Estimation of Snowmelt Runoff in Himalayan Catchments Incorporating Remote Sensing Data

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1 Snw and Glacier Hydrlgy (Prceedings f the Kathmandu Sympsium, Nvember 1992). IAHS Publ. n. 218, Estimatin f Snwmelt Runff in Himalayan Catchments Incrprating Remte Sensing Data K. B. THAPA The Central Department f Meterlgy, TriBhuvan University, TriChandra Campus Building, Kathmandu, Nepal Abstract This paper presents the result f the hydrlgical investigatins, based n pht interpretatin f the Himalayan catchments in and arund Nepal alng with the functinal relatinships f premnsnal snwmeltrunff separately with temperature and snw cvered area. Available Landsat images, temperature, and streamflw data have been analysed frm 1975 t Regressin equatins fr temperature versus streamflw, and snw cvered area versus streamflw have been arrived at with limited data. Because f the uncertain winter precipitatin and the inherent sunny spring, the latter relatinship gives a mre reasnable spring melt frecast. This study demnstrates the peratinal value f the satellite data fr predicting the spring runff f remte Himalayan catchments. INTRODUCTION Snw is an imprtant cmpnent f the hydrlgical cycle in the Himalayan regins. A reasnable snwmelt estimate in the dry seasn is essential fr the reginal planning f water resurces. T achieve this bjective, data such as the snw cver, snw depth, and water equivalent are necessary besides the energy transfer t the snw. Snw cver is an imprtant index fr predicting the spring melt, and it is interpreted better than the ther snw parameters. URGENCY OF SNOW HYDROLOGY The Himalayan rivers are amngst the wrld's biggest in length as well as in transprt capacity. These are substantially fed by the thawing snw. There is a pressing demand n hydrlgical studies f the Himalayan catchments fr which relatively little is knwn. Perhaps, this is ne f the main stumbling blcks in a sund planning f the water resurces prjects. Hwever, limited studies relating t thehydrmeterlgical and physical factrs affecting the snw melt runff in the Himalayan catchments have indeed been reprted. A few are f Rang & Salmnsn (1976), Dhanju (1977), Gupta et al. (1982), Yamada et al. (1984), Ives (1986), and Xuezhi & Jian (1988).

2 70 K. B. Thapa A gd frecast f the snwmelt runff during the dry seasn has nw thus becme bligatry fr the municipal supply, irrigatin, and hydrpwer. CATCHMENTS AND DATA Catchments have been selected arund the nrthern brder f Nepal. The rivers in these catchments are perennial in nature, carrying significant dry seasn flw. It is als interesting t nte that a few f these are transhimalayan in rigin. Landsat images have been btained frm the Remte Sensing Centre, Ministry f Frest, Nepal. The hydrmeterlgical data have been acquired frm the Department f Hydrlgy and Meterlgy, Ministry f Water Resurces, Nepal (1988). CLIMATE In the Himalayan regins a great variety f climatic patterns exist due t the intricate relief features. In summer, mnsn nrmally cmmences in mid June and cntinues till mid September. During the premnsn seasn, March t May, thunderstrms are frequent. The passage f western r extra trpical disturbances mving frm west t east during Nvember t April bring relatively mre winter precipitatin t the western Himalayas. The summer mnsn and winter rains amunt t abut 85% and 15% f the ttal annual precipitatin respectively. The average annual rainfall ranges frm abut 250 mm in the dry regins t abut 4500 mm in the humid regins. Within a shrt distance f abut 200 km, the altitude f m asl in the subhimalayan regins, sars up t an average f 7000 m asl in the great Himalaya. Thus, widi this wide diverse tpgraphy the temperature in Nepal ranges frm trpical heat, with 30 C in summer and 15 C in winter, t the Arctic frst, belw 0 C thrughut the year. Wind speed varies with altitudes, and in general, it is abut 50 t 60 km/h at 6 km elevatin, and can reach rund 120 km/h at the summits (Ramanathan, 1977). METHODS Remte sensing prvides an easy and efficient methd t assess snwcver in inaccessible and hazardus areas. Sme catchments substantially cvered with snw have been selected fr this study. The study has been subdivided int tw cmpnents: (a) The analysis f the Landsat Images, and (b) The estimatin f the snwmelt runff in the premnsn perid.

3 Estimatin f snwmelt runff incrprating remte sensing if! i\ s S H \ O \ O \ O > ^ v O * C «P > 0 0 ^ < O t N c c c^ H M "^ CO "t d CO "* asr*** 0\ O M W Tt «T 8 O CO CO CO O O CO CO CO <»2 Q <s S CO CO CO Tf ^ *H O O O \ \C t 00 0O OO <fi " cs <s <s CS 00 ** es i es 8 t 8 en m CO CO <S CN 8 8 es c <s C 0 0 \ C 0 * ^ 0 * «S CS O VT) KT> *$ "<f ^O H Os CO OS CS CO C O» ^ C O * H O O V O V > V O TJ CO CS VO << CO CO < *$ \rt v~> \ri \r> p \ ts v *«* cs ** CO O CO VI f CO CO.. ^ ^J. ^ r r \ * c r^ GO r CO CO CO «,H CO ««O H << Tj V) i r VO VO v,31 m,11,1 r ^* r h CO VO CO CO CO CO O \ r^ «> <$ vn CO O c *n r c f» Ox «ji r «r^ r» c CO O N n h h CO *H c^^r^rrr*r'r^r^rr^r*'<*irir^w) r r r^ ^ e*ï en ^ en cs cs cs cs cs CS i çn cs cs r r^ m ^ en cs es es cs s a *0 CO ON Tf CO r^ en CS cs 1 en M es» fi. II t~ r~ ^ en en CS CS CS es r^ CO is cs I t~ en J es cn v"i is cs 3;. is es M m < litillilimil a «Bill S 5 3 â Sh.H < a s <S fs «il < < S et

4 72 K. B. Thapa ANALYSIS OF THE LANDSAT IMAGES The catchments upstream f the gauging statins, as tabulated in table 1, have been analysed with available Landsat Images f scale 1: 500,000. It has been reprted (Thapa, 1980) that in the Himalayan regins, the snw cver gradually increases frm September t March, and afterwards it depletes due t melting. Therefre, images particularly arund March have been selected. Images f band 5 (0.6 t 0.7 micrns)) have been used, because it prvides the best cntrast between snw cver and snw free terrain fr visual interpretatin and delineating purpses. The verlays have been traced ut frm the images and the areal extent f snw cver has been planimetered carefully. The results are tabulated in Table 1. ESTIMATION OF SNOWMELT RUNOFF IN THE PREMONSOON SEASON First, crrelatin study between temperature and snwmelt runff (Fig. 1 and Fig. 2) was made fr Langtang Khla Watershed, a subcatchment f Trisuli. The analysis was further extended between snw cvered area and snwmelt runff as depicted in Fig i Langtang Khla Watershed Area: 344 km 2 Altitude: 3920m asl Mnths: March.April, May(1986,1988,1989) Q = 2.54 T ' CO a> e 3 O g CD D) t jc CO Q _ ~.f ] r~r\ m i n r r i i i i i i i i i Temperature in C CT) Fig. 1 Mean daily temperature vs. mean daily discharge.

5 Estimatin f snwmelt runff incrprating remte sensing data Langtang Khla Watershed Area: 344 km 2 Altitude: 3920m asl Mnths: March.April, MayCl986,1988,1989) Q = EXP C Fig I I I I 1 I I I Mnthly Mean Temperature in C CT) 2 Mnthly mean temperature vs. mnthly mean discharge. CONCLUSIONS The results btained frm this study are quite encuraging particularly in view f the limited data having been used. Satellite can prvide the necessary repetitive snw cver data in the inaccessible terrains f the Himalayas. Statistical relatinships f the first rder apprximatin (Figs 1 t 3) have been derived. Snw cvered area befre melt seasn generally fluctuates depending n the western disturbances, while the temperature during the melt seasn nrmally des nt. Therefre, it is reasnable t use the relatinship Ï1400 Q1200 Q = C0.090 A+329.8ÎX10 6 r 2 = «1000 E CD 800 ^. ^^ 5= 600 O c <r (), i I 2 I I I I I I I I Snwcvered Area 10 3 km 2 CAD Fig. 3 Estimated snwcver vs. measured runff fr sme Himalayan catchments. i 12 I 14

6 74 K. B. Thapa between the snw cvered area and the spring melt runff fr predicting purpse. A mre representative melt runff relatin can be derived by installatin f gauging statins further upstream near the snw bund areas. Due t few and sparse data, many different catchments have been lumped tgether fr this study (Fig. 3) Analysis with individual catchment shuld give better results. Big river systems in the Himalayas riginate in different cuntries, and therefre, sharing f data must evlve fr mre meaningful results. With an imprved data base, better snwmelt runff mdels can be tested, and mdified t suit the cnditins prevailing in the Himalayan catchments. Acknwledgements The authr is deeply indebted t HMG f Nepal, Ministry f Water Resurces, Department f Hydrlgy and Meterlgy, Ministry f Frest, Remte Sensing Centre and ICIMOD fr making available the necessary data fr this study. REFERENCES Dhanju, M. S. (1977) Snw and ice mnitring by remte sensing. Internatinal Wrkshp n Ice and Snw, Natinal Cmmittee fr IHP, New Delhi, 39 pp. Gupta, R. P., Duggal, A. J., Ra, S. N., Sankar, G. & Singhal, B. B. S. (1982) Snwcver Area vs. Snwmelt Runff Relatins and its Dependencen Gemrphlgy. J. Hydrlgy. His Majesty's Gvernment f Nepal, Ministry f Water Resurces, Department f Hydrlgy and Meterlgy, Hydrlgical Recrds f Nepal, 15 June, Ives, J. D. (1986) Glacial Lake Outburst Flds and Risk Engineering in the Himalaya. Kathmandu, Nepal, Nvember 1986, ICIMOD Occasinal Paper N. 5. Rajna, V. K. (1977) Meltwater discharge and surface runff studies at Gara Glacier In: Internatinal Wrkshp in Ice, Snw and Avalanches (Prc. frm Manali, 1318 April, 1977). Indian Natinal Cmmittee fr IHP, New Delhi. Rang, A. & Salmnsn, V. V. (1976) Satellite snw bservatin and seasnal streamflw frecasts. Hydrlgy and Oceangraphy Branch Gddard Space Flight Center, Greenbelt, Maryland, January Final Reprt n. AA, Cntract n. NA Ramanathan, A. S. (1977) The climatlgy f the Himalayas. In: Internatinal Wrkshp in Ice, Snw and Avalanches (Prc. frm Manali, 1318 April, 1977). Indian Natinal Cmmittee fr IHP, New Delhi. Shunying, Z. & Qunzhu, Z. (1988) Frecasting snwmelt frecasting runff using NO AA/TIROS satellite data fr the Huanghe River and Heihe River. Memirs f Lanzhu Institute f Glacilgy and Gemrphlgy 6. Chinese Academy f Sciences, 75. Thapa, K. B. (1980) Analysis fr snwmelt runff during premnsn mnths in Beas using satellite imageries. Department f Hydrlgy, University f Rrkee, MTech Thesis, 73 pp. Xuezhi, R. & Jian, W. (1988) Mediumrange predictin analysis and equatin f snwmelt runff Heihe River in Mt. Qihian. Memirs f Lanzhu Institute f Glacilgy and Gemrphlgy 6. Chinese Academy f Sciences, 64. Yamada, T., Mtyama, H. & Thapa, K. B. (1984) Rle f glacier meltwater in discharge frm the glacial watersheds f Langtang Valley. In: Data Centerfr Glacier Research, Japanese Sciety f Snw and Ice, 6171.

SNOW AND AVALANCHES FORECASTING OVER THE ANDES MOUNTAlNS. Jose A. Vergara* Departamento de Geoflsica, Universidad de Chile

SNOW AND AVALANCHES FORECASTING OVER THE ANDES MOUNTAlNS. Jose A. Vergara* Departamento de Geoflsica, Universidad de Chile SNOW AND AVALANCHES FORECASTNG OVER THE ANDES MOUNTAlNS Jse A. Vergara* Departament de Geflsica, Universidad de Chile Rene len, Camins y Nieve, ANDNA-CODElCO, CHLE ABSTRACT: During the last three years