Kalu Ganga (කළු ගඟ)

Kalu Ganga (Sinhala: කළු ගඟ; literally: Black River) is a river in Sri Lanka. Measuring 129 km (80 mi) in length, the river originates from Sri Padhaya and reach the sea at Kalutara. The Black River flows through the Ratnapura and the Kalutara District and pass the city Ratnapura. The mountainous forests in the Central Province and the Sinharaja Forest Reserve are the main sources of water for the river.

Kalu Ganga basin is one of the most important river basins in Sri Lanka which receives very high rainfalls and has higher discharges. Due to its hydrological and topographical characteristics, the lower flood plain suffers from frequent floods and it affects socio-economic profile greatly. During the past several years, many researchers have investigated climatic changes of main river basins of the country, but no studies have been done on climatic changes in Kalu Ganga basin. Therefore, the objective of this study was to investigate precipitation trends in Kalu Ganga basin. Annual and monthly precipitation trends were detected with Mann-Kendall statistical test. Negative trends of annual precipitation were found in all the analyzed rainfall gauging stations. As an average, -0.98 trend with the annual rainfall reduction of 12.03 mm/year was found. April and August were observed to have strong decreasing trends. July and November displayed strong increasing trends. In conclusion, whole the Kalu Ganga basin has a decreasing trend of annual precipitation and it is clear that slight climatic changes may have affected the magnitude and timing of the precipitation within the study area.