Lal P. Muthuwatta

Mapping basin-level water productivity using remote sensing and secondary data in the Karkheh River Basin, Iran

This article deals with water productivity (WP) assessment at a range of spatial scales for the Karkheh Basin, Iran. Sub-catchment to basin-scale estimates are based on an innovative method that uses readily available satellite images and routine secondary data. The farm-scale results are derived from the field survey of 298 farmers. The results show large variations in the WP, which indicate considerable scope for improvement. Inclusion of livestock changes both the magnitude and patterns of overall WP at the sub-catchment scale. This stresses the need for holistic accounting of all agricultural enterprises in water (re)allocation policies.

A SWAT evaluation of the effect of climate change on the hydrology of the Volta River basin

The SWAT (Soil and Water Assessment Tool) was used to evaluate the impacts of a climate scenario based on IPCC A1B emissions on flows in the Volta River basin in West Africa for 2021–2050 and 2071–2100, using 1983–2012 as the reference period. Overall, the simulation indicates increased variability and a decrease of up to 40% in river flow as a consequence of decreasing rainfall and increasing temperature. In particular, the analysis shows smaller absolute but greater relative changes in the hydrology of the northern (upper) part of the basin, particularly at the end of the century.

Regional variation in suicide rates in Sri Lanka between 1955 and 2011: a spatial and temporal analysis

BackgroundBetween 1955 and 2011 there were marked fluctuations in suicide rates in Sri Lanka; incidence increased six-fold between 1955 and the 1980s, and halved in the early 21st century. Changes in access to highly toxic pesticides are thought to have influenced this pattern. This study investigates variation in suicide rates across Sri Lanka’s 25 districts between 1955 and 2011. We hypothesised that changes in the incidence of suicide would be most marked in rural areas due to the variation in availability of highly toxic pesticides in these locations during this time period.MethodsWe mapped district-level suicide rates in 1955, 1972, 1980 and 2011. These periods preceded, included and postdated the rapid rise in Sri Lanka’s suicide rates. We investigated the associations between district-level variations in suicide rates and census-derived measures of rurality (population density), unemployment, migration and ethnicity using Spearman’s rank correlation and negative binomial models.ResultsThe rise and fall in suicide rates was concentrated in more rural areas. In 1980, when suicide rates were at their highest, population density was inversely associated with area variation in suicide rates (r = −0.65; p < 0.001), i.e. incidence was highest in rural areas. In contrast the association was weakest in 1950, prior to the rise in pesticide suicides (r = −0.10; p = 0.697). There was no strong evidence that levels of migration or ethnicity were associated with area variations in suicide rates. The relative rates of suicide in the most rural compared to the most urban districts before (1955), during (1980) and after (2011) the rise in highly toxic pesticide availability were 1.1 (95% CI 0.5 to 2.4), 3.7 (2.0 to 6.9) and 2.1 (1.6 to 2.7) respectively.ConclusionsThe findings provide some support for the hypothesis that changes in access to pesticides contributed to the marked fluctuations in Sri Lanka’s suicide rate, but the impact of other factors cannot be ruled out.

Vegetation growth zonation of Sri Lanka for improved water resources planning

Abstract Water resources planning depends on the physical environments, notably on the vegetation and hydrological conditions in river basins. Vegetation growth—both natural and human induced—has a strong dynamic behavior which, especially at larger scales, is difficult to survey in the field. Low cost imagery from the NOAA–AVHRR satellite provides new opportunities to estimate vegetation development and biomass production. Composite maps of biomass production were compiled as the primary basis to establish a growth zone classification. A total of 92 vegetation growth zones were delineated by visual interpretation. Digital vector maps of land use and soil type, as well as digital raster maps of moisture availability index, soil moisture and actual evapotranspiration have been explored to describe vegetation growth zones from satellite data. These vegetation growth zones will contribute more to water resources planning than existing agro-ecological zonations and land use mapping, because vegetation growth is based on the environment and has strong linkages with the hydrological processes occurring in different parts of the basin. It provides a vehicle to relate water demand and water use in river basins to various types of vegetation.

Actual and perceived causes of flood risk: climate versus anthropogenic effects in a wet zone catchment in Sri Lanka

ABSTRACT The Kalu Ganga Basin in Sri Lanka is generally flooded once a year. A network of low-lying lands acts as natural retention and storage that captures floodwater, minimizing damage. An increase in the flood frequency has been observed in recent years. It is commonly perceived that this increase is caused by a rise in the frequency and severity of ‘very wet’ precipitation events. We conclude that land-use changes may have played a larger role in generating floods.

Trend and variability of rainfall in two river basins in Sri Lanka: an analysis of meteorological data and farmers’ perceptions

ABSTRACT Selected rainfall characteristics derived by analyzing observed rainfall data in two Sri Lankan river basins (Malwathu Oya and Kalu Ganga) were compared with the perceptions of farmers. The rainfall characteristics used for this analysis are trends, onset and cessation dates, length of the growing period, number of rainy days, and length of the dry spell. Farmers’ perceptions of changes in those characteristics were collected through household surveys. The majority of farmers in both river basins failed to recognize the long-term upward trend in annual rainfall. They also failed to describe the adaptation measures they were currently practising.