Hourly Time Step Research Articles

Improving Forecast Skill of Lowland Hydrological Models Using Ensemble Kalman Filter and Unscented Kalman Filter

AbstractFor operational water management in lowlands and polders (for instance, in the Netherlands), lowland hydrological models are used for flow prediction, often as an input for a real‐time control system to steer water with pumps and weirs to keep water levels within acceptable bounds. Therefore, proper initialization of these models is essential. The ensemble Kalman filter (EnKF) has been widely used due to its relative simplicity and robustness, while the unscented Kalman filter (UKF) has received little attention in the operational context. Here, we test both UKF and EnKF using a lowland lumped hydrological model. The results of a reforecast experiment in an operational context using an hourly time step show that when using nine ensemble members, both filters can improve the accuracy of the forecast by updating the state of a lumped hydrological model (Wageningen Lowland Runoff Simulator, WALRUS) based on the observed discharge, while UKF has achieved better performance than EnKF. Additionally, we show that an increase in the ensemble members does not necessarily mean a significant increase in performance. WALRUS model with either UKF or EnKF could be considered for hydrological forecasting for supporting water management of polders and lowlands, with UKF being the computationally leaner option.

APIFLAME v2.0 biomass burning emissions model: impact of refined input parameters on atmospheric concentration in Portugal in summer 2016

Abstract. Biomass burning emissions are a major source of trace gases and aerosols. Wildfires being highly variable in time and space, calculating emissions requires a numerical tool able to estimate fluxes at the kilometer scale and with an hourly time step. Here, the APIFLAME model version 2.0 is presented. It is structured to be modular in terms of input databases and processing methods. The main evolution compared to version 1.0 is the possibility of merging burned area and fire radiative power (FRP) satellite observations to modulate the temporal variations of fire emissions and to integrate small fires that may not be detected in the burned area product. Accounting for possible missed detection due to small fire results in an increase in burned area ranging from ∼5 % in Africa and Australia to ∼30 % in North America on average over the 2013–2017 time period based on the Moderate-Resolution Imaging Spectroradiometer (MODIS) Collection 6 fire products. An illustration for the case of southwestern Europe during the summer of 2016, marked by large wildfires in Portugal, is presented. Emissions calculated using different possible configurations of APIFLAME show a dispersion of 80 % on average over the domain during the largest wildfires (8–14 August 2016), which can be considered as an estimate of uncertainty of emissions. The main sources of uncertainty studied, by order of importance, are the emission factors, the calculation of the burned area, and the vegetation attribution. The aerosol (PM10) and carbon monoxide (CO) concentrations simulated with the CHIMERE regional chemistry transport model (CTM) are consistent with observations (good timing for the beginning and end of the events, ±1 d for the timing of the peak values) but tend to be overestimated compared to observations at surface stations. On the contrary, vertically integrated concentrations tend to be underestimated compared to satellite observations of total column CO by the Infrared Atmospheric Sounding Interferometer (IASI) instrument and aerosol optical depth (AOD) by MODIS. This underestimate is lower close to the fire region (5 %–40 % for AOD depending on the configuration and 8 %–18 % for total CO) but rapidly increases downwind. For all comparisons, better agreement is achieved when emissions are injected higher into the free troposphere using a vertical profile as estimated from observations of aerosol plume height by the Multi-angle Imaging SpectroRadiometer (MISR) satellite instrument (injection up to 4 km). Comparisons of aerosol layer heights to observations by the Cloud-Aerosol Lidar with Orthogonal Polarization (CALIOP) show that some parts of the plume may still be transported at too low an altitude. The comparisons of the different CTM simulations to observations point to uncertainties not only on emissions (total mass and daily variability) but also on the simulation of their transport with the CTM and mixing with other sources. Considering the uncertainty of the emission injection profile and of the modeling of the transport of these dense plumes, it is difficult to fully validate emissions through comparisons between model simulations and atmospheric observations.

Calibrating Hourly Precipitation Forecasts with Daily Observations

AbstractCalibrated high-temporal-resolution precipitation forecasts are desirable for a range of applications, for example, flood prediction in fast-rising rivers. However, high-temporal-resolution precipitation observations may not be available to support the establishment of calibration methods, particularly in regions with low population density or in developing countries. We present a new method to produce calibrated hourly precipitation ensemble forecasts from daily observations. Precipitation forecasts are taken from a high-resolution convective-scale numerical weather prediction (NWP) model run at the hourly time step. We conduct three experiments to develop the new calibration method: (i) calibrate daily precipitation totals and disaggregate daily forecasts to hourly; (ii) generate pseudohourly observations from daily precipitation observations, and use these to calibrate hourly precipitation forecasts; and (iii) combine aspects of (i) and (ii). In all experiments, we use the existing Bayesian joint probability model to calibrate the forecasts and the well-known Schaake shuffle technique to instill realistic spatial and temporal correlations in the ensembles. As hourly observations are not available, we use hourly patterns from the NWP as the template for the Schaake shuffle. The daily member matching method (DMM), method (iii), produces the best-performing ensemble precipitation forecasts over a range of metrics for forecast accuracy, bias, and reliability. The DMM method performs very similarly to the ideal case where hourly observations are available to calibrate forecasts. Overall, valuable spatial and temporal information from the forecast can be extracted for calibration with daily data, with a slight trade-off between forecast bias and reliability.

Nearly zero energy target and indoor comfort in Mediterranean climate: Discussion based on monitoring data for a real case study

The paper discusses the results of a monitoring campaign performed during the spring and autumn with the purpose to evaluate the operational energy performance of an existing nearly zero energy building (nZEB). It is located in Benevento, a middle-size city of South Italy with typical Mediterranean climate.A methodology for real-time nZEB performance analysis is proposed by taking into consideration the implications of the continuous interplay between external conditions and indoor occupant requirements as well as between on-site generation and the building loads with the resulting interaction with the energy grid. It takes into account the inertial properties of building envelope and the occupant perception in term of thermo-hygrometric and visual comfort as well as of indoor air quality. Compilation and assessment of appropriate quantitative indicators are proposed basing on data with hourly time step for finding the optimal management of the internal and external shades and the ventilation system. Moreover it is discussed how daily variations can influence the efficiency of the whole building-HVAC system with particular attention to the pre-handling system based on an earth-water heat exchanger.

Crossing the rural–urban boundary in hydrological modelling: How do conceptual rainfall–runoff models handle the specificities of urbanized catchments?

AbstractLandscape differences induced by urbanization have prompted hydrologists to define a fuzzy boundary between rural‐ and urban‐specific hydrological models. We addressed the validity of establishing this boundary, by testing two rural models on a large sample of 175 French and United States (US) urbanized catchments, and their 175 rural neighbours. The impact of urbanization on the hydrological behaviour was checked using four metrics. Using a split‐sample test, we have compared the performances, parameter distributions, and internal fluxes of GR4H and IHACRES, two conceptual and continuous models running at the hourly time step. Both model structures are based on soil moisture accounting reservoirs (infiltration, runoff, and actual evapotranspiration) and quick flow/slow flow routing components, with no consideration of any specific feature related to urbanization. Results showed: (a) Except for the ratio of streamflow flashiness to precipitation flashiness, the range of hydrological signature metrics in rural catchments encompassed the specificities of urbanized ones. Overall, the urbanized catchments showed higher ratios of mean streamflow to mean precipitation (median values: 0.39 vs. 0.27) and streamflow flashiness to precipitation flashiness (0.13 vs. 0.03), besides lower baseflow index (0.42 vs. 0.62) and shorter characteristic response time (3 vs. 14 hr). (b) The performances of GR4H revealed no significant distinction between rural and urbanized catchments in terms of Kling–Gupta Efficiency (KGE), whereas IHACRES better simulated urbanized catchments, especially during summer. (c) With respect to differences in urbanization level, the GR4H and IHACRES parameters showed different distributions. The differences in parameters were consistent with the differences in hydrological behaviour, which is promising for a model‐based assessment of the impact of urbanization. (d) The models agreed less in reproducing the internal fluxes over the urbanized catchments than over the rural ones. These results demonstrate the flexibility of conceptual models to handle the specificities of urbanized catchments.

Evaluation of the ERA5 reanalysis as a potential reference dataset for hydrological modelling over North America

Abstract. The European Centre for Medium-Range Weather Forecasts (ECMWF) recently released its most advanced reanalysis product, the ERA5 dataset. It was designed and generated with methods giving it multiple advantages over the previous release, the ERA-Interim reanalysis product. Notably, it has a finer spatial resolution, is archived at the hourly time step, uses a more advanced assimilation system and includes more sources of data. This paper aims to evaluate the ERA5 reanalysis as a potential reference dataset for hydrological modelling by considering the ERA5 precipitation and temperatures as proxies for observations in the hydrological modelling process, using two lumped hydrological models over 3138 North American catchments. This study shows that ERA5-based hydrological modelling performance is equivalent to using observations over most of North America, with the exception of the eastern half of the US, where observations lead to consistently better performance. ERA5 temperature and precipitation biases are consistently reduced compared to ERA-Interim and systematically more accurate for hydrological modelling. Differences between ERA5, ERA-Interim and observation datasets are mostly linked to precipitation, as temperature only marginally influences the hydrological simulation outcomes.

Hourly operational assessment of HVAC systems in Mediterranean Nearly Zero-Energy Buildings: Experimental evaluation of the potential of ground cooling of ventilation air

The main purpose of this study is to evaluate, based on experimental data, the potential of pre-cooling the ventilation air based on ground-to-water heat exchanger, coupled with an intermediate water-to-air exchanger, during the summer period. The case study for this investigation is an existing nearly zero energy building located in Benevento, a middle-size city of South Italy with typical Mediterranean climate. Measurements of several performance parameters with four different HVAC possible configurations are shown as well as monitoring of energy uses and indoor microclimatic conditions in order to verify if comfort conditions inside the building are guaranteed together with the achievement of ‘nearly zero energy target’.Indeed, the study intends to assess the interaction between building and power grid and evaluate the temporal correspondence between building load and PV generation with hourly time step. The discussion about the hourly energy balance serves as reference to export or improve management and design strategies in regions with comparable climate conditions.

Vehicle-to-Grid in Standard and Fast Electric Vehicle Charging: Comparison of Renewable Energy Source Utilization and Charging Costs

Croatia aims to achieve 10% of its energy production from the renewable energy sources in the total energy consumption in the transport sector. One of the ways to achieve this goal is by the use of electric vehicles. This work comparatively analyses the financial and social aspects of vehicle-to-grid charging in standard and fast charging mode, their impact on the renewable electricity production and the total electricity consumption regulated through variable electricity prices. Data were taken for the wider urban area of the Dubrovnik region. The assumption is that the Dubrovnik region will be self-sufficient by the year 2050 with 100% renewable electricity production and that all conventional vehicles will be replaced by electric vehicles. This work aims to show that the fast charging based on 10 min time steps offers more opportunities for flexibility and utilization of renewable generation in the energy system than the standard charging based on hourly time step. The results of this work showed the opposite, where in most of the scenarios standard charging provided better results. Replacement of the existing two tariff model in electricity prices with variable electricity prices contributes to the stability of the energy system, providing better regulation of charging and higher opportunities for renewable electricity utilization in standard and fast charging and reduction of charging costs. According to the financial aspects, fast charging is shown to be more expensive, but for the social aspects, it provides electric vehicles with more opportunities for better competition in the market.

Comparison of Greenhouse Energy Requirements for Rose Cultivation in Europe and North Africa

The ornamental plant production in greenhouses is widespread. A quantitative assessment of greenhouse energy consumption and its variability in space and time is strategic to improve the sustainability of the cultivation. The specific environmental features of the cultivation areas can strongly affect the sustainability of the production. A dynamic simulation model of greenhouse energy balance with an hourly time step was developed and parameterized for a state-of-the-art greenhouse to evaluate the heating requirements for cut-flower roses. This ornamental crop has been used as model species for its high energy requirement for flower production. The energy demand for rose production has been analyzed with an energy balance model with an hourly time step. After a preliminary analysis on the period 1973–2019, the final analysis was carried out on the 30-year period (1990–2019), representative of the current climate. Results show a gradient southwest–northeast of energy needs with relevant effects on economic and environmental sustainability. More specifically, four large sub-areas are identified, namely the central-southern Mediterranean (yearly requirements below 600 MJ m−2 year), the northern Mediterranean, and the area influenced by the mitigating effect of the Atlantic Ocean (600–1200), the central-European area (requirements of 1200–1800), and the Northern European area (above 1800).

Utilization of res using seawater source heat pump with and without energy storage: Comparison of Thermal and Battery Energy Storage

Heat and cooling stands out with the great potential in decarbonisation since they have a large share in the final energy consumption. Power-to-heat technologies may contribute to the heat sector decarbonisation as well as the integration of renewables if they are sufficiently flexible. They are also shown to have a good effect on the system costs. This work will analyse the potential of seawater heat pump system for the utilization of high share of electricity production from the renewables. The Old City of Dubrovnik is selected as a case study because of its specific situation. A large number of the outdoor units are not well approved by UNESCO since the Old City is under the protection of the UNESCO World Heritage Centre. The results of the study showed that the combination of wind and solar electricity production can cover 67% of load for stand-alone seawater heat pump system based on hourly time step. Utilization of renewable electricity generation, for this case, resulted in 433.71 tCO2/y emission reduction. System based on 10 minutes time step gave poorer results by 6%. System with the additional energy storage gained best results in the case of combined wind and solar electricity generation, as well. It resulted in storage capacity reduction by 78% ac-cording to the case of solar electricity generation and by 60% according to the wind electricity generation. Battery energy storage resulted in 40 times lower volume and 13 times higher investment costs and levelised cost of heat in comparison to the thermal energy storage.

TOPMELT 1.0: a topography-based distribution function approach to snowmelt simulation for hydrological modelling at basin scale

Abstract. Enhanced temperature-index distributed models for snowpack simulation, incorporating air temperature and a term for clear sky potential solar radiation, are increasingly used to simulate the spatial variability of the snow water equivalent. This paper presents a new snowpack model (termed TOPMELT) which integrates an enhanced temperature-index model into the ICHYMOD semi-distributed basin-scale hydrological model by exploiting a statistical representation of the distribution of clear sky potential solar radiation. This is obtained by discretizing the full spatial distribution of clear sky potential solar radiation into a number of radiation classes. The computation required to generate a spatially distributed water equivalent reduces to a single calculation for each radiation class. This turns into a potentially significant advantage when parameter sensitivity and uncertainty estimation procedures are carried out. The radiation index may be also averaged in time over given time periods. Thus, the model resembles a classical temperature-index model when only one radiation class for each elevation band and a temporal aggregation of 1 year is used, whereas it approximates a fully distributed model by increasing the number of the radiation classes and decreasing the temporal aggregation. TOPMELT is integrated within the semi-distributed ICHYMOD model and is applied at an hourly time step over the Aurino Basin (also known as the Ahr River) at San Giorgio (San Giorgio Aurino), a 614 km2 catchment in the Upper Adige River basin (eastern Alps, Italy) to examine the sensitivity of the snowpack and runoff model results to the spatial and temporal aggregation of the radiation fluxes. It is shown that the spatial simulation of the snow water equivalent is strongly affected by the aggregation scales. However, limited degradation of the snow simulations is achieved when using 10 radiation classes and 4 weeks as spatial and temporal aggregation scales respectively. Results highlight that the effects of space–time aggregation of the solar radiation patterns on the runoff response are scale dependent. They are minimal at the scale of the whole Aurino Basin, while considerable impact is seen at a basin scale of 5 km2.

Weather Radar Data for Hydrological Modelling: An Application for South of Primorye Region, Russia

This paper describes the experience of using weather radar data to simulate a catastrophic flood caused by intense rains that occurred in the period from August 5 to 8, 2017 in the south of Primorye, Russia. The Amba River (243 km²), where historical discharge peak was measured, was chosen as the test watershed of this study. Weather radar hourly precipitation fields with a spatial resolution of 1 km and a modified version of the kinematic-wave-based geomorphologic IUH model were used to estimate the hydrograph at the watershed outlet. The simulation was performed with an hourly time step; using the precipitation grids obtained from initial radar reflectivity data, and then using bias-correction based on precipitation measurement at the closest meteorological station. In the preliminary tests, the simulated discharge was found underestimated about two times in comparison with the observed discharges. After performing a precipitation bias-correction, the simulated and observed discharges showed good accordance.

Impact of sum-of-hourly and daily timesteps in the computations of reference evapotranspiration across the Brazilian territory

Estimating reference evapotranspiration (ETo) in 24 h timesteps has been considered sufficiently accurate for a long time. However, recent advances in weather data acquisition has made it feasible to apply the hourly procedures in ETo computation. Hourly timesteps can improve ETo estimates accuracy, for data averaged daily may misrepresent evaporative power during parts of the day. Only a few studies have assessed vast databases, yet, studies considering tropical regions are basically inexistent. The objective of the present study was to assess the differences between daily ETo computations performed on 24 h (ETod) and hourly (EToh) timesteps for the Brazilian territory. Daily and hourly ETo computations were performed according to the standardized ASCE (American Society of Civil Engineers) Penman-Monteith equation. Large daily weather variations of meteorological parameters resulted in ETod generally underestimating EToh, while lower variations resulted in ETod overestimating. Overall, ETod overestimated EToh in 0.7%, with monthly percentage bias ranging from -3.9% to 2.9%. This study considered one year of data from 567 automatic weather stations and, despite acknowledging the existence of interannual climate variability, findings strongly agreed with relevant literature. ETod predominantly overestimated EToh during wet periods in warm regions. Thus, this behavior is observed almost year-round for the tropical monsoon and rainforest climate, in the Amazon and Pantanal biome. For the tropical savannah and semi-arid climate, ETod overestimated EToh during wetter periods (main crop harvest) but underestimated along the dry season (second harvest). On the other hand, ETod predominately underestimated EToh for colder regions, such as the Pampa (humid sub-tropical climate), regardless of rainfall. The Cerrado and Caatinga are likely to be affected most, for EToh is underestimated in periods of lower water availability, making adequate irrigation techniques fundamental.

Modelling of global solar irradiance on sloped surfaces in climatic conditions of Kraków

Abstract The paper presents calculations of global solar irradiance on inclined surfaces of any orientation in the hourly time step. For computational purposes there were used the data from typical meteorological years (TMY) available in a form of text files on the website of the Ministry of Infrastructure and Development. Hourly solar global horizontal irradiance from measurements from the file for Kraków was used as input for five anisotropic models (Hay, Muneer, Reindl, Perez and Perez according to the new PN-EN ISO 52010-1 standard). Direct normal and diffuse horizontal and then global irradiances were calculated. To illustrate the effects of using different models, for the exemplary residential building, monthly solar heat gains and heating demand was determined according to the monthly method of PN-EN ISO 13790. In comparison to the solar data from the TMY, an average decrease in the value of solar gains amounted 37%, what resulted in an increase in the calculated heat demand of the building by 10%. This is very important since this change takes place without any modernisation works.

Using Remote Sensing Based Metrics to Quantify the Hydrological Response in a City

We propose a remote-sensing based metric approach to evaluate the hydrological response of highly urbanized areas and apply it to the city of Brussels. The model is set-up using 2 m resolution hyperspectral data. Next, it is upscaled to the city level, using multi-spectral Sentinel-2 data with 20 m resolution. We identify the total impervious area, the vegetation cover and the leaf area index as important metrics to derive a timeseries of spatially distributed net rainfall, runoff and infiltration from rainfall data. For the estimation of the actual evapotranspiration we use the potential evapotranspiration and the available water storage based on the interception, the depression storage and the infiltration. Additionally, we route the runoff to the outlet of selected sub-catchments. An important metric for the routing is the timing to the outlet which is approximated using the total impervious area and the hydrological distance to the outlet. We compare our approach to WetSpa model simulations and reach R 2 values of 98% for net rainfall, 95% for surface runoff, 99% for infiltration and 97% for cumulative evapotranspiration. The routing in the Watermaelbeek catchment is evaluated with discharge observations and reaches NSE values of 0.89 at a 2 m resolution and 0.88 at a 20 m resolution using an hourly timestep. At the timestep of 10 min and a 20 m resolution the NSE is reduced to 0.76. For the Roodebeek catchment we reach an NSE of 0.73 at a spatial resolution of 20 m and an hourly timestep. The results presented in this paper are optimistic for using spatial and temporal metrics retrieved from remote sensing data to quantify the water balance of urban catchments.

Optimal sizing of an AC‐coupled hybrid power system considering incentive‐based demand response

This study investigates the impact of incentive-based demand response on the optimal economic sizing of hybrid power systems for a remote area in South Australia. The hybrid power systems are modelled as AC-coupled system with various power generation and energy storage systems including diesel generators, solar photovoltaics, wind turbines, battery storages and flywheels. Operating reserve requirements are introduced to ensure a specified reliability with variable renewable energy generation and consumer loads. Incentive-based demand response is introduced to allow a reduction in customer loads, up to a maximum value, during peak load events. Customers receive a financial benefit as an incentive for the total demand response energy reduction. Active power operation of four different power system configurations is modelled over one year in hourly time steps. The study uses real data for customer demand, wind speed, solar insolation and ambient temperature profiles in a specific location. The hybrid power systems with demand response are optimised to minimise the system net present cost in project lifetime (20 years) using a particle swarm optimisation algorithm. Sensitivity analysis of levellised cost of energy for various values of the maximum demand response power and the incentive payments are also carried out.

Evaluation of a radiation-based empirical model for estimating hourly reference evapotranspiration for high-altitude climatic conditions: A case study for the state of California

High-altitude (>800 m) climatic conditions for the four stations in arid, semiarid and subhumid climatic zones were examined to evaluate their influence on radiation-based empirical estimations of reference evapotranspiration ( $${ET}_{\mathrm{o}}$$ ) on an hourly time step. The empirical method utilises the incoming solar radiation and the relationship between a function of relative humidity and vapour pressure deficit. The empirical method overestimated $${ET}_{\mathrm{o}}$$ by 21.4%, on a yearly basis, 27.0% for the winter period and 16.3% for the summer period, compared with the estimations of the American Society of Civil Engineers Penman Monteith (ASCE PM) (2005) method. Various meteorological variables included in the energy and the aerodynamic term of the ASCE PM (2005) method were investigated with respect to altitude. The increasing trend of incoming solar radiation combined with the decreasing trend of relative humidity, both with respect to altitude were the main causes for the underestimation of the empirical radiation method. The empirical method was adjusted for high-altitude climatic conditions by multiplying the values by the ratio of the atmospheric pressure corresponding to the altitude of the station to the atmospheric pressure at sea level. The adjusted values were overestimated by 3.4% compared to the estimations of the ASCE PM (2005) method (higher overestimation: 9.1% and lower overestimation: 0.8%). The value of $$0.073\hbox { mm h}^{-1}$$ was considered as the upper limit for the satisfactory performance of the empirical method. The root mean square error (RMSE) values ranged from 0.038 to $$0.054\hbox { mm h}^{-1}$$ and the $$R^{2}$$ values ranged from 0.95 to 0.97. The values of the wind speed and vapour pressure deficit (not included in the empirical method) were divided into intervals and the RMSE values between the values of the estimations of the empirical method and the values of the estimations of the ASCE PM (2005) were calculated for each interval. The RMSE values calculated for the intervals of the values of the wind speed ranged from 0.036 to $$0.065\hbox { mm h}^{-1}$$ and were satisfactory. The vapour pressure deficit values <2.5 kPa also yielded satisfactory RMSE values and accounted for 96.1% of the data.

Assessment of freshwater discharge into a coastal bay through multi-basin ensemble hydrological modelling

Coastal basins of the Brittany peninsula (France) are hydrological hot spots. A high level of nutrient pollution affects many of these basins and causes algal blooms in several coastal bays; nine have been a specific focus of the European Commission since 2007. The flux of each contributing basin flowing into these bays must be examined to assess the conditions and explore mitigation options. However, this task encounters a large lack of data since most of the basins are ungauged. In this context, this study developed a method which facilitates transposition of hydrographs from gauged basins to ungauged neighbouring basins of interest. Inverting a simple geomorphology-based transfer function of the gauged basin which describes travel time through channels enables the net rainfall time-series to be estimated from the discharge time-series of donor basins. To estimate the net rainfall of a given ungauged catchment, several net rainfall time series of gauged catchments are averaged. The resulting net rainfall is then transposed onto the ungauged target basin and convoluted by its own transfer function to estimate the hydrograph. This allows the transposition of as many hydrographs as there are different donor basins. This ensemble prediction enables the proportion of prediction uncertainty that is due to the heterogeneity in hydrological behaviour to be estimated. Moreover, the time-series of the donor basins are combined to estimate the ungauged net rainfall time-series. This provides a discharge prediction which values all available measurements. The method was applied to the highly controversial Saint Brieuc Bay, where it was possible to quantify the contribution of each coastal basin, even those influenced by dams, and ultimately the entire volume of fresh water entering the bay at an hourly time step. This work opens perspectives to additionally refine estimation of the associated nutrient fluxes.

Comparing Statistical and Semi-Distributed Rainfall–Runoff Models for a Large Subtropical Watershed: A Case Study of Jiulong River Catchment, China

In this contribution, the authors present their preliminary investigations into modeling the rainfall–runoff generation relation in a large subtropical catchment (Jiulong River catchment) on the southeast coast of China. Previous studies have mostly focused on modeling the streamflow and water quality of its small rural subcatchments. However, daily runoff on the scale of the whole catchment has not been modeled before, and hourly runoff data are desirable for some oceanographic applications. Three methods are proposed for modeling streamflow using rainfall outputted by the Weather Research Forecast (WRF) model, calculated potential evaporation (PET), and land cover type: (i) a ridge regression model; (ii) NPRED-KNN: a nonparametric k-nearest neighbor model (KNN) employing a parameter selection method (NPRED) based on partial information coefficient; (iii) the Hydrological Simulation Program-Fortran (HSPF) model with an hourly time step. Results show that the NPRED-KNN approach is the most unsuitable method of those tested. The HSPF model was manually calibrated, and ridge regression performs no worse than HSPF based on daily verification, whilst HSPF can produce realist daily flow time series, of which ridge regression is incapable. The HSPF model seems less prone to systematic underprediction when replicating monthly-annual water balance, and it successfully replicates the baseflow index (the flow intensity) of the Jiulong River catchment system.

Influence of different battery charging strategies on residual grid power flows and self-consumption rates at regional scale

Battery storage systems can help to integrate excess Photovoltaic (PV) energy into the local energy systems but also increase the request for higher self-consumption rates of the households. This study uses a spatially resolved approach with hourly time steps to analyze the influence of batteries on the domestic residual loads on a regional scale. A domestic energy component is developed consisting of a PV-system model, the demand component, and a battery storage device. The study area is located in the south of Bavaria and 4906 households with PV-systems between 3 and 10 kWp power were selected assuming a battery capacity of 6.2 kWh in average. Three charging strategies for domestic battery storage systems are assessed: (1) Maximization of self-consumption, (2) Fixed feed-in limit of 70% of the PV-peak power, and (3) Daily dynamic feed-in limit based on ideal forecasts. The best result is obtained through the third strategy with a self-consumption of 78.5% on average and the highest reduction of the grid flows by 20% by damping grid excesses. The influence of the charging strategy rises with increasing size of PV- and battery storage systems and therefore residual loads. Regional variations are further caused by the meteorological conditions, different PV- and battery sizes and parameters and demand profiles on municipal scale. Consequently, a sufficient sample size with different set-ups is recommended for a full evaluation of battery charging strategies.