|
|
| MALDIVES Post-Tsunami Agricolture
Brief |
| |
| 18 April 2005 |
Contents:
Introduction
Overview
Natural Conditions
Tsunami Impact Assessment
The way forward
Sources |
Introduction |
 |
|
The December 2004 Tsunami approached and swept over the Maldives
in an East-West Direction. The low elevation of the islands
makes them very vulnerable to any rise in sea-level, and thus
especially to tsunamis. It has been estimated that one third
of the population of the country was severely affected, 1,300
people injured, 83 confirmed dead and another 25 missing and
feared dead, 39 islands severely damaged, 14 completely destroyed
and people remaining had to be evacuated. Nearly 12,000 people
were displaced from their own islands and another 8,500 have
been temporarily relocated to other places on their own islands.
Livelihoods of many have been disrupted if not destroyed and
the impact on the National Economy is likely to be substantial
given that it is based largely on tourism, fisheries and agriculture.
Furthermore, disruption to services has been substantial. Stand-alone
electricity supplies on many islands were destroyed as well
as telecommunication facilities, and these are now being slowly
restored. It is estimated that 15 percent of islands suffered
disruption to water supplies and 25 percent of islands suffered
major damage to their essential infrastructure facilities including
jetties and harbors. |
|
|
In the first weeks after the disaster
FAO embarked on preliminary damage assessments that were followed
by more in-depth missions investigating short and long-term impacts
of the disaster to agriculture and land and water resources. The combined
findings resulted in a representative assessment that is summarized
in this text. On basis of the assessments FAO initiated projects to
ensure and monitor the recovery of agriculture in the affected areas.
The logistics of providing any level of service to the dispersed population
even in normal times is a daunting matter. Provision of essential
infrastructure services and their maintenance is fraught with transport
difficulties and associated high cost, and is unusually challenging
at the best of times. The needs of the post-tsunami efforts face similar
problems.
|
Overview |
|
|
| The Maldives is a large and spread group
of widely dispersed islands in atolls spanning a distance of
some 900 Kilometers more or less stretched from North to South.
The population is about 300,000 at latest count. The country
consists of a total of some 1,190 islands of which199 were inhabited
islands prior to the Tsunami. Of these, only 28 have a land
area greater than one square kilometer. The total land area
(covering all islands) varies in time but on basis of recent
satellite measurements is currently indicated to be in the order
of 230,000 ha. Al this land has similar sandy type coral soils
and it is estimated that only 10 % of the land area has worthwhile
agricultural potential. |
 |
The geographical shape of the island varies from elongated (mostly
in North-South direction), horseshoe shaped, triangular to circular
but in almost all cases the East-West cross-section does not extend
beyond 1-2 km. The elevation above mean sea level is generally stated
to be only some 1.0-1.5 m. Some islands have pronounced marshy depressions
(these are locally referred as taro lands, as they are suitable for
growing the taro crop). One third of the inhabited islands have a
population of less than 500, whilst 70 percent have a population of
less than 1,000. Around 100 islands are of agricultural significance.
Almost all of the farming is small holder subsistence farming. A total
of 32 non-inhabited islands are leased for private sector commercial
farming but in most cases development has yet started. |
Natural conditions |
|
|
As the country is located in the Western part of the Indian Ocean
, the climate is warm and humid for most of the year. Rainfall is
quite widespread and has an increasing trend from North (average 1840mm)
to South (3500mm). Two monsoon seasons dominate the climatic regime;
these are the high rainfall SW monsoon and the somewhat drier NE monsoon
which respectively prevail from May/June till September and from October/November
till February. There is a very distinct dry season from January to
April with the heavy rainy season expected to begin usually around
May.
All soils are calcareous residual soils derived from weathered coral
formations that form the bed-rock foundation of these islands. The
weathered layer is usually not more than 50-70 cm deep and consists
almost entirely of medium sized calcium-carbonate sand grains. The
topsoil of some 15- 20 cm thickness is dark colored by organic matter
from cleared natural vegetation. As the soils do not have silt and
clay material that provides soils with adsorption capacities for water
and nutrients, all holding capacity of these soils is vested in the
organic matter of the topsoil and in the little capillary holding
capacity of medium-sized sand. Natural fertility of the soils is very
low and total water retention capacity of the root zone (at field
capacity) is probably not more than 30-40 mm. The soils have a very
high vertical permeability. The hydraulic conductivity (K-value)¹
of the medium sized-sand and the coral bedrock is in the order of
several meters per day. Rainwater infiltrates without producing run-off.
All islands show the typical geohydrological sea island feature of
a fresh water lens floating on deeper saline groundwater. The fresh
water lens is periodically replenished by the rainfall recharge and
depleted by the local groundwater use for household, irrigation and
industrial water, groundwater uptake by the vegetation and lateral
outflow to the sea (most houses have roof systems to collect rain
water for cooking and drinking). The ground water table is present
at depths of only twenty to fifty centimeters below ground level in
most locations. The depth of the fresh water lens is a few meters,
probably a little deeper in the South than in the drier North. |
Tsunami Impact Assessment |
|
|
The tsunami waves generally approached the Maldives islands from the
East. The tide in visited area was reported to be in the order of
0.50 - 0.75 m. The tsunami occurred at low tide but nevertheless the
waves were high enough (reaching to 2-3 m + MSL at the sea side) to
sweep over some (parts) of the islands. Three waves swept over the
islands in a 2-3 minutes interval, lasting less than 6-7 minutes in
total. Afterwards the flood water drained back to the sea which process,
depending on local topography lasted between 0.5 hr to a full day
with some of the enclosed depressions remaining inundated for several
days.
 |
| Young fruit-trees
dying from salt stress |
|
Agricultural impacts
Agriculture on almost all islands is restricted to growing field
crops and fruit trees. There are no livestock or fodder crops.
Principal field crops are: water-melon, pumpkin, cucumber, cabbage,
cassava, sweet potato, yam, chilies and taro. These crops are
generally cultivated in cleared plots in the natural jungali
vegetation (a mixture of flood and salt-resistant bushes and
shrubs, intermixed with coconut trees. The plots vary in size
from 0.5 to 1 acre with individual plots usually being separated
by a strip of jungali. Usually, no facilities are installed
apart from a shallow dug well (for manually watering crops)
and an elementary shelter. Fruit trees are generally grown within
the walled compound around the houses and include mango, papaya,
bread fruit, stone apple, drumstick and various citrus varieties.
Papaya and bananas are grown both in the compound and in the
field plots. |
|
The agricultural impact of the tsunami
is generally limited to the loss of field crops and the dying of fruit
trees due to osmotic stress and toxicity of the flood water. Very
little erosion of the agricultural fields or deposition of sediments
was observed. Damage to infrastructure (irrigation/ drainage/road
systems, fences, farm buildings, etc.) also appears to be negligible
as little infrastructure had been constructed. All field crops in
the flooded areas are lost beyond rescue. Almost all fruit trees have
shed their leaves and many appeared to be dead, It was, however, observed
in the beginning of March that a fair percentage of the fruit trees
(estimated at some 30-50 %) sprouted again and formed new shoots.
At the same time, most mango trees, however, showed no sign of life
but some apparently dead bananas sprouted again after being cut back.
Coconuts and all natural vegetation, apart from some limited leave
shedding show no signs of suffering. Young trees (especially seedlings)
have suffered more than mature trees. Local people generally confirmed
that the sprouting was induced by rains. The best sprouting was generally
observed in areas where strong rains had occurred quite soon after
the tsunami but people also stated that trees had responded to rains
which came as late as 6-7 weeks after the saline flooding. Some households,
of their own initiative, started applying excess water to their fruit
trees soon after the Tsunami and they have had success with the trees
responding by showing new growth.
|
Impacts on the soils
Although most of the saline flood water eventually drained back
to the sea and the period of flooding in some cases was quite
short, enough sea water infiltrated or remained on the land
to leave a considerable salt load in the soil. After the retreat
of the saline flood water, most of this salt remained in the
root zone, raising the soil salinity in this zone to an estimated
level as high as EC e =50-60 dS/m (thresholds for most crops
and fruit trees is EC e
<4 dS/m)². These high soil salinity values prevailed
for some time after the flooding, until the arrival of the first
rain. Post-tsunami rainfall has been varied and is in line with
the decreasing trend in total rainfall in a South to North direction.
Between December and early March, there had been more than 150
mm in the southern islands in a few intensive falls whilst in
the northern islands visited there has been about just over
100 mm but only one event of which was over 40 mm and the others
smaller. These rains have leached out most of the salts and
reduced soil salinity in the root zone to safe levels. |
 |
| FAO
Soil Salinity Assessment Mission |
|
|
Due to topographic differences and
variance in rainfall salinity is still a problem in some areas, especially
in the North. This remaining salinity is confirmed by disappointing
experiences of the few farmers who have started planting again (failed
cucumber seedlings) and by the analysis results of the soil samples
taken in affected fields. Unlike in other regions the tsunami flood
has not caused any deterioration of soil structure, since there is
no silt/clay fraction. Dispersion of organic matter was observed in
some fields but this has not materially affected the soil structure.
Impacts on groundwater
The tsunami flooding has salinized the groundwater by three mechanisms:
| 1) |
The saline flood water has raised
the watertable and as such salinized the upper groundwater.
All salts leached from the soil profile have also ended up in
this upper groundwater layer; |
| 2) |
Many of the wells have been flooded and thereby
locally salinized the surrounding groundwater; |
| 3) |
the sea water not only flooded the land surface
but also intruded laterally into the groundwater aquifer, thereby
salinizing the fresh water lens over some distance inland (generally
confirmed by the high salinity measured in the sea-side wells). |
The first mechanism presumably led to a rather uniform and area-wide
salination of the upper groundwater zone (where the land was flooded).
The second mechanism locally added to this salination while the third
mechanism salinized the fresh water lens from the sea side. The measured
salinity values reflect this variation. Salinity levels in flooded
wells were found to be mostly in the range of EC = 5-7 dS/m. (as compared
to pre-tsunami salinity levels of EC = 0.5-0.6 dS/m). As the groundwater
is generally only used for general household purposes and not for
drinking/cooking water, most flooded village wells were operational
quite soon. Water quality in the wells improved after a few days by
draining and dilution from the fresh water lens.
In the long run (1 year), spatial variations in the salt concentration
of the groundwater will have evened due to ground water flow, salt
diffusion, advection and dispersion, dilution³
by rain and other mixing processes while in the still longer run,
all tsunami added salts may be expected to drain back to the sea.
Although full completion of the latter process will take considerable
time (several years), it is conceived that one good rainy season with
several intense showers will flush out enough salts from the fresh
water lens to be safe for agricultural purposes.
Processes related to the flow of soluble salts in the soil: diffusion
is a chemical activity, the flow of ions (salt molecules) from areas
of high concentration to low concentration; advection is the mechanical
transport of soluble salts through groundwater movement and dispersion
is the subsequent dilution, influenced by pore shapes and sizes. Dilution
can also occur by simply adding fresh (rain)water, diminishing the
overall salt-concentration. |
The way forward |
|
|
 |
| Affected tree
showing new sprouts |
|
Practical advice
tor farmers on coping mechanisms with salinity
After initial severe salinisation of agricultural lands, most
field crops and fruit trees have died. In areas where the rains
were on time, some of the trees survived. Post-tsunami rainfall
has cleaned most of the affected area and it is expected that
after the monsoon season, all salinity problems will be eradicated.
Nevertheless, there are some relevant measures that farmers
can take to ensure crop and fruit tree survival, such as:
| - |
Farmers (in the North)
should begin re-planting at the onset of the first heavy
rains (>50-60 mm). |
| - |
Farmers should be advised not to irrigate
field crops with well water of EC > 5 dS/m and to over-irrigate
(daily with 50% more water than normal practice) when
the well water is of marginal quality (EC ~ 4 dS/m). |
| - |
Farmers on northern islands and close
to the sea should limit their abstractions from the wells
in order to prevent intrusion of deeper salts. |
| - |
Water conservation is to be promoted
through mulching and run-off reducing measures. |
|
|
Short term interventions
needed
| - |
Provision of seeds and seedlings
of fruit-trees to farmers on affected islands to quickly re-establish
their livelihoods and help them return to normality. (Inputs
currently being procured by FAO for immediate distribution) |
| - |
Provision of extension services to tree-owners
at the Agricultural Centers, on how to enhance tree survival/recovery
chances through watering/pruning. |
|
Mid-term interventions needed
Present expertise in salinity management in the MFAMR is very limited
and although the current tsunami related salinity problems may be
expected to be essentially of a temporary nature, it is considered
that the country needs to strengthen its capacity in this field of
expertise. This need arises from the prevailing geohydrological regimes
of these coral islands under which all irrigation water is drawn from
a thin fresh groundwater lens floating on highly saline deeper groundwater.
The water and salt balances of these fresh water lenses should be
carefully managed and monitored in order to assure that the irrigation
water salinity remains within safe limits. Expertise is also needed
to monitor the capillary salination of the root-zone during the dry
season. Under the Tsunami relief operations, FAO has already provided
15 salinometers (EC-meters) and training to MFAMR staff on how to
use them. |
The medium term activities needed related to salinity are:
| - |
raising the awareness and establishing
elementary knowledge on salinity hazards facing the country's
agriculture amongst the staff of the MFAMR; |
| - |
establishment of a dedicated, suitably equipped
soil salinity laboratory at the Hanimaadhoo Agricultural Centre; |
| - |
providing professional training to selected
staff of the Hanimaadhoo Centre in salinity assessment and management; |
| - |
establishing a program for the monitoring
and assessment of salinity conditions in the fresh water lens,
the salinity of irrigation (well) water and of soil salinity
in the root zone; |
| - |
establishing an exchange and networking relationship
with other salinity centers in the region (a.o. Central Soil
Salinity Research Station at Karnal , India ; Centre for Saline
Agriculture in Dubai ); |
|
These activities could be part of a comprehensive project to strengthen
integrated land and water resources management, and take into consideration
soil fertility, other water quality aspects, etc. |
Sources |
|
|
The main sources for this brief were drawn from FAO-consultancy missions
and technical reports by L. Smedema (soil specialist) and A. Somesan
(water management specialist). Missions were carried out in collaboration
with the Ministry of Fisheries, Agriculture and Marine Resources (MFAMR)
and supported by the FAO-Maldives Representative and AG Tsunami Coordination
at FAO-HQ.
|
¹ Hydraulic
conductivity is a measure for the ease with which the soil pores permit
water movement. It depends on the type of soil, porosity, and the
configuration of the soil pores. For an explanation of this and other
technical terms on salinity used in this text, check the FAO-field
guide: 20
things to know about the impact of salt water on agricultural land
in Aceh Province
² EC is Electrical
Conductivity, a measure of soil and water salinity; and is measured
in deci-Siemens per meter (dS/m). ECe refers to the salinity of the
saturated extract of the soil.
³
Processes related to the flow of soluble salts in the soil: diffusion
is a chemical activity, the flow of ions (salt molecules) from areas
of high concentration to low concentration; advection is the mechanical
transport of soluble salts through groundwater movement and dispersion
is the subsequent dilution, influenced by pore shapes and sizes. Dilution
can also occur by simply adding fresh (rain)water, diminishing the
overall salt-concentration.
|
|
