Climate Change and the Application of Rainwater Harvesting

7/21/2019 Climate Change and the Application of Rainwater Harvesting

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ACSAD Conference on Rainwater Harvesting as an Option for Adaptation to Climate Change in Arab Region,

2022 May 2013 in Beirut, Lebanon

Climate Change and the Application ofRainwater Harvesting

Prof. Dr. Dieter PrinzProfessor (retired) at Karlsruhe University / KIT, Institute of Water and River Basin

Management, Karlsruhe, Germany

Abstract

The Arab World is changing at a tremendous rate:Not only political unrest (Arab Spring), buteven more the changes in lifestyles, increasing population, growing urbanization andeconomic development will shape the future of this part of the world.Global Climate Changeis just an additional stress: Most probably, the climate in the MENAregion will become even hotter and drier with more extreme weather events,such as stronger

storms, longer droughts, and heavier floods.Rainwater is an underutilized resource and has to be included in any water resourcesplanning in Arab region. Rainwater, including overland flow, can be (1) used on-the-spot (in-situ rainwater management) for agricultural use or recharge, or (2) collected, concentratedand stored (Rainwater Harvesting). Rainwater harvesting is defined here as the collection andconcentration of rainwater and runoff and its productive use for domestic and livestockconsumption, the irrigation of annual crops, pastures and trees and for groundwater recharge.We distinguish three methods of rainwater harvesting (RWH), depending on the size of thecatchment: Microcatchment Water Harvesting, Macrocatchment Water Harvesting andFloodwater Harvesting. Various RWH techniques are applied to meet the requirements of theuser (human beings, domestic animals, crop plants) and the type of use, e.g. as drinkingwater, for irrigation, for groundwater recharge etc.

Climate Changeimpacts the application of rainwater harvesting by (1) shifting the applicationbelts of RWH methods synchronously to the shifting of the ecological belts, and (2) altering theapplication of techniques, the physical structures and the kind and volume of water storage tofit to the altered climatic conditions. Exemplary some adaptation measures are given: (1)Higher water demands of people, crops and livestock due to higher temperatures have to bemet by an increase in catchment area and/or by increasing runoff coefficients on catchmentareas and/or by a higher water use efficiency, supplemented by an increase in storagevolume. (2) Higher rain intensities and more erratic rainfall demand a larger catchment-to-cropping-area ratio and a strengthening / raising of water harvesting structures (bunds, dams,walls). (3) Adaptation to more/larger floods can be achieved by increasing size of structures forwater diversion, for impoundment and spill of excess water.Rainwater harvesting can, in combination with in -situ rainwater management, more water

storage and Supplemental Irrigation, contribute to a more secure water supply, to a reducedflood and soil erosion risk, to improved agricultural production. However, it is only a single outof numerous elements which have to integrated in a water resources management which cancope with future climatic and socio-economic challenges.To achieve the objective of satisfying future water demand in the Arab region by making bestuse of rainwater resources, an Integrated Water Resources Management(IWRM) approachshall be applied. The most important tools to adopt are a suitable policy (including laws andregulations), adapted spatial, watershed-based planning, capacity development at variouslevels, stakeholder participation and a sound environmental management.

Prof. Dr. sc. agr. Dieter Prinz, D-76133 Karlsruhe, Damaschkestr. 124, Germany, e-mail:

[email protected],phone: +49-(0)721-758990
mailto:[email protected]:[email protected]:[email protected]


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1 Introduction

The Arab region is one of the worlds most water-scarce regions with a growing population anda high share of climate-sensitive agriculture. Tremendous economic, demographic and socialchanges have been taking place during recent decades and will continue for the decades tocome, such as migration from rural to urban areas, movement from traditional farmingactivities to manufacturing and service sector and changes in lifestyle. A high degree ofdiversity exists across the Arab Region.The region is particularly vulnerable to Climate Change. Climate Change will pose anadditional stress on the ecological and socio-economic systems of the region, which arealready under pressure. Land degradation, desertification, loss of biodiversity and finally areduction in food and water security of the region will aggrevate in future.

2. The General Setting

Population: The population of the Arab countries nearly tripled between 1970 and 2010,climbing from 128 million to 359 million. According to UN projection, the Arab Region will haveabout 600 million inhabitants by 2050, increasing by two-third, i.e.about 240 million morepeople than in 2010 (Mirkin 2010). The total fertility declined from 6.8 children per woman in1970-1975 to 3.6 children per woman in 2005-2010 and is expected to fall to 2.1 children perwoman by 2045-2050 (UN-DESA 2009). While some countries are at or near the replacementlevel, in other countries high fertility persists (UN-ESA 2012).

Fig. 1: Urban population trends 1970 to 2050 in Arab countriesSource: Schaefer 2013, based on UN-ESA 2010

Urbanisation:The Arab region is one of the most urbanized regions in the world: Between1970 and 2010 the region experienced 400% urban growth; during the next 40 years a growth

of 200% is expected: Whereas in 2010 about 56% of the total population lived in cities, in 2050the percentage will have risen to 68% (Fig. 2). Cairo will remain the largest city of the Arabregion, growing to 16 million inhabitants in 2050. The urbanization process is driven by


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economic development, migration to oil-rich countries, drought and conflict, the importancevarying by sub-region (Schaefer 2013). Water demand of urban dwellers is generally higherthan of rural ones, causing the overall water demand to increase.

3 Climate Change and its impacts3.1 Temperatu re

The people of the Arab region are used to adapting to severe heat and drought. Most parts ofthe Arab region are arid with high mean annual temperatures, ranging from 20C to 25C inthe desert regions, up to 28C on the Arabian Peninsula and between 15C and 20C in theMediterranean and subtropical zones. Within the past 100 years a warming trend has beenobserved by most meteorological stations in the Arab region.For recent years almost all stations showed a positive trend of 0.3C to 0.4C per decade,which is expected to continue during the 21st century (Fig. 3). This likely warming by 3 to 4 0Cduring this century is roughly 1.5 times the global mean response. According to IPCC (2007;

A1B emission scenario),warming will be evident in allseasons, with the greatestincrease in summer (Fig. 4).The Arab countries areexpected to see increasedtemperatures of at least 2

Celsius in the next 15-20years.

Fig. 3: Projected temperatureincrease due to climate

change for late this century. Mean annual temperature change, 1980 1999 to 2080 2099Source: Verner 2012, p. 56

Fig. 2: Urban and rural populations of the Arab region 1980 - 2050

Source: ESCWA 2009


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In urban areasheat waves and an increased heat island effect will impact living conditions(such as a decreasing water quality, worsening air quality, and ground ozone formation), willheighten the water demand and result in increased pressure on groundwater resources, whichare currently being extracted in most areas beyond the aquifers recharge potential. A3increase in nighttime temperatures in cities (additional to the overall 3 temperature increaseby 2080) is forecasted.

Fig. 4: Mean seasonal temperature changes for the 2080s projected for various Morocconcities (downscaled from HadCM3 model under the A2 emission scenario).Source: Verner 2012, p. 68, based on Wilby 2007

The anticipated changes in temperature show strong differences as well in total values as in

seasonal values between cities even of the same country. Wilby (2007) studied the situation in

Morocco, and he predicts smallest temperature increases in Agadir (coastal station) and

largest in Ouarzazate in the Atlas Mountains, where the summer temperature is projected to

rise by more than 6C by the 2080s. The frequency and severity of heat waves is projected to

increase (Verner 2012).

For the planner, changes in extremes are more interesting than changes in average values as

they do have a stronger and often long lasting effect on peopleslife. In regard to temperature,

not only the general increase of mean temperature, but in particular an increase of extreme

warm days, will increase the risk of heat stress. According to Diffenbaugh et al. 2007, the

number of days with a dangerous or extremely dangerous heat index is dramatically increased

along the Mediterranean coast of all Arabic countries by the end of the century in comparison

with the present baseline period (Fig. 5). The peak changes may be up to 65 days per year

(Verner 2012).

3.2 Impact on rainfal l and water resources

The reduction in rainfall and hence in (renewable) water availability is a problem effecting

many parts of the world, particularly in Africa, the Americas and Australia (Fig. 6). According to

IPCC, the MENA region is the region most severely affected by climate change, particularly

because the effects will accentuate already severe water scarcity (Verner 2012). Much of the

Arab region will undergo significant reductions in precipitation levels and increases intemperatures that will increase evapotranspiration rates, reduce soil moisture and natural

groundwater recharge (Bates et al. 2008).


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Fig. 5: Probability of monthly heat index above 300C. Measured changes in 1990-2009 andprojected changes in 2040-59 and 2080-99 in comparison with baseline period 1960-79Source: Verner 2012, p. 72 (high emission scenario), based on Diffenbaugh et al. 2007

The region experiences grave spatial differences in rainfall, varying from less than 50 mm/a in

Central Sahara to almost 1000 mm/a at the border to Southern Sudan (Evans 2010).

Fig. 6: Change in water availability compared with average 1961-1990 (%). 2050 based onIPCC scenario A1 (IPCC 2007)


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During the last two decades, there has been a significant reduction in the amount ofprecipitation in most parts of the area. According to IPCC (2007, Chapter 11, p. 866) annualrainfall is likely to decrease in much of Mediterranean Africa and northern Sahara, with thelikelihood of a decrease in rainfall increasing as the Mediterranean coast is approached (Fig.7 & 8).

Fig. 7: Mean annual rainfall

in second half of 20th

century in Arab countries

Source: Verner 2012, p. 46

Fig. 8: Mean annual rainfall

change, 1980-99 to 2080-99

Source: Verner 2012, p.56


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An average reduction in precipitation, ranging from 10%30% for this century in the MENAregion, was forecasted by several studies. Within the Arab region stark differences will occur:The Levant (Syria, Lebanon, Palestine) will be one of the regions in the Middle East mostaffected by changes in precipitation (Alpert et al. 2008). High resolution climatic models predicta 25% decrease in mean annual precipitation in the Middle East that coincides with increasesin mean annual temperature up to 4.5C towards the end of the twenty-first century (Suppanet al. 2008).According to IPCC projections, total regional renewable water shortage will be about 200cubic kilometers per year in 204050. Unfortunately, the demand is expected to rise by

about 25 percent in 202030 and up to 60 percent in 204050, whereas renewable supply willdrop by more than 10 percent over the same period in the region. As a result, unmet demandfor the entire Middle East and North Africa region, expressed as a percentage of total demand,is expected to increase from 16 percent currently to 37 percent in 202030 and 51 percent in204050 (Verner 2012, p.112).A look at the world map (Fig. 6) reveals, that large parts of the USAand Southern Canada, ofEurope and Brazil will suffer from reduced precipitation, too, which might reduce foodexports from these countries in future food, which will be badly needed by most Arab

countries.

The differences within the region and within countries will be substantial (Fig. 9). Highertemperatures and reduced precipitation will increase the occurrence of droughts, an effect thatis already materializing in the Maghreb.

Fig. 9: Scenario of mean temperature and annual rainfall evolution in 2050 (a) rise in meantemperature (0C), (b) variation in mean rainfall (%) in TunisiaSource: Omrani & Ouessar (2012)


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3.3 Changes in run off

The runoff in North Africa and the eastern Mediterranean (including the headwaters of the

Euphrates and Tigris) is expected to drop by up to 50 percent, southern Saudi Arabia and East

Africa (including the headwaters of the Nile) will experience increases in runoff by up to 50

percent (Verner 2012). The decreases in run-off are mainly due to higher temperatures(sometimes in conjunction with lower rainfall figures), which lead to higher evapotranspiration

losses (Evans 2009).

3.4 Flooding

Climate change is expected to increase the frequency and intensity of flooding.

Fig. 10: Lebanese farmerswatch flood waters after theirland was inundated in Jadra,south of Beirut in January2013. The flood was causedby heavy rain in the coastalareas.Photo: ADTECH / Internet

The increasing frequency of flash floods in many Arab cities is due to

increasing rainfall density

the widespread sealing of urban surfaces and the steady loss of green spaces

inefficient and clogged drainage networks,

settlements in upslope areas, deforestation of slopes

constructions (roads, buildings, squatter settlements in wadis (Fig. 10).

As a result, the size of the population affected by floods in Arab cities has multiplied in the

past 10 years to 500,000 people across the region.

3.5 Sealevel rise and seawater intr usio n

The sealevel is rising worldwide and might reach 0.5 m at the end of the century. An elevation

of that magnitude will cause large tracts of land and many cities of the Arab region inundated,

e.g. 1800 km2of the Nile delta, affecting 4 million people.

The reduction in precipitation in conjunction with the sealevel rising induced by climate

change is expected to affect coastal communities by seawater intrusion. The coastal aquifers

of the Levant and North Africa already suffer from seawater intrusion that has caused

salinization of thousands of wells (Verner 2012, p. 127).


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3.6 Shif t ing o f ecological belts

The pace of shifting of ecological belts northwards differs depending on landscape and is

lowest in mountainous areas. Projections range from 7.5 km per decade (Evans 2009) to 100

km. A value of 30 km per decade might be regarded as an average value.

3.7 Ag ricul tural produc t ion

The impacts of climate change will

bring about a profound change in

all fields of agriculture. In regard to

cropping, in future a higher portion

of precipitation will be lost as

evaporation & transpiration will be

increased and deep percolation

reduced significantly. Runoffremains more or less at same

level (Fig. 11).

Fig. 11: Schematic drawing of

average hydrologic conditions

under semi-arid climate. Compari-

son between conditions late 20th

century and second half of 21st

century.

In most of the MENA countries, the agricultural sector is the largest consumer of water. On

average, it accounts for approximately 80% of water budgets, but reaches 90% and above for

six countries in the region. The reduction in rainfall, aggrevated by higher temperatures, will

affect negatively rainfed agriculture, the reduction in renewable water resources the irrigation

sector. Together they will decrease the regions agricultural output by 20-40% by 2080 (Verner

2012) (Fig. 12). In addition, agriculture yields in rainfed areas, are expected to fluctuate more

widely, ultimately falling to a significantly lower long-term average.

The impacts of climate change will bring about a reallocations of the water resources at the

expense of the agricultural sector, as has already been the case in Yemen, Jordan, Israel, and

Libya (Verner 2012).

It is no longer debated, that climate change in arid lands will cause a productivity decrease of

agriculture, rangeland and forestry, but biodiversity, soil organic matter and soil fertility are

also negatively affected. This will worsen poverty and food insecurity. Populations will be

forced to migrate

Evans (2009) analyzed the impact of climate change in the Middle East. According to his

study, 8,500 square kilometers of rainfed agricultural land will be lost by midcentury and

170,000 square kilometers by the end of the century in the area covering the Islamic Republic

of Iran, Iraq, Lebanon, the Syrian Arab Republic, the West Bank and Gaza.


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Fig. 12: Cereal productivity in North Africa under a scenario of the IPCC showing atmosphericCO2 concentrations at 520-640 ppm by 2080Source: GRID-UNEP Vital Graphics; orig. from PNUD Rapport sur le Developpement Humain2006

3.8 Socio-econ omic impacts

Climate change will interact with other social, economic and political variables to exacerbate

social and political vulnerabilities. In general, climate change acts as a threat multiplier for

vulnerable countries and populations (Sowers et al. 2011).

Displacement and migration is becoming an increasingly important issue due to the changing

climate.

Climate change disproportionately affects the poor and has a greater impact on the daily lives

of women. Poor people have little capacity to respond to higher water demand and extreme

events, and in Yemen, for example, women must travel greater distances to fetch fresh water

(Stern 2006).

If no measures to build resilience are taken in the next 30 to 40 years, climate change couldlead to a cumulative reduction in household incomes of about 7 percent in Syria and Tunisia.Yemen - because of the expected declines in agriculture - could suffer an income reduction of24 percent.In Jordan, the fourth driest country in the world, this fall in water supply would be disastrous.At present, it needs 1.5 million cubic metres of water to meet demands, but only 900,000 cubicmetres are available. A temperature increase and rainfall reduction, compounded with agrowing population, will result in extreme food and water insecurity (Verner 2012).

3.9 Future water demand in MENA countries

Keeping in mind the already tenuous water supply situation today in most Arab countries, thefuture will ask for even more strenuous efforts to cover the water demand.

How will the water demand look like in about 50 years time?

Population rise will contribute to the total water demand in 50 years time by about 70%,

Migration to cities, changing lifestyles and industrial development will be responsiblefor at least a 15 % increase

Global warming will cause at least a rise of 35% above todays level. In total.

The total water demand will most probably be 120% above the present one (Fig. 13),

but rainfall will be about 15% less than today (25 % at the end oft he century).


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Fig. 13: Three major factors contribute to an ever increasing water demand in MENAcountries: (1) Population increase, (2) industrial development, urbanisation & lifestyle and (3)

Global warming. The figures are just indicative and vary considerably between countries.

Configuration of impact factors

Fig. 14 visualizes the most important drivers and impacts of climate change in the Arab region.

Fig. 14: Most important drivers and impacts of climate change in the Arab region. First order

impacts are given in white, second order impact in light yellow and third order impacts indarker yellow.


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4 Rainwater Harvesting

4.1 Overview

Dry areas suffer not only from limited rainfall but also from inefficient use of this scarce

resource: - a large portion of rainwater is lost directly or indirectly, and becomes unavailablefor domestic use or agriculture. Water harvesting is in general a low-cost, easy-to-use,environ-mentally-friendly way to recover a large part of this lost water. But water harvestingcan not only alleviate water-related stress for human beings, livestock and agricultural crops,but also substitute and recharge groundwater, reduce flooding and soil erosion risk and canimprove living conditions in general (Fig. 15) (Falkenmark et al. 2001).

Fig. 15: The goals of rainwater harvesting in dry areas

Water harvesting is defined here as the collection and concentration of rainwater and runoffand its productive use for domestic and livestock consumption, for irrigation of annual crops,pastures and trees and for groundwater recharge. Rainwater harvesting has got a longtradition in the MENA countries. The earliest water harvesting structures are believed to havebeen built 9000 years ago in the Edom Mountains in southern Jordan to supply drinking waterfor people and animals (Prinz, 1996). Oweis et al. (2004) provide an overview of indigenous

water harvesting systems in this region.

The basic principle of agricultural water harvestingis to capture precipitation falling on onepart of the land and transfer it to another part, thereby increasing the amount of wateravailable to the latter part. The objective is to provide enough water to crops on one part of the

land to support economical agricultural production.There are some other terms under the umbrella of agricultural water harvesting such asRunoff rrigation,Runoff farmingand Spate irrigation(for f loodwater harvesting).


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Fig. 16: Position of rainwaterharvesting with and withoutSupplemental Irrigation com-

pared to other types ofagricultureSource: Prinz 1996

4.2 Methods and Techniques of Rainwater Harvesting

4.2.1 The three method s of agricul tural water harvest ing

There are several classifications of agricultural water harvesting methods, but the most

commonly used system is based on the size of the catchment, i.e. micro-catchments, macro-

catchments and floodwater harvesting:

Micro-catchments are < 0.1 hectares in size.

Macrocatchment systems are long-slopes systems (0.1200 hectares total size) and

Floodwater systems have got catchment areas >200 hectares.

Agricultural rainwater harvesting shall be a linking

element between rainfed and irrigated agriculture,

soil and water conservation and supplemental

irrigation (Fig. 20). When planning water harvesting

projects, the principles of Integrated Water

Resources Management (IWRM)shall be applied.

Fig.16 The position of agricultural rainwater

harvesting between rainfed and irrigated agriculture,

integrating elements of soil and water conservation

and supplemental irrigation.


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4.2.2 Rooftop and Courtyard Water Harvest ing

Rooftop and Courtyard Water Harvesting describes installations on and around buildings tofacilitate rainwater collection, mainly to cover drinking water / domestic water demand or touse the collected water for groundwater recharge. In a wider sense, the harvesting of waterfrom roads, bridges, parking lots and other sealed areas in urban environments are covered by

this technique, too.

5 Adaptation of Water Harvesting Techniques to Climate Change

5.1 Water Harvest ing Techniques for Ag ricul ture / in Rural Areas

5.1.1 RWH and the shift of ecological belts

Climate Changeimpacts the application of rainwater harvesting by

shifting the application belts of RWH methods synchronously to the shifting of the ecologicalbelts (Fig. 17), and

altering the application of techniques, the physical structures and the kind and volume ofwater storage to fit to the altered climatic conditions.

Fig. 17: The application zones of the various WH methods will in general move with the

relevant ecological belts, but changes in CCR and runoff coefficient will allow to apply the WH

techniques in zones with lower precipitation than before. This will retard the process of climate

change impacting agricultural production.

As the ecological belts, defined by their rainfall and temperature characteristics, are shifting,

synchronously the belts where grazing or rainfed croppingare feasible will shift, too. Areas,which have been marginally suitable for grazing will turn to become desert (a process, which


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takes already place since decades due to overgrazing). Areas marginally suitable today forrainfed agriculture will turn to become grazing areas and so forth.

The application zones of the various WH methods willl move with the relevant ecological belt.

These application zones are defined by their minimum average precipitation amounts:

The various WH methods need to be viable:

Floodwater harvesting techniques in MENA countries need a minimum of 100 mm/a inmost of the catchment area to yield ample volumes.The minimum precipitation for macrocatchment systems is in the range of 150 to 200

mm/a.

For microcatchmenttechniques this limit stands in the range of 200 to 250 mm/a.

5.1.2 Countermeasures

There is a wide range of possible adaptation measures in rural areas:

Higher water demands of people, crops and livestock due to higher temperatures have tobe met

a. by an increase in catchment area and/or by increasing runoff coefficients oncatchment areas

b. by a higher water use efficiency (e.g. using an efficient water supply system,cultivating crops in greenhouses, keeping other growing conditions (e.g. soil fertility)at high level, covering the soil with plastic or organic mulch etc.)

c. by an increase in storage volume.

Higher rain intensities and more erratic rainfall demanda. a larger catchment-to-cropping-area ratioandb. a strengthening / raising of water harvesting structures(bunds, dams, walls).

Adaptation to more/larger floods can be achieved e.g.

c. by increasing size of structuresfor water diversion,d. by enlarging the impoundmentande. by designing larger / stronger spillwaysto evacuate excess water.

The drier the area, the more there is the need for supplemental irrigation, i.e. storage ofwater for life-saving irrigation. Interannual water storage above ground or in aquifers isneeded to deal with longer-lasting droughts.

This is also true for areas under spate irrigation, depending on floodwater. Floodwaterharvesting will in future experience a smaller number of floods, but these will be even morevoluminous (and presumely more destructive).


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Fig. 18: The most important countermeasures in rural areas of the Arab region to curb theimpacts of climate change

5.1.3 Achieving a higher water use efficiency

The harvested water has to be utilized as efficiently as possible, today and even more infuture. There are many ways to arrive at a higher water use efficiency in agriculture, inhouseholds and in combinations of both.

Fig. 19: Model of re- and multiple use of rainwater in a rural environment


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Fig. 19 shows a model for efficient rainwater use in a rural environment: Water from rooftopand courtyard is collected (A), stored in a tank (B), and either used for domestic purposes (C)or to fill a fishpond (D). The nutrient rich water is used for irrigation (E). The Greywater isstored in a tank (F) and used for toilet flushing. The blackwater is treated in a constructedwetland (G) and the effluent is used for tree crop irrigation (H).

There is an urgent need for efficient use of rainwater under water scarcity conditions in farmingand in rural areas in general. Reuse and multiple use of rainwater are often part of it.

5.2 Water Harvest ing in Urban Enviro nments

5.2.1 Future problems of water management in urban areas

The various implications of climate change in regard to water management in urbanareascan be summarised as follows:

The process of urbanization will accelerate in future and more and more people will be inneed of a reliable water supply.

Higher temperatures will bring about an increasing water demand (per city dweller) to besatisfied by the water works, causing further stress on already scarce water resources.

The flow of permanent rivers will be even more erratic and in general lower than before.

Flood disasters will be more frequent and of larger magnitude (Fig. 20).

The regeneration of groundwater will be lower.

The water supply and wastewater collection networks have to be expanded permanently;high investments (and sufficient manpower) will be needed to satisfy the demand.

More efforts have to be invested in training people how to save water and to make use ofrainwater

Surge of national and regional conflicts (e.g. between agriculture and the other economicsectors) over the use of shared water resources might develop.

Increase in water-related diseases due to the deterioration of water quality.

There is a need for rethinking in dealing with floods: Instead of practicing a water excess

management, which aims (only) at

trying to evacuate the flood waters as

quickly as possible, the goal should

be to make best use of the water

already in the upper and middle parts

of the catchment and finally in flood

diversion basins in the lowlands.

Fig. 20: Flood aftermath in Jericho.January 9th, 2013

Source: MIDDLE EAST demotix.com


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5.2.2 The potential of urban rainwater harvesting

Equipping as many urban buildings as possible with RWH devices and storing the runoff in

tanks could

contribute to a realively safe, decentralized water supply to be used at least for domestic (ifnot for drinking) purposes,

minimize the water supply problems (and costs) of water works,

minimize the stormwater volume, avoiding floods to a large extent (Koenig 2001).

Recommended further RWH measures in the city are

capturing rainfall from any sealed surface(e.g. parking lots) to recharge local aquifers or to

use it for domestic purposes such as toilet flushing (IRHA 2010)

creating as many infiltration pondsas feasible in suitable locations to catch rooftop runofffrom large buildings for recharge purposes

keeping as many green spaces (parks, public lawns, gardens) in the city andi mproving thesoils infiltration capacity in those spaces.

Taking Beirut as an example: The city's metropolitan area covers 67 square kilometers; the

average annual rainfall is given as 860 mm/a (Wikipedia 2013). Hence Metropolitan Beirut

receives a total of 57.6 mio m3of rainwater annually. When recognizing reduction in rainfall

due to climate change, and calculating with 800 mm/a, we still have a potential of 53.6 million

m3 rainfall. According to Worl Bank figures, the daily water demand of Beirut is around

250,000 m3daily, which adds up to 92 million m3 per year. A comparison of these figures

shows the huge potential of rainwater harvesting in an urban agglomeration . As still a

considerable volume of water is (legally and illegally) pumped from groundwater, any quantityof rainwater infiltrating into the ground (natural or artificial groundwater recharge) can be

regarded as an asset.

What is needed, is the development (and implementation) of innovative solutions, such as

the collection of rainwater not per building, but per settlementor even per (newly constructed)

suburb (Fig. 21): The rainwater from all buildings could be collected, stored in a tank or cistern,

purified and pumped back to the water users. When the water demand exceeds the stored

rainwater volume, water from other sources (surface or groundwater) is added to the system.

In most cases a two-pipe water supply systemwill be needed: One system for drinking

wateronly and another one for general domestic purposes, lower in water quality. This two-pipe water supply system can be complemented by a two-pipe wastewater collection

system: One system for (reusable) greywater and another one for black water, to be treated

in a municipal treatment plant. Some hotels at the Jordanian side of the Dead Sea practice this

already.


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Fig. 21: Instead of individual rainwater collection per building it might be more economic tocollect it as communal activity, (e.g. if a housing complex or even a suburb is established byone company).

Source: Prinz 1999

5.2.3 The need for holistic solutions

Many cities in Arab region are located at or near the sea, suffering from

urban growth,often beyond the capacity of the administration to keep even modestinfrastructural standards,

dwindling renewable water resources

rising temperatures and reduced precipitation due to climate change

rising sea levels

seawater intrusion into coastal aquifer fostered by overexploitation

growing number of storms and floods with rising magnitudes.

Beirut is a good example of a city showing all the above mentioned features (Fig. 22).

Fig. 22 : The coastal aquifer of Beirut is endangered by seawater intrusion, as the natural

recharge became smaller and groundwater extraction in Beirut area increased constantly


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Spatial planning is an indispensable tool to solve these problems. To overcome (at leastpartially) the major water-related problems of a city like Beirut,the implementation of a holisticconcept is needed, starting with measures in the upper parts of the watershed (Fig. 23).

Fig. 23: Spatial dimension of the

application of recommendedmeasures in Greater Beirut Area

Source of map: Google Earth2013

Some of the measures toimplement are:

o Protecting vegetation inupper catchment areas,

prohibiting any settlement thereo Carrying out soil andwater conservation measureswithin the upper and middlereaches of the catchmento Catching and storingrunoff / overland flow upstreamof the city (Structural methods

such as recharge dams, spreading basins). The collected water can either be used as areserve for municipal water supply or devoted to recharge groundwater

o Practicing RWH on as many buildings as possible within the city (Small scale RWHtechniques)

o Improving the soils infiltration capacity in still green spaceso Capturing rainfall from any sealed surface (e.g. parking lots) to recharge local aquifers.

Legal interventions(i.e. laws & regulations and their enforcement) are necessary to stop orreduce (legal and illegal) water pumping , to stop the construction of further settlements and topractice RWH in the city.

A common problem hindering water efficiency improvements in buildings is linked to the tariffsystem. In many parts of the Arab world,considerable segments of water users are still notcharged for water according to their actual consumption. Instead, their water tariffs arebased on fixed costs (Mirata & Emtairah 2010).

The potential of urban WH will remain untapped and water conservation measures notintroduced unless changes in water tariff are fixed and enforced.

6 General Considerations

As shown above, the already existing water-related problems will be aggrevated by climatechange. The water demand of agriculture, industry and municipalities is constantly rising andthe existing renewable water resources from groundwater and surface water (permanentstreams and rivers) can not cover the demand (Fig 24). Therefore rainwater and overland flowin wadis have to be examined carefully to what extent they can fill the gap now and in future.


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Fig. 24: Rainwater,overland flow and wadiflow are sources of waternot fully utilized. Theirdevelopment afteradaptation to climatechange can besignificant to balancesupply and demand. Theprinciples of IWRM haveto be applied.

Rooftop Water Harvesting in urban environments isstrongly linked to

urban planning, incl. surface water management

spatial per-urban planning,

architectural design of buildings and courtyardsand

watershed management incl. soil & waterconservation measures (Fig. 25).

Fig. 25: Linkages of Rooftop Water Harvesting in urbanenvironments

Planning within the IWRM frameworkneeds

a holistic approach, taking into considerations all aspects of water demand and supplymanagement,

the analysis of all available and potential sources of water and

the means to save water (water conservation).

The objectives are satisfying future water demand of people, agriculture, industry and

environment by adapting RWH to climate change (Fig.26)

The role of RWH, in conjunction with soil and water conservation measures, is to retard

climate change impacts by making better use of the scanty rainfall.


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Fig. 26: Goals, objectives, approach and tools of an IWRM scheme applied to our topic

Fig. 27: Parties involved in water harvesting for agricultureSource: Oweis et al. 2012


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To make full use of the potentialof water harvesting, particularly to combat climate change

impacts,

suitable laws and regulationsrelated to land and water use have to enable water harvesting

activities,

the farmers and city dwellers alike have to be well informed and convinced; theirparticipation in the decision-making process is essential,

modern tools, such as remote sensing and GIS, have to be employed to identify suitable

areas for collection and storage

the harvested water should be utilized in aneffective way, as well in agriculture as in urban

environments. Re-use and multiple use of the harvested water is indispensable.

demonstrations and applied researchactivities have to be carried out,

skilled personnel for the hydrological & engineering planning and execution tasks has to be

available, when larger projectsare to be installed,

micro-credits and/or subsidies as well as scientific support is needed by the authorities,

when larger-scale WH systems are to be implemented,a well trained and motivated extension service will be needed, when beneficiaries are not

familiar with rainwater harvesting at all or with the methods to apply (Prinz 2002, Fig. 27).

When planning rainwater harvesting projects, the principles of Integrated Water Resources

Management (IWRM)shall be applied.

Rainwater harvesting is an option

to optimize the use of rainwater to meet the increasing water demand,

to stabilize agricultural production to a certain extent and to retard the impacts of

climate change in spite of moving ecological beltsto reduce wastage of runoff and diminish flooding risk,

but its implementation depends totally on the availability of the enabling framework

conditions.

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Climate Change and the Application of Rainwater Harvesting

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