Melting Himalayas: Flood and freshwater shortage

Though melting at Arctic sea is a serious issue, melting at Himalayas is more concerned by public. Himalayan mountains contain 40% of freshwater over the world and thousands of glaciers, and they are the source of the seven greatest rivers in Asia. 20% of the world’s population rely on Himalayan glaciers as water sources. Large proportion of glaciers here are fed by snowfall from summer monsoon, however, global warming reduces precipitation from monsoon and extends melting period (Bolch et al., 2012). This leads to many serious problems. There is a nice video called “Himalayan Meltdown” introducing these problems. I just put its trailer here for you to get a feel for how serious the melting at Himalayas is.

One major issue threatening Asia is glacier lakes. Melted water forms thousands of glaciers lakes in the region, and water in glacier lakes can accelerate melting rate via transmit heat efficiently to glacier in contact with glacier ice (Bolch et al., 2012). Meanwhile, many of these lakes are likely to burst at the seams. For example, Glacial Lake Outburst Floods (GLOFs) Assessment (2010) identified  more than 200 lakes in the region likely to burst. When they burst, villages at downstream are threatened and may destroyed  by floods. Governments put a lot of effort into reduce the water level of glacier lakes. Bhutan Government had successfully reduced water level of Lake Thorthormi. However, this is not a permanent solution as long as glaciers keep melting and feed the lake. 

Another problem is drought. Since global warming reduces precipitation from seasonal monsoon, the proportion of runoff based on glacier melted water increase (Bolch et al., 2012). When glacier dries up, there will be serious issues in water supply. According to the video, some villages have faced water shortage. Downstream discharge is significantly affected by upstream discharge. Immerzeel et al. (2010) used A1B SRES scenario to simulated mean upstream discharge (Figure 1), and found decreases in major Asian rivers. They concluded that 4.5% of the total population will have food security problem due to decreasing water supply.

Figure 1. Simulated mean upstream discharge.