Here is another paragraph about "karezes"

Background- Arable Land and Irrigation:
The UN reports that approximately 85 percent of the country's population is directly dependent on agriculture. Agriculture and
animal husbandry have historically been the most important items of Afghanistan’s Gross National Product. According to the
Cooperative Institute for Applied Meteorology at University of Missouri-Columbia, only about 12 percent of Afghanistan's
total area is arable. Most of the land is semi-area to arid with very rugged terrain. The irrigated areas are known as ‘Abi’ and
the dry farmed areas are called ‘Lalmi’. Nearly 50 percent of the arable land is irrigated and three-quarters of it is located
north of the Hindu Kush Mountains. The short growing season at elevations above 2000 meters permits only one crop to be
grown. Two crops a year can be grown at lower elevations, if enough water is available. Canal systems convey some 80-85
percent of the irrigation water, while the traditional karezes, springs, and wells feed the remaining 15-20 percent. According to
FAO’s Land Cover Atlas of Afghanistan and FAO AQUASTAT data, the equipped annual irrigated land amounts to some 2.5
million hectares. However, an estimated 30 percent of all irrigation systems are believed to have been damaged or destroyed
by the war. Adding in the effects of abandonment, neglect and lack of maintenance, another 15 to 20 percent of the irrigation
infrastructure is probably unusable for agricultural purposes. Hence, the actual irrigated land amounts to 1.2–1.3 million
hectares, decreasing every year. The decline in irrigation availability and efficiency has exacerbated the already-failing crop
production.