E-Kantipur

Water is a precious gift of nature, essential for human survival. Water is required for basic human needs such as drinking, cooking and bathing, for irrigation to grow crops, for hydropower to produce energy, for industry and for the environment. Water is also an inherent component of an ecological chain on which all life-supporting systems depend. Especially for the Nepali society water from the mountains also has an important cultural and spiritual significance.

Therefore, any change in the hydrological system and water resources could have a direct effect on society, environment and economy. There are very complex relations between climate, hydrology and water resources. Climatic processes influences the hydrological processes, vegetation, soils and water demand. Because of this, any change in climate may put serious pressure on hydrological systems and water resources. 

From various studies it is found that the changing climate will have significant impacts on the availability of water, as well as the quality and quantity of water that is available and accessible. Besides, rising global temperature will lead to an intensification of the hydrological cycle, resulting in dryer dry season and wetter rainy season, and a subsequently heightened risk of extreme and frequent floods and droughts, which is already evident in Nepal’s monsoon-dominated climate. Almost every year in Nepal, there is a usual problem of landslides and floods during the rainy season because of the too much water, whereas there is common problem of drought during the dry season because of too little water. Hence, climate change would further increase this seasonal imbalance of water in Nepal.

Climate experts have warned that Himalayan water resources will dry up within some years as the glaciers are retreating rapidly due to increasing green house gas emissions. It has been discovered that almost 67 percent of Himalayan glaciers have retreated in the past decade. For example, the Rikhasambha glacier in Nepal’s Himalayas has retreated by 300m during 1974-1999, whereas it retreated by 51m per year in 1998-99.  Similarly Imja glacier in Khumbu region is retreating at the rate of 74m per year while within 30 years the Khumbu glacier has retreated over five kms. If this trend continues, there will be no glaciers left in Nepal’s Himalayas by 2080. This continued retreat of glaciers will have many quantitative impacts. In areas that are heavily dependent on water runoff from glaciers that melt during warmer summer months, a continuation of the current retreat will eventually deplete the glacial ice and reduce or eliminate runoff. A reduction in runoff will affect the country’s ability to irrigate crops and will reduce summer season flow necessary to keep reservoirs replenished.

The melting of glaciers has become a serious concern in the Himalayan region because of the growing risk of glacial lake out-burst floods (GLOFs). The biggest damage due to GLOF was recorded in Nepal in 1985. This GLOF caused a 10-15m high surge of water and debris to flood down the Bhote Koshi and Dudha Koshi rivers for 90 kms. At its peak, 2,000 cubic metres per second of water was being discharged, two to four times the magnitude of maximum monsoon flood levels. It destroyed the almost complete Namche small Hyde-l Project, which at the time cost approximately Rs. 45 million. Twenty-one GLOF events have adversely affected Nepali territories in the recent past and to date 20 potentially dangerous glacial lakes have been documented. While this only provides a picture of static risk, site-based monitoring of specific glacial lakes has shown evidence of increasing lake volumes over time. This trend in increasing lake volume correlates with observed trends in temperature increases at high altitude in the Nepal Himalayas.

Globally, the number of devastating inland floods has doubled in the last decade (1996-2005) as compared to the three decades between 1950 and 1980, while related economic losses have increased by a factor of five. Even in Nepal, analysis of 24-hour rainfall events exceeding 100mm in the June-October period for the years 1971-1980 and 1980-1990 has indicated an increasing trend of hazardous rainfall events in Nepal. The flood catastrophes of 1993, 1998 and 2008 are in agreement with the increasing trend of hazardous rainfall.

In 1993, about 28,000 people in mountain areas and 42,000 people in the lowland were affected. About 160 people in the highland and over 1,000 people in lowlands were killed due to devastating flood and landslides in the Bagmati, Kulekhani and Narayani basin. Even in 1998, in Syangja, high intensity rainfall caused catastrophic floods with water levels reaching up to 6.2 m, killing 55 people and destroying 640 houses.

From 2000 onward, Nepal has had regular floods during rainy season. Among them the devastating flood of 2008 displaced millions on either side of the Nepal-India border, leaving thousands dead, after the Kosi River broke its banks in Nepal. On the other hand, the most severe projections (due to climate change) for Nepal show that runoff could reduce by 14 percent. This would not only reduce the electricity generation of existing plants but also affect irrigation systems, power grain mills and the drinking water supply. Besides, this runoff decrease will affect Nepal’s economically feasible hydropower potential; however, with only 1-2 percent of that potential currently developed, it will be quite some time before opportunities to expand the hydropower supply are constrained by climate change.

Several studies around the globe have shown the demand for water increasing tremendously due to an increasing population, expanding agriculture, rapid urbanisation, and economic development. Simultaneously, unplanned development of surface and ground water resources, haphazard disposal of municipal and industrial wastes and application of agricultural inputs has led to the problem of water quality deterioration and pollution, presenting new challenges to water management and conservation. Today, in most ecological zones and river basins of Nepal the hydrological cycle is being modified quantitatively and/or qualitatively by human activities such as changes in cropping pattern, land-use pattern and over exploitation of water storage, irrigation and drainage.

Sustainable water management and greater support for the environment should be among the country’s top priorities in the next few years. Towards this end, it is important

to assess the available water resources in the context of future national requirements and include the anticipated impact of climate change in national and regional long-term development strategies.

(Upadhyay is a professor at the Central Department of Environmental Science, Tribhuvan University)

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