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Hydrology and Glaciology
1.0 INTRODUCTION
Water in the landscape is not only a necessary component for life, it is the fundamental driver of landscape denudation and landform development. Hydrology is the study of the processes which cycle water between the oceans, atmosphere, and land surface. It is the scientific study of the movement, distribution, and quality of water on Earth and other planets, including the hydrologic cycle, water resources and environmental watershed sustainability. Understanding the physical processes which dictate the interaction of water with the landscape is fundamental to managing our resources in the face of mounting environmental challenges and natural resource pressures.
Hydrology has been a subject of investigation and engineering for millennia. For example, about 4000 BC the Nile was dammed to improve agricultural productivity of previously barren lands. Mesopotamian towns were protected from flooding with high earthen walls. aqueducts were built by the Greeks and Ancient Romans, while the history of China shows they built irrigation and flood control works. The ancient Sinhalese used hydrology to build complex irrigation works in Sri Lanka, also known for invention of the Valve Pit which allowed construction of large reservoirs, anicuts and canals which still function.
2.0 THE HYDROLOGICAL CYCLE
The hydrological cycle is the process, powered by the sun's energy, which moves water between the oceans, the sky, and the land.
We can start our examination of the hydrologic cycle with the oceans, which hold over 97% of the planet's water. The sun causes evaporation of water on the surface of the ocean. The water vapor rises and condenses into tiny droplets which cling to dust particles. These droplets form clouds. Water vapor usually remains in the atmosphere for a short time, from a few hours to a few days until it turns into precipitation and falls to the earth as rain, snow, sleet, or hail.
The five main processes included in the hydrologic cycle are condensation, precipitation, infiltration, runoff, and evapotranspiration. The continuous circulation of water in the ocean, in the atmosphere, and on the land is fundamental to the availability of water on the planet.
Some precipitation falls onto the land and is absorbed (infiltration) or becomes surface runoff which gradually flows into gullies, streams, lakes, or rivers. Water in streams and rivers flows to the ocean, seeps into the ground, or evaporates back into the atmosphere.
Water in the soil can be absorbed by plants/trees and is then transferred to the atmosphere by a process known as transpiration. Water from the soil is evaporated into the atmosphere. These processes are collectively known as evapotranspiration.
Some water in the soil seeps downward into a zone of porous rock which contains groundwater. A permeable underground rock layer which is capable of storing, transmitting, and supplying significant amounts of water is known as an aquifer.
More precipitation than evaporation or evapotranspiration occurs over the land but most of the earth's evaporation (86%) and precipitation (78%) take place over the oceans.
The amount of precipitation and evaporation is balanced throughout the world. While specific areas of the earth have more precipitation and less evaporation than others, and the reverse is also true, on a global scale over a few year period, everything balances out.
World Water Supply by Location
Oceans - 97.08%
Ice Sheets and Glaciers - 1.99%
Ground Water - 0.62%
Atmosphere - 0.29%
Lakes (Fresh) - 0.01%
Inland Seas and Salt Water Lakes - 0.005%
Soil Moisture - 0.004%
Rivers - 0.001%
Only during the ice ages are there noticeable differences in the location of water storage on the earth. During these cold cycles, there is less water stored in the oceans and more in ice sheets and glaciers.
It can take an individual molecule of water from a few days to thousands of years to complete the hydrologic cycle from ocean to atmosphere to land to ocean again as it can be trapped in ice for a long time.
3.0 INFILTRATION
Infiltration - seepage of atmospheric precipitation through a porous aeration zone - is studied for assessing the values of groundwater recharge or natural resources. The intensity of groundwater infiltration recharge is determined by:
(a) climate factors (difference between atmospheric precipitation and evapotranspiration), (b) the nature and degree of topographic relief, which determines the level of natural drainage and the relation between atmospheric precipitation, slope runoff and seepage into the aeration zone, and (c) the geological structure of the territory, i.e. the filtration properties of the rocks constituting the aeration zone, and the depth of groundwater.
Influation is the process of penetrating of atmospheric precipitation into an aquifer by mountain rock fracturing, through karst sinkholes and pores. Infiltration is characterized by a laminar groundwater movement, and influation, by turbulent flow.
The value of infiltration groundwater recharge is determined by filtration properties, the thickness of the aeration zone, the amount of atmospheric precipitation, and its evaporation. It is measured in millimeters of water inflowing into the groundwater for a particular time interval (usually per year, month or recharge period). In its most common form, infiltration recharge can be determined by the following water balance equation: W = P - E - R ± S
where
W -is infiltration
P - atmospheric precipitation
E -evaporation (evapotranspiration)
R -surface runoff and
S -change of moisture storage in the aeration zone
(unsaturated zone).
In a relatively flat landscape, infiltration recharge is concentrated along fissures and in more permeable rock, and also in separate depressions of micro- and macro-relief. In the latter case, during recharge periods dome-shaped elevations of groundwater level are created beneath the depressions. These elevations are later redistributed over the aquifer, to form a leveled curve dispersion.
Groundwater, pumped from beneath the earth's surface, is often cheaper, more convenient and less vulnerable to pollution than surface water. Therefore, it is commonly used for public water supplies. Hydrologists estimate the volume of water stored underground by measuring water levels in local wells and by examining geologic records from well-drilling to determine the extent, depth and thickness of water-bearing sediments and rocks. However, Ground water pollution most often results from improper disposal of wastes on land. Major sources include industrial and household chemicals and garbage landfills, industrial waste lagoons, tailings and process wastewater from mines, oil field brine pits, leaking underground oil storage tanks and pipelines, sewage sludge and septic systems. Hydrologists provide guidance in the location of monitoring wells around waste disposal sites and sample them at regular intervals to determine if undesirable leachate--contaminated water containing toxic or hazardous chemicals--is reaching the ground water.
Groundwater is a critical resource in India, accounting for over 65% of irrigation water and 85% of drinking water supplies. However, on current trends it is estimated that 60% of groundwater sources will be in a critical state of degradation within the next twenty years. In the most seriously affected north-western states, recent satellite measurements indicate an average decline of 33 cm per year from 2002 to 2008.
4.0 AQUIFIERS
An aquifer is a body of saturated rock through which water can easily move. Aquifers must be both permeable and porous and include such rock types as sandstone, conglomerate, fractured limestone and unconsolidated sand and gravel. Fractured volcanic rocks such as columnar basalts also make good aquifers. The rubble zones between volcanic flows are generally both porous and permeable and make excellent aquifers. In order for a well to be productive, it must be drilled into an aquifer. Rocks such as granite and schist are generally poor aquifers because they have a very low porosity. However, if these rocks are highly fractured, they make good aquifers. A well is a hole drilled into the ground to penetrate an aquifer. Normally such water must be pumped to the surface. If water is pumped from a well faster than it is replenished, the water table is lowered and the well may go dry. When water is pumped from a well, the water table is generally lowered into a cone of depression at the well. Groundwater normally flows down the slope of the water table towards the well.
Ground water has to squeeze through pore spaces of rock and sediment to move through an aquifer (the porosity of such aquifers make them good filters for natural purification. Because it takes effort to force water through tiny pores, ground water loses energy as it flows, leading to a decrease in hydraulic head in the direction of flow. Larger pore spaces usually have higher permeability, produce less energy loss, and therefore allow water to move more rapidly. For this reason, ground water can move rapidly over large distances in aquifers whose pore spaces are large or where porosity arises from interconnected fractures. Ground water moves very rapidly in fractured rock aquifers. In such cases, the spread of contaminants can be difficult or impossible to prevent.
Aquifers are natural filters that trap sediment and other particles (like bacteria) and provide natural purification of the ground water flowing through them. Like a coffee filter, the pore spaces in an aquifer's rock or sediment purify ground water of particulate matter (the 'coffee grounds') but not of dissolved substances (the 'coffee'). Also, like any filter, if the pore sizes are too large, particles like bacteria can get through. This can be a problem in aquifers in fractured rock (like the Snake River Plain, or areas outside the sediment-filled valleys of southeast Idaho).
Clay particles and other mineral surfaces in an aquifer also can trap dissolved substances or at least slow them down so they don't move as fast as water percolating through the aquifer. Natural filtration in soils is very important in recharge areas and in irrigated areas above unconfined aquifers, where water applied at the surface can percolate through the soil to the water table.
Despite natural purification, concentrations of some elements in ground water can be high in instances where the rocks and minerals of an aquifer contribute high concentrations of certain elements. In some cases, such as iron staining, health impacts due to high concentrations of dissolved iron are not a problem as much as the aesthetic quality of the drinking water supply. In other cases, where elements such as fluoride, uranium, or arsenic occur naturally in high concentrations, human health may be affected.
Any activity which creates a pathway that speeds the rate at which water can move from the surface to the water table has an impact. Excessive addition of fertilizer, agrichemicals, and road de-icing chemicals over broad areas, coupled with the enhanced recharge from crops, golf courses and other irrigated land and along road ditches, are common reasons for contamination arising from non-point sources.
5.0 PRECIPITATION AND EVAPORATION
Precipitation is any type of water that forms in the Earth's atmosphere and then drops onto the surface of the Earth. Water vapour, droplets of water suspended in the air, builds up in the Earth's atmosphere. Precipitation condenses, or forms, around these tiny pieces of material, called cloud condensation nuclei (CCN).
Precipitation is part of the water cycle. Precipitation falls to the ground as snow and rain. It eventually evaporates and rises back into the atmosphere as a gas. In clouds, it turns back into liquid or solid water, and it falls to Earth again. People rely on precipitation for fresh water to drink, bathe, and irrigate crops for food.
The most common types of precipitation are rain, hail, and snow.
Rain: Rain is precipitation that falls to the surface of the Earth as water droplets. Raindrops form around microscopic cloud condensation nuclei, such as a particle of dust or a molecule of pollution.Rain that falls from clouds but freezes before it reaches the ground is called sleet or ice pellets.
Hail: Hail forms in cold storm clouds. It forms when very cold water droplets freeze, or turn solid, as soon as they touch things like dust or dirt. The storm blows the hailstones into the upper part of the cloud. More frozen water droplets are added to the hailstone before it falls. Unlike sleet, which is liquid when it forms and freezes as it falls to Earth, hail falls as a stone of solid ice. Hailstones are usually the size of small rocks, but they can get as large as 15 centimeters (6 inches) across and weigh more than a pound.
Snow: Snow is precipitation that falls in the form of ice crystals. Hail is also ice, but hailstones are just collections of frozen water droplets. Snow has a complex structure. The ice crystals are formed individually in clouds, but when they fall, they stick together in clusters of snowflakes. Snowfall happens when many individual snowflakes fall from the clouds. Unlike a hail storm, snowfall is usually calm. Hailstones are hard, while snowflakes are soft. Snowflakes develop different patterns, depending on the temperature and humidity of the air.
Global warming also causes changes in global precipitation. When the planet is hotter, more ice evaporates in the atmosphere. That eventually leads to more rainy precipitation. It usually means wetter weather in parts of North America, for example, and drier conditions in tropical areas that are usually humid.
Water is removed from the surface of the Earth to the atmosphere by two distinct mechanisms: evaporation and transpiration.
Evaporation can be defined as the process where liquid water is transformed into a gaseous state. Evaporation can only occur when water is available. It also requires that the humidity of the atmosphere be less than the evaporating surface (at 100% relative humidity there is no more evaporation). The evaporation process requires large amounts of energy. For example, the evaporation of one gram of water requires 600 calories of heat energy.
Transpiration is the process of water loss from plants through stomata. Stomata are small openings found on the underside of leaves that are connected to vascular plant tissues. In most plants, transpiration is a passive process largely controlled by the humidity of the atmospheric and the moisture content of the soil. Of the transpired water passing through a plant only 1% is used in the growth process. Transpiration also transports nutrients from the soil into the roots and carries them to the various cells of the plant and is used to keep tissues from becoming overheated. Some dry environment plants do have the ability to open and close their stomata. This adaptation is necessary to limit the loss of water from plant tissues. Without this adaptation these plants would not be able to survive under conditions of severe drought.
It is often difficult to distinguish between evaporation and transpiration. So we use a composite term evapotranspiration. The rate of evapotranspiration at any instant from the Earth's surface is controlled by four factors:
Energy availability: The more energy available the greater the rate of evapotranspiration. It takes about 600 calories of heat energy to change 1 gram of liquid water into a gas.
The rate and quantity of water vapor entering into the atmosphere both become higher in drier air.
The wind speed immediately above the surface. Many of us have observed that our gardens need more watering on windy days compared to calm days when temperatures are similar. This fact occurs because wind increases the potential for evapotranspiration. The process of evapotranspiration moves water vapor from ground or water surfaces to an adjacent shallow layer that is only a few centimeters thick. When this layer becomes saturated evapotranspiration stops. However, wind can remove this layer replacing it with drier air which increases the potential for evapotranspiration.
Water availability: Evapotranspiration cannot occur if water is not available.
On a global scale, most of the evapotranspiration of water on the Earth's surface occurs in the subtropical oceans.In these areas, high quantities of solar radiation provide the energy required to convert liquid water into a gas. Evapotranspiration generally exceeds precipitation on middle and high latitude landmass areas during the summer season. Once again, the greater availability of solar radiation during this time enhances the evapotranspiration process.
6.0 GLACIOLOGY
Glaciology is the study glaciers, more specifically of ice in the environment. Important components are seasonal snow, sea ice, glaciers, ice sheets and frozen ground. The extent of these types of ice reflects the present and past climate.The large areas covered by snow and sea ice reflect solar radiation away from the Earth's surface and thereby influence the heat balance of the earth.
Because these ice components are only decimeters to meters thick, they can change on time scales as short as seasons and can influence climate at all time scales. Glaciers and ice sheets are hundreds to more than one thousand meters thick and change significantly only on decadal or much longer time scale. On these longer time scales they can influence atmospheric circulation and global sea level. More locally all of these types of ice influence hydrology, geomorphic processes and pose various natural hazards.
Glaciology is inter-disciplinary in its nature as it combines geology, physical geography, geomorphology, climatology, hydrology, biology and has significant ecological impacts.
7.0 ACCUMULATION AND ABLATION
Glaciers grow through a process called accumulation and waste away through a process called wastage, or ablation. Accumulation is the addition of snow and ice to a glacier. There are different processes that factor into accumulation, the most common among them being snowfall directly onto the glacier. Accumulation also occurs when other forms of precipitation such as freezing rain hits the ice mass. A significant amount of accumulation can be attributed to wind-blown snow that settles onto the glacier or snow that flows onto the glacier via an avalanche.
Ablation is the reverse process of accumulation. It means 'the removal of snow or ice from a glacier.' Ablation mostly occurs due to melting of snow during the warmer months of the year, but it can also be the result of wind erosion that blows snow from the glacier. Sublimation, a direct change from a solid to gas can be another cause of ablation. Calving is another form of ablation in which large chunks of ice break off the glacier and fall into the water. Calving gives birth to floating masses of ice called icebergs.
Glaciers are dynamic structures, and they keep changing their form and size. They are said to be retreating if the leading edge of the glacier does not travel as far as it previously did because ablation exceeded accumulation. On the other hand, a glacier is said to be advancing if the leading edge of the glacier moves forward faster than the rate of ablation. Scientists determine if a glacier is retreating or advancing by measuring where the terminus, or leading edge of the glacier, is located. The terminus is sometimes called the snout of the glacier, as if the glacier is being led by its nose.
Knowing the location of the terminus helps scientists determine the glacier mass balance, which is simply the balance between accumulation and ablation. If there is equal balance between these two factors, then a glacier is said to be in equilibrium and it does not change in size.
7.1 Glacial Deposits
Glacial deposits refer to the various means by which materials carried by a glacier can be released from the ice and deposited on underlying surfaces or in surrounding areas. Glacial deposition can occur directly from the glacier itself or from several associated processes involving glacial meltwater. Glaciers can erode, transport and deposit materials that range in size from the finest clay particles to blocks of rock hundreds of metres in size. Thus there is a wide range of glacial depositional landforms in the province, the most prominent of which include eskers, former lake beds, deltas, and various types of moraines from ridged to flat to hummocky plains. Till typically has undergone little or no sorting by meltwater, so the resulting deposit is poorly sorted and contains a wide range of particle sizes, from grains of clay to boulders, jumbled together. The different types of glacial and ice sheet depositions are:
- Glacial flour - rock ground to the texture of a fine powder. It usually flows out of a glacier as sediment in a glacial meltwater stream running from the glacier.
- Till - refers to an unconsolidated and unsorted mixture of sediment, clay, gravel, and rocks deposited by a glacier.
- Moraine - a French word that refers to any glacier-formed accumulation - there are a variety of moraines.
- Terminal moraine - an accumulation at the outermost edge of where a glacier or ice sheet existed.
- Recessional moraine - moraine located "behind" the outermost edge of a glacier, formed when the glacier lingers in one spot for a long time.
- Ground moraine - gently rolling hills and plains deposited by ice.
- Lateral moraine - ridges of till on the sides of a glacier.
- Medial moraine - a moraine formed when two glaciers merge (a tributary and trunk glacier) and their lateral moraines come together to form a single moraine.
- Push moraine - a moraine created by till that was a moraine deposited by an earlier glacier that once covered the area.
- Ablation moraine - a moraine formed from material that fell upon the glacier.
- Glacial erratics - large boulders that had been carried by the ice and deposited. They are much different in size than surrounding till.
7.2 Glacial Movements
Glaciers can move more than 15 meters a day. The factors which control glacial flow, velocity and motion are
- Ice geometry (thickness, steepness),
- Ice properties (temperature, density),
- Valley geometry,
- Bedrock conditions (hard, soft, frozen or thawed bed),
- Subglacial hydrology,
- Terminal environment (land, sea, ice shelf, sea ice), and
- Mass balance (rate of accumulation and ablation).
Glaciers in temperate zones tend to move the most quickly because the ice along the base of the glacier can melt and lubricate the surface. The larger volumes of ice on steeper slopes move more quickly than the ice on the more gentle slopes farther down the valley. The various types of glacial movements are
- Internal Deformation (Plastic flow)
- Basal Sliding and
- Soft bed subglacial deformation
Internal deformation: If the glacier flows just by internal deformation, then it is likely that rates of creep decrease with depth, with fastest ice movement at the surface and slowest (or no) ice movement at the base and at the valley sides, where resistive stresses are highest. Ice deforms because it is plastic. If large stresses are applied it can crack in a brittle manner (forming crevasses or calving ice bergs). Plastic flow causes glacial ice buried underneath more than about 50 meters to move like a slow?moving, plastic stream. The central and upper portions of a glacier, as do those portions of a stream, flow more quickly than those near the bottom and sides, where friction between the ice and valley walls slows down the flow.
Basal sliding: Glaciers can slide because ice melts under pressure, resulting in a film of water at the ice-bed interface. This can facilitate decoupling and enhance fast ice flow. If the glacier bed is rough, with many bumps and obstacles, this increases melting and ice flow. This process is known as regelation. If water pressures become high enough, cavities can form at the ice-bed interface, causing sliding with bed separation. This reduces basal friction and allows faster ice flow. Sliding velocity is controlled by basal shear stress and effective pressure, which is the difference between ice overburden pressure and water pressure the entire glacier moves as a single mass over the underlying rock surface. The pressure from the weight of the glacier generates a layer of water that helps the ice glacier move downslope. This process is called basal sliding.
Soft bed subglacial deformation: Subglacial till is the deposition of sediments of unsorted glacial till. Fine sediments, such as clay and sand, are not cohesive and therefore deform readily when shear stress is applied to them if they have a high pore-water pressure (so, like basal sliding, subglacial deformation depends on high basal water pressures). If basal shear stress (the gravitational driving dress) is greater than the yield strength of the till, deformation occurs, resulting in glaciotectonic movements.
8.0 GLACIATION AND THE HIMALAYAS
After Antarctica and Africa, the Himalayas have the third largest deposit of ice and snow in the world. The Himalayan range encompasses about 15,000 glaciers, which store about 12,000 km3 (3000 cubic miles) of fresh water. Its glaciers include the Gangotri and Yamunotri (Uttarakhand) and Khumbu glaciers (Mount Everest region), Langtang glacier (Langtang region) and Zemu (Sikkim). The Himalayas have a profound effect on the climate of the Indian subcontinent and the Tibetan Plateau. They prevent frigid, dry winds from blowing south into the subcontinent, which keeps South Asia much warmer than corresponding temperate regions in the other continents. It also forms a barrier for the monsoon winds, keeping them from traveling northwards, and causing heavy rainfall in the Terai region. The Himalayas are also believed to play an important part in the formation of Central Asian deserts, such as the Taklamakan and Gobi.
Siachen Glacier: The Siachen glacier is located in the extreme north-central part of Jammu and Kashmir near the India and Tibet border. It stretches to a length of about 72 km; it is the largest glacier in the world outside the Polar Regions. Siachen is situated on the north-facing slopes of the Karakoram Range. It is the source of the Mutzgah or Shaksgam River that flows parallel to the Karakoram Range before it enters Tibet. The central part of Siachen glacier is a vast snowfield. It mainly lies in a vast trough, which is about 2 km wide and scattered with rocks and boulders on its sides. Large tributary glaciers like the Mamostang and Shelkar Chorten open into the main glacier from both sides of its trough. Numbers of icefalls are formed at the meeting point of trunk glacier and small valley glaciers. A group of three glaciers i.e. North, Central and South lies to the east of the Siachen. It is known as the Rimo glacier group. The altitude of this glacier is between 6,000 and 7,000 m above sea level. The Siachen glacier can be traveled via Skardu in Ladakh.
Baltoro Glacier: Baltoro glacier is located in Jammu and Kashmir in an area called Baltistan on the southern slopes of the central Karakoram Range. It stretches to a length of 62 km. It is the second largest glacier in the Himalayan region. Shigar River, which is a tributary of the Indus River, originates from this glacier. Other large tributary glaciers supply the main Baltoro glacier. The central part has a vast snowfield and the trough of this glacier is very wide. This glacier can be accessed via Skardu in Ladakh.
Biafo Glacier: Biafo glacier is located in Ladakh, Jammu and Kashmir in an area called Baltistan on the south slopes of the Karakoram Range. It stretches to a length of 60 km. The main stream, which originates from Biafo glacier flows into a tributary of the Indus River called the Shigar River. In this area there is no vegetative cover.
Hispar Glacier:In the Himalayan region Hispar glacier is the third largest glacier. It is located in Ladakh, Jammu and Kashmir on southern slopes of the Karakoram Range. It stretches to a length of 60 km. There is no vegetation of any kind in this area. Many small glaciers join the main glacier on both sides. The central part of the glacier is a vast snowfield while its sides contain debris eroded by the huge body of moving ice.
Nubra Glacier: The Nubra glacier is located in Ladakh, Jammu and Kashmir on the southern slopes of the Karakoram Range. Nubra River originates from this glacier flows into the Shyok River. Just like the other glaciers the central portion of the glacier forms a vast snowfield. Vegetation is totally absent in this area as it lies above the snow line. The place can be access via Leh in Ladakh.
The other glaciers in Uttaranchal regions are:
- Bandarpunch Glacier
- Dokriani Glacier
- Chorbari Bamak Glacier
- Khatling Glacier
- Doonagiri Glacier
- Tiprabamak Glacier
Seasonal meltwater from the Himalayan glaciers is one of the main sources of freshwater reserves that directly sustain people living in the region, especially in arid and semi-arid areas. At varying degrees and times, about 1.3 billion people living in the Himalayan river basins rely on both meltwater and monsoon waters to sustain their livelihoods, mainly for irrigation, drinking, sanitation and industrial uses (9, 46, 33). Net irrigation-water demand is high in this region, but per capita water availability is very low-around 2000 to 3000 m3/capita/year-which is farless than the world average of 8 549 m3/capita/year)
Ground-based studies on monitoring of the Himalayan glaciers require enormous effort in terms of time and logistics due to lack of atmospheric oxygen in high altitudes, trekking in rough terrain and cold climatic regimes. Despite these difficulties, the efforts made by many expedition teams have led to the generation of vital information on the fluctuations of Himalayan glaciers in terms of mass balance or simply snout monitoring. Remote sensing is another technique that has been used.
According to a study published in Nature Climate change in 2012, a majority of glaciers in the Tibetan Plateau and the surrounding regions are retreating. The Tibetan Plateau and surrounding regions contain most of the world's glaciers outside the polar region. The total glacier area in this region is 100,000 square kilometres. The most intensive shrinkage is found in the Himalayas (excluding the Karakoram). Here the reduction is greatest both in terms of length and area, and also the difference between ice accumulation and loss (mass balance). In contrast, the least reduction is seen in the Pamir Plateau.
These results however contradict the Tibetan Plateau glacier loss results provided by the GRACE satellite. The Gravity Recovery and Climate Experiment satellite measurements found the glaciers in the Tibetan Plateau were actually growing, and Asian glaciers, in general, were losing ice much slowly than previously suggested.
According to the Nature Climate Change paper, the rate of shrinkage of Himalayan glaciers (southeastern Tibetan Plateau) in terms of length was 48.2 metres per year and the rate of area reduction was 0.57 per cent per year during the study period (1970s to 2000s). The mass balance was negative (meaning more ice loss), and it ranged from -1,100 mm per year to -760 mm per year with an average of -930 mm per year. In the case of the Pamir Plateau, the rate of retreat was just 0.9 metres per year and area reduction rate was 0.07 per cent per year. What is really significant is that the Muztag Ata Glacier in the eastern Pamir region had a positive mass balance for four of the five years of observation.
8.1 Causes
There is a direct link between atmospheric circulation, and in turn precipitation, and glacier shrinkage. The reason for intensive glacier shrinkage in the Himalayas can be traced back to the circulation pattern, and in turn the amount of precipitation.
The Himalayas gets its precipitation from the Indian monsoon, while the Pamir Plateau gets it from the westerlies.
Records confirm that the precipitation during the period 1979 to 2010 decreased in the Himalayas while it increased in the case of eastern Pamir Plateau. Moreover, the Indian monsoon is weakening and the westerlies are strengthening which influences the precipitation patterns. This has resulted in greater shrinkage of glaciers in the Himalayas, while the Pamir Plateau shows the "least reduction in length and area, and positive mass balance (meaning increased ice accumulation).
Temperature rise also affects glacier shrinkage. According to the report, An increasing warming trend at higher elevations has been observed over the Tibetan Plateau and the warming rate increases with elevation. The warming to be "highest between 4,800 metres and 6,200 metres above mean sea level. In places dominated by the westerlies, such as the Karakoram and the Pamir plateau, glaciers gain their mass mostly from winter snow, and so are less affected by warming because temperatures in winter are still below zero. In the eastern and central Himalayas, however, it snows mainly during monsoon season, and a slight increase in summer temperatures can affect glaciers drastically.
8.2 Effects
Due to global warming, the Indo- Gangetic basin of the Indian subcontinent, where water supply is dominated by melting snow and glacier ice, will be faced with severe environmental problems. Negative impacts, including seasonal shifts in water supply, fl ood risks and increased precipitation variability, will eventually offset benefi ts incurred by shortterm increases in runoff from glacier melt. Tibetan ice-fi elds and glaciers are critical resources for one sixth of the world's population because they sustain dry-period low flows for major rivers, such as the Indus, Ganges and Brahmaputra Rivers, in the south western Himalaya. The Indus and Ganges Rivers currently have little outflow to the sea during the dry season and are in danger of becoming seasonal rivers due to climate change and increased water demand. The surface area of glaciers across the Tibetan Plateau is projected to decrease from 500,000 square kilometres measured in 1995 to 100,000 square kilometers in 2030, thereby threatening regional rivers and water resources. Himalayan glacier melt water surpluses which include high altitude thinning of ice fields in western Tibetan Plateau are likely to shrink much faster than currently predicted, with substantial consequences for approximately a billion people. With glacial and snow retreat, many of the semi-arid mountains, inhabited by some 170 million people, will lose several of their local springs and streams, so essential to villages and livestock grazing. In addition, increasing fl ash fl oods and rockslides degrade roads and trails.
The Indian National Action Plan on Climate Change addresses the urgent and critical concerns of the country through a directional shift in the developmental pathways. It identifies measures which will promote developmental objectives while addressing issues relating to climate change efficiently and effectively. The Himalayan ecosystem is one of its eight missions with a long-term approach and well defined time-lines for achieving the goals of the Action Plan. The ecologically sensitive Himalayan mountain system is prone to adverse impacts of climate changes on account of anthropogenic emissions of Green House Gases and developmental activities of the region.
The Himalayas have a large area with perennial snow cover and the largest concentration of glaciers outside the Polar Regions. The glaciers provide around 8.6 x 106 cubic metres of water annually. There is global concern that glaciers are receding at faster rates on account of climate change and global warming.
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