Variation trend and response relationship of temperature, precipitation and runoff in Baiyangdian Lake Basin

As the largest freshwater lake in the North China Plain, Baiyangdian Lake is a key hydro-confluence that is critical for flood prevention, sedimentation mitigation, irrigation, water supply and maintenance of ecological balance of the area. Since the 1960s, surface runoff in Baiyangdian Basin has continuously dropped, water quantity greatly reduced and lake-drying frequency increased due to the impact of climate change and human activities. The decreasing water quantity has reduced ecological function of the lake, further affecting socio-economic development and ecological security in the region. Using observed daily temperature and precipitation data at 7 meteorological stations along with monthly runoff data from 3 typical hydrological stations for the period 1957-2012, the change characteristics in temperature, precipitation and runoff in the Baiyangdian Lake Basin were analyzed. In this study, the cumulative anomaly method, Mann-Kendall test and Morlet wavelet analysis method were used to determine the trends and abrupt changes in mean annual temperature, precipitation and runoff. The purpose of this study was to develop data support and reference base for improving ecological environment and reasonable utilization of water resources in the area. The results showed that the climate in the study area had a significant warming trend with an abrupt increase of temperature since 1988. Especially, the increase of temperature in both winter and summer contributed more to temperatures rising. Annual precipitation showed a decreasing trend with obvious fluctuation. The decrease in summer precipitation (1.72 mm·a^-1) was higher than that in the other seasons. Increasing temperature along with decreasing precipitation were the dominant trends, further aggravating dry and hot climatic conditions and lake-drying in the region. There was an obvious decreasing trend in runoff due to the effect of temperature and precipitation. There was a negative correlation between runoff and temperature and a positive correlation between runoff and precipitation at annual scale. At seasonal scale, runoff was positively correlated with temperature and precipitation. Summer runoff in Fuping, Daomaguan and Zijingguan hydrological stations decreased by 0.85 m³·s^-1·a^-1, 0.72 m³·s^-1·a^-1 and 0.66 m³·s^-1·a^-1, respectively. The intervals of change in mean annual temperature, precipitation and runoff were obvious. Also the fluctuations in runoff and precipitation were consistent, suggesting that the response of runoff to precipitation was more prominent. The change in runoff was not only influenced by temperature and precipitation, but also by other climatic factors, water conservancy projects, agriculture and local geological conditions. In future studies, it was needed to further analyze the effect of each factor on the runoff in order to comprehensively understand the driving factors of runoff in the basin.