In cooperation with the International Water Management Institute (IWMI), the 

KnoWat project trained 30 experts from Sri Lanka to use and interpret WaPOR 

datasets. Key partner institutions, including the Irrigation Department, 

Department of Agrarian Development, Department of Land Use Policy Planning, Department of Census and Statistics as well as the University of Peradeniya now have the tools to use WaPOR for managing water resources better. 

The data are freely available on FAO’s WaPOR portal. The user can access data on evapo-transpiration, or water consumption by vegetation. Data are available for 10-day intervals, and aggregated by growing season, or every 10 days. This data can be used, for example, to analyze water productivity at irrigation scheme level, and as an input to water balance studies at catchment or basin scale, for better water management. FAO and partners in Sri Lanka currently discuss arrangements for WaPOR coverage beyond 2022. 

Partners currently evaluate to use WaPOR data for monitoring Sustainable Development Goal Indicator 6.4 on water stress, and for the Environmental Economic Accounting of water resources. 

Crop water productivity assessment 

To demonstrate the usefulness of WaPOR portal at the scheme level in areas of scare water resources, the KnoWat project carried out a crop water productivity assessment for better water management in the Southern Malwathu Oya Catchment in 2022. 

The Southern Malwathu Oya Catchment is part of the Malwathu Oya river basin, one of the major agricultural areas in the country. The effects of climate change have affected the area. Today it is prone to extreme weather events such as severe water scarcity and floods, challenging farmers’ work and lives. Inefficient water-use in agriculture, particularly in paddy, and poor irrigation infrastructure exacerbate the situation. 

The area covered by WaPOR extends over 779 km2, including the fields of more than 200 000 farmers. The water productivity assessment considered only paddy rice cultivation, as the main crop with the most significant water consumption through irrigation. 

Main findings 

The water productivity assessment analyzed the rice yield in the project area during the Maha monsoon season (1 October–30 March) between 2015 and 2022. Yields of paddy rice ranged from 3.8 to 4.8 tonnes/ha. The highest yield was achieved in 2017–2018. Yields are lower than in other districts in Sri Lanka, but around the global average of irrigated rice yield (4.5 tonnes/ha). 

To understand the underlying causes of low water productivity of paddy in certain areas within the pilot area, irrigation performance indicators such as adequacy or uniformity were assessed. They reveal that irrigation is not adequate or uniform across the basin. 

The assessment shows that in the Southern Malwathu Oya Catchment, both the land and crop water productivity of the paddy rice cultivated during the Maha season has a high spatial and temporal variability. The results can be used by irrigation experts to identify hot spots and bright spots increase the water productivity in Malwathu Oya basin. 

The assessment also analyzed the yield assessment in the Nachaduwa irrigation area (left). In this area, irrigated crop yield reaches values above 6 tonnes/ha, while in the rest of the catchment farmers seem to produce less, between 2 and 5 tonnes/ha. It can therefore be interesting to study the reasons for the higher yields. Do farmers in Nachaduwa apply good practices that farmers in other areas can benefit from? 

The challenges identified by the assessment included uncertainties in the land cover maps provided by WaPOR, which may have been affected by the high cloud cover of the satellite images during the main growing period. In some areas, the size of the fields, which were often too small (less than 1 hectare) to be detected by remote sensing at 30 meters resolution is a limiting factor. For a good application of WaPOR for irrigation performance assessment, reliable local data on crop cover and crop calendar are needed. WaPOR works best on large fields with a uniform crop cover and calendar, such is the case in the Nachaduwa irrigation scheme. 

In the future, application of WaPOR for water productivity and irrigation performance assessment should be more seamless thanks to ongoing research projects by university students supported by the KnoWat project in collaboration with IWMI. 

Voices from the field 

“The WaPOR database is very helpful in the tasks performed by the Irrigation Department for water resources planning. After assessing the water availability and the water use efficiency for better water management, we can plan better our actions, especially in the dry zone of Sri Lanka where almost all the major, medium irrigation schemes are situated.” 

Engineer Medhani A. Jayakody, Chief Engineer of the Water Resources Planning Branch, Irrigation Department of Sri Lanka