4. But now at the beginning of the
21st century the situation is quite different:
In many semiarid regions of the world population growth is putting pressure
on water supplies for drinking water, for animals and for agriculture.
Agriculture and water projects based on high energy input and sophisticated
technology appear more and more unsustainable.
At the same time, old re-approved or new technologies and / or modern
materials made it possible to have a new approach to the construction
of storage tanks and catchment areas.
All this led to a new expansion of rainwater harvesting systems both in
regions where they had been used as well as in areas where they have been
unknown until now.
Once again some examples to illustrate this point:
In the loess plateau in the North and Northwest of China where rainfall
is low and groundwater is very scarce people have been experimenting a
lot with rainwater harvesting. Agriculture in this region relies mainly
on rain as water source. In the last years, the local government of the
Gansu Province implemented a so-called "121" rainwater catchment
project: the government supported each family to build one (1) water collection
field, two (2) storage tanks and one (1) land to plant cash crop. The
project has successfully settled the drinking problem for 1.3 million
people (260,000 families) and their 1.18 million livestock. Since 1997,
a rainwater catchment and irrigation project has followed up, aiming to
supply water for supplemental irrigation with a high efficient water saving
method. The rainwater is collected on the courtyard (Fig.
4) or slope field lined with concrete slabs and stored
in the underground tanks. It is easy to create a water pressure for pipe
or drip irrigation in this region. Cash crops such as vegetables, medical
herbs, flowers and fruit trees as well as nurseries were planted. Farmers
in the northern mountainous area of Yuzhong county have been very delighted
about the vegetables grown in their own greenhouses, irrigated by rainwater
tanks. This is the first time in history that greenhouses are built to
grow such vegetables as pepper, eggplant, tomato and squash at an elevation
of 2,300 m above sea level and with only 300 mm of annual precipitation.
Rainwater harvesting has become a strategic measure for the social and
economic development in this semiarid region.
In the semiarid region of Brazil, agriculture has been introduced only
in the recent past. The local population had no possibility to experience
with rainwater harvesting methods much less a possibility to learn how
to live and work in a semiarid climate. But now, especially due to population
growth and environmental degradation, people have to learn how to live
in this rural semiarid region extending over 900 000 km². Reliable
surface water is supplied for a very small area by the San Francisco River
and the groundwater in the mostly crystalline subsoil is scarce and saline.
Therefore rainwater is the most reliable source of water for humans and
From experiences of the past and from other semiarid regions we learned
that the sustainability of water harvesting systems is based on the combination
of the basic needs of the farmers, the local natural conditions and the
prevailing economic and political conditions of the region.
The people learn to live in a semiarid region by creating a new culture
of relation to the environment and to water. This new relationship to
the environment and water has been particularly fostered by the many grassroots
organizations in the region. Nevertheless, there are still big irrigation
projects underway along the Sao Francisco River. Large companies are planning
to irrigate large areas to raise cash crops for export.
Three main topics were developed geared at guaranteeing peoples' sustainable
living in Brazil's Northeast:
- Climate and water management: How does the semiarid climate work and
what consequences does it have for agriculture. Establish preventive measures
such as rainwater harvesting in order to have water reserves for the dry
- Animal husbandry: Provisions for keeping small animals, especially sheep
and goats, adapted to the semiarid climate. Storing of water and fodder
for the dry months, de-worming, etc.
- Water harvesting agriculture: catch run off to have crops even in years
with poor rainfalls; planting drought resistant crops like sorghum; planting
trees like the natural umbuzeiro (Spondias tuberosa) well suited for a
Together with the rural people, the water problem has to be managed in
three ways, using all the available kinds of water supply (ground, surface
and rainwater). It is necessary to have:
a - drinking water for every family (supplied by cisterns, shallow wells,
b - community water for washing, bathing and for animals (supplied by
ponds, ground catchment rock-cisterns, riverbed-cisterns, shallow wells,
c - water for agriculture (supplied by sub-surface impoundments, supplemental
irrigation, road catchments for irrigation of fruit trees, use of furrows
for storing rainwater in situ = inter-row water harvesting);
d - emergency water for drought years (supplied by deep wells and smaller
dams strategically distributed). This point is a transitory solution as
long as points 1 - 3 are not completely achieved.
Different types of rainwater harvesting in Northeastern Brazil are:
Until now, among various cistern types used to resolve the drinking water
problem in rual areas in Northeast Brazil, the concrete plate cistern
made of cement plates (50 cm wide, 60 cm long and 3 cm thick) 14-gauge
binding wire and plastered in and outside has been the most constructed
cistern. As the adherence between the concrete plates sometimes is insufficient,
tensions can cause cracks through which the water can leak.
For this reason, in the future the wire mesh concrete cistern (using a
cast during the first construction phase) will probably be the most used
and appropriate type for cistern construction in the region. This type
of cistern hardly leaks and if so, it can be easily fixed. It is also
useful for small and big cistern building programs (Fig.5).
An underground lime and bricks cistern remembers the Abanbars of Iran
and the Chultuns of Mexico (Fig.
In different parts of the semiarid region there is a revival of hand-dug
rock cisterns; a traditional way to harvest water for the dry season.
Their water is normally used for animals, but after filtering can be used
for drinking purposes as well (Fig.7).
Sub-surface impoundments / dams store surface rainwater runoff for a later
application: the barriers are dug below the ground surface in a shallow
soil toward the impervious crystalline subsoil. Then earth or rockfill
dams are built with a PVC sheet on the upstream face avoiding seepage.
On the watered upstream soil it is possible to plant crops or fruit trees.
In addition there is almost always an underground cistern to use the water
for humans, animals or irrigation. Even in the first months of the dry
season, it is possible to plant a second time and even in the driest years
these impoundments are never without water (Fig.8).
The so called life-saving / supplemental irrigation impoundments collect
rainwater runoff from a big natural ground catchment area. Downstream
the impoundment people plant annual crops like beans, corn or sorghum.
If there is a drought spill during the rainy season, people can water
the fields with the help of gravitation from the impoundment. If they
don't need the water, they can plant again in the dry season and use the
water for irrigation of a second crop (Fig.9).
Inter-row harvesting in situ e.g. pre- and post seeding furrowing, partial
ploughing or water stopping furrows. "In situ" rainwater catchments
are suitable for the existing planting systems and they can be implemented
with the help of machines or animals (Fig.10).