Abstract—Climate change will affect various aspects of hydrological cycle such as rainfall. A change in rainfall will affect flood magnitude and frequency in future which will affect the design and operation of hydraulic structures. In this paper, trends in sub- hourly, sub-daily, and daily extreme rainfall events from 18 rainfall stations located in Tasmania, Australia are examined. Two non- parametric tests (Mann-Kendall and Spearman’s Rho) are applied to detect trends at 10%, 5%, and 1% significance levels. Sub-hourly (6, 12, 18, and 30 minutes) annual maximum rainfall events have been found to experience statistically significant upward trends at 10% level of significance. However, sub-daily durations (1 hour, 3 and 12 hours) exhibit decreasing trends and no trends exists for longer duration rainfall events (e.g. 24 and 72 hours). Some of the durations (e.g. 6 minutes and 6 hours) show similar results (with upward trends) for both the tests. For 12, 18, 60 minutes and 3 hours durations both the tests show similar downward trends. This finding has important implication for Tasmania in the design of urban infrastructure where shorter duration rainfall events are more relevant for smaller urban catchments such as parking lots, roof catchments and smaller sub-divisions. Keywords—Climate change, design rainfall, Mann-Kendall test, trends, Spearman’s Rho, Tasmania. I. INTRODUCTION MPACTS of climate change on rainfall has important implication in water resources management since a change in rainfall will impact droughts, floods and catchment hydrological processes, which will in turn affect various aspects of agriculture, ecology, infrastructure and environment [1]-[8]. The future rainfall at many locations will be changed significantly due to climate change [9]. Warming of the climate system has potential impacts to intensify the global hydrological cycle, causing exacerbation of extremes such as floods and droughts [10]. It has become an important research question to investigate trends in historical rainfall data. However, due to irregular topography and complex atmospheric circulation rainfall intensity shows notable spatial variability [11]. Although increase in global temperature leads to increase rate of precipitation, it has been found that for some regions there is no trends in the annual rainfall [12], [13]. To characterize possible changes in climatic extremes and assess the knock on effects, trends analysis has extensively O. U. Laz is with the EnviroWater Sydney, Australia (e-mail: orpita12@yahoo.com). A. Rahman is an Associate Professor in water engineering in the School of Computing, Engineering and Mathematics, University of Western Sydney, Australia, Building XB, Room 2.48, Kingswood, UWS, Locked Bag 1797, Penrith, NSW 2751, Australia (e-mail: a.rahman@uws.edu.au). been used on hydrological time series data at different parts of the world [14], [15]. Some studies on the trends analysis of rainfall can be found in [16]-[25]. Most of these studies observed increasing trends in short duration storms and not any significant increasing trends for medium to long duration storms. Due to the high rainfall variability in Australia, the number of hydrological impact studies due to climate change has increased in recent years. In order to improve water management, researchers attempted to evaluate changes in the spatial and temporal patterns of rainfall. The majority of research has examined changes in annual, seasonal, monthly and daily rainfall data, whereas studies for sub daily rainfall are limited. The main findings are that there is an increase in annual rainfall in the northern parts of Australia whereas eastern and southwest regions exhibit decreasing trends in annual rainfall [26]-[32]. Tasmania has complex spatial rainfall patterns [33]. Consequently, understanding and making future projections of Tasmanian rainfall are challenging. Rainfall variability is influenced by various remote drivers [e.g. El Nino–Southern Oscillation (ENSO), Southern Hemisphere Annular Mode (SAM), Indian Ocean Dipole (IOD)] [34]. There have been limited studies on Tasmanian rainfalls as compared with mainland Australia. Many researchers have highlighted the role of the westerly airstream in conveying air across Tasmania’s west coast where it undergoes lifting over the rugged topography resulting in higher annual rainfall over the western highlands. However, there is a significant ‘rain shadow’ over parts of eastern Tasmania and the midlands [35]-[37]. In regards to the projections for changes to rainfall in Tasmania, the increase in precipitation may be confined to the west coast with stronger winds contributing to greater evaporation [38]. Godfred-Spenning and Gibson [39] have conducted an analysis of the synoptic weather systems which produce rainfall over the 'Hydro' catchments and concluded that over the period of the study, there were no significant trends in the data; however, the frequency of occurrence of ‘northerly depressions’ had increased. Tasmania has experienced two wet periods in the 1950s and in the 1970s, and a dry decade in the 1940s. According to Srikanthan & Stewart [40] in the period 1910 to 1990, there were no statistically significant trends in the mean annual rainfall in Tasmania. Downward trends in rainfall over the period 1970 to 1990 was present, and this has continued from 1990 to 2007 [37]. Orpita U. Laz, Ataur Rahman Trends in Extreme Rainfall Events in Tasmania, Australia I World Academy of Science, Engineering and Technology International Journal of Environmental and Ecological Engineering Vol:8, No:12, 2014 824 International Scholarly and Scientific Research & Innovation 8(12) 2014 ISNI:0000000091950263 Open Science Index, Environmental and Ecological Engineering Vol:8, No:12, 2014 publications.waset.org/9999827/pdf