Download full report in pdf format - Natural Resources Institute

Box 17. Water-related myths
Water-related myths that were found to be relatively common during the Water Audit
included:
. Water harvesting is a totally benign technology. Although water harvesting technologies
can produce huge benefits, intensive drainage line treatment, in particular, can
significantly reduce water resource availability to “downstream” communities. In some
cases, this negative trade-off does not matter; in others, severe hardship can result.
. Planting trees increases local rainfall and runoff. The reality is that forests exert a
small, almost insignificant influence on local rainfall and, notwithstanding a small
number of exceptions, catchment experiments generally indicate reduced runoff from
forested areas as compared to those under shorter vegetation.
. Runoff in semi-arid areas is 30-40% of annual rainfall. Although localised runoff and
runoff from individual storms can be high, annual runoff at the micro-watershed
scale (or greater) in semi-arid areas tends to be much lower than 30-40%.
. Rainfall has decreased in recent years. With few exceptions, studies of long-term
rainfall records, that have used data from a single set of rain gauges, have not shown
a significant decrease (or increase) in mean annual rainfall.
. Aquifers are underground lakes. The reality is that check dams and other waterharvesting
structures usually only have localised impacts on groundwater levels and
aquifers rarely behave like underground lakes. Or put another way, localised recharge in
one place rarely leads to an immediate rise in groundwater levels many kilometres away.
. Water use of crops depends mainly on crop type. A common misconception is that the
daily water use of crops is directly related to the crop type and that evaporation rates are
many times higher from some crops as compared to others. The reality is that, assuming
that a crop is well supplied by water and has a full canopy (i.e. the crop completely
shades the ground), the daily rate of evaporation is driven primarily by the
meteorological conditions (e.g. radiation, wind speed, dryness of the air).
. Aquifers once depleted stay depleted. A pessimistic view of aquifer depletion is that this
is an irreversible process. The reality is that, in most cases, aquifers can be re-established
or replenished as long as the balance between recharge and extraction is swung towards
recharge. This can occur as a result of increased recharge, decreased extraction or both.
6.2 Water-related risks
Experience in the region has shown that there
are a number of water-related risks associated with
watershed development and with the source
protection measures implemented as part of rural
water supply programmes. These
include:
. Increased borewell construction and
increased irrigation by individual
landowners: In most cases, the prime
motivation of farmers to become involved
in soil and water conservation programmes
and the construction of water
harvesting structures is not altruistic. It is
to increase the water resources that are
available to them for irrigation.At the
watershed scale, this is justified only if the
resources that are being “harvested” do not
have a higher value if they are put to
other uses.
· Increased borewell construction and
increased irrigation by “poor” landowners:
Successful watershed development projects
often improve the financial status of
relatively poor farmers such that they are
able to take loans for constructing
borewells and installing pumps. As above,
this is fine as long as the water they
“harvest” does not have alternative
higher-value uses (e.g. as a source of
domestic water supply).
74