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• Extreme precipitation in BJRB showed an obvious upward trend over the past 45 years. • The spatial distribution of water conservation in the BJRB showed an increasing trend from south to north. • Water conservation reflected a significant role in water storage. • Water conservation is affected by extreme precipitation. Water conservation, which has been regarded as one of the most crucial ecosystem service functions of river basins, is a key factor for sustainable development, that has garnered widespread attention in the context of climate change. However, little attention has been paid to daily water conservation and its response to extreme precipitation events. In this study, we selected the Beijiang River Basin (BJRB) as the study area, which is an important ecological barrier for the Guangdong-Hong Kong-Macau Greater Bay Area (GBA), based on the distributed hydrological model WEP-L (Water and Energy transfer Processes in Large River basin) and water balance equation, the spatiotemporal characteristics of extreme precipitation and four daily water conservation indicators (maximum 1 day, maximum 3 day, maximum 5 day, maximum 7 day water conservation) in the BJRB from 1965 to 2009 were analysed, and the responses of these indicators to extreme precipitation were investigated. The results reveal that (1) the amount (RX1day, RX3day, RX5day, RX7day, R95p, and R99p), intensity (SDII), and frequency (R50mm) of extreme precipitation increased in the BJRB during 1965–2009, with SDII undergoing a significant increase. (2) The four water conservation indicators were positive, indicating that the watershed reduced peak flow during the extreme precipitation period by accumulating precipitation. The rate of increase of the four water conservation indicators were lower than that of extreme precipitation indices, there will be more extreme precipitation converted into surface runoff, thereby increasing the risk of flooding. The four indicators increased in the southern and northern regions of the BJRB, while decreased in the central region during 1965–2009. (3) The four indicators were generally positively correlated with most of the extreme precipitation indices in the northern BJRB, especially RX1day, RX3day, RX5day, RX7day, R99p, and R50mm. The results provide a scientific reference for water conservation adaptation to extreme precipitation variations, protection of the ecological environment, and the prevention and reduction of disasters in the region. [ABSTRACT FROM AUTHOR]

• WEP-L model is an effective measure to quantitatively evaluate water conservation. • Multi-temporal scales of water conservation were quantitatively evaluated. • Quantity of water conservation were different under extreme precipitation. • Precipitation was the main factor affecting water conservation. Water conservation is one of the most critical ecosystem service functions of river basins and is an important indicator of regional eco-environmental conditions. Beijiang River Basin (BRB) is an important water source and ecological barrier for the Guangdong-Hong Kong-Macau Greater Bay Area (GBA), and its water conservation function is of widespread concern. In this study, based on the hydrological model WEP-L (Water and Energy transfer Processes in Large River basin), and the water balance principle, we analysed the multiple time-scale characteristics of water conservation in the BRB during 1960–2018 and revealed the response of water conservation to climate change based on scenario setting and hydrological simulation. The results showed that annual water conservation exhibited an insignificant reducing trend of −4.69 mm/10a. Water conservation reduced insignificantly in spring, summer, and autumn, while it showed a nonsignificant increasing trend of 4.69 mm/10a in winter. The spatial distribution of water conservation in the BRB was low in the south and high in the north, mainly due to the spatial distribution of land use. Precipitation was the main factor affecting water conservation. The results can provide a reference for water resource planning and management, and provide a theoretical foundation for ecosystem restoration and reconstruction. [ABSTRACT FROM AUTHOR]