Rainfall and Streamflow Trends in the Upper <em>Maduru Oya</em> Sub-watershed in Sri Lanka: A Comparative Study Using Different Statistical Methods

Analysis of historical data on rainfall and streamflow provides useful information for water resources management in a river basin. The objective this study was to assess the variations trend analysis upper Maduru Oya sub watershed Sri Lanka during 30 year period (1989 October 2019 September) using daily from two gauging locations (Padiyathalawa Bibile) average one location (Padiyathalawa). Descriptive statistics were used variations. Mann Kendal Trend Test (MK test) Innovative method (ITA) analyze trend, Sen’s Slope Estimator magnitude trend. Based MK test, most trends obtained are an increasing direction, decreasing direction. Rainfall found Padiyathalawa not statistically significant. Annual, First Inter Monsoon, March, May time scales showed significant upward at Bibile (p<0.1) while January, April, September negative Padiyathalawa. results displayed by all three tests very good agreement rainfall. ITA similar types 77%, 95% 41% streamflow, respectively. A positive (ρ<0.01) strong lower correlation between value Z test Changes sufficient explain observed streamflow. Therefore, future research should be directed causal aspects change watershed.