Daily Water Balance Model Research Articles

Analysis of Stormwater and Rainwater Harvesting Potential Based on a Daily Water Balance Model: A Case Study of Korea

The increasing intensity of rainfall resulting from climate change is projected to worsen the inundation of urban areas by floods. As a viable alternative, stormwater harvesting presents an opportunity to enhance water supply reliability while reducing pressure on both water resources and urban stormwater drainage systems. The stored rainwater can be supplied with a radius of one kilometer around the storage facility, so less pumping energy is consumed compared to supplying the stored rainwater far away from the storage facilities. To visually depict the characteristics of the selected storage facility, land cover maps were created using ArcGIS. These maps were created for a circular region with a radius of one kilometer around each studied storage facility. In this study, a daily water balance model was formulated using spreadsheets to assess the potential of harvesting stormwater and rainwater for various pre-existing storage facilities. Five different types of storage facilities were selected for this study. The term “SRWH facility evaluation criteria” as a whole is used for the storm or rain (SR) water supply satisfaction rate, the SR guarantee rate, and the SR utilization rate. The results provide evidence that, for each selected studied storage facility, the SR water guarantee rate can potentially surpass 70% under conditions of low water demand. Moreover, we investigated the potential of the existing storage facilities to work as multifunctional resources, while the original purpose for which each facility was constructed remains un-affected.

Spatial and Climatic Variabilities of Rainwater Tank Outcomes for an Inland City, Canberra

Most of the studies on rainwater harvesting analysis present the outcomes for particular cities, representing a single set of results for a specific city. However, in reality, significant spatial and weather variabilities may exist, due to which presenting only one set of results for a particular city would be misleading. This paper presents the potential weather and spatial variabilities on the expected water savings and supply reliability through the domestic rainwater tank for an inland city. An earlier-developed daily water balance model, eTank, was used for the calculations of annual water savings and reliability. An Australian inland city, Canberra, was selected as a case study and relevant daily rainfall data were collected from the Australian Bureau of Meteorology website. For the analysis of spatial variation, two rain gauge stations within the city of Canberra were selected. For each station, from the historical data, three years were selected as dry, average and wet years. For each weather condition, annual water savings and reliabilities were calculated for different demands with different tank sizes up to 10,000 L connected with different roof sizes. Then, variations in annual water savings and reliabilities among different weather conditions, as well as among different stations, were evaluated. It was found that, with regard to annual water savings, a maximum variation of 68.6% can be expected between dry and wet weather; however, only a 15.4% maximum spatial variation is expected among the selected stations. Regarding reliability, a maximum variation of 123% is expected between dry and wet weather. Whereas, only a 17% spatial variation is expected among the selected stations. Such a study will provide valuable insights for rainwater tank users and stakeholders on potential variabilities due to weather and spatial differences.

Assessment of Rainwater Harvesting Facilities Tank Size Based on a Daily Water Balance Model: The Case of Korea

Factors affecting rainwater resource management for the present and future include population growth, urbanization, and climate change. Rainwater harvesting (RWH) allows multiple urban water-related issues to be mitigated. In this study, a spreadsheet-based daily water balance model was developed to analyze the existing laws and regulations regarding the storage tank size of RWH facilities. Six buildings at different locations were selected for this study. Two are office buildings, two are school buildings, and two are sports buildings. The term “RWH facility evaluation criteria” is collectively used for rainwater supply satisfaction rate, rainwater guarantee rate, and rainwater utilization rate. A green roof can hold the rainwater for some time, reducing the peak flow and runoff volume. The results provide evidence that, among the selected studied buildings, buildings having a combination of a green roof and RWH facility score the highest in terms of RWH facility evaluation criteria, even though the actual tank size is much smaller than the standard tank size. This is the case with the Yesan County Office, in which a green roof connected to a small (66 m3) rainwater storage tank is installed. As a green roof can decrease the runoff volume, the rainwater can be managed efficiently with less pumping energy and only a small storage tank.

Assessing the Impacts of Climate Change on Rainwater Harvesting: A Case Study for Eight Australian Capital Cities

Due to climate change, freshwater supply will be limited at many locations around the globe. Rainwater harvesting (RWH) has emerged as an alternative and sustainable freshwater source. In this study, the impacts of climate change on water saving as well as the reliability of a RWH system are investigated using data from eight Australian capital cities. Both historical and projected rainfall data were incorporated into a daily water balance model to evaluate the performance of a RWH system in relation to its reliability, water savings and scarcity. Indoor (toilet and laundry), outdoor (irrigation) and combined (indoor plus outdoor) water demands were considered for a 5 m3 tank size. It has been found that in the future period, the water savings and reliability of a RWH system will reduce slightly across the selected cities. Different capital cities of Australia will experience different level of performance for a RWH system depending on their locations, water uses and seasons. The findings of this study will be useful to water authorities and policy makers to plan for a sustainable RWH system under changing climate conditions.

Influence of rainfall time series indicators on the performance of residential rainwater harvesting systems

Despite having abundant water sources, some Brazilian regions are likely to face water scarcity within the following decades. In this sense, rainwater harvesting (RWH) systems are considered viable solutions. This study evaluates the influence of rainfall time series indicators on the tank sizes, volumetric reliability and potential for potable water savings in residential buildings in Brazil. The study aimed to determine the most suitable rainfall conditions for RWH systems design. RWH systems were simulated for 27 Brazilian cities considering a daily water balance model. Total water demands and rainfall time series were considered for each city, and RWH-relevant indicators characterised each time series. Generally, cities with higher rainfall availability required smaller tank sizes and yielded greater volumetric reliabilities and potential for potable water savings. Cluster analysis was also used to investigate if similar rainfall patterns generate similar simulation results. Euclidean distance criteria grouped similar time series into ten clustering schemes. Coefficients of variation for tank sizes decreased within each scenario as more clusters were used, i.e. this method is feasible to design rainwater storage tanks. The remaining performance indicators did not show significant variation among the tested clustering scenarios. Similarity analysis resulted in increasingly similar results within each group as the clustering became more refined. As the main conclusion, correlation analysis presented the Seasonality index and indicators related to dry periods as the most influential towards the performance of RWH systems.

A new small-scale system of rainwater harvesting combined with irrigation for afforestation in mine area: Optimizing design and application

Afforestation plays a crucial role in the remission of water and soil erosion, adsorption of heavy metals, and protection of soil microbial community structure for mining areas. However, soil drought, the variability of precipitation, and low rainwater use efficiency severely limit the early survival rate of trees. A new small-scale system of rainwater harvesting combined with irrigation (RWHI) for afforestation in mining areas was established, which consisted of a rainwater catching board, storage tanks, and ceramic emitters. A daily water balance model under variable water supply was presented and experimentally verified to confirm the optimum catchment area, the storage capacity of tanks, and the rated discharge of ceramic emitters. Taking the Wuda mining area in Wuhai, China, as a case study, three representative years, including dry, normal, and wet years were selected by analysing local rainfall features. The results showed that the soil water content in the root zone maintained a suitable range (between field capacity and wilting coefficient) using the RWHI system. With the aim of the maximum system operating reliability for various weather conditions and tree species, it was recommended that the rated discharge of the ceramic emitter of 6 ml h−1, storage tanks of 25 L, the catchment area of 1 m2, and filling water schedule of twice a year were employed. A generalised equation for the estimation of the filling water amount was given. The vegetation coverage of the mine was significantly improved, and the survival rate of trees (Murraya paniculate) exceeded 90% using the RWHI system. It was indicated that the RWHI system has a broad application prospect in the afforestation of the mining areas.

Economical viability analysis of an innovative gravity‐driven rainwater harvesting system for a commercial office building

AbstractGravity‐driven rainwater harvesting (RWH) system showcases a promising alternative solution to reduce energy consumption in rainwater recycling. However, the economic efficiency is one of the most concerns with regard to the adoption of this green infrastructure. In this study, a commercial official building has a rooftop area of 1600 m2 and with 560 inhabitants was assumed to apply two configurations of RWH system (i.e., gravity system and pressure system), and comparative study was conducted to evaluate the economic performance of two RWH systems. The potential water saving quantity of the RWH system was simulated based on a daily water balance model and their expected economic efficiency were discussed in terms of benefit cost ratio and net present value. Results shown that only when the building height is higher than 102 m or the property rent is less than 0.4 CNY (China Yuan) per square metre per day, can make the gravity system economically attractive. This study provides an innovative approach to utilize roof rainwater in a more low‐energy mode; it is of great significance to promote building energy‐saving and carbon reduction.

Effect of Rainfall Regime on Rainwater Harvesting Tank Sizing for Greenhouse Irrigation Use

The use of rainwater harvesting tanks to supply human water needs is an old and sustainable practice. In the case of covering irrigation demand in greenhouse agriculture, the potential is huge. Still, the relative research worldwide is low, while it is nearly absent in Greece. In this study, the rainwater harvesting tank size for irrigation use of greenhouse tomato cultivation was investigated by applying a daily water balance model in three regions of Crete Island (Greece) with significant greenhouse areas. Daily rainfall data from three representative rainfall stations of the study areas characterized by different rainfall regime for a 12-year time series were used. Additionally, the daily irrigation water needs for a tomato crop during an 8-month cultivation period were used. The greenhouse roof was defined as catchment area of the rainwater harvesting system and greenhouse areas of 1000, 5000 and 10,000 m2 were studied. In all areas examined, a tank of 30–100 m3 per 1000 m2 of greenhouse area could reach approximately 80–90% reliability. Higher values of reliability (reaching 100%) could be achieved mainly with covered tanks. Tank size for 100% reliability in covered tanks, ranged from 200 m3 (per 1000 m2 of greenhouse area) in the study area with high mean annual rainfall depth (974.24 mm) and moderate mean longest dry period (87.67 days), to 276 m3 (per 1000 m2 of greenhouse area) in the study area with relatively low mean annual rainfall depth (524.12 mm) and high mean longest dry period (117.42 days). For uncovered tanks, a 100% reliability value could be reached only with a tank size of 520 m3 (per 1000 m2 of greenhouse area) in the study area with high mean annual rainfall depth and moderate mean longest dry period.

Evaluation of Rainwater Harvesting Systems in Three Major cities of New South Wales

Rainwater harvesting (RWH) systems are becoming more popular to reduce pressure on mains water as well as to serve as a sole freshwater supply system in rural areas. Australia is a large continent with highly variable rainfall and hence performance of a RWH system varies from location to location. This paper presents reliability and water-saving potential of a RWH system in three major cities namely Sydney, Newcastle and Wollongong of New South Wales (NSW) State of Australia. A python-based daily water balance model is built to analyse the performance of a RWH system, which uses rainfall, loss, water demand and roof catchment data. To enable selection of ideal rainwater tank size for the selected locations, three different water uses (toilet and laundry, irrigation, and combined use) and five tank sizes (1, 5, 10, 20 and 30 kL) are considered. It is found that the rainwater tank size is influenced by roof area, number of users, water demand and rainfall characteristics. This study will help in decision-making regarding implementation of a RWH system in these Australian cities. This research also contributes towards achieving water related sustainable development goals (SDG).

Spatiotemporal characteristics analysis of water saving potential and economic effectiveness of rainwater harvesting system in China

Abstract The financial viability of a rainwater harvesting (RWH) system is highly determined by regional conditions such as rainfall pattern and water prices. Successful implementation of rainwater harvesting systems depends largely on the identification of suitable sites. This paper presents the water saving potential and economic effectiveness of rainwater harvesting systems across eight major cities in China, using a daily water balance model. Results show six to 81 days (or 1.6% to 22.2%) of dependability can be achieved by using a rainwater harvesting system over these cities. The annual water saving efficiency ranges from 10% to 37% and the benefit–cost ratio varies between 0.45 and 1.20 across the studied cities. South China achieves the maximum annual water saving and the highest benefit–cost ratio, while southeast China has the most regular profile of precipitation use. Northwest China was found to be the region with the worst performance, both in yearly water saving and in regularity of rainwater use on a yearly scale. It was also found that the RWH system is not financially feasible in the northeast, southwest and central plains due to the benefit–cost ratios being smaller than 1.0.

Optimum tank size for large rainwater harvesting system

AbstractThe efficiency of rainwater tank systems depends on tank size, local climate, and potable water demand. This study investigates optimum tank size to maximize water saving potential in semi‐arid Southern California using a simple daily water balance model. The model evaluates the performance of various tank varying sizes collecting rainwater from 10,000 m2 rooftop area of a college campus for the local historical dry, average, and wet years. Results show tank sizes of 130–630 m3 having 100% capture efficiency but system reliability varies from 2.8% to 37.75% in the dry to wet years, respectively. An optimal tank size range is derived from the reliability curves that represent the tank system performance in the local climate. Optimal tank size ranges from 180 to 240 m3, which can capture more than 64% of the roof runoff and thus the campus can reduce on an average 10% of urban water demand.

Superiority of water balance modelling for rainwater harvesting analysis and its application in deriving generalised equation for optimum tank size

In an urban setup optimum size of rainwater tank is a critical factor, as the space required for the rainwater tank is limited and expensive. Several methods have been used for the analysis of potential rainwater harvesting. Some authors used Rippl method for rainwater tank sizing. However, through Rippl method, required size often becomes too big and not feasible in an urban space. This paper presents a water balance modelling concept for rainwater harvesting analysis and its application in determining optimum tank size for rainwater harvesting. Results of the daily water balance model were compared with an earlier study results through Rippl method using daily rainfall data for the city of Nablus (Palestine). Daily rainfall data was collected for the city and from the collected data, three years were selected as dry, average and wet years. Using a typical average rainwater demand and the roof sizes used in the published study, and daily rainfall data for the selected years, annual water savings were calculated for varying tank sizes. From the simulated results, it is clear that for tank sizes beyond certain threshold volumes, annual expected water savings remain unchanged. It is found that Rippl method calculated optimum tank sizes are almost double the optimum tank sizes determined through eTank simulations. Finally, several optimum tank sizes were calculated for different roof sizes and demands considering an average weather condition. It is found that the optimum tank sizes can be correlated with the roof size and rainwater demand, which can be incorporated into a single generalised equation for optimum tank size. The equation calculated results are very close to the original optimum tank sizes found through manual calculation.

A Daily Water Balance Model Based on the Distribution Function Unifying Probability Distributed Model and the SCS Curve Number Method

A new daily water balance model is developed and tested in this paper. The new model has a similar model structure to the existing probability distributed rainfall runoff models (PDM), such as HyMOD. However, the model utilizes a new distribution function for soil water storage capacity, which leads to the SCS (Soil Conservation Service) curve number (CN) method when the initial soil water storage is set to zero. Therefore, the developed model is a unification of the PDM and CN methods and is called the PDM–CN model in this paper. Besides runoff modeling, the calculation of daily evaporation in the model is also dependent on the distribution function, since the spatial variability of soil water storage affects the catchment-scale evaporation. The generated runoff is partitioned into direct runoff and groundwater recharge, which are then routed through quick and slow storage tanks, respectively. Total discharge is the summation of quick flow from the quick storage tank and base flow from the slow storage tank. The new model with 5 parameters is applied to 92 catchments for simulating daily streamflow and evaporation and compared with AWMB, SACRAMENTO, and SIMHYD models. The performance of the model is slightly better than HyMOD but is not better compared with the 14-parameter model (SACRAMENTO) in the calibration, and does not perform as well in the validation period as the 7-parameter model (SIMHYD) in some areas, based on the NSE values. The linkage between the PDM–CN model and long-term water balance model is also presented, and a two-parameter mean annual water balance equation is derived from the proposed PDM–CN model.

Effect of roof size on the rainwater harvesting tank sizes and performances using Tangki NAHRIM 2.0

Global warming and increasing population have direct impacts on water demand all over the world. Usage of potable water in Malaysia is high if compared with other countries and the source of potable water is mainly surface water. Rainwater harvesting is one of the popular alternatives to water resources around the world. However, even Malaysia is a country with an abundance of rainfall, rainwater harvesting is still unpopular. Different size of houses has different roof sizes which will subsequently require different sizes of rainwater tanks. This study utilized Tangki NAHRIM 2.0 (TN2); a web application to determine the optimal tank size for a rainwater harvesting system for five different roof sizes for non-potable demand. TN2 simulation uses a daily water balance model with rainfall input from a built-in database by adopting the yield-after-spillage (YAS) convention. The optimum rainwater tank sizes for five different roof sizes are found to be between 2.6 m3 and 3.8 m3 with water-saving efficiency values between 59% to 76.2% and 30.9% to 53.9% for storage efficiency. A bigger tank size offers higher watersaving efficiency but with lower storage efficiency. The output will be useful for the application of RWHS to residential houses.

Reliability Analysis of Rainwater Harvesting Tanks for Irrigation Use in Greenhouse Agriculture

Rainwater harvesting is an ancient water management practice that has been used to cover potable and non-potable water needs. In recent years, this practice is adopted as a promising alternative and sustainable source of water to meet irrigation needs in agriculture in arid and semi-arid regions. In the present study, a daily water balance model was applied to investigate the size of rainwater tanks for irrigation use in greenhouse begonia and tomato cultivation in two regions of Greece with significant greenhouse areas. For the application of the water balance model, daily rainfall depth values of a 12-year time series (2008–2020) from representative rainfall stations of the study areas were used, as well as the daily water needs of the crops. The greenhouse roof was assumed to be the water collection area of the rainwater harvesting system with values ranging from 1000 to 10,000 m2. The analysis of the results showed that in the case of the begonia crop, the covered tanks ranged from 100 to 200 m3 per 1000 m2 greenhouse area with a reliability coefficient that ranged from 65 to 72%, respectively, to meet the water needs of plants. Further increase of the reliability coefficient was carried out with disproportionately large volumes of tanks. In the case of the tomato crop, covered tank volumes ranged from 100 to 290 m3 per 1000 m2 of greenhouse area, and had a reliability coefficient of 90% to 100%, respectively, while uncovered tanks had a maximum reliability coefficient of 91% for a critical tank volume of 177 m3 per 1000 m2 of greenhouse area and decreased for any further increase of tank volume.

Effects of Climatic and Soil Data on Soil Drought Monitoring Based on Different Modelling Schemes

Satisfactory requirements for the spatial resolution of climate and the influences of soil data in defining the starting points, endings, and the intensities of droughts have become matters of discussion in recent years. The overall inclusiveness of the modelling tools applied is also frequently discussed. In this light, five model setups (MSs) of the daily SoilClim water balance model were developed and tested for the Czech Republic (CR) in the 1961–2020 period. These included two versions of the SoilClim model, two sets of soil data, and two sets of climatic data at different spatial resolutions. MS1–MS4 were based on local, spatially-interpolated data from meteorological stations (500 × 500 m resolution), while MS5 was developed for global drought monitoring, based on the coarser ERA5-Land reanalysis (0.1° × 0.1°). During the 1961–2020 period, all the MSs indicated strong, statistically significant increases in the occurrence of 10th-percentile soil drought in the April–June season; however, trends remained largely non-significant for the remainder of the year. Variations among MS1–MS4 demonstrate that the range of soil property input data affects results to a lesser extent than different modelling schemes. The major simplification of the model grid in MS5 still led to an acceptable conformity of results, while the non-conformities disclosed may be explained by differences between meteorological inputs. Comparison with the Palmer Drought Severity Index (PDSI) confirmed that the SoilClim model depicts the variability of soil drought occurrence in greater detail, while PDSI tends to highlight the most severe events. The discussion arising out of the study centers around model uncertainties and the expression of soil drought episodes in different MSs.

Dynamic modelling of rainwater harvesting with green roofs in university buildings

University buildings may contribute significantly to the urban demand of potable water, particularly in small and medium communities with large universities. In this regard, alternative sources of water supply contribute to minimizing the pressure on natural resources. This paper investigates the applicability of rainwater harvesting (RWH) systems to partially compensate the daily non-potable water demand in university buildings. The traditional daily water balance model was improved to enhance the accuracy of the performance analysis and design optimization of the RWH system by accounting for consumption and runoff variability. The novel algorithm was tested using real daily water consumption data for two university buildings located in Portugal. In addition, different scenarios were evaluated combing RWH systems with extensive green roofs and different runoff distributions over time. The findings indicate that the use of real daily water consumption data instead of average values influences the final results, especially in buildings with fluctuating water consumption patterns over time up to 11%. Regarding the runoff coefficient, it was verified that variable values are recommended compared to the average values. Runoff variability associated with the installation of green roofs was found to decrease RWH system performance due to reduced stormwater runoff. However, the scenario with 50% of the catchment area covered by extensive green roofs showed promising results, decreasing the potential water saving less than 6% and increasing the volume of retained water by almost 15%.

Assessing Irrigation Water Use with Remote Sensing-Based Soil Water Balance at an Irrigation Scheme Level in a Semi-Arid Region of Morocco

This study aims to evaluate a remote sensing-based approach to allow estimation of the temporal and spatial distribution of crop evapotranspiration (ET) and irrigation water requirements over irrigated areas in semi-arid regions. The method is based on the daily step FAO-56 Soil Water Balance model combined with a time series of basal crop coefficients and the fractional vegetation cover derived from high-resolution satellite Normalized Difference Vegetation Index (NDVI) imagery. The model was first calibrated and validated at plot scale using ET measured by eddy-covariance systems over wheat fields and olive orchards representing the main crops grown in the study area of the Haouz plain (central Morocco). The results showed that the model provided good estimates of ET for wheat and olive trees with a root mean square error (RMSE) of about 0.56 and 0.54 mm/day respectively. The model was then used to compare remotely sensed estimates of irrigation requirements (RS-IWR) and irrigation water supplied (WS) at plot scale over an irrigation district in the Haouz plain through three growing seasons. The comparison indicated a large spatio-temporal variability in irrigation water demands and supplies; the median values of WS and RS-IWR were 130 (175), 117 (175) and 118 (112) mm respectively in the 2002–2003, 2005–2006 and 2008–2009 seasons. This could be attributed to inadequate irrigation supply and/or to farmers’ socio-economic considerations and management practices. The findings demonstrate the potential for irrigation managers to use remote sensing-based models to monitor irrigation water usage for efficient and sustainable use of water resources.

Rainwater Harvesting Potentials in Commercial Buildings in Dhaka: Reliability and Economic Analysis

Despite numerous studies on residential rainwater tank, studies on commercial rainwater tank are scarce. Corporate authorities pay little heed on this sustainable feature. With the aim of encouraging corporate authorities, this study presents the feasibility and economic benefits of rainwater harvesting (RWH) in commercial buildings in the capital city of Bangladesh, where water authority struggles to maintain town water supply. The analysis was conducted using a daily water balance model under three climate scenarios (wet, dry and normal year) for five commercial buildings having catchment areas varying from 315 to 776 m2 and the storage tank capacity varying from 100 to 600 m3. It was found that for a water demand of 30 L per capita per day (lpcd), about 11% to 19% and 16% to 26.80% of the annual water demand can be supplemented by rainwater harvesting under the normal year and wet year climate conditions, respectively. The payback periods are found to be very short, only 2.25 to 3.75 years and benefit–cost (B/C) ratios are more than 1.0, even for building having the smallest catchment area (i.e., 315 m2) and no significant overflow would occur during monsoon, which leads to both economic and environmental benefits. Though the findings cannot be translated to other cities as those are dependent on factors like water price, interest rate, rainfall amount and pattern, however other cities having significant rainfall amounts should conduct similar studies to expedite implementations of widescale rainwater harvesting.

Tangki NAHRIM 2.0: an R-based water balance model for rainwater harvesting tank sizing application

Abstract Tangki NAHRIM, a desktop application developed in 2008, is widely used for the calculation of optimal tank size for rainwater harvesting in Malaysia. Here we present an overview of the updated version, Tangki NAHRIM 2.0 (TN2) which was developed in the R computing environment. In TN2, a rainwater harvesting system is simulated using a daily water balance model with rainfall input from a built-in database by adopting the yield-after-spillage (YAS) convention. Proposed tank sizes are evaluated based on water saving and storage efficiencies. These results are then visualised in charts showing the relationships between tank sizes and both efficiency measures to help users select the optimal tank size based on their criteria of choice. A simulation was conducted based on a typical Malaysian household for domestic non-potable use as a case study. A web-based GUI for TN2 was developed in R Shiny framework for the public. The GUI has the advantage of being accessible online from any device, and will be able to facilitate the adoption of rainwater harvesting systems by the public at large.