沙漠研究 22-1, 87 -90 (2012 )"ICAL 1 / DT X"

Journal of Arid Land Studies－Refereed Paper－Urban Rainfall Harvesting to Alleviate Water Shortages and Combat
Desertification in the Arid Land of Jordan
Majed ABU-ZREIG*1), Ayat HAZAYMEH2)
Abstract: Water harvesting can alleviate the chronic water supply shortages in Jordan, increase cropping land area, improve thelivelihood of population and eventually combat desertification. A systematic study was undertaken to evaluate the use of rooftop
rainfall harvesting in urban areas, study the socioeconomic value, determine the optimum rainfall collection tank volume and thepotential contribution of rainfall harvesting to the national domestic water supply budget. The potential water supply volume fromrooftop rainfall harvesting can reach 14.7 million m3/year, comprising of about 6% of the domestic national water supply. Analysisof domestic water supply rate in relation to average rainfall depth and number of cisterns in each governorates indicated that the public
water supply rate decreased in governorates with high rainfall depth and large number of cisterns. Cistern number among
governorates increased with rainfall depth indicating a good adaptation behavior to water shortages. Optimum cistern volume charts
were constructed for some governorates as a function of family consumption rate and house roof area. These charts can be used as
tool to determine the optimum rainfall cistern volume as related to consumption rate and rooftop area. An immediate and nationwide
awareness and legislative program is needed to spread rooftop rainfall harvesting among the whole population of Jordan and region
with similar climates.
Key Words: Rooftop rainfall harvesting, Tank size and water supply

1. Introduction
The increasing need to provide potable water due tourbanization and population increase demanded developmentof nontraditional water resources for domestic uses. As such,rooftop and open yard rainfall harvesting is gaining a lot ofinterest recently not only in arid countries such as Jordan,
Tunisia but also in humid countries like Germany, Japan,
Sweden and Brazil to reduce urban runoff, improve water self
dependent facilities and reduce the cost of water (Chisi, et al.,2007; Kahinda et al., 2007).
In arid climates rainfall harvesting can be the only sourcesof potable water in some cases. Until the development ofwell drilling and piping, which started in 1940 for wealthierfamilies, the whole population of Jordan was totally dependent
on rainfall harvesting for domestic uses (Nydahl, 2002). In
1991, the public water supply network has reached about 97%
of households in Jordan due to intensified urbanization.
While population increases, water demand also increases dueto the increased standard of life style and the dependence oneasy accessed water supply. However, the traditional inhouse rainfall harvesting systems became more and moreignored.
Very few studies have focused on rooftop and court yard

rainfall harvesting systems (Abdullaa and Al-Shareef, 2009).
But their study used was limited to technical aspects and used
the average annual rainfall in each area and without
considering the low-depth rainfall events that often produce norunoff. The objective of this paper is to analyze the current
notions and practices of the Jordanian population to rooftop
rainfall harvesting, estimate the potential resources fromin-house rainfall harvesting at the national level, determine theoptimum volume of rainfall harvesting tank in some areas andidentify methodologies to reinitiate and promote rooftop
rainfall harvesting among Jordanians.

2. Materials and Methods
Information about type and area of houses, main sources ofdrinking water and number of cisterns for each governorate in
Jordan were collected from the Department of Statistics in
Jordan (DOS, 2004). The average rainfall depth and watersupply rate in various governorates was taken from theMeteorological Department and the Water Authority,respectively.
The potential volume of rainwater that can be collectedfrom each governorate based on the average rainfall and thetotal roof of individual houses and apartment building werecalculated.
The potential volume of rooftop rainfall* Corresponding Author: majed@just.edu.jo
P.O.Box 3030, Irbid 22110, Jordan
1) Professor of Water Resources and Environmental Engineering, Civil Engineering Department, Jordan University of Science and Technology2) Graduate Student ,Water and Environmental Engineering ,Civil Engineering Department, Jordan University of Science and Technology, Irbid, Jordan.

harvesting for the whole country is calculated simply byadding up the volume of water that can be collected in eachgovernorate.
Rooftop rainfall volume RRV for each governorate can becalculated from the following equation
𝑅𝑅𝑅 = 𝐶 ∙ 𝑅𝑒 ∙ 𝐴/1000(1)Where RRV is the annual roof rainwater volume that can becollected from each governorate (m3), Re is the effective
average annual rainfall (mm), (Re is equal to the annual rainfall
excluding small rainfall events less than 2 mm that produce norunoff); A is the total roof area of individual house andapartment buildings in each governorate (m2), C is the runoff
coefficient; and 1000 is a conversion factor.
An appropriate runoff coefficient, C, must be determined.
The runoff coefficient lump sums the proportion of losses andit depends not only on the type of roof but also on the amountof rainfall. Since almost all roof areas are made of concrete C
was fixed at a value equal to 0.8. Many other researchers
used a runoff coefficient of 0.8 for concrete roofs (Abdullahand Al-Shareef, 2009; Ghisi et al, 2006). However, Li et al.
(2004) reported that the runoff coefficient of concrete surface
varied from 46 to 70%. Nevertheless, a loss of 20% in
rainfall and C value of 0.8 seemed to represent roof systems inJordan.

3. Results and Discussion
3.1 Sizing of rainwater collection tank
The high cost of rooftop rainfall harvesting systems comesmainly from the cost of collection tanks or cisterns. The mostcommon types of tanks in Jordan are made of reinforcedconcrete. Therefore, an attempt was made to determine thecost of reinforced concrete tanks based on the market prices ofconcrete, steel and labor. The result of this analysis is shownin Figure 1 at which the tank cost was shown as a function ofvolume and water depth. As shown in the figure, the cost
increases with volume in nonlinear fashion and also with water
depth. It seemed that 3 to 3.5 tank depth is practical and
10000
9000
8000
7000
6000
5000
4000
3000
2000
1000
0

Total cost (JD)

Tank Volume m3
100
90
80
70
60
50
40
30
20
100

1xxd2

3

45

Tank depth (m)Fig. 1. Relationship between the cost, volume and depth of square
reinforced concrete tank.

results in the lowest cost. As the cost increases with volume,
one should determine the optimum volume that can satisfy thisneed.
Therefore, many efforts have been made to design an
optimum tank size that can accommodate supply and demandwith cost (Anonymous, 2001)
Several methods were used to estimate the required storagetank capacity that varies in their complexity. One of thesemethods depends on the demand of households. The tankvolume is simply equal to the cumulative demand volume
needed by a household in a given period of time. Thismethod is suitable in high rainfall regions where rainfall is nota limiting factor. The other method depends on the supply
side, which in turn depends on the volume of rainfall that canbe collected from a specific area in a specific period of time.
This method is used in arid and semi-arid regions where
rainfall depth is the limiting factor. The tank volume
calculated from rainfall and rooftop area during period of time
represents the maximum tank volume possible for that case.
However, the optimum, tank volume depends on thesupply or rainfall volume rate and demand, the consumption
rate. Mass curve analysis can be used to calculate theoptimum size of a tank for a supply and demand series witheither graphical or analytical techniques. The amount ofstorage that must be provided is a function of the expectedinflow, supply, to the tank and outflow, demand, from the tank.
Mathematically, this may be stated as follows:∆S = O-I(2)
Where ∆S: change in storage volume during a specified
time interval; I: total inflow volume during this period; O: total
outflow volume during this period.
The cumulative
deficiency between outflow and inflow (O-I) is calculated overa preselected time series. The maximum cumulative value
would be the required storage to mach supply with demand inthat specific period.
Thirty years of monthly rainfall data, from 1976 to 2005,
were used to determine the optimum rainwater tank volume for
Irbid governorate. However, this volume should not exceed
the maximum total volume of rainfall that could be collectedfrom a given roof or yard area. The optimum tank volume
for various combinations of roof area and demand rate wascalculated for each Irbid governorate and the result is shown inFigure 2. The maximum tank volumes that should not beexceeded, based on rainfall supply volume, are also shown in
the figures. Using such figures, one can determine theoptimum tank volume that would probably meet the demandrate for the wet 8 months for a given rooftop area. The Figure
also shows clearly the influence of demand rate and rainfall
volume and pattern in Irbid governorate. Tank volume
increases with an increase in the demand rate and rainfall depth.

Optimum tank volume (m3)220200180160140120100806040200

Water usage
m3/month

Table 1. Potential volume of harvested water in the twelve
governorates of Jordan.

IRBID

18

Maximum tankvolume curve

16

Governorate

14
12

Totalarea(m²)

Average

Effective+

Potential

rainfallrainfallrunoff++

(mm)

(mm)

harvested (m3)

108
6
4

0

50

100

150

200

250

300

350

400

450

2

Roof area (m )Fig. 2. The optimum tank volume in relation to rooftop area andwater usage; Irbid governorate.

The optimum tank volume charts are being constructed forthe whole of Jordan and on finer grid to cover various parts ineach governorate. As an Example the rainfall depth andpattern in Mafraq governorate varied widely from about 200
mm to as low as 50 mm per year and calculating the tankvolume based on the average rainfall depth results in large error.
Therefore, the Government of Jordan should adopt asystematic program to promote rainfall harvesting and publish
design pamphlets to be used by local people and contractors.
Rooftop rainfall harvesting is being practiced widely in
Irbid and the number of cisterns is about 27 000 which is far
higher than any other governorate. This is followed byAjloun, 2650 and Amman with only 600 cisterns as shown in
Table 2. This seemed to be illogical since Amman shouldhave much higher number of cisterns due to its high population
density and high living standards compared to othergovernorates that can afford the cost of rainfall harvesting
system. However, the public water network in Amman
covers most of the population and is the most reliable among
all other water networks in Jordan. Therefore, residents ofAmman feel safe in terms of water supply and lack themotivation to build an in-house rainfall collection system.
Immense awareness and legislative efforts should be made topromote in-house rainfall harvesting systems among the
population of Jordan in general and Amman residents inparticular.
3.2 Potential water supply from rooftop rainfall harvesting
The national total water supply from rooftop rainfall
harvesting can be estimated from the total areas of houses,
villas and apartment buildings and the average effective rainfall
over each governorate and a runoff coefficient of 0.8. The
potential rooftop water harvesting for Jordan is about 14.8
million cubic meters comprising about 6% of the total
domestic water supply in Jordan (Table 1). About 64% of
the rainwater is collected from the Amman and Irbid
governorates due to their high population, housing density andAmman

17672244

490

441

6,234,768

Irbid
MafraqAjloun11018556
37259441343588

411
169
645

370
152
581

3,260,611
453,373
623,962

Jerash1796600

352

317

455,330

Zarqa
Balqa

59076193784513

136
624

122
562

578,474
1,700,306

MadabaKarak
Tafileh
Ma’an
Aqaba

15720253045775
9717131297056883681

339
359
270
43
35305
323
243
39
32

383,700
787,272
188,901
40,15722,269T O TAL
14,729,122+ Rainfall events of depth<5 mm were not included. ++ Runoff
harvested = Total area (m2)*Effective rainfall (m) * 0.8
Table 2. Summary of cisterns, consumption rate and average
rainfall for Jordanian governorates.
Water

Average

Number ofsupply

rainfallGovernorate

cisternrate (l/c-d)

(mm)

Amman

612

163

480

Irbid

26941

97

427

Mafraq

136

187

161

Ajloun

2641

71

582

Jerash

802

76436

Zarqa

242

133

144

Balqa

1538

155530Madaba

69

127

320

Karak

162

148

350

Tafileh

14112

242

Ma’an

47

208

42

Aqaba

25

228

32

T O TAL

33229

high rainfall depth. All other governorates contribute about
35% of the total harvested rain. Therefore, efforts should
focus on Irbid and Amman residents to promote in-houserainfall harvesting.
Analysis of the relationship among number of cisterns,
public water supply rate and average rainfall in eachgovernorate, shown in Table 2, gives an insight on thepopulation behavior and management actions of the watersector in Jordan. Analysis may clarify the reason of
decreasing water supply rate for governorates with high rainfall
depth. Water supply rates for governorates seemed toWater supply rate (l/c.d)

250
200
150100y = -24.4Ln(x) + 284
R2 = 0.54

5001

10100

1000

10000

Number of cisterFig. 3. Relationship between average public water supply andnumber of cisterns for Jordanian governorates.

decrease with the number for cisterns logarithmically as shownin Figure 3 reflecting the conception of government
dependence on cisterns as a source of domestic water supply
for the population. This may also be affected by population
behavior towards water needs. A population with cisterns
may feel more secure and less dependent on public watersupply thus reducing people's demands for more water supplies.
This result showed clearly that spreading and renewing theculture of rainfall harvesting among the population of Jordan
will ultimately reduce the need for additional domestic watersupplies in the whole country.
The number of cisterns increased with average rainfall
depth in the Jordanian governorates. The population seemedto evaluate the economical efficiency of rooftop rainfall
harvesting internally and therefore respond in building morecistern in high rainfall areas compared to low rainfall areas.
The authors believe that governments should invest urgently
into more awareness, legislative and financial and technicalsupport programs to spread rooftop rainfall harvesting among
Jordan population and that the population of Jordan will
respond positively.

4. Conclusion
This research has shown the importance of rooftop rainfall
harvesting and analyzes the needs to adopt an integrated
approach to spread its use at the national level. Rooftop
rainfall volume can increase domestic water supply by about
14.7 m3/year comprising 6% of the domestic national watersupply. Analysis of the number of cisterns, rainfall depth andpublic water supply among governorates have shown thatpeople have developed adaptation behavior and self-reliancefor water supply as the public water supply seemed to decreasein high rainfall governorates having a high number of cisterns.
Water managers also seemed to rely on population judgment tosecure their own water supply as they decrease the supply rate
for governorates of high rainfall and high number of cisterns.
A technical chart to determine the optimum size of rainfall
harvesting tank has been developed for various governorates.
Such charts will help people to build the most economical
water harvesting tank that satisfy the needs for their house.
Under the current water crises, the government of Jordan
should move ahead with intensive awareness, financial, andtechnical programs to spread the use of rooftop rainfall
harvesting in the country.

References
Abdulla F.A., Al-Shareef A.W. (2009): Roof rainwaterharvesting systems for household water supply in Jordan.
Desalination, 243 195–207
Anonymous (1999): Centre for the Analysis and Disseminationof Demonstrated Energy Technologies (CADDET).
Combined and stepped use of energy in Sumida City Office;
Available at http://www.etis.net.
Anonymous (2001): Recommendations for designing
rainwater harvesting system tanks. Milestone A6: Report A4,Development Technology Unit, School of Engineering,
University of Warwick, Warwick, England.
Department of Statistics (DOS), (2004): Annual Report,Amman, Jordan, www.dos.gov.jo.
Ghisi E., Montibeller A., Schmidt R.W. (2006): Potential for
potable water savings by using rainwater: An analysis over
62 cities in southern Brazil. Building and Environment, 41:
204–210.
Kahinda Jean-marc M., Taigbenu A.E., Boroto J.R. (2007):Domestic rainwater harvesting to improve water supply inrural South Africa. Physics and Chemistry of the Earth. 32:
1050–1057.
Li Xiao-Yan, Zhong-Kui X., Yan Xiang-Kui. (2004): Runoff
characteristics of artificial catchment materials for rainwater
harvesting in the semiarid regions of China. AgriculturalWater Management, 65: 211–224.
Nydal H. (2002): Archeology and water management inJordan. C.-uppsats i arkeologi, Institutionen for Arkiologi
och antic Historia, Upsala University, Sweden.