ORIGINAL PAPER Spatio-temporal rainfall variability in the Himalayan mountain catchment of the Bagmati River in Nepal Dinesh Tuladhar 1 & Ashraf Dewan 1 & Michael Kuhn 1 & Robert J. Corner 1 Received: 21 September 2018 /Accepted: 21 August 2019 # Springer-Verlag GmbH Austria, part of Springer Nature 2019 Abstract Rainfall records between 1970 and 2015 from 12 rain gauge stations are used to examine the variability of rainfall patterns in the Himalayan mountain catchment of the Bagmati River. Based on monthly and annual rainfall distributions derived from daily records, this study analyzes the spatial and temporal variation of long-term trends and departures of 5-yearly average rainfall from the long-term mean. Both monthly and annual results show considerable spatial variabilities over rather short distances (< 25 km). Long-term trend results based on the Mann-Kendall test on homogenized time series showed a significant decrease in annual rainfall at four stations and significant increase at one of the stations. The 5-yearly departures from long-term mean showed that most of the stations received higher rainfall in the 1970s while the rainfall between 2005 and 2015 was substantially lower at several stations. Monthly breakdown of long-term trends and 5-yearly departures provided additional insight in rainfall variations that are not necessarily reflected by the annual results. Some stations have significant changes in rainfall for few months even though the annual rainfall does not change significantly, while a few of the significant monthly trends were, in fact, opposite to the annual trend. Month-wise investigation of 5-yearly departures from the long-term mean also suggests that the annual results are cumulative results of varying combinations of monthly changes rather than due to any particular group of months behaving similarly. The valuable information derived from monthly analysis is expected to assist in planning and management of water resources. Keywords Rainfall . Trend . Spatial variation . Climate change . Bagmati . Himalayan mountain . Nepal 1 Introduction Precipitation plays a major role in balancing the fresh water budget of a region. Long-term and seasonal variations in pre- cipitation, combined with spatial variations within a region, can add significant challenges for the understanding and modeling of water resources on global, regional, and even localized scales. Due to increased atmospheric moisture con- tent caused by the increase in global average temperature, it is expected that extreme precipitation events become more fre- quent and intense, especially in mid latitudes and wet tropics (Dore 2005; Pachauri et al. 2014; Stocker 2014). Future var- iability in precipitation related to the El Niño–Southern Oscillation (ENSO) is also expected to intensify at regional scales (Stocker 2014). Some large-scale patterns of precipita- tion changes in different parts of the world have already been linked to climate change (Trenberth 2008). On a global scale, as the result of delayed retreat coupled with either earlier or unchanged onset, monsoon periods are projected to be longer toward the end of the twenty-first century (Stocker 2014). In general, it is projected that many wet regions, especially in mid to high latitude areas, will receive increased precipitation while corresponding dry areas become drier (Dore 2005; Mishra and Herath 2014; Trenberth 2011). In Southeast Asia, average precipitation increased by up to 10% between 1986 and 2005 (Pachauri et al. 2014). Indian monsoon rainfall in peninsular India is expected to increase in future while it may decrease in central India and around the Bay of Bengal (Stowasser et al. 2009). Also, local variations in topography and atmospheric circulation paths can cause significant differences in spatial distribution and long-term changes in regional rainfall (Anders et al. 2006; Barros 2004; Diodato et al. 2010; Gadgil 1977). Analyzing rainfall data between 1961 and 2000 for 141 stations, Jiang et al. * Dinesh Tuladhar Dinesh.tuladhar@postgrad.curtin.edu.au 1 School of Earth and Planetary Sciences, Curtin University, Bentley, Perth, WA 6102, Australia Theoretical and Applied Climatology https://doi.org/10.1007/s00704-019-02985-8