Pathway analysis to quantify the relationship between runoff and meteorological factors in re-identifying seasonality throughout the Ashi River watershed, Northeast China

At the watershed scale, weather types show variability and heterogeneity throughout a basin; as a result, unified weather conditions are not realistic for analyzing the underlying surface response. The Ashi River watershed was selected as a case in the present study, and weather types were redefined. Statistics on the spatial and temporal changes of meteorological factors from 1989 to 2015 and path analysis were used to identify the relationship between meteorological factors and runoff. Results showed that (1) statistical weather analysis revealed multidimensional heterogeneity of season types. The weather was clearly diverse in the sub-basins. The redivided times for the seasons were 61 days for spring, 55 days for summer, 48 days for autumn, 201 days for winter, and a frozen period (spring, summer, autumn) and non-frozen period (winter). (2) Temperature decreased by 0.35 °C over the past 27 years, and it increased gradually from the southeast to the northwest. Precipitation and runoff increased from 1989 to 2015. Mutations in precipitation and runoff occurred in 1994 and 1998. Temperature, precipitation, and runoff varied across frozen and non-frozen periods. (3) In different typical hydrologic years, meteorological factors affected runoff in different ways, and the direct effect of temperature on runoff was larger and positive. Precipitation in the flood year had a significant and direct impact on runoff in the non-frozen period, while evaporation had a significant and indirect impact on runoff in the dry year. The barometric pressure also had different impacts on runoff in the dry and median years. The purpose of this study was to provide scientific guidance for local agricultural production and water distribution.