Precipitation or rainfall (in tropics) is an important climatic parameter and the studies on rainfall are commonly hampered due to lack of continuous data. To fill the gaps (missing observations) in data, several interpolation techniques are currently used. However, the lack of knowledge on the suitability of these methods for Sri Lanka is a practical problem. In view of this problem, this study is aimed at comparing a few selected methods used for the estimation of missing rainfall data with a new method introduced by the authors to determine their suitability in Sri Lankan context. The methods studied were Arithmetic Mean (Local Mean) method, Normal Ratio method and Inverse Distance method. The new method introduced by the authors is named as Aerial Precipitation Ratio method. In this approach, rain gauging stations where complete monthly rainfall data sets are available were selected in such a way that the selected stations represent each of the seven major Agro-ecological zones of Sri Lanka. This selection procedure of stations makes it possible to generalize the results to the entire country. The period of data ranged from 15 years in the case of mid country intermediate zone to 28 years Up country intermediate zone and Mid country wet zone. Subsequently, monthly rainfall data of each station were estimated using the data of surrounding stations based on the above selected methods so that actual data and the estimated data can be compared. Each estimated series was compared with the actual data series using different statistical comparison techniques. These comparisons include Descriptive Statistics of Error, Root Mean Square Error, Mean Absolute Percentage of Error and Correlation Coefficient. Results of the study show that the Inverse Distance method is the most suitable method for all three Low-country zones (wet, intermediate, and dry).

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Soil erosion is one of the major factors that contributes to land degradation in the up and mid country of Sri Lanka. It is important to assess the rate of soil erosion under different environmental and socioeconomic contexts to identify and apply suitable management interventions. A number of parametric models have been developed to predict soil erosion at drainage basins. Yet Universal Soil Loss Equation (USLE) is the most widely used empirical equation for estimating annual soil loss from small agricultural lands. This study was carried out with the objective of developing a land degradation assessment model using a geospatial approach. The study area was Kandaketiya DS division in Badulla district. USLE together with some socioeconomic factors were used to develop the model for predicting land degradation. Slope length (L) and slope gradient (S) factors were derived from Digital Elevation Model. Rainfall erosivity (R) factor was determined using a correlation developed for Sri Lanka in a past research. Soil erodibility (K) factor was derived from the soil map. Crop management (C) factor and Erosion control practices (P) factor related to land cover derived from remotely sensed data taken from the literature. Annual soil erosion was computed using the above factors. The computed soil erosion map was coupled with the socioeconomic factors on population density, agricultural land to man ratio, land to man ratio and number of Samurdhi beneficiaries to assess the land degradation severity. The results showed that marginal tea lands are the highest contributor to soil loss in the study area. According to the study, soil erosion and population density contributed more to the land degradation. A strong negative relationship was found between land degradation and land to man ratio.

Agriculture-related water pollution is a serious concern in major agricultural areas in the country. This study was conducted with the objective of reviewing the existing situation of agricultural activities and their implications on the environment and society in Nuwara Eliya Divisional Secretariat Division. A questionnaire survey with 50 households in 15 Grama Niladhari divisions was conducted in the year 2008 for gathering information on nature of fertilizer and agro-chemical use, land management practices, condition of water sources and socioeconomic and environmental implications of water pollution. The study revealed that the majority of sample farmers in the study area are engaged in unacceptable agricultural activities. Root crops and vegetables are mainly cultivated at two to four times per year without proper soil conservation practices. The fertilizer and pesticide rates applied by the farmers are highly variable but in some occasions about 10 times higher than the rates recommended by the Department of Agriculture. The riparian vegetation has been cleared in many places to gain land for cultivation, exposing the streams to agricultural runoff. It was revealed that drinking water sources of 45 % of the households surveyed are located in highly vulnerable areas for agricultural pollution. The main socioeconomic issues observed include loss of family income, health issues, psychological effects and effect on family wellbeing. The environmental implications observed include land degradation, soil erosion, sedimentation, water contamination and degradation of aesthetic value. In addition, the study identified that the organizations working on environment and water resources do not collaborate with each other and long term measures have not been taken to control the agricultural water pollution. Awareness creation on agricultural pollution and associated environmental issues is of key importance. A strong collaboration should be developed within the institutions involved in agriculture, environmental management and administrative activities in the area to formulate a sustainable agricultural system in the Nuwara Eliya district.