To better understand irrigation in the context of basinwide water use, a water
accounting study was carried out at Kirindi Oya subbasin in Sri Lanka (Bakker et al.,
1999; Renault et al., 1999). Water resources in the area were primarily developed for irrigation. Initial studies pointed out that the amount of water evaporated from non-crop
vegetation was in the same order of magnitude as that for rice and field and vegetable
crops grown in the area. Remote sensing was used to carry out a more in-depth analysis to
classify land types, and then to estimate evapotranspiration by land type. The results,
shown in Table 2, reveal that evapotranspiration of non-crop vegetation is significant, and
needs to be taken into consideration in the operations and performance assessment of
cascade-type irrigation systems in the humid tropics.