Attribution Analysis of Runoff Change in Min-Tuo River Basin based on SWAT model simulations, China

Abstract

To consummate watershed data and better quantify the impact of climate changes and human activities on runoff, we examined the changes and response mechanisms of runoff in the Min-Tuo River Basin, China. In the examination, the Soil and Water Assessment Tool (SWAT) model was used to simulate possible evapotranspiration, actual evapotranspiration, and runoff in 1980, 1990, 1995, 2000, 2005, 2010, and 2015 under different land-use conditions. SWAT weather generator was used to supplement the missing meteorological data. This study presents a quantitative analysis of the climatic and anthropogenic factors contributing to the runoff alteration in the Min-Tuo River Basin using the Budyko methods. The results suggested that the reduced precipitation was the main cause of runoff reduction. The contributions of precipitation, possible evapotranspiration, and underlying surface alterationsof runoff were 56.18%, 37.08%, and 6.74%, respectively. Sensitivity analysis indicated that the runoff alteration was most sensitive to changes of landscape parameters. The aridity index and all the elasticities showed a spatial variations in the Min-Tuo River Basin. The influence of the three factors on runoff reduction varied with seasons. During the high-flow period, changes of the precipitation and possible evapotranspiration and underlying surface had the greatest effect on runoff reduction, while changes of underlying surfaces had the least effect.

Figure 1

Time series of simulated and observed monthly streamflow with respect to precipitation (P) at Shaba, Luding, Shimian, Luzhou, Gaochang, and Zipingpu gaging stations during the calibration and vadidation periods.

Figure 2

Average annual runoff in each of the major sub-basins between 1981 and 2014.

Figure 3

Year of abrupt change in each sub-basin.

Figure 4

The relationships between elastic coefficient of each factor and aridity index, underlying surface parameters. (a,b) Represent Climatic elasticity, Landscape parameter elasticity, respectively(Note: blue, green, red and orange represent the elastic coefficients of all factors in the Dadu, Qingyi, Minjiang and Tuojiang River Basin, respectively).

Figure 5

Aridity index and the elasticities of runoff.

Figure 6

Maps showing the aridity index and elastic coefficient for each factor; (a,b,c,d) Reperesent the aridity index, precipitation elasticity, possible evapotranspiration elasticity and landscape parameter elasticity, respectively. (Note: the maps were generated with data available from the Chinese Geospatial Data Cloud using Matlab (version R2016a; https://cn.mathworks.com/)).

Figure 7

Relative percent change in runoff within each major sub-basin.

Figure 8

(a) Change in annual runoff within the sub-basins; colors refer to contribution of the three factors to the total change); (b) Percent contribution to the change in runoff by the three examined factors within each basin (abscissa denotes 89 sub-basins).

Figure 9

Changes in runoff within the sub-basins to changes in the factors during periods of high flow, normal flow, and low flow. (Note: H, N, L indicate the period of high flow, normal flow and low flow, respectively. (a,b,c) Represent the Changes in runoff within the sub-basins to changes in precipitation, possible evapotranspiration and underlying surfaces, respectively.).

Figure 10

Variation in precipitation (a,b,c) and possible evapotranspiration (d,e,f) within each basin during wet, normal river flow and dry periods.

Figure 11

Average annual rainfall in each basin between 1981 and 2014.

Figure 12

Basin and sub-basin distribution within the study area. (Note: the maps were generated with data available from the Chinese Geospatial Data Cloud using ESRI’s ArcGIS (version 10.1; http://www.gscloud.cn/). And the numbers represent the sub-basin numbers).