Abstract:
Sri Lanka is an agrarian country that relies on paddy cultivation in the Dry
zone. Yala season determined on tank water and cascade systems have been impacted
by recent drought conditions highlighting the importance of water resource manage-
ment and food security. Crop Water Productivity (CWP) plays a crucial role in ensur-
ing the equilibrium between crop yield and water consumption. This research em-
ployed Remote Sensing (RS) and Geographic Information System (GIS) to analyse
the CWP of paddy in 2022-Yala season in Kala Oya basin, covering 2,873 km², with
approximately 560 km² paddy land. The study mainly used Net Primary Production
(NPP) data, Actual Evapo-Transpiration and Interception (ETIa), and land use data
obtained from the Wapor Portal and ESA World Cover, and occupied mapping anal-
ysis, buffer analysis, and zonal statistical analysis with the Model Builder within
ArcGIS. The mapping analysis revealed that eastern, central, and western regions of
the catchment in proximity to Kala Wewa, exhibited high paddy yields while the
southeastern part of the basin, closer to Dewahuwa and Ibbankatuwa Wewa, demon-
strated a higher CWP. Notably, central and western parts of the basin, in the vicinity
of Rajangana and Angamuwa Wewa, showed optimal conditions characterised by low
CWP and high yields. Moreover, a declining trend of average CWP and yield was
displayed with the distance from irrigation canals and streams. Paddy yield within the
canal buffer ranges from 0.166 kg m-² (100 m) to 0.159 kg m² (500 m), while the
stream buffer exhibits yield from 0.160 kg m-² (100 m) to 0.152 kg m-² (500 m). Sim-
ilarly, CWP for the canal buffer varies from 0.442 kg m-³ (100 m) to 0.428 kg m-³
(500 m) and for the streams from 0.424 kg m- (100 m) to 0.409 kg m-³ (500 m). In
conclusion, the study emphasises the significance of water source proximity, specifi-
cally tank water and cascade systems, influencing CWP and paddy yield within the
Kala Oya basin. To optimise CWP in the basin necessitates an expansion of the irri-
gation network within cascade systems and continuous monitoring of the CWP and
yield. Further, to gain a comprehensive understanding on paddy CWP within the tank
cascade systems, an extended long-term spatial analysis is necessary.
