Attribution analysis of runoff change in Buha River basin based on Budyko hypothesis
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Abstract:
The water cycle is one of the most significant hubs in the interaction among ocean, land and atmosphere, playing a crucial role in how global climate and ecological environment evolved. Watershed hydrological systems have been significantly altered by global climate change and human activities in recent decades. As a result, the attribution analysis of runoff changes in watersheds under the dynamic landscape and the quantitative identification of the contribution rate of the core driving factors of runoff change have emerged as the main research topics for scholars at home and abroad. The Budyko hypothesis-based elastic coefficient approach had been acknowledged as an effective technique for attribution analysis of runoff change, with the attributes of straight forward computation and a clear explanation of physical concepts. Hence, the Buha River basin, a climate change-sensitive region in the northeastern Qinghai-Tibet Plateau is chosen as the research object. Based on the water-heat coupling equilibrium theory of Budyko hypothesis, the contribution of various factors to the change in basin runoff is analyzed and quantified. A scientific foundation for further exploring the hydrological evolution law of the basin and water resources planning is thus formed.Based on the hydrometeorological data of precipitation, runoff and temperature from 1958 to 2018, moving average and linear estimate techniques were used to analyze the trend of the hydrometeorological components. The mutational characteristics of runoff series were analyzed and identified by applying the Mann-Kendall trend test technique and the Pettitt Test method. Derived from the theory of the water-heat coupling equilibrium equation under the Budyko hypothesis, the contribution of various factors to runoff change was analyzed and quantified, and the influence of precipitation intensity, potential evapotranspiration, and underlying surface change on runoff change was quantitatively evaluated, with the main driving factors of runoff change identified. In the Buha River basin, the features of alternating increase and decrease had been indicated from the interannual variation of climatic variables, and the fluctuation grew from 1958 to 2018. An upward trend can be obviously seen from potential evapotranspiration, precipitation, and annual runoff depth, with increased rate of 0.825 mm/a, 1.416 mm/a and 0.536 mm/a respectively. The runoff mutation took place in 2001. Therefore, the runoff sequence was divided into two periods: the reference period (1958-2001) and the change period (2002-2018). The average runoff depth increased by 32.7 mm during the changing period to 83.3 mm, with a 64.5% relative change rate from the reference period. The precipitation increased by 86.4 mm compared with the base period, and the relative change rate was 26.8%. In comparison to the base period, the potential evapotranspiration increased by 50.3 mm, and the relative change rate was 5.5%. The runoff coefficient (R/P) increased compared to the base period, while the drought index (E0/P) declined. Both were greater than 1.0, indicating that the research region was an arid area, nevertheless the dryness decreased year by year. The elastic coefficients of runoff to precipitation, potential evapotranspiration and underlying surface suggested that the Buha River basin was sensitive to the change in precipitation and insensitive to alter potential evapotranspiration, with value of 2.35, ?0.98 and ?1.73 respectively. There has been little change and relative stability in the main land use types, yet there has been some slight variation between them.Precipitation had the greatest influence on runoff, with a contribution rate of 97.12%, accounting for 86.27% of the total. Potential evapotranspiration was contributing at a rate of ?10.85%, and underlying surface was contributing at a rate of 13.73% to runoff. While potential evapotranspiration has a negative impact on the rise in runoff, a positive contribution can be found in the change of precipitation and the underlying surface. The change in precipitation is the main influencing factor of runoff increase in Buha River basin, followed by changes in underlying surface, while the impact of potential evapotranspiration was minimal.Buha?River；Budyko?water-energy?equation；attribution?analysis；runoff?variation；elastic?coefficient
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