has been established for the study region. According to integrated flood control capability of riverside residents, the characteristic water levers and rainfall threshold values were determined in this case. The results indicate that the warning and safety levels are 54.0 and 55.3 m, respectively. The analysis results show that the warning should be issued when the net rainfall intensity is 70 mm h−1 or 110 mm for 6 h condition. And considering the effectiveness of disaster avoidance, variable characteristic water levers of the hydrologic station for flood warning in different village were determined on the basis of the flood control capability of each village. The relationship between hydrologic numerical value and inundating influence was established in a one-to-n way.

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

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

Comparative modeling of the effect of thinning on canopy interception loss in a semiarid black locust (Robinia pseudoacacia) plantation in Northwest China

Canopy interception loss is a key component of forest hydrological cycle that determine the amount of net rainfall reaching forest floor together with drought/climate stressors affecting dryland forest plantations. A good understanding of the relationship between canopy interception loss and forest management such as thinning is important for improved watershed management and ecological services. In this study, we measured event-based rainfall partitioning for a thinned (TH, with 38% basal area removed) and a control (CT) Robinia pseudoacacia forest plantation during leafed and leafless seasons in 2015 in the semiarid Loess Plateau region in China. Interception loss from both forest plots were simulated using the Revised Gash Analytical Model (RGAM) and the WiMo model. The results showed that observed annual throughfall, stemflow and interception loss were respectively 80.8%, 1.7% and 17.5% of the gross rainfall under CT. The corresponding values under TH were 87.9%, 0.8% and 11.3%, respectively. The RGAM and WiMo models were well calibrated and validated using filed data collected in leafed and leafless seasons. The analyses suggested that models accurately predicated interception loss under both CT and TH conditions and captured seasonal variations in canopy and meteorological parameters. The RGAM model was most sensitive to the ratio of mean evaporation rate to mean rainfall intensity, and canopy storage capacity in leafed season, and to the ratio of mean evaporation rate to mean rainfall intensity in leafless season. Moreover, 37.2% and 42.1% of the interception in leafed season evaporated from the canopy respectively during rainfall event and after rainfall. The corresponding values for leafless season were respectively 49.3% and 22.4%. Overall, the performance of the optimized RGAM and WiMo models were satisfactory with respect to modeling error (−6.9 − −2.9%) and Nash-Sutcliffe model efficiency (0.80–0.94), although that of the optimized RGAM model was slightly superior to WiMo model. The models would facilitate the implementation of water-oriented management in semiarid forest plantations through a more accurate simulation of the impact of thinning on interception loss.