# water availability module (43_water_availability)¶

## Description¶

The water availability module determines the water that is available in MAgPIE. The following water sources are currently implemented: surface water, groundwater, technical (like desalination etc). Additionally, this module hosts the main water constraint that requires water withdrawals to be smaller or equal to available water. Information is passed to and received from the 42_water_demand module.

## Interfaces¶

### Input¶

Name Description Unit A
vm_watdem Amount of water needed in different sectors mio. $m^3$ x

The last columns of the table indicate the usage in the different realizations (numbered with capital letters)

### Output¶

Name Description Unit
im_wat_avail Water availability mio. $m^3$

### Interface plot¶

Figure 0: Information exchange among modules.

## Realizations¶

### (A) total_water_aug13 (default)¶

Calculation of available water
The calculation of available water as described below happens in the MAgPIE preprocessing. See lpj2magpie for further details.
This realization only considers renewable water resources, i.e. runoff generated from precipitation. All runoff is assumed to enter rivers, neglecting groundwater recharge. Other water resources such as fossil groundwater, discharge from melting glaciers or desalination are also not considered.
The calculation of available water per grid cell is based on LPJml1 simulations. For each river basin, total annual runoff in the basin constitutes the amount of water available in one year. Irrigation water can however only be supplied to the plants during their growing period. In order to account for that in MAgPIE, we calculated for each grid cell the mean growing period over all crops based on LPJml1 sowing and harvesting dates. Some data has been excluded from the calculation:
• Winter crops in the northern hemisphere (sowing date later than June 29th and harvest date later than December 31st) because we assume that irrigation does not take place during winter time.
• Data points with crop yields below 10% of the world average yield. Such a low yield indicates that the site is not appropriate for this specific crop and the LPJml1 growing period simulation is likely to be distorted.

Water available for irrigation in each basin thus only consists of the total runoff occurring in the mean growing period in all basin cells except for cells where water storage in terms of dams is present (taken from Biemans 20112). In this case, total annual runoff is available.

The distribution of basin runoff in the growing period to the individual grid cells is done using LPJml1 discharge as a weight.

There is an interface to the 42_water_demand module. If exogenous non-agricultural water demand exceeds available water - which can happen in the water_demand "detailed" realization - the missing amount is available from groundwater to avoid infeasibility.

Water constraint

The water constraint, $q43\_water(j)$, assures that, in each cluster, the sum of water withdrawals in all sectors ($vm\_watdem(wat\_dem,j)$) does not exceed available water from all sources ($v43\_watavail(wat\_src,j)$):

$\sum\limits_{wat\_dem} vm\_watdem(wat\_dem,j) \le \sum\limits_{wat\_src} v43\_watavail(wat\_src,j)$

Limitations
There are currently no known limitations of this realization

## Definitions¶

Name Description Unit A
$v43\_watavail(wat\_src,j)$ Water availability from different sources mio. $m^3$ x
$f43\_wat\_avail(j)$ Surface water available for irrigation per cell mio. $m^3$ x

The last columns of the table indicate the usage in the different realizations (numbered with capital letters)

## Developer(s)¶

Anne Biewald, Markus Bonsch