Land degradation due to hydro-salinity in semi-arid regions
Using gis and remote sensing
Nasir Mahmood Khan* and Yohei Sato**
Graduate Student* and Professor**
Department of Biology and Environmental Engineering
Graduate School of Agricultural and Life Sciences,
The University of Tokyo
1-1-1 Yayoi,
Bunkyo-ku, Tokyo 133-8657, Japan
Tel: +81-3-5841-5344, Fax: +81-3-5841-8169
Email: aa97093@mail.ecc.u-tokyo.ac.jpt*
KEY WORDS: Remote Sensing, GIS, Hydro-Salinity, NDVI, Interpolation, FDP
Abstract
Fourth drainage project located in the center of Punjab province of Pakistan was selected as a research field. A newly introduced tile drainage system and remodeled surface drains have gradually reduced the waterlogging problem, however, salinity still remains in patches in the area. The present study describes an attempt to monitor land and water management scenarios that caused deterioration of vast productive land, using satellite data.
IRS-IB LISS-II digital data acquired were digitally analyzed along with other field data sets and topographical maps. False Color Composite and unsupervised classified image shows that most of the waterlogging and salinity problems are located along the drainage canals. The buffering analysis along the drainage and irrigation canals was performed to see the hydro-salinity impact on productivity in terms of its vegetation vigor. The Normalized Difference Vegetation Index (NDVI) tends to be lower along drainage and higher along the irrigation canals. It is probably because of the inequity water distribution and locational disadvantage of the down-stream farmers as well. A contrast example of an enterprise model-farm near the project area was observed which does not show any locational unbalance/inequity but exhibits comparable high NDVI values almost all over the farm area, except fallow lands. The extent of waterlogged soils was also estimated through GIS analysis from more than 150 peizometers locations lying within the study area. It was found that 24.5%, 22.0% and 63.4% of the mapped area was under risk of waterlogging (_ 200cm) during 1990, 1993, and 1996 respectively. Evidence is presented that the existing drainage system along with use of groundwater for irrigation reduces the extent of waterlogged soils. However, the reuse of poor quality water to supplement irrigation supplies by the downstream farmers and the failure of a few drainage sumps are likely to disturb the water balance resulting into increased risk of waterlogging and salinity in the area.
Introduction
Environmental land degradation has recently become a global, urgent issue and is now being considered with high priority, specially in the developing counties, to
meet food and fiber demands of accelerated population pressure with the limited available resources. Secure balance in the global supply and demand for food has forced humans to develop agriculture in semi-arid to arid lands, which are generally less suitable for agriculture and sensitive to environmental changes. Irrigation systems have always been considered as an effective way of increasing agricultural production since ancient times to bridge the gape of water shortage. Owing to irrigation systems, the farmers have obtained quite stable productivity but they started facing an acute problem of waterlogging and salinity due to seepage from the huge system in most of the developing countries like Pakistan. The farmers, many local and international organizations are struggling now against the so-called "white death" of their lands. Land degradation due to waterlogging and subsequent salinization has been so enlarged that it is now being regarded as a global environmental problem, desertification. It is, therefore, important to monitor land and water management scenarios causing severe land
degradation and low productivity. Remote sensing is one of the key tools in monitoring local, regional and global environmental issues. More recently, much attention has been paid to spatial analysis due to merging of geographic information system (GIS) and satellite images for environmental research and applications. The conventional means are however, not only difficult and time consuming but also laborious due to vagaries of the weather. It is prudent to use such emerging technique with an emphasis to its application in semi-arid areas. The present paper describes an attempt, where in IRS-1B, LISS-II (Indian Remote Sensing Satellite) digital data have been used along with other maps and field data, to monitor land degradation due to hydro-salinity and low agricultural productivity (vegetation condition).
Research Field
A reclamation project called
as "FDP" (Fourth Drainage Project) was launched to
mitigate the twine menace of waterlogging and
salinity, in 1983. The FDP area is located in the
center of Punjab province of Pakistan and consists
of Schedule-I and Schedule-II units. The
Schedule-I area covering about 70,000ha was
selected as a research filed, lies between 31° 02'
to 31° 45' N and 72° 50' to 73° 22' E (Figure 1).
It was estimated that 77% and 43% of the total
area was under high watertable conditions and
salinity respectively, before the installations of
a new tile drainage system (Table 1). Mean annual
rainfall of the locality is <350mm out of which
nearly 75% occurs during monsoon season (July-
September). The mean monthly maximum temperature
is between 19.4 - 41.2 C°. The mean annual
evaporation is as high as 2100mm.
Physio-graphically, the area is nearly level to
very gentle slope (average topo-gradient is 0.02%)
with mean sea level of 190m. Geologically, the
soils are alluvial deposits classified as silt
loam, loam, and silt clay loam and loamy sands.
There are two cropping seasons i.e. Rabi (winter)
and Kharif (summer). Main Rabi crops are wheat,
sugarcane, pulses, and fodder while corn, paddy,
cotton, sugarcane, and fodder occupy lands in
kharif season.
