Streamflow trends of Kelani river basin in Sri Lanka (1983-2013)

Abstract

; https://orcid.org/0000-0003-4635-3285) This article is published under the Creative Commons CC-BY-ND License (http://creativecommons.org/licenses/by-nd/4.0/). This license permits use, distribution and reproduction, commercial and non-commercial, provided that the original work is properly cited and is not changed in anyway. Abstract: The assessment of hydro-climatic trends is useful in water resource planning, especially in river basin scale. This study investigated the trends of streamfl ow in the Kelani river and its association with rainfall over a 31-year period. Streamfl ow and rainfall were assessed using Innovative Trend Analysis (ITA) method and Mann Kendall test (MK) with Sen's slope estimator. The association between streamfl ow and average catchment rainfall was studied using Spearman's rho correlation coeffi cient (ρ). Both ITA and MK tests confi rmed the decreasing annual and seasonal streamfl ow trend from mid-stream to downstream of the Kelani river basin. A decreasing trend of rainfall was recorded at 75 % and 63 % stations during the southwest monsoon (SWM) and second inter-monsoon (SIM), respectively. However, annual, northeast monsoon (NEM) and fi rst inter-monsoon (FIM) rainfall showed an increasing trend at 63 %, 88 % and 100 % stations, respectively. There was a signifi cant association between streamfl ow and catchment rainfall (p < 0.05) for 70 % of stations suggesting that the variation of streamfl ow is mainly attributed to the variation of catchment rainfall. The decreasing trend of streamfl ow and rainfall during SWM and SIM towards the downstream area with the increasing temperature trend indicate a drying tendency of the Kelani river basin over the study period.