Is the sea level rising due to the use of groundwater and irrigation?

Answer

Dear Joseph

The drying up of large lakes and inland seas and in particular the large-scale consumption of fossil groundwater for irrigation and consumption makes a significant contribution (20-25%) to the current rise in global sea level of 3 mm/year. According to recent calculations (2012), the sea level rise due to groundwater abstraction would explain 0.6 mm/year and thus about 20% of the annual rise. Researchers expect this factor to increase to 0.8 mm/year over the next 30 years. The contribution of the drying up of the Aral Sea and other lakes is rather limited (by the way, the construction of reservoirs also hinders this process somewhat). This can be estimated approximately: the surface of all oceans and seas is approximately 360,000,000 km². To raise the sea level worldwide by 1 cm, there is therefore an extra amount of water of about 3600 km³ need water. In 1960, the Aral Sea contained about 1,100 km³ water. If the lake were to dry up completely (which is already 80%) that would add a total of about 3 mm to the global sea level. Incidentally, something is added to this as a result of the simultaneous fall in the groundwater level around the Aral Sea. By comparison, the Caspian Sea – the world’s largest closed inland sea – contains about 70,000 km³ water and would add ‘only’ about 20 cm of sea level if it dries up. It is unlikely that this will happen anytime soon, although the Caspian Sea has been a lot smaller than it is now on several occasions in the last 10,000 years.