Geoscience Reference
In-Depth Information
Table 24.2.
Extent and severity of desertification in irrigated areas, rain-fed
croplands and rangelands in the areas classed as drylands in Asia (in Thousands of
Hectares). (From UNEP,
1992b
.)
Tot a l
Moderate
or worse
Slight to
none
Ve r y
severe
%
degraded
Areas shown
Total area
Moderate Severe
Irrigated area
92,021
60,208
24,335
5,788
1,690
31,813
35
Rain-fed
cropland
218,174
95,890
100,638
18,578
3,068
122,284
56
Rangeland
1,571,240 383,630
485,221
691,602 10,787
1,187,610 76
and so far quite rare. A related problem is the lack of a unified national strategy
for monitoring and implementing optimal land management procedures, given that
responsibility still lies in the hands of individual state agencies, not all of which are
able to perform these roles wisely and efficiently.
24.9 Desertification in Asia
Themost comprehensivemaps of the present extent of global and regional land degrad-
ation and desertification so far available are those published by UNEP (
1992a
;
1997
).
In Asia as a whole, 56 per cent out of a total area of 218.2 million hectares of rain-fed
cropland were classed as degraded (
Table 24.2
), of which 122.3 million hectares were
ranked as being moderately to very severely affected (UNEP,
1992b
). Corresponding
figures for rangelands in Asia (1,571.2 million hectares in total) amounted to 76 per
cent, or 1,187.6 million hectares, being moderately to very severely affected (UNEP
1992b
). Irrigated areas in Asia covered 92 million hectares, with 35 per cent, or
31.8 million hectares, being moderately to severely affected (UNEP,
1992b
). In all
cases, the arid and semi-arid areas were the most severely affected, but the dry sub-
humid areas were most vulnerable to future change, since they were far more densely
populated and had less collective experience in adapting to extreme climatic vicis-
situdes. Within the arid and semi-arid regions, there was often a considerable body
of detailed information available to assist pastoralists in managing their resources
more effectively, as in the Cholistan Desert of Pakistan (Mohammad,
1989
; Rao et al.,
1989
).
Salinization has been a major problem in the Indus Valley since before the 1950s
and has become more evident in the drier parts of China in the last twenty years. In
both cases, the root causes were over-irrigation, inadequate drainage and locally rising
groundwater-tables. One concern is what the impact of current warming trends in this
region might be. Higher temperatures will probably lead to an increase in water losses
from crops through transpiration and from canals through evaporation, leading to
