Hvdrological Aspects of Alpine and High Mountain Areas (Proceedings of the Exeter Symposium, July 1982). IAHS Publ. no. 138.

Water resources investigation in Pakistan with the help of Landsat imagery — snow surveys 1975-1978

R, N, TARAR Hydrology and System Analysis, Water and Power Development Authority, Lahore, Pakistan

ABSTRACT Pakistan with a population of about 80 million is mostly dependent upon agriculture in the Indus basin, served through the world's largest contiguous irrigation system developed over the last lOO years. The Indus basin is drained by the River Indus and its five major tributaries namely: Kabul, Jhelum, Chenab, Ravi and Sutlej. Snowmelt - excluding Ravi and Sutlej exclusively assigned to India under the Indus Waters Treaty 1960 - contributes about 70% of the annual flow of the rivers, thus highlighting the need for development of reliable forecasting techniques. With accurate seasonal/ sub-seasonal runoff predictions of the beginning of the snowmelt period in early spring, a more confident and rational planning of the water resources of the basin can be attempted through the online facilities of reservoirs, inter-river link canals and the vast irrigation system. Some rudimentary procedures are already being used but real improvements are expected only if snow surveys are made every year. While ground methods of snow surveys, though necessary, are quite expensive, time consuming and difficult, with the advent of Land Satellites it has become possible to map even the most inaccessible snowfields at fixed intervals. This paper presents the results of a study initiated by the Pakistan Water and Power Development Authority (WAPDA) in 1975 to evolve prediction techniques using Landsat imagery acquired for selected areas over the upper Indus basin. Through analysis and interpretation of snow cover and runoff data from 1975-1978, a simple predictive correlation of the type R = aA + b has been developed where A is areal extent of snow cover in March/April and R the resultant runoff from 1 March/1 April to 31 August (snowmelt season). Attempts are underway to test the procedure in actual practice, but the situation is complicated by the presence of glaciers, which tend to melt more when the snow cover is thin. For this reason, it may be necessary to initiate international research efforts on the assessment of glacier melt to river flow in the upper Indus basin on a long-term and seasonal basis.

INTRODUCTION Pakistan covers the major part of the Indus basin drained by the

177

178 R.N.Tarar

River Indus and Its five major tributaries of Kabul, Jhelum Chenab Ravi and Sutlej (Fig.l). The Indus basin stretches f r o ^ dfsttt

Sub-Basin Boundary

. International Boundary

Streamgauging Station

River Course

Exist ing Reservoir

Proposed Reservoir

-BASINS

I Shyok River At Yogo

26 I

2. Indus Ri 3 Hunza River AI 3 GUgit River At 5. Indus River At 6. Astore River At

ndus River At

Kochuro Dainyor Bridge Alam Bridge Partob Bridge Doyian lesham

8. Kishanganga River At Muizoforabad 9. Kunhar River At Naran

10-Kunhar River At Garni Habibultah 11. Jhelum River At Koholo

!2.Cri i tral River At Chitral 13- Swot River At Kalom

14 Kabul River At Nowshera

72 ?4 ye

FIG.l Pakistan upper Indus basin.

Scale

Miles loo

160 80 0

highlands of Tibet (China) to the Arabian Sea over a distance of about 2000 m iles (3200 km) . with the division of rivers of the IQfio8 ^ n between I n d i a ^ Pakistan under the Indus Waters Treaty I960, Pakxstan is entitled to receive only the water from the

Chenab .™" 3 ^ ^ I n d U S ^ ^ ( i n c l u d i n 3 K a b u 1 ' ^elum and

abnuf lntan^S h&S±CallV a n agrarian country with a population of about 80 million mostly dependent upon the irrigated agriculture in the Indus basin. This is served through the world's largest ™ f ^ U S " R a t i o n system in the Indus plains developed over the last 100 years or so. The system is fed through 16 diversion dams coZTcTli f ° m i l S S ( 5 8° k m ) ° f ^ ter- r iver link canals which TTZrt\ TTrn n V e r S U n d 6 r P a k i s t a n ' s control with the eastern rivers diverted upstream by India. m addition, the system has

Water resources in Pakistan 179

three major storage reservoirs namely Mangla, Tarbela and Chasma at the upstream "rim" of the Indus plains which regulate as well as supplement the water needed for agricultural and other purposes.

The rivers of the Indus basin rise in mountains with elevations ranging from 15 OOO to 25 OOO ft (4500 to 7500 m) a.m.s.l. These mountains are covered with snow during winter (January to March). The snow starts melting in early March in some basins and in April in others and continues throughout the summer. River flows consist mostly of snowmelt during this period.

It is estimated that snowmelt contributes about 70% of the annual river flow of Indus, Jhelum and Chenab. Thus for effective river management not only man-made but also natural storage has to be considered in the form of perennial ice and snow accumulated on the high mountains of the Himalaya, Karakoram and Hindu-Kush.

To meet the food and fibre requirements of its burgeoning population, Pakistan is giving the highest priority to water resource planning, development and management including floods. Recently a flood forecasting and warning project has been completed under a joint cooperative programme of WMO/UNDP, the Government of the Netherlands and the Government of Pakistan. Although with the completion of this project an infra-structure has become available for short-range flood peak/stage prediction with the help of computerized models using real-time river and rainfall data collected through telemetry and radar, streamflow forecasting will not be complete until data for the contribution from snow and glacier melt are known. The prediction of seasonal river runoff from March/ April to end of August - which consists largely of snowmelt in the upper basins - is of vital importance for the efficient utilization of the limited water supply to optimize agricultural production.

Predictions of snowmelt runoff cannot be made without conducting snow surveys. Generally snow-pack water-equivalent, precipitation, temperature and soil moisture indices are used in regression equations to derive runoff correlations. There are also procedural errors in point measurements and their extrapolation to large basins or sub-basins. Above all, in the present Pakistan setting of restrained funding, limited know-how and limited access to the upper river basins, the related ground observations may be hard to undertake.

Among major concerns within Pakistan hydrology which have not yet been adequately addressed are many related to snow and ice. On the other hand, snow surveys provide the basic data for runoff determination. Thus Pakistan WAPDA being the largest organization for development and management of water resources including storage reservoirs etc., is aware of this fundamental necessity and is trying to do what it can within the existing constraints.

From 1961-1968, WAPDA conducted ground snow surveys in Kunhar sub-basin (No.9 in Fig.l) for determining depth of snow, water-equivalents, density of snow and soil moisture at different levels in representative snow courses. These surveys were limited in area and extent and were abandoned due to technical as well as financial difficulties. The results of this study were published in a report titled "Snow Survey of West Pakistan 1961-68" (WAPDA,1969).

The water supply for most of the rivers of the world is derived larqely from snow and glaciers that accumulate in the mountainous

180 R.N.Tarar

areas. Consequently, reliable water-supply predictions and flood forecasting require accurate measurement of the water-equivalent and areal extent of mountain snow-packs. Ground data collection methods cannot provide either the desired areal coverage or observational frequency. However, the capabilities of remote sensing from Earth-orbiting satellites offer promise for the development of improved snow surveillance techniques.

The potential for snow survey from space was recognized by investigators such as Fritz (1963) and Tarble (1964) using TIROS data. Since then, specific techniques to map snow-cover distributions from satellite photography have been developed. An operational guide for this was prepared by J. C. Barnes and C. J. Bowley for Environmental Science Services Administration (ESSA) of USA in 1968. It discussed the characteristics of the Advanced Vidicon Camera System (AVCS) and Automatic Picture Transmission (APT). In their final report Barnes & Bowley (1969) concluded that the use of satellite data had facilitated interpretation of snow-covered areas.

Nimbus 3 which carried the High Resolution Infrared Radiometer (HRIR) system provided data suitable for initial snow surveillance in the infrared spectral range. In 1970, Salomonson & Maeleod (1972) used Nimbus imagery for conducting hydrological observations over the basins of the Niger and Indus rivers. In their report they indicate that even the low-resolution data easily available from meteorological satellites would be valuable in these regions. Thus information of the spatial and temporal distribution of the snowmelt process in the River Indus basin was now available. Using the image dissector camera system on Nimbus 3 and 4, Salomonson & Maeleod mapped the areal extent of snow cover for 1969 and 1970 over the Indus river basin to correlate the monthly runoff. The results indicated that some success might be achieved in predicting the seasonal runoff volume if the areal extent of snow and the location of the snowline were monitored by satellite.

In 1975, using six years of snow-cover satellite data and corresponding runoff records, Rango et al, (1977) extended the original research on the Indus river basin. In order to conduct this study, images over the Indus and Kabul rivers for April were selected from Environmental Science Services Administration (ESSA) and National Oceanic and Atmospheric Administration (NOAA) satellite data and used to extract snow-covered areas in early spring. These were then related to seasonal runoff for the period 1967-1972 using regression analysis. The two basins selected were the River Indus above Besham and the River Kabul above Nowshera. For the River Indus, the correlation between snow-covered area and runoff was significant at the 95% level with five years of record whereas for the River Kabul it was at the 99% level.

Thus from the previous studies it was clear that the data obtained from meteorological satellites could not only be utilized for snow surveys but that its utility would increase with future advances in technology with the launching of Earth Resources Technology Satellites (ERTS).

With the launching in early 1973 of the first of very high resolution ERTS-1, it became possible to map the surface of the Earth at fixed intervals with repetitive coverage. This provided a

Water resources in Pakistan 181

facility to monitor snow cover in remote inaccessible mountainous terrains with much less effort and time as compared to conventional ground observation methods. In order to develop the data interpretation techniques and methods, a number of technical papers and handbooks were published by agencies like NASA and World Meteorological Organization (WMO). Also, symposia and seminars were held from 1972 to 1981 to transfer this technology to the developing countries and a number of papers were presented by different investigators on the basis of their work (McClain, 1973; Meier, 1973; Wiesnet, 1973; Wiesnet et al., 1974; Andersen & Odegaard, 1980; Bowley et al., 1981).

The prediction of seasonal runoff using high-resolution temporal and areal snow-cover data obtained from ERTS-1 and Landsat-2 was pioneered in the United States by the Soil Conservation Service and the Army Corps of Engineers. Subsequently, WAPDA also decided to make use of Landsat data for monitoring snow cover in the upper Indus basin for prediction of snowmelt runoff. Accordingly, in 1975 WAPDA entered into an agreement with NASA to supply Landsat imagery acquired over the Indus basin.

By utilizing Landsat-2 imagery of the upper Indus basin rivers for the years 1975-1978, WAPDA has attempted to derive a basis for snowmelt runoff predictions during the crucial period of March/ April through August. This paper highlights the outcome of related studies including the further strategy to pursue research in the field of snow and ice hydrology.

WAPDA STUDY

The study area is bounded by the geographic coordinates lat. 33°N -37°N and long. 71°E - 78°E as depicted in Fig.l. It can be seen that the River Indus at Besham (No.7) is the main source of inflow to Tarbela reservoir whereas the River Jhelum at Kohala (No.11) has a similar position for the Mangla reservoir. As these two reservoirs are crucial for the system, more emphasis has been given to the prediction of river flows at these two stations.

The main right-bank tributary, the River Kabul, joins the Indus downstream of the Tarbela dam. Another major dam is going to be constructed at Kalabagh about 123 miles (200 km) below Tarbela. Thus prediction of flows of the River Kabul at Nowshera (No.14 in Fig.l) would not only be desirable but valuable for the management of the Kalabagh reservoir, but it has been deferred for subsequent study.

This study has been confined to 13 sub-basins (S.No.1-13 in Fig.l), whose particulars are described in Table 1.

STUDY PERIOD AND DATA SOURCE

Landsat imagery of the upper Indus basin (Fig.l) for the period 1975-1978 formed the basis of this study. The images were obtained from NASA through Pakistan Space and Upper Atmospheric Research Commission (SUPARCO) under an agreement titled "Water Resources Investigation in Pakistan with the Help of ERTS Imagery - Snow Surveys". Under this agreement, NASA supplied free of cost 49 images for 1975 and 95

182 R.N.Taxai

TABLE 1

S. Basin/'Sub-basin No.

Drainage area Remarks

2 2

miles km x 10' x lo'

I.River Indus 1. 2.

3.

4.

Shyok at Yogo Indus at Kachura Hunza at Dianyor Bridge Gilgit at Alam Bridge

13.0 43.5

5.1

10.1

33,

111. 13.

25

.3

.4

.0

.9

5 . Indus at Partab 55.0 141.0 Bridge

6. Astore at Doyian 1.6 4.0 7 . Indus at Besham 62.7 160.5

Highly glacierized area draining Batura,Haspar,Kumdan and Shamshal etc. well-known glaciers in the Biafo Glacier system; rivers drain portions of the Hindu-Kush,Karakoram and Himalayan mountains ; heavy snow-pack accumulation in winter which starts melting in early April and produces high Indus runoff.

Partly glacierized area but carries impact of water coming from upstream glacierized areas.

II.River Jhelum 8.

9.

10.

11.

Kishanganga (Neelum) at Muzaffarabad Kunhar at Naran Kunhar at Garhi Habib Ullah Jhelum at Kohala

III.River Kabul

2.

0. 0.

9.

.8

.4

.9

.6

7.

1. 2.

24.

.2

.O

.4

.6

12. Chitral at Chitral 4.4 11.3 13. Swat at Kalam 0.8 2.0

Almost non-glacierized area; some glaciers/avalanches in Kunhar valley; snow accumul­ation is less than comparable northern latitudes ; snowmelt starts early February due to low basin altitude.

Partially glacierized area; average snow accumulation.

* Corresponding to Fig.l

images for 1976 in Multi-Spectral Scanner (MSS) bands 4, 5 and 7 acquired between March and August. Later on, NASA requested payment, which was arranged by Pakistan for 66 images in 1977 and 46 images in 1978 for the period March to April in MSS band 5 only. During 1979, no purchase order for images could be placed due to lack of funds. In 1980, the images acquired were either out of the study area or had substantial cloud coverage and thus could not be used. Efforts were made to procure images for 1981 through the National Remote Sensing Agency of India but results were not fruitful As such the study has been confined to data available for 1975-1978. Naturally, the results could have been further refined and improved if more data had been available.

Water resources in Pakistan 183

METHODOLOGY

From amongst the 18 day interval Landsat coverage of the upper Indus basin, workable images were selected. These were interpreted using Colour additive Viewer/Zoom Transfer Scope and transparent overlays for each selected image were prepared. On these overlays, the snow-covered area was marked in colour and calculated with a planimeter. The percentage of snow-covered area in each of 13 sub-basins (Fig.l) was obtained by comparing the planimetered snow area to the corresponding total area.

Based on the recorded daily discharge data for the nearest WAPDA stream-gauging station(s), 18 day runoff per square mile was computed for the individual sub-basins. The percentage snow-covered area and 18 day per square mile discharges were then plotted on a time base.

Plots for the years 1975-1978 in respect of the River Indus at Besham (Tarbela reservoir) and the River Jhelum at Kohala (Mangla reservoir) are shown in Figs 2 and 3 respectively. A close examination of these plots indicates that a relationship exists between the average percentage snow cover of the basin(s) on a particular date and the resulting snowmelt runoff during the subsequent period. In order to evolve a suitable runoff prediction base, the percentage of snow cover on 1 March or 1 April of a particular year (depending upon the characteristic of each sub-basin) was averaged and compared with the corresponding total observed runoff from 1 March/1 April to 31 August. Rainfall runoff, if available, was subtracted from the total discharge in order to correlate the snow cover direct with snowmelt runoff.

A regression equation of the type R = aA + b where A is the area under snow on 1 March/1 April and R the runoff from 1 March/1 April to 31 August was attempted for various sub-basins using the Landsat data from 1975-1978. For the purpose of regression analysis, 13 sub-basins of study area were formed into groups having similar characteristics such as highly glacierized, partially glacierized and non-glacierized.

DISCUSSION AND RESULTS

Study results concerning computed snow cover and corresponding observed runoff for sample groups are presented in Table 2. This shows that in the case of highly glacierized areas (Hunza & Gilgit) more snow accumulation produces less runoff and vice versa, whereas in the case of partial and non-glacierized areas the trend is generally reversed.

Further, the temporal snow coverage and 18 day runoff (Figs 2 and 3) reveal that snow accumulation increases from south to north. The snow starts melting earlier (in mid-February) in the southern latitudes (Jhelum basin) and stays longer in the northern latitudes (Indus basin), where it starts melting generally towards the end of March. The higher elevation Indus basin has a higher average percentage of snow-covered area in early April than does the Jhelum basin. In addition, the Indus basin not only produces a greater total seasonal flow but also a larger water yield per unit area than

184 R.N .Tarar

18 Day Total Discharge CFS/mil«

•/. Snow Cover

Water resources in Pakistan 185

18 Day Total Discharge In CFS/~Mlle

J8«>o MOUS H

186 R.N.Tarar

TABLE 2 Snow cover versus observed runoff

S.No* Location Year Snow Runoff Characteristics coverf (acre-

ft xlO6)'.

1. River Shyok at 1975 - - Glacierized area Yogo 1976 88 5.99

1977 95 7.77 1978 97 9.92

3. River Hunza at 1975 93 6.17 Highly Dainyor Bridge 1976 91 6.78 glacierized area

1977 86 8.89 1978 83 10.33

4. River Gilgit at 1975 89 Alam Bridge 1976 89

1977 85 1978 82

7. River Indus at 1975 88 Besham 1976 79

1977 82 1978 84

11. River Jhelum at 1975 70 Kohala 1976 73

1977 71 1978 80

* Corresponding to Fig.l + 1 March for Kohala and 1 April for others § 1 March/1 April to 31 August. 1 acre-foot = 12 33 m

does the Jhelum basin. In general, it can be assumed that fruitful snowmelt in the whole Indus basin starts around the early part of April every year. By the end of June about 50% of the basin (lower elevations) becomes free of snow. On the remaining 50% (higher elevation) snow cover, melting continues through summer. Towards the end of August a recession starts in the snowmelt hydrograph until it hits the base towards the end of October, still leaving between 10-15% of snow cover.

The study has resulted in the derivation of regression equations for each of the 13 sub-basins in Fig.l. Sample results for each of the distinct groups are listed in Table 3. This indicates that statistically the equations are significant as the correlation coefficient between A and R represented by r varies from 0.889 to 0.996. Further, based on four years of record deviation between computed and observed runoff is within ±10%. Though these equations seem promising, the degree of confidence for making particular flow predictions has not been established so far due to

10.02 10.78 12.20 15.55

41.01 38.04 38.19 40.65

8.24 14.48 11.40 17 .24

Highly glacierized area

Partially glacierized area

Non-glacierized area

Water resources in Pakistan 187

TABLE 3 Sample snow cover regression equations for various Indus basin locations

Type S.No.* Location Equation^ Correlation Characteristic coeffici ent (rz)

R=3.162A-31. 301

R=45.233-8.257A

7.539A R=0.710A+

0.159

I. 1. River Shy ok at Yogo

II. 3. River Hunza at Dainyor Bridge

4. River Gilgit R=77.885-at Alam

III. 2. River Indus at Kachura

5. River Indus at Partab Bridge

6 . River As tore at Doyian

7. River Indus at Besham

IV. 8. River Kishanganga (Neelum) at Muzaffarabad

9. River Kunhar at Naran

10. River Kunhar at Garhi Habib Ullah

11. River Jhelum at Kohala

V. 12. River Chitral at Chi tral

13. River Swat at Kalam

R=1.032A+ 0.888

0.941

0.996

0.935

0.889

R=1.798A+ 0.908 0.440

0.960

Glacierized

Highly glacierized

Highly glacierized Combined group having impact of water from glacierized and partially glacierized areas

Non -glacierized area

Partially glacierized

* Corresponding to Fig.l f A is measured in thousand square miles (1 square mile = 259 ha)

and R in million acre feet (1 million acre feet = 1.233 km )

n o n - a v a i l a b i l i t y of t i m e l y L a n d s a t d a t a on snow c o v e r . Sample u s e o f t h e c o r r e l a t i o n s t o p r e d i c t s e a s o n a l (March-August)

snowmelt r u n o f f f o r t h e s u b - b a s i n s m e n t i o n e d u n d e r Group IV of T a b l e 3 i s i l l u s t r a t e d i n F i g . 4 . S i m i l a r c u r v e s f o r o t h e r s u b - b a s i n s have a l s o b e e n d e v e l o p e d f o r p r e d i c t i n g s e a s o n a l r u n o f f .

188 R.N.Tarar

20

16

6 R

un

off

(10 A

c

T l

8

4

® /

7

3 * X

®

/ •

Snowcover on

/ •

L E G E N D

O 1975 X 1976

• 1977 g _ . _ 1978

3 March 1 ( 10 Sq Miles)

Derived Correlation Equation List Of Stations ( G r o u p - I V )

» 2 - n I 5 ? o A * ° " 4 4 0 I. Kishangango River Ai Muzatfarabad

R = March —August Snowmelt Runoff ( M A F ) 2. Kunhar River A1 Naran

A = Area Under Snow on March l ( i 03 Sq. Miles) 3 K u n h a r R n r e r A l G a r h i H ° » i b u l l a h

71- = Correlat ion Coefficient Between A a R 4. Jhelum River Al Koholo

FIG.4 Indus river basin - Pakistan. curve for streamflow forecasting.

Sample correlation

FURTHER OUTLOOK

The study conducted by WAPDA so far - basically as desk work -indicates that

(a) Landsat snow-coverage data for remote areas are susceptible

to treatment to yield seasonal streamflow predictions by applying

a regression equation of the type R = aA + b.

(b) The methodology used is simple, inexpensive and less time-

consuming than ground methods.

(c) To make use of the study in actual practice, timely

availability of Landsat data is essential.

As such the relationships are at best preliminary and would need

to be improved and refined by supplementation through field data

collection and application of improved analytical tools and

procedures. It is also recognized that two important elements in

the glacier hydrology scene in Pakistan are that:

(a) glaciers are very important both for water supply and for the

release of dam-breach floods, and

(b) there is very little local expertise in this field of

hydrology.

There is little point in training technicians and other

Water resources in Pakistan 189

professionals without also implementing research projects in snow

and ice. There are two projects which look promising for the near

future.

(a) Assessment of the contribution of glacier melt to river flow

in the upper Indus basin, particularly in the Karakoram mountains,

on a long-term and a seasonal basis. Being a very large and

ambitious project, it could be broken down into a number of

component sub-projects. The breakdown might involve a synthesis

and evaluation of all data already gathered followed by field

measurement projects in certain relatively accessible sub-basins

followed by an analysis of results. To start with, concentration

may be on a basin such as the Hunza above Gilgit which is accessible

and in which a considerable amount of data has already been gathered.

Then the results of this highly glacierized basin could be compared

with others such as the Swat or Kunhar basins which have smaller

proportions of glacier cover.

(b) Monitoring and forecasting glacier-related catastrophic floods.

A system could be set up to assess flood potential, flood likelihood

and possible flood damage within the Karakoram mountains. This

system would make use both of ground observations and monitoring by

remote sensing (satellites and aircraft).

The basic raison d'être of both these studies in Pakistan would

be better utilization of water resources for energy production and

irrigation. For that Pakistan would welcome technical assistance,

including collaboration, from developed countries having the

necessary expertise.

ACKNOWLEDGEMENTS The author is grateful to NASA for providing

financial support and to EROS Data Center, Sioux Falls, South Dakota,

USA for sending the imagery. Thanks are also due to SUPARCO for

providing assistance by way of instruments and training for

interpretation of images. The author is grateful to WAPDA

formations of Surface Water Hydrology Project for providing runoff

data and Mr Sardar Ali Choudhri, Project Director, Hydrology and

Investigation Directorate for providing the services of his staff

and particularly Mr Sana Ullah, Senior Research Officer, who spent

long hours on the interpretation of images and compilation of results

to help complete this paper. Particular mention needs to be made of

Dr Gordon J. Young, Canadian National Hydrology Research Institute,

who during his Pakistan visit of April 1981, helped in restructuring

this paper. My thanks are also due to Dr J. W. Glen and a referee

for rendering assistance and advice in the preparation of the paper.

REFERENCES

Andersen, T. & Odegaard, H. (1980) Application of Satellite Data for Snow Mapping. Norwegian National Committee for Hydrology, Oslo.

Report no.3.

Barnes, J.C. & Bowley, C.J. (1969) Satellite Surveillance of

Mountain Snow in the Western United States. (Final Report, Contract No.E - 196-68 prepared for Dept of Commerce, Environmental Services

Administration) Allied Research Associates, Inc., Concord, Mass.

190 R.N.Tarar

Bowley, C.J., Barnes, J.C. & Rango, A. (1981) Application systems verification and transfer project. Vol.VIII. Satellite snow mapping and runoff prediction handbook. NASA Technical Paper 1829.

Fritz, S. (196 3) Snow surveys from satellite pictures. In: Proc. first Int. Symp. on Rocket and Satellite Meteorology (ed. by H. Wexter & J. E. Caskey), 419-21. North-Holland, Amsterdam.

McClain, E.P. (1973) Snow Survey from Earth Satellites. World Meteorological Organization, Geneva. WMO Publ. no. 353.

Meier, M.F. (1973) Evaluation of ERTS imagery for mapping and detection of changes of snow cover on land and on glaciers. In: Symp. on Significant Results obtained from the Earth Resources Technology Satellite-1, Goddard Space Flight Center, March 1973. Vol. 1, Sect.A, 863-875. NASA SP-327.

Rango, A., Salomonson, V.V. & Poster, J.L. (1977) Seasonal streamflow estimation in the Himalayan region employing meteorological satellite snow cover observations. Wat. Resour. Res. 13(2), 109-12.

Salomonson, V.V. & MacLeod, N.H. (1972) Nimbus hydrological observations over the watersheds of the Niger and Indus rivers. In: 4th Ann. Proc. Earth Resources Rev. 5-1-5-11. NASA Doc. MSC 05937.

Tarble, R.D. (1964) Areal distributions of snow as determined from satellite photographs. In: Erosion Continentale, Précipitations, Hydromêtrie, Humidité du Sol (Proc. Berkeley General Assembly, August 1963), 372-375. IAHS Publ. no. 65.

WAPDA (1969) Snow Surveys of West Pakistan 1961-68. Surface Water Hydrology Project, Pakistan Water and Power Development Authority, Lahore.

Wiesnet, D.R. (1973) Detection of snow conditions in mountainous terrain. In: Earth Resources Technology Satellite-1. (Symp. Proc. Goddard Space Flight Center, Sept. 1972), 131.

Wiesnet, D.R., McGinnis, D.F. & McMillan, M.C. (1974) Evaluation of ERTS-1 Data for Certain Hydrological Uses. (Final Report prepared for Goddard Space Flight Center).