IMPACT OF CLIMATE CHANGE IN WATER ...

International conference on Climate Change in relation to Water and Environment (I3CWE-2015) Department of Civil Engineering 1 DUET - Gazipur, Bangladesh

IMPACT OF CLIMATE CHANGE IN WATER AVAILABILITY OF LOWER BRAHMAPUTRA RIVER BASIN Pk., S.1, Magumder, T. K.2 and Hossain M. S.3 Abstract: This research scrutinizes the impact of climate change in future water availability of lower Brahmaputra river basin. The state of art and mathematical modelling techniques has been used to estimate future water availability considering climate change prediction scenarios. A semi distributed, lump and conceptual type hydrological model has been developed using MIKE BASIN modeling tool of Danish Hydraulic Institute (DHI). Data required for model development has been collected from both primary and secondary sources. Climate change prediction scenarios have been supplied by International Centre for Integrated Mountain Development (ICIMOD). Analyzing model results, it is observed that the Brahmaputra river flow is increasing with years in most of the climate change predictions which become more significant in pre-monsoon months: April, May and June. In future 2020, the change of flow varies between -5% and 20% in the month of April whereas it varies from -20% to 32% in the month of June in 2050. Keywords: Brahmaputra, climate change, mathematical model, mike basin, DHI, ICIMOD and change of flow

1. Introduction The ‘Hindu Kush-Himalayan (HKH) region’, sometimes called the ‘Roof of the World’, is the source of ten of the largest rivers in Asia including the Brahmaputra, which ranked as the highest specific discharge system in the world (Datta et al., 2004). It contains the largest amount of snow and ice found outside the Polar Regions, including more than 100,000 square km of glacier cover, which is recognised as an extremely fragile environmental vulnerable to climate change. The Himalayan region plays an important role in global atmospheric circulation, biological and cultural diversity. Environmental change in the greatest Himalayans affects most of central and South Asia, and the mainland of Southeast Asia (Bongartz et al., 2007). The recently published fourth assessment report of the Intergovernmental Panel on Climate Change (IPCC 4AR) (IPCC, 2007) concludes that the average global temperature is very likely to increase between 1.8 °C and 4 °C by the year 2100. Although uncertainties about the rate and magnitude of climate change and potential impacts prevail, it is generally agreed that climate change is gradually and powerfully changing the ecological and socio-economic landscape in the HKH region, particularly in relation to water, with significant implications for mountain communities and livelihoods, as well as downstream users (Eriksson et al., 2009). Moreover the melting glaciers due to raising temperature will have a negative effect on water supplies in this region in the next few decades (Barnett et al. 2005). The previous researches clearly indicate that the climate change impacts surely affect surface water availability of HKH region along with the mighty Brahmaputra river.

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Shubhra Pk., Institute of Water Modelling, [email protected] 2 Tarun Kanti Magumdar, Institute of Water Modelling, [email protected] 3 Md. Sahadat Hossain, Institute of Water Modelling, [email protected]

The Brahmaputra basin is a house of more than 80 million people out of which 58.3 % reside is Bangladesh, 38.4 % in India, 2.5 % in Tibet of China and the rest 0.8 % in Bhutan (Rahman et al., 2009). People living in India and Bangladesh are largely depending on river water for irrigation, industrial and drinking water supply. A vast species of plants and animals living in these areas are totally depending on Brahmaputra river water. Any change in river water availability can affect the whole biodiversity, ecosystem, agriculture and development system of the basin. In order to build resilience of the communities and create opportunities, proper measurements are needed. Along this vein, Himalayan Climate Change Adaptation Programme (HICAP) is undertaken by International Centre for Integrated Mountain Development (ICIMOD) to build climate resilient mountain communities in the HKH having special focus on women (ICIMOD, 2011).Under this program four focus areas in the three river basins have been selected for climate change impact assessment on water availability (ICIMOD, 2011). In the Brahmaputra river, there are two focus areas: one in the upper Brahmaputra basin i.e. in Tibet of China, and another in the lower Brahmaputra basin in India (ICIMOD, 2011). This study has been carried out to examine the impacts of climate change in water availability in the focus area of lower Brahmaputra river basin. 2. Focus Area in Lower Brahmaputra River Basin The study area spreads over fifteen districts of Assam, Arunachal Pradesh and Nagaland states of India comprising a total area of 28430 sq. km. The upstream catchment that contributes inflow to the study area is around 327700 sq. km. Major river flowing towards or through the area are: the Brahmaputra river itself, the Dibang, the Lohit, the Burhiding, the Subansiri and the Dhansiri river (Figure 1). Mean annual rainfall in the study area varies ranging from around 1600 mm in the south-west to around 4000 mm in the north-east. Total area under cultivation in the area is around 6788 sq. km. where net irrigation area is around 2798 sq. km. The estimated population in the area is around 6.45 million (Haub, 2007). Topographically major parts of the study area are valley and floodplain of the Brahmaputra river. Elevation varies ranging from around 50 m to 4500 m. Figure 1 shows the detail map of the study area and Figure 2 shows the area elevation curve developed based on satellite estimated Shuttle Radar Topography Mission (SRTM) land terrain data.

Figure 1: Detail map of the study area

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Figure 2: Area-elevation curve of the study area (Source: SRTM land terrain) 3. Data Collection and Study Methodology 3.1 Data for hydrological model development To develop a hydrological model general data required are topographic, land use, meteorological and hydrological data. These data has been collected from both primary and secondary sources. Primary data and information have been collected from relevant organisations such as International Centre for Integrated Mountain Development (ICIMOOD), Bangladesh Water Development Board (BWDB) and Institute of Water Modelling (IWM). Secondary data have been collected from various international, governmental and local organisations as well as published articles, books, documents and reports. Hydrological data for the Brahmaputra river obtained from Institute of Water Modelling (IWM). 3.2 Data for climate change prediction ICIMOD has provided a total ten sets of future climate change prediction under two Representative Concentration Pathways (RCPs), four Global Circulation Models (GCMs) and one Regional Climate Model (RCM). The selected ten sets of future climate prediction under two RCPs, four GCMs and one RCM are listed in following Table 1. Table 1: Selected climate change prediction scenarios Sl. No. Description Rcp Selected Model 1 Dry, Cold Rcp45 Gis-E2-R-R4i1p1_Rcp45 2 Dry, Warm Rcp45 Ipsl-Cm5a-Lr-R4i1p1_Rcp45 3 Wet, Cold Rcp45 Ccsm4-R5i1p1_Rcp45 4 Wet, Warm Rcp45 Canesm2-R4i1p1_Rcp45 5 Dry, Cold Rcp85 Gfdl-Esm2g-R1i1p1_Rcp85 6 Dry, Warm Rcp85 Ipsl-Cm5a-Lr-R4i1p1+Rcp85 7 Wet, Cold Rcp85 Csiro-Mk3-6-0-R3i1p1_Rcp85 8 Wet, Warm Rcp85 Canesm2-R4i1p1_Rcp85 9 Rcp45 Bccr 10 Rcp85 Bccr

3.3 Study methodology The study has been accomplished based on secondary data and information available in the public domain. The state of art technology and mathematical model has been used for assessment of water resources in the Brahmaputra basin. Hydrological model of the Brahmaputra basin has been developed using MIKE BASIN software of Danish Hydraulic Institute (DHI water & Environment). Present as well as future water availability considering climate change impacts has been calculated from MIKE BASIN model results. 4. Mathematical Model Development A semi distributed, lump and conceptual type hydrological model of the Brahmaputra river basin has been developed using MIKE BASIN modelling tool. MIKE BASIN is a water management tool developed by DHI for addressing water allocation, conjunctive water use, reservoir operation and water quality issues. To develop hydrological model flow direction has been calculated using land terrain data of SRTM. Rivers sketched in the basin are: Brahmaputra, Dibang, Lohit, Buri Dihing, Dhansiri, Kopili, Subansiri, Kameng, Manas, Sunkosh, Dudkumar, Dharala, and Teesta. The entire Brahmaputra river basin has been sub-divided into 54 sub-catchments. Mean area rainfall for each sub-catchment has been computed by using the weightage of each station to the sub-catchment. A rainfall runoff model has been developed using Nedbør-Afrstrømnings-Model (NAM) of DHI. The NAM model comprises 54 sub-catchments, 118 rainfall stations, 6 evaporation stations and 4 temperature stations. Potential evapo-transpiration required in the model has been computed from available evaporation records multiplying by the factors ranging from 0.30 to 0.80 depending on the soil condition and vegetation coverage: 0.3 used for bare hilly catchments and 0.8 used for densely vegetated plane lands. For snow fed catchments, the areas under different elevations have been computed by accumulating areas calculated for each incremental elevation using SRTM Digital Elevation Model (DEM). The NAM model has been simulated for 6 consecutive years (2002 to 2007) based on common period of available data. MIKE BASIN model comprises a network of river system including catchments and node. Time series runoff generated by simulation of NAM model at each catchment is given as input at the catchment nodes of the basin. MIKE BASIN then routes the inflow given at all catchments to the outlets using hydrological routing method: Linear reservoir, Muskingum and Wave translation. The Brahmaputra basin model developed based on MIKE BASIN has been calibrated by comparing the model result against rated discharges at Bahadurabad of Bangladesh. A Comparison plot of model result against rated discharge at Bahadurabad of Bangladesh is shown in Figure 3.

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FigureBahadurabad_Q-Rated 3: Comparison[m^3/s] plot of MIKE BASIN based model result against rated discharge at MIKEBASIN [m^3/s] BrahmaputraBahadurabad, Basin Runoff atBangladesh Bahadurabad of Bangladesh

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The focus area gets water from its upstream catchments as well as from runoffs generated from local 60000 rainfall. To analyze the impact of climate change, total available flow has been calculated by summing locally generated runoff with water coming from upstream catchments. A 40000 heterogeneous effect of climate change on river flow is observed in four different future decades and ten future prediction scenarios. Some scenario shows increase of flow while some other 20000 shows decrease. Two prediction scenarios: GIS-E2-R-r4i1p1_rcp45 and IPSL-CM5A-LRr4i1p1+rcp85 produce significant decrease in flow especially in summer months (March to June). 0 Jan Feb Mar Apr Maymostly Jun shows Jul the Aug Oct in Nov Dec among The prediction scenario: BCCR_RCP45 highestSepincrease river flow 2004 2004 2004 2004 2004 2004 2004 2004 2004 2004 2004 2004 the ten scenarios. Variation of change in flow is more in summer months (March to June). In future 2020, the change of flow vary ranging from - 8 % (in June) to 20 % (in April). In future 2050, the change in river flow vary ranging from – 20 % to 30 % in June. Figure 4, 5, 6 and 7 show variation of change in river flow in future 2020, 2030, 2040 and 2050 due to climate change under ten prediction scenarios. Change of flow due to CC in the focus area in future 2020 20

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5. 100000 Results And Discussions

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Figure 5: Changes of flow in the focus area due to climate change in future 2030

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Figure 6: Changes of flow in the focus area due to climate change in future 2040 Change of flow due to CC in the focus area in future 2050 30

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Figure 7: Change of flow in the focus area due to climate change in future 2050

6. Conclusions The effect of climate change on the water availability in the Brahmaputra basin has been analyzed using predicted evaporation and rainfall of five climate prediction models with two RCPs. It is observed that in most of the scenarios, simulations show increase trend of flow due to climate change. In far future, the change of flow in the basin increases, and becomes more significant in pre-monsoon months: April, May and June. This significant change in pre-monsoon period may cause an adverse effect on agriculture in the focus area of lower Brahmaputra river basin. In future 2020, the highest change of flow is observed in the month of April which is around -5 % to 20 % whereas in 2050, that is about -20 % to 32 % in June. In monsoon (July October) and dry (November – March) periods, the change of flow is almost positive in all scenarios. The extra flow in monsoon months may increase monsoon flood level and prolonged the duration of flood. The additional flow in dry period will be beneficial in agricultural, industrial and drinking water supply. 7. Acknowledgement The authors thankfully acknowledge the financial support of International Centre for Integrated Mountain Development (ICIMOD) for this study and Bangladesh Water Development Board (BWDB) for providing necessary data. The authors also acknowledge the technical support of Prof. Dr. M. Monowar Hossain, Executive Director of Institute of Water Modelling (IWM) and Sardar M Shah-Newaz, Director, Flood Management Division, IWM. 8. References Datta B. and Singh V. P., Hydrology, in: The Brahmaputra Basin Water Resources. Kluwer Academic Publisher, Netherlands, 139- 195, 2004. IPCC, Climate Change 2007, The Scientific Basis. Cambridge University Press: Cambridge, 2007. ICIMOD, The Himalayan Climate Change Adaptation Programme (HICAP). International Centre for Integrated Mountain Development (ICIMOD). 2011http://www.icimod.org/?q=4779 (14 June 2011). Bongartz, K., W., A Flugel, J. Pechstadt, Xu Jiangchu, and Tandong Yao, Analysis of Climate Change Trend and Possible Impacts in the Upper Brahmaputra River Basin – the BRAHMATWINN Project. Acta Press, 2007. Barnett T. P., Adam J. C. and Lettenmaier D. P., Potential impacts of a warming climate on water availability in snow-dominated regions. Nature, 438, 303-309, 2005. Haub C., The Future Population of India: A Long-range Demographic View. Population Reference Bureau, 1875 Connecticut Ave., NW, Suite 520, Washington, DC 20009, 2007. Mutreja, K.N., Applied Hydrology. Tata McGraw-Hill Publishing Company Ltd, New Delhi, 1995. Eriksson, M., Vaidya, R., Jianchu, X., Shrestha A. B., Nepal, S. and Sandstrom, K., The Changing Himalayas : Impact of Climate Change on Water Resources and Livelihoods in the Greater Himalayas. International Centre for Integrated Mountain Development, GPO Box 3226, Kathmandu, Nepal, 2009. Rahaman M. M. and Varis O., Integrated water management of the Brahmaputra basin:Perspectives and hope for regional development. Natural Resources Forum 33, 60– 75, 2009.