With global warming and the consequent melting of the freshwater polar caps and glaciers, it may seem counterintuitive to say that this world climate change will exacerbate the problem of scarcity of freshwater supplies in many countries. A United Nations Environment Programme report says that by 2050, scarcity would have jumped from 3% in 1995 to 18% (see pie chart above).
Why is this so? In a nutshell, this is because in general, global warming accelerates the hydrological cycle. Warmer air causes more water to evaporate. A warmer atmosphere can hold more water vapor, so more water is available to fall back to Earth when it rains or snows. As a result, extreme precipitation events should become more frequent and intense. Rainfall patterns will continue to change around the world. Computer models project that, as warming progresses, the temperate regions as well as Southeast Asia will receive more precipitation. Ah, so you say, we expect to have more water then, not less. Not so fast: because of the changes in the hydrological regime, when it rains, it will really rain (and cause severe floods, like our friends in Kinabatangan, Kota Belud and Kota Marudu only know too well) but the droughts will be longer. You know, like 4 months already this year in Sabah. In addition, the rise of the sea level will impact on our coastal freshwater supplies by saltwater intrusion.