Statistical Evaluation and Trend Analysis of ANN Based Satellite Products (PERSIANN) for the Kelani River Basin, Sri Lanka

Abstract

Satellite-based precipitation products, (SbPPs) have piqued the interest of a number of researchers as a reliable replacement for observed rainfall data which often have limited time spans and missing days. The SbPPs possess certain uncertainties, thus, they cannot be directly used without comparing against observed rainfall data prior to use. The Kelani river basin is Sri Lanka’s fourth longest river and the main source of water for almost 5 million people. Therefore, this research study aims to identify the potential of using SbPPs as a different method to measure rain besides using a rain gauge. Furthermore, the aim of the work is to examine the trends in precipitation products in the Kelani river basin. Three SbPPs, precipitation estimation using remotely sensed information using artificial neural networks (PERSIANN), PERSIANN-cloud classification system (CCS), and PERSIANN-climate data record (CDR) and ground observed rain gauge daily rainfall data at nine locations were used for the analysis. Four continuous evaluation indices, namely, root mean square error (RMSE), (percent bias) PBias, correlation coefficient (CC), and Nash‒Sutcliffe efficiency (NSE) were used to determine the accuracy by comparing against observed rainfall data. Four categorical indices including probability of detection (POD), false alarm ratio (FAR), critical success index (CSI), and proportional constant (PC) were used to evaluate the rainfall detection capability of SbPPs. Mann‒Kendall test and Sen’s slope estimator were used to identifying whether a trend was present while the magnitudes of these were calculated by Sen’s slope. PERSIANN-CDR performed well by showing better performance in both POD and CSI. When compared to observed rainfall data, the PERSIANN product had the lowest RMSE value, while all products indicated underestimations. The CC and NSE of all three products with observed rainfall data were also low. Mixed results were obtained for the trend analysis as well. The overall results showed that all three products are not a better choice for the chosen study area.

Appraisal of Satellite Rainfall Products for Malwathu, Deduru, and Kalu River Basins, Sri Lanka

“…This is the first study to evaluate the selected SRPs for three major river basins, which fall into three different zones in the country. The previous studies carried out by Perera et al [16,17] is not focusing on the dry and inter-mediate zones separately. Therefore, this particular study focuses on all three climatic zones of the country, thus marking the novelty and the great importance this study has to society.…”

“…Evaluation of SRPs for the Mahaweli River basin, which is the longest river in Sri Lanka, had already been carried out by Perera et al [16]. A similar study was carried out due to the importance of the Kelani River basin, as a frequently flooding river basin [17]. Nevertheless, Sri Lanka geographically has a radial pattern of river basins covering most of its land and therefore, the river basins are the heart of the country [18].…”

“…[12][13][14][15]. However, most of the river basins in Sri Lanka are not tested for these SRPs (except for a couple of river basins, such as the Mahaweli and Kelani River basins [16,17]).…”