The capital of Peru, Lima, with a fast growing population exceeding 8 million, considered as a megacity, has to draw a major part of its water supply from the River Rimac. Due to very dry conditions (average annual rainfall of 9 mm) and large seasonal variations of river flow, also groundwater is being used as a source of water supply. Groundwater abstraction is in excess of the resources available. 

Perhaps the most dramatic effect of climate change is the variation of the hydrological cycle. This includes the melting of glaciers, rising sea-levels and significant changes in temperature and precipitation patterns throughout the world (IPCC, 2007). The situation in regions that already suffer from extreme water scarcity will further aggravate. One of the areas most seriously affected by climate change are the Andean countries: The Tyndall Centre for Climate Change Research states that Peru is the third-most sensitive country when it comes to impacts of climate change on precipitation and water availability (Rosenberger, 2006). The shortage of water is expected to be even more severe due to mayor intensity and frequency of the El Niño / Southern Oscillation phenomenon. These impacts of climate change are felt not only in the mountainous regions, but far more so in the large conurbations which are characterised by huge demands on water resources. The Metropolitan region of Lima and Callao in Peru is a particularly significant example of a conurbation heavily dependent on water.

Yuracmayo lake in the mountains of Lima (4355 m ASL). Photo: C. León 2011

The Metropolitan area of Lima and Callao is characterised by a number of features typical of emerging megacities, such as:

• Today, Lima has about 8,5 million inhabitants. Due to the large number of informal settlings in peri-urban areas (Asientamientos Humanos), this number is characterised by some uncertainty.
• High population growth (annual growth rate of 2 %), in particular due to an influx of poorer people, putting an additional pressure on those parts of Lima lacking appropriate supplies of electricity, water and sanitation.
• The population of Lima covers all social levels of society. In 2007, 18 % of its population were living in severe poverty. 
• Irregular water supply due to arid climate (only 9 mm annual mean precipitation) and irregular flow characteristics (significant seasonal rainfall variations in the Andean mountains, which serve as the main source of water supply).
• Polarisation between poor and rich districts, conflicts about basic resource availability, high social mobilisation potential when policies are regarded as unfair or putting further burdens on the poor

The diversity of the various parts of Lima also results in the fact that, for different parts of the city, potentially different solutions (e.g. for wastewater treatment technologies) out of the multitude of potential solutions might be optimum. Therefore, locally conducive solutions have to be found, which, at the same moment, also contribute to an overall favourable water management concept.

With regard to water supply and sanitation, Lima is characterised by the following: At present, the water supply network covers 80,6 % of the population of Lima, leaving 19,4 % of the population (mainly in the hilly parts of the town) without access to the drinking water network. About 77 % of the population is connected to the public sewer network. Only about only 17 % of the wastewaters receive some form of treatment. The major part of wastewater is discharged either in the rivers or directly into the Pacific Ocean, only 5 % of the treated wastewaster is reused for irrigation.

Strong interactions with the energy system lie not only in the inherent need for energy for water pumping and wastewater treatment (with important implications on operational costs), but even more so in the joint use of reservoirs (affected by climate change and with conflicting usage patterns) for water supply and for energy production.

The table below shows that, in difference to other southamerican megacities, Lima has severe problems in respect to availability of water resources for drinking purposes.

City	Population (Mill.)	Water production (m3/s)	Water reserves (Mill. m3)	Reserves per capita(m3/inh.)	Precipitation (mm/year)	Non-revenue water (%)
Rio de Janeiro	9	52	(*)	0	1170	57
Sao Paulo	25	90	2073	83	1500	37
Santiago de Chile	5.9	24	900	153	384	29
Bogotá	6.5	25	800	123	800	35
Lima	8.6	20	282	33	9	35

* has no problems with water sources because of large river flow and high precipitations.
Source: Annual Reports of main Water and Sanitation Companies of South America.