**1. Introduction: Era of climate change**

The surface water has been the cradle of civilisations since the beginning of human history. The social and economic well-being of human beings is directly affected by availability of fresh water. The use of water in domestic, agriculture as well as industrial sector has increased the stress on fresh water. The major fresh water sources, the rivers, are turning into water bodies unfit for proper use. The pollutants have also reached the groundwater and contaminated the clean water source. Climate change is another threat posed on the availability of fresh water. Change in the climate during the last few decades is described by the changes in variables of climate such as temperature, humidity, wind velocity etc. in different parts of the world. This climate change is caused by the warming of the earth's atmosphere as a result of increasing greenhouse gas (GHG) emissions, change in land-use pattern and emission of aerosols and other pollutants through various anthropogenic activities. Thus climate variability in a particular region may be observed at hourly and daily basis in addition to monthly, seasonally, annually and decadal variability [1].

Climate change will cause significant impact on our water resources since it is directly related to changes in patterns of precipitation. The effects of climate change are already visible in many parts of the world. Many countries in the world are negatively affected by the impacts which range from increased frequency and intensity of floods and droughts, severe water scarcity, increased intensity of erosion,

retreating glaciers, sea level rise, decreasing snow cover, increased sedimentation in water bodies, deteriorating quality of water and damaged ecosystems [2]. The impact of climate change on surface waters, as studied for Moldova, East Europe, has shown increase in temperature and precipitation from 1945 to 2011. The annual average temperature was predicted by climate models to increase by 2°C between 2010 and 2039, and up to 3°C by next thirty years. However, the predictions for precipitations indicated that total amount of precipitation could decrease steadily or remain stable by the end of the century, with seasonal variability [3].

The human populations are exposed to various climate change related risks. The modifications of climate often result in unpredicted cyclones, storms, floods, droughts and heat waves and with increased intensity. The water availability in surface water bodies get altered as a consequence; modified river flow regime and altered ground water recharge play a significant role. Indirect effects of changing climate causes siltation of reservoirs, coastal floods and salt-water intrusion in coastal aquifers are most common occurrences (**Figure 1**). These various factors are interrelated and they affect the human population intensely and in most unpredictable way [1]. Various sectors which directly depend on water resources, such as agriculture, hydropower, navigation etc. are getting affected and have devastating societal impacts like effects on health of large scale of population and economy of many countries [2].

#### **1.1 Extreme events**

Extreme events have caused major disasters in many parts of the world in last couple of decades. A stronger link is detected between the changing weather patterns and warming of the atmosphere. Extreme heat and drought with changing seasons are being experienced in many tropical and sub-tropical regions. The number of flood disasters have increased several times [4]. Storms and flash floods have increased frequency in mountainous regions [4, 5]. In tropical and sub tropical regions, the event of extreme rainfall is anticipated on land because of increasing convective activity during summer monsoon. Warmer atmosphere facilitates heavy moisture bearing clouds and rainfall is intensified. Extensive and continuous rainfall have triggered disastrous effects such as landslides, subsidence and submergence under water. The annual flows would become more unstable, spring and flash floods will become more common and increase the peak flow [3]. The run-off is expected to increase in many parts of the world. Increased snowfall and frigid weather are also linked with moisture in the warmer atmosphere. The non-climatic factors of human actions have exposed and increased the vulnerability, making these regular events more hazardous. The geographical location and socio-economic dynamics play a very important role in turning extreme events into disasters.


#### **Figure 1.**

*Climate change impacts on flow of surface water (adapted from UNECE guidance document).*
