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Evaluation of rooftop rainwater harvesting system for non-potable demands&estimation of system carbon footprint under climate change effects



The main goals of this study are summarized as two sections 1-impact assessment of climate change on Domestic Rainwater Harvesting Systems (DRHS) reliability, 2-estimation of equivalent mitigation of carbon footprint of the project in a pilot site.

Reliability of DRHS is evaluated for current (from1992 to 2005) and future period (from 2017 to 2030). Thus, at the first step, all rain gauge stations with monthly scale are selected in Birjand City located in the east of Iran. Then monthly climate data are simulated using the outputs of General Circulation Models (GCMs) from 14 GCMs as large-scale climate data of Coupled Model Intercomparison Project Phase 5 (CMIP5) projections. Then, the GCMs output will be downscaled spatially through Bias-Correction Spatial Disaggregation (BCSD) method. Interpolated monthly precipitation values for Birjand rain gauge station are achieved automatically by means of the ordinary Kriging method during current and future periods. The reliability contour lines of DRHS are knows as one of the main production of first section. The reliability of DRHS will be assessed by a specific combination of rooftop area and storage tank capacity.

Energy consumption and GHGs emission particularly carbon dioxide may be mitigated by DRHS implementation. Estimation of carbon footprint is performed based on energy consumptions. Also equivalent mitigation of carbon footprint is evaluated based on reduction in energy consumptions due to DRHS usage. The values of energy saving are calculable based on actual data of energy consumption in different parts of municipal water delivery (public water) such as supply, conveyance and distribution. Also economic analysis is linked to the Benefit per Cost (B/C), Net Present Value (NPV) and Internal Rate of Return (IRR) indices based on the water and energy saving. Amounts of CO2 footprint reduction based on energy saving of DRHS implementation are resulted as second section output.

Is this proposal for a practice or a project?


What actions do you propose?

Obviously DRHS implementation has both construction and maintenance costs which are considered as cost value. These cost are paid for purchase of storage tank, assemble of conveyance system, preparing of rooftop area, repairs, treatment and filtering, and other relative tasks. The maintenance of DRHS system mainly consists in periodical cleaning of the rooftop area and the internal space of the storage tank (Sazakli et al., 2007; Dillaha and Zolan, 1984).  Also amount of water saving during specific period comprises economic value which may be accounted for as benefit value. This water saving reduces energy requirement and mitigates carbon footprint consequently. High values of rooftop area and volume of storage tank can save more water in a rainfall event while these may be leaded to more cost for implementation. In other expression we have a Tradeoff between water saving and cost of DRHS implementation. Economic indices are calculated for all probable cases DRHS similar to reliability. Value of benefits and costs are calculated at the end of every year and converted to present value by considering of discount rate and finally B/C, NPV and IRR indices may be evaluated for all DRHS combinations similar to reliability.

Who will take these actions?

In our proposal we think that household consumers/people are the most important recipients of the benefits from the installation of DRHS. Although there are no encourage, incentive or facilities provided to support this program, but it can contain several benefits such as safe and reliable water supply, improvement of health and security, environmental conservation, etc. The residents can easily have a DRHS for their building to take the advantage of it to save energy and money.

The governmental organizations such as Iran Construction Engineering Organization (IRCEO), Regional Water Company (RWC), Natural Disaster Management Organization (NDMO) and Water and Wastewater Authority (WWA) can have a significant role in this action, as well. The IRCEO which authorizes final construction license for any building can set the regulations for the installation of DRHS in all buildings. Also this organization must arrange limitations and penalty against offenders. The RWC can inform people about the DHRS advantages and encourage them to install it.  Since water distribution network in a city or village is authorized by WWA then this company should determine the rate of water consumption and prints water bills for any consumer rationally. The stress on distribution network can be reduced and the management of distribution is easier by relying on DRHS. Thus in this proposal we have assumed two roles for WWA: presentation of fund supports for costs of DRHS installation, consider a penalty (insert additional money in water bills) for offender consumer that use of public water (water distribution network) for unnecessary consumptions.

 The NDMO which is responsible in natural disasters such as storm, flooding, earthquake conditions also can pay a part of supporting funds or incentives for the installation of DRHS.

Where will these actions be taken?

Birjand City is considered as the start point to implement the proposed action. This area faces with serious challenges related to the water deficit. It may be inferred that a millimeter of rainfall can be potentially very important in this region. Household water supply has been trouble due to the scarcity of water. Thus, policymakers are searching to novel solutions for conservation and optimal use of current water resources.

Birjand city is the center of Southern Khorasan Province. This city, with an arid cold climate, is located in the east of Iran (Fig 1). The annual pan evaporation, average temperature, precipitation, and relative humidity are 2250 mm, 16.5 °C, 170 mm and 37% respectively.

Fig. 1. Location of the study area (adopted from jafarzadeh et al, 2017)

The proposed action in this work can be taken in any residential region of the country which has concerns in water resources particularly arid climate.

In addition, specify the country or countries where these actions will be taken.


Country 2

No country selected

Country 3

No country selected

Country 4

No country selected

Country 5

No country selected


What impact will these actions have on greenhouse gas emissions and/or adapting to climate change?


With the adequate operation and right maintenance of the collection areas, conveyance, filter and storage tank systems, acceptable quality of water may be obtained by DRHS. Notice that DRHS brings water by minimum consumption of energy. In DRHS all of steps (harvesting of rainfall, water moving in conveyance system and storage of water in tank) are performed relying on gravity force and without energy. It reduces energy required of treatment, cleaning, pumping and distribution. Thus Energy is saved and will have been for more people. In other expression lifeline (or life style) of people can be optimal by DRHS and lower energy consumption. Carbon dioxide production is much decreased (so that nears to zero) by less consumption energy generally. Hence DRHS implementation can reduces concentration and emission of greenhouse gases (GHGs) therefore interaction between climate change and DRHS is liked properly.

For example, Panahian et al, (2017) showed that can improve CO2 footprint by relying on Rainwater Harvesting Systems (RHS) in Sydney of Australia. Results of their study showed that there is a reduction of equivalent CO2 emission from 155.9 kg to 240 kg (based on storage tank capacity) in year. Also research of Rahman et al, (2014) indicates that with an 1850 m2 for rooftop catchment, about 69,026 gallons can be harvested and about 100 kWh electricity energy could be saved in Dhaka City of Bangladesh and over one year.

Also DRHS can to bring water required for small-scale irrigation practices such as small garden in yard of building and area of green spaces increase consequently. More green spaces can capture up more concentration of atmospheric carbon dioxide. Therefore DRHS can help to reduction of carbon dioxide in atmosphere.

Results of Valdez et al, (2016) indicate that RWH has a noticeable effect on GHG emission and flooding. Outcomes of this study show RWH in Mexico City could mitigate GHG emissions, reduce flooding risk and increase flexibility and reliability of Mexico City.


Decreasing and increasing trends of rainfall and temperature due to climate change impact, endangers available water resources especially in arid climate (IPCC, 2007).According to Fourth Assessment Report (AR4) of IPCC, rainwater harvesting systems are capable of reduction of GHGs emission about 6 Gt carbon dioxide in one year at 2030 (IPCC, 2007). Several researches reveal that rainwater harvesting can mitigate carbon dioxide emission, vulnerability of water supply, energy and water consumptions (Mithraratne and Vale, 2007; Blunt and Holt, 2007). DRHS help to save of water resources by less rely on fresh water. Several household water demands such as yard washing, garden irrigation, toilet flashing, etc. (unnecessary consumptions) are reparable by DRHS.

What are other key benefits?

There is a potential in case study that other clean energies be used next to DRHS implementation.

There are two vital advantages to use the solar clean energy in Birjand City: 1- Birjand receives notable number of hour of sunshine in one day generally. Thus this City has noticeable potential in generation of solar clean energy. 2- There are a much villa houses which has been considered in their yard a significant space as canopy for refuge of injuries of sever sunlight. In regard to these advantages, it is capable to be used as a catchment canopy which harvests solar power and rainwater simultaneously (Fig 2). It is combination of rainwater harvesting and solar photovoltaic panels and may be named Solar and Rainwater Harvesting System (SRHS). SRHS must be equipped to solar panels and DRHS components simultaneously. In this system photovoltaic panels (by a moderate slope) are installed on rooftop of buildings and conducts rainwater into the storage tank. Solar panels should be clean (with a Nano layer of anti-dirt) and covered with an antireflective layer for most efficiently. Objective of this system is cover of a specific section of water demand and electricity needs by harvest of natural resources.


Fig 2. Solar and rainwater harvesting system

Main objective of implementation of DHRS is help to secure of water, although it can to have good impacts on economy and environment which are counted in following:

DRHS save rainfall before it becomes dirty. Therefore DRHS can reduce energy requirement for cleaning of urban runoff and it has reduced the costs of treatment of wastewater. In large scale it can reduce local or national funds by its widespread implementation.

Also it can improve health security of citizens in crisis conditions such as earthquake, storm and flooding. Moreover it can secure water for necessary consumptions in times which water distribution network is off due to crisis of shortage water or power outage.

It reduces consumptions and money saving is increased consequently thus DRHS can improves families’ incomes significantly.

DRHS can reduce risk of storm water flow from municipal sources. It decreases event of flooding, short peak flows, storm discharge from urban catchments and runoff velocity. In other words risk of floods can be decreased by maintain a noticeable section of rainfall in storage tanks of DRHS.

Climate change impact and increasing population decrease access to water and cause more pressure on environment and ecosystem. DRHS reduces stress on water resources and can to secure a section of consumptions by harvesting of rainfall. Therefore it can to have effective role for conservation of water resources in environment and natural ecosystems. Life of several hundred of plants and animals depend on water availability and DRHS can salvage them.


What are the proposal’s projected costs?

We divide costs into two sections: implementation and maintenance. Implementation costs is comprised of purchase of storage tank, assemble of conveyance system, preparing of rooftop area, repairs, treatment and filtering.  Totally anticipated cost will be under $5500. These costs are described in follow.

Water quality depends on type of roof materials which are been influenced by sun lights and air pollutants. Therefore prepare and repair of roof area is essentially step. These tasks must be performed before the rainfall season. Costs of this section are a function of rooftop area and it doesn’t too much on the project.

Conveyance system includes gutter and spout. Gutter and spout must be made of inert materials. But Gutter can be used or conveyance system is just performed by spout. Also length of spout depends on building height. Common materials that is used for Gutter is aluminum. We haven’t especially limitation for spout materials. Anything can be used to get the water down from the gutters or roof. Conveyance system must be designed for good flows, storm events, and easy cleaning. The cost of this part depends on volume of harvested rainfall directly and roof area indirectly and varies between $1000 up to $1500.

Treatment and filtering cost depends on target of consumption. Initial filtering by light cost such as debris traps are adequate for proposed consumptions in this proposal. In this case we don’t need to especially energy for filtering.

Most cost of our proposal is considered for storage tank which save harvested rainfall for demands. In high capacity tanks we save more water and in other side will have more costs. In a building with constant roof area larger storage tank need to better conveyance system with more costs. Therefore in a specific building storage tank capacity limits other costs. This item may be costed $3000 up to $3500. 

Hence we prefer to relate the total cost of implementation as a function of storage tank capacity based on assessment of performed exercises.


We consider an exploitation duration of DRHS which is described in next paragraph. Also time requirement for performing this proposal is explained as “Tentative Timeline”.

We consider a period which its length is 15 years and starts from first 2017 and finishes in end of 2030. Also results are expected to be presented for this period. But DRHS can continue until that conveyance system and storage tank not be obsolete. DRHS implementation in short term has very advantage in water supply that its economic, environment, health and security advantage can increase in long term. Water saving and energy reduction next to improvement of emission of GHGs are impacts of long term implementation of DRHS. Initial assessments show that DRHS can potentially secure more of 50% of household water demand in a family by 5 persons in short term. 

Tentative Timeline

The following table illustrates Gantt chart of schedule of relevant actions. It shows time requirement of activities during the study lifetime. Proposal starts from first of 2018 and continues to end of 2019.

About the author(s)

Mohsen Pourreza-Bilondi is an assistant Professor in Dept. of Science and Water Engineering of University of Birjand. His major contribution is summarized in optimization approaches and uncertainty estimation with Bayesian and non –Bayesian frameworks. He also conducted some researches involved with water harvesting systems, groundwater modeling, hydrological modeling and water resources planning.

Hadi Memarian, as the Assistant Professor in Watershed Management Department of the University of Birjand works mainly on the application and hydrologic analysis of rainwater harvesting systems in Iran and published several books and papers in this field.

Ahmad Jafarzadeh is PhD student of water resources engineering in Dept. of Water Engineering, University of Birjand. He resides in Birjand city and has interested in climate change and groundwater modeling. He spent his undergraduate and master science in university of Birjand. Major of him researches returns to climate change impacts on groundwater.

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