Comparison of Different Analyzing Techniques in Identifying Rainfall Trends for Colombo, Sri Lanka

Abstract

Identifying rainfall trends in highly urbanized area is extremely important for various planning and implementation activities, including designing, maintaining and controlling of water distribution networks and sewer networks and mitigating flood damages. However, different available methods in trend analysis may produce comparable and contrasting results. Therefore, this paper presents an attempt in comparing some of the trend analysis methods using one of the highly urbanized areas in Sri Lanka, Colombo. Recorded rainfall data for 10 gauging stations for 30 years were tested using the MannKendall test, Sen’s slope estimator, Spearman’s rho test, and innovative graphical method. Results showcased comparable findings among three trend identification methods. Even though the graphical method is easier, it is advised to use it with a proper statistical method due to its identification difficulties when the data scatter has some outliers. Nevertheless, it was found herein that Colombo is under a downward rainfall trend in the month of July where the area receives its major rainfall events. In addition, the area has several upward rainfall trends over the minor seasons and in the annual scale. Therefore, the water management activities in the area have to be revisited for a sustainable use of water resources.

Analysis of Statistical Downscaling Model (SDSM) projected future rainfall in Northwestern, Western and Southern provinces of Sri Lanka

“…Increasing trends for annual rainfall were identified in Colombo in previous studies (Malmgren et al 2003). Increasing trends during the NEM season in Colombo demonstrated in this study are in-lined with the finding of Perera et al (2020). The increasing trends in annual rainfall in Galle, Colombo, and Katunayake are similar to the direction of trends observed by Amarasinghe (2020).…”

Assessing the influence of climate variability and land cover change on water resources in the Wami river catchment, Tanzania

“…The statistical trend was computed by using the Zc value. A positive value of Zc indicates an upward, and a negative indicates a downward trend (Perera et al 2020). The statistic Zc has a normal distribution to test for either an upward or downward trend at α level of significance (usually 5% ±Z1-α/2 = 1.96) (Gocic and Trajkovic 2013;Perera et al 2020)).…”

Trends and Variabilities in Rainfall and Streamflow: A Case Study of the Nilwala River Basin in Sri Lanka

“…Several studies, including Abeysingha [27], Perera et al [28], Alahacoon and Edirisinghe [29], and Ruwangika et al [30], studied rainfall and streamflow trends in Sri Lanka. These studies identified an increasing rainfall trend over the country that was most prominent in the eastern, southeastern, north, and north-central areas.…”