Background As sole surface edible water source area, Miyun Reservoir plays an critical role in urban sustainable development of Beijing. The previous studies, however, limited by sparse distribution and data missing of ground hydrometorological observation stations, could not delineate the hydrometeorological characterisitics systematically and totally in the catchment of Miyun Reservior, accurate and confident data for ecohydrological models parameterization at watershed scale are not available as well. It is neccessary to study long-term trend of related hydrometeorological parameters.

Methods Using PERSIANN-CDR (Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks-Climate Data Record) precipitation dataset and derivative standardized precipitation index (SPI) at 1-, 3-, 6- and 12-month scales, we analyzed spatio-temporal pattern of precipitation and drought in 1983-2017 and further tested their significance (at 0.05 level) based on time series datasets with contextual Mann-Kendall (M-K) method.

Results 1) We divided annual precipitation into three stages as year 1983-1998, year 1999-2009 and year 2010-2017, among which annual precipitation had greater fluctuation around multi-year mean during year 1983-1998, annual precipitation was lower than multi-year mean during year 1999-2009, and annual precipitation had smaller fluctuation around multi-year mean during year 2010-2017, annual precipitation fluctuated around the multi-year mean precipitation (479.37 mm) with insignificant trend statistically, even if a continuous decreasing existed in the first 10 years of this century. 2) Monthly precipitation occurred mainly from July to September with maximum in July, spatially, greater precipitation occurred in northern and northeastern parts, while small precipitation occurred in southwestern part. M-K test result shows that monthly precipitation increased with insignificant trend statistically in the whole catchment. Grid-based SPI values at 4 scales (1-, 3-, 6- and 12-months) showed that drought events happened occasionally, but intensity was light or medium, no extreme event could be found. In the meantime, three continuous drought events happened during study period coincided well with precipitation change trend. 4)M-K test results for SPI at 4 scales show that SPI1, SPI 3 and SPI6 increased and SPI12 decreased with insignificant trends statistically, in other word, drought was characterized by increasing from monthly scale to seasonal scale, then decreasing slightly at half-yearly scale and finally reducing drastically in yearly scale.

Conclusions Totally, annual and monthly precipitation amounts in this catchment fluctuate at spatial scale, no significant change trend in temporal scale can be found. However, a lasting and decadal drought defined by SPI could be detected in start of 21st century which would inevitably affect negatively on key ecological program such as Beijing-Tianjin Sand Source Control Program implemented in this period. In conclusion, this study does reflect the long-term precipitation and drought trend and provide more scientific data on revegetation management and water source area protection in Miyun Reservoir catchment, which can be used to paramerize the ecohydrylogical models at watershed scale. In addition, the effects of drought on ecological project and its ecosystem services especially water quality and quantity should be focused in future research.