Final Report-Climate Change Effects on hydrology and water resource availability in the Nadi Basin

CLIMATE CHANGE EFFECTS ON HYDROLOGYAND WATER RESOURCE AVAILABILITY IN THE

NADI BASIN

IWRM COURSE 10 PROJECT REPORT

ANDRE SIOHANE & RINESH RAM

4rd Day of December 2009

Introduction

Climate change spawns the alteration of normal climate that we know or weather pattern that wehave been experiencing for the past years or decades and has the ability to alter the water qualitysignificantly by changing the ability of watersheds to manage wastes and pollutants.

This investigation highlights findings on the effects of climate change on the hydrology and thewater resource availability in the Nadi Basin.

Our research reflects the effect on surface and subsurface water and flow, their chemical and physicalproperties, and their reactions with their environment, including their relation to living things. Inaddition, effects on the water availability in sufficient quantity and quality at a location appropriatefor a given demand.

The results emphasize that the impact of climate change on hydrology and water resources,associated with the water supply constraints and continued urban growth, demand new approachesto the management of water resources in the Nadi Basin.

Background of Nadi Basin

Nadi is located on the western side of Viti Levu (Fiji’s western division). The westerndivision (Sigatoka to Rakiraki) is a relatively dry zone and is subject to large seasonal andinter-annual climatic variation.

Physical Characteristics

Watershed areaWatershed Perimeter

516 km2

156.28 kmMajor Rivers & Creeks Nadi River

Namosi RiverNawaka RiverMasi CreekMalakua CreekLawatoya Creek

Typical Weather

Nadi is located on the rain shadow side if VitiLevu where the weather is mostly humid anddry.

The annual rainfall in this dry zone area averages around 200o mm. Typically, winterweather in the Nadi region has clear or partly cloudy skies, much sunshine, a well-developed west to northwesterly sea breeze by day (south easterlies are predominant atnight and in all months except from August to March when wind is generally from thenorthwesterly quarter), and relatively cool nights. In summer, thunderstorm activity iscommon and responsible for brief spells of high-intensity rainfall (Melchior Mataki,January 2006).

The Fiji group of islands is surrounded by a huge body of water and is affected by globalland regional-scale climatic events such as El Nino and La Nina resulting from inter-annual

variations of the strength of the ‘‘Walker Circulation’’ over the equatorial Pacific Ocean andassociated droughts and/or floods, tropical cyclones, and high waves (Melchior Mataki,January 2006).

Materials and Methods

Research for this study included literature review, enquiries made in the Nadi basin withinvarious government departments, resorts, with stakeholders, and observing watersheds,carried out over a period of seven days.

Fiji Meteorological Service provided available data forannual/monthly/maximum/minimum rainfall & temperature from their climate databasefor various stations located within the Nadi Watershed. Data for Nadi Airport stationspanned from 1942 to 2009, while data for stations located at Nausori Highlands andNawaicoba ranged from 1959 to 2003, and Vaturu Dam from 1982 to 2009.

For investigating variation or fluctuation in rainfall and temperature, data with gaps wasnot used. This resulted in the use of only Nadi Airport data from 1948 to 2008 (60 years).

Due to a large percentage of gaps, the data from stations in Nausori Highlands, Nawaicoba,and Vaturu Dam was not used for any analytical purpose.

Data from the Public Works Department (Water Supply) was mostly in the form ofinformation about the water supply network within Nadi basin, storage capacity,challenges faced, and resolutions.

Climate Change

Change in normal climate that we know or a change in the weather pattern that we havebeen experiencing for the past years/decades.

Change in weather means a change in the processes within the hydrological cycle, whichdevelops the weather, and eventually leading to changes in the physical and chemicalcharacteristics of surface and subsurface water resources. Evaporation and precipitation arethe two most important processes in the hydrological cycle that govern the weather in anygiven location where their rates depend on land & sea surface temperatures, which decidesthe intensity of rainfall and temperature.

Global warming is the key to the climate change, where scientists have proven that thecause is the increase in temperature from greenhouse gas emissions into the atmosphere.

Increased frequencies, magnitude or intensity of weather disaster occurs worldwide todaysuch as tropical cyclones, hurricanes associated with floods and also droughts have greatimpact on the environment, infrastructure, economy and loss of human life’s are the signsof the impact of climate change.

As for the Nadi basin, climate change has already affected the basin with several naturaldisasters, such as drought in 1997-1998 and then again follow by a flood in 1999, 2007 &2008- these events are rare but now seems that flooding has become frequent.

Effects of Climate Change on Hydrology

At Present

Increasing trend of surface temperature (Melchior Mataki, January 2006).Continuous variation of surface temperatures, especially between the dry and wetseason (see graphs 4 & 5)

o Increase in both nighttime and daytime temperatures. Nighttimetemperatures show greater increase then daytime temperatures

Rainfall

o events of heavy rainfall/rainfall intensity and flooding due to depressions andla nina. According to some residents, the flood of January 2009 was the worstin 50 years.

o significant variation between yearly rainfall

Long Term Impacts

Long term impacts may lead to increased evaporation/transpiration, and harm tofreshwater ecosystems

As surface temperatures increase the speed of the hydrological cycle would increase,resulting in faster evaporation and more precipitation (Foundation, 2009)

o This may result in a more saturated wet season (November to April)

o Increased rainfall, especially the intensity, will lead to increased runoff andcases of landslides. Erosion results will be severe in areas that have minimumto zero soil cover.

o Changes in precipitation can lead to both positive and negative impacts onwater quality. The net effect on water quality for rivers, lakes, andgroundwater in the future depends not just on how climate might change butalso on a wide range of other human actions (Perlman, 2001).

Increase in flooding events and flood risk. Damage to property and human health. Increased precipitation, flood prone location, sea level rise are attached to flood risk. Sea level rise affecting for Nadi Town is a major concern (Times, 16 October 2008)

o Floods can increase human exposure to pathogens, as contaminantsare spread by floodwaters (David Scott, 2003).

o Flooding increases the amount of runoff from fields and rate ofsedimentation on riverbeds and estuaries. This can add greatquantities of sediment and nutrients to the water. Excess nutrientscause algae blooms, which can disrupt the aquatic life and greatlyimpair the quality of the water.

o The topography of the Nadi Basin is as such that increasingprecipitation events can increase the momentum and volume of river

flows that may cause the degradation and aggradation of the variousriver channels, making the river system unstable leading torestructured watercourse networks.

Increase in intensity & frequency of extreme droughts events

o The nature and severity of any particular drought episode is dependent onthe duration and magnitude of the rainfall deficit. The sequence of droughtimpacts is felt first felt in systems with small water storage capacity: shallowsoils may be affected by a relatively short period of below average rainfallwhereas an extensive aquifer may have sufficient storage to be little affectedby drought duration relative to the volume of storage and withdrawal.

While droughts minimize the amount of runoff, they can also cause thewater quality to decrease. Drought intensity may increase every dry season(March to October)

o Droughts have the capacity to boast a broad range of impacts and as a result,it can be defined and quantified in a number of different ways. The fourdefinitions/types of drought are (David Scott, 2003):

• meteorological or climatological drought• agricultural drought • hydrologic data• socio-economic drought

El nino/la nina events. ENSO episodes have a significant impact on the climate and can produce extensive wet and dry cycles (David Scott, 2003) causing extreme droughts and devastating floods. Global trends show that the temperature during el nino events have increased over the years.

Sea level riseo Higher sea levels associated with thermal expansion of the oceans and

increased melting of glaciers will push salt water further inland in rivers,deltas, and coastal aquifers (Perlman, 2001).

Over time Nadi town and flood vulnerable areas, situated on thedelta, will frequently face inundation (Times, 16 October 2008)

Sinking of the delta land area will may cause damage toinfrastructure (Times, Mayor Fights Sinking Feeling , 28October 2008)

o Sea-level rise may alter coastal circulation patterns, destruction of transportation infrastructure in low-lying areas, and increased pressure on coastal levee systems

o Sea-level rise will also influence freshwater coastal ecosystems and coastal aquifers/boreholes

Change in salinity levelso Long dry periods strongly coupled to sea surface temperatures may

impact the quantity and salinity of groundwater

o Other impacts of sea-level rise are likely to include changes in salinity distribution in estuaries, and composition of aquatic ecosystems in the tidal zone

More intense tropical cyclones, cyclone wind speed and more damaging storm surgeas a result of increased ocean surface temperatures

Impacts of Climate Change On Water Resource Availability

While droughts minimize the amount of runoff, they can also cause the waterquality to decrease. Sediment and minerals, such as iron and manganese, are moreconcentrated towards the bottom of the water supply. During a drought, when thelevel of water decreases, the concentration of sediment and minerals in the waterincreases. Water may be available but it may be of inferior quality.

Sea level rise would adversely affect the quality and quantity of freshwater suppliesin many coastal areas; especially areas where water withdrawal is from wells,boreholes, and aquifers (Perlman, 2001). Coastal aquifers supporting large amountsof human use are at greatest risk. These may experience salt-water intrusion.

Lakes are known to be sensitive to a wide array of changes in climate. Even smallchanges in climate can produce large changes in water and salinity levels ofNawaicoba Lake (Perlman, 2001). Other effects of increased temperature on lakescould include higher thermal stress for cold-water fish, improved habitat for warm-water fish and increased productivity, lower dissolved oxygen as result of heatingand algal blooms, and degraded water quality.

The direct effects of climate change on water and freshwater ecosystems will sparkserious concerns for changes in vegetation patterns, possible extinction of endemicfish species already close to their thermal limits, declining area of wetlands, andconcerns about stream health, which will determine how and for what purpose thewater may be used.

Large changes in the reliability of water yields from reservoirs could result fromsmall changes in inflows due to diminished rainfall in severe dry seasons or dryseason prolonged by an el nino event.

Recommendations

Improve water storage infrastructure: Good effect of climate change is theopportunity given to urban and rural communities and farmers to store water dueto increased rainfall during wet season

Capacity building in all water sectors and communities and awareness onsustainable use of water

Local and commercial water use plan to promote sustainability. This may beadapted by the water authority and communities

Nadi Basin Catchment Committee to have consultation with members of catchmentcommittees that already exist in the pacific region, to learn from the challenges theyfaced and resolutions they applied

It is important that greater emphasis be placed on meteorological andenvironmental monitoring, vulnerability assessments be undertaken and adaptationoptions

o e.g restriction of commercial and residential development in flood pronecoastal/floodplain areas

o Improve and promote continuous monitoring of rainfall/temperature,discharge, coastal water quality, and reef/coral health. For Nadi, it isimportant for all resorts and similar operators to ensure monitoring ofcoastal water quality and reef/coral health for the benefit of marineecosystems/organisms and tourism

Monitor the water resource characteristics of the Nadi Basin, by data collection onhydrology, climate, and behaviour of the rivers to the context of climate change andfor disaster responses. Database useful data for better understanding of the waterresource

Develop and implement effective water demand management programs through:

o investigating the system loss (leakage Control)

o and pressure reduction program (reduce pressure during off peak hours toincrease the life of pipes)

o Introduce Water Use Efficiency program in the tourism industry (eg. low flowshowerheads, reuse wastewater, low flow toilets etc.

Encourage construction of water reservoirs upstream for economic development,flood mitigation, and water availability during low rainfall period. This will improvewater resource management and supply to communities

Public and community awareness programs on the climate change impacts on thebasin water resource, natural disasters and water use

Government support for the IWRM Nadi Basin Catchment Committee forsustainability after the 5 year project period

Develop policies and regulation to protect the watershed, monitor the uses and thedevelopment that occurs at the basin, such as buffer zones, re-planting forest etc...

Conclusion

The objective for this research was to identify Climate Change Effects on the Hydrologyand Water Resources Availability in the Nadi basin. We conclude that:

Climate change adverse effects in the Nadi basin come as events of heavyrainfall/rainfall intensity, increasing surface temprratures, landslides,flooding, and coastal inundation of low lying areas

At present the watershed is being more affected by human activity, in variousland uses which have the capacity to increase the effects of climate changeten fold

There is need for the awareness/capacity building of decision makers andcommunities concerning the effects of climate change to better prepare Nadifor impacts of climate change in the future

Bibliography

Centre, F. M. (2009). Rainfall & Temperature data for Nadi Airport (1942- 2009). Nadi: Fiji Meteorological Centre.

David Scott, M. O. (2003). PACIFIC DIALOGUE ON CLIMATE CHANGE: SYNTHESIS REPORT. Suva: SOPAC.

Foundation, S. D. (2009). Safe Drinking Water Foundation. Retrieved November 7, 2009, from THE EFFECT OF CLIMATE CHANGE ON WATERBORNE DISEASES: www.safewater.org

Melchior Mataki, K. C. (January 2006). Baseline Climatology of Viti Levu (Fiji) and Current Climatic Trends. Pacific Science , 49-68.

Perlman, D. (2001, June 15). Mindfully.org. Retrieved November 22, 2009, from Global warming to affect water supply:More rainfall means smaller Sierra snowpack: www.mindfully.org

Times, F. (28 October 2008). Mayor Fights Sinking Feeling .

Times, F. (16 October 2008). Sinking Feeling for Town.

Appendix

Rainfall/temperature Data from 1942 to 2009 for Nadi Airport (Centre, 2009)

Figure 1

Rainfall Trends at Nadi Airport: Annual rainfall

y = 0.034x + 1818R² = 2E-06

0

500

1000

1500

2000

2500

3000

3500

4000

1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

Total R

ainfall (m

m)

years

Graph of Annual Rainfall (mm) for Nadi Airport from 1942 to 2008

Nadi Airport Annual Rainfall (mm) Total

Linear (Nadi Airport Annual Rainfall (mm) Total)

5 per. Mov. Avg. (Nadi Airport Annual Rainfall (mm) Total)

La nina period from 07/98 to o7/2000

El nino period from 04/97 to 06/98

Notes:- The graph shows no significant

change in annual rainfall- Note variation between yearly

rainfall

The above graph shows the annual rainfall on Nadi Airport from 1942 to 2008

There was no significant increase in the annual rainfall over this period, however,there is frequent and large rainfall variation

Figure 2

Rainfall Trends at Nadi Airport: Wet Season

y = 3.1247x - 4873.3R² = 0.0248

0.0

500.0

1000.0

1500.0

2000.0

2500.0

3000.0

1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

Total Rainfall (m

m) from

Novem

ber to A

pril

Years

Graph of rainfall for the wet season at Nadi Airport from 1942 to 2008

Total

Linear (Total)

5 per. Mov. Avg. (Total)

El nino period from 04/97 to 06/98

La nina period from 07/98 to o7/2000 Notes:- Slight rise in rainfall

(up to 3 mm)- Significant variation in rainfall

The graph above shows the development in rainfall behavior in the wet season overa period of 66 years with the range of rainfall values fluctuating between 800 mmand 1700 mm.

Figure 3

Rainfall Trends at Nadi Airport: Dry Season

y = -0.1038x + 277.96R² = 0.0051

0.0

20.0

40.0

60.0

80.0

100.0

120.0

140.0

160.0

1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

Total R

ain

fall (m

m) from

May to O

ctober

Years

Graph of rainfall for dry season at Nadi Airport from 1942 to 2008

Nadi Airport - Monthly Total Rainfall (mm) Average

Linear (Nadi Airport - Monthly Total Rainfall (mm) Average)

5 per. Mov. Avg. (Nadi Airport -Monthly Total Rainfall (mm) Average)

Notes:- Slight fall in rainfall (up to 0.12 mm)- Significant variation in rainfall

The graph above shows the development in rainfall behavior in the dry season overa period of 66 years with the range of rainfall values fluctuating consistentlybetween 80 mm and 100 mm.

Figure 4

Temperature Trends at Nadi Airport: Annual Maximum

y = 0.003x + 23.85R² = 0.029

28.8

29

29.2

29.4

29.6

29.8

30

30.2

30.4

30.6

30.8

1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

Tem

perature (degrees celsiu

s )

Years

Graph of Nadi Airport Annual Maximum Air Temperature (˚C) Average from 1942 to 2008

Nadi Airport Annual Maximum Air Temperature (˚C) Average

Linear (Nadi Airport Annual Maximum Air Temperature (˚C) Average)5 per. Mov. Avg. (Nadi Airport Annual Maximum Air Temperature (˚C) Average)

Notes:- Slight rise in temperature

(up to 0.003 mm)- Significant variation in temperature

The graph shows the range of temperature values fluctuating between 29.5 and 30.1degrees

Figure 5

Temperature Trends at Nadi Airport: Annual Minimum

y = 0.0118x - 2.9103R² = 0.1651

19

19.5

20

20.5

21

21.5

22

1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

Tem

perature (degrees celsiu

s)

Years

Graph of Nadi Airport Annual Minimum Air Temperature (˚C) Average from 1942 to 2008

Nadi Airport - Average Monthly Minimum Air Temperature (˚C) Average

Linear (Nadi Airport - Average Monthly Minimum Air Temperature (˚C) Average)

5 per. Mov. Avg. (Nadi Airport -Average Monthly Minimum Air Temperature (˚C) Average)

Notes:- Slight rise in temperature

(up to 0.0145 mm)- Significant variation in temperature

The graph shows the range of temperature values fluctuating between 19.7 and 20.54degrees

Figure 6

Figure 7

Figure 8

Figure 9

The graph shows the range of temperature values fluctuating between 25.7 degrees and 26.7 mm

Figure 15

Trends of ENSO events from 1925 to 2010 (Global Data bank)