Study of the Spatiotemporal Characteristics of Meltwater Contribution to the Total Runoff in the Upper Changjiang River Basin

Yuan-Hao Fang,Xingnan Zhang,Tao Zhang,Guo-Yue Niu,Jinfeng Zhu,Wenzhi Zeng

doi:10.3390/w9030165

Abstract

Melt runoff (MR) contributes significantly to the total runoff in many river basins. Knowledge of the meltwater contribution (MCR, defined as the ratio of MR to the total runoff) to the total runoff benefits water resource management and flood control. A process-based land surface model, Noah-MP, was used to investigate the spatiotemporal characteristics of MR and MCR in the Upper Changjiang River (as known as Yangtze River) Basin (UCRB) located in southwestern China. The model was first calibrated and validated using snow cover fraction (SCF), runoff, and evapotranspiration (ET) data. The calibrated model was then used to perform two numerical experiments from 1981 to 2010: control experiment that considers MR and an alternative experiment that MR is removed. The difference between two experiments was used to quantify MR and MCR. The results show that in the entire UCRB, MCR was approximately 2.0% during the study period; however, MCR exhibited notable spatiotemporal variability. Four sub-regions over the Qinghai-Tibet Plateau (QTP) showed significant annual MCR ranging from 3.9% to 6.0%, while two sub-regions in the low plain regions showed negligible annual MCR. The spatial distribution of MCR was generally consistent with the distribution of glaciers and elevation distribution. Mann-Kendall (M-K) tests of the long-term annual MCR indicated that the four sub-regions in QTP exhibited increasing trends ranging from 0.01%/year to 0.21%/year during the study period but only one displayed statistically significant trend. No trends were found for the peak time (PT) of MR and MCR, in contrast, advancing trend were observed for the center time (CT) of MR, ranging from 0.01 months/year to 0.02 months/year. These trends are related to the changes of air temperature and precipitation in the study area.

Highlights

Precipitation in the form of rainfall can trigger runoff generation process when it reaches the land surface and a specific threshold is satisfied, e.g., the rainfall intensity exceeds the infiltration capacity of the soil or rainfall occurs in an area with saturated soil
We mainly focus on the runoff and snow processes because they are directly related to our analysis of Melt runoff (MR) and MCR
By further analyzing the corresponding climatology temporal variation in MR (Figure 5k–m; black dashed line), we found that the lag time between the MCR peaks of JSJSY and YLJ resulted from MR variation, which is related to the air temperature differences

Summary

Introduction

Precipitation in the form of rainfall can trigger runoff generation process when it reaches the land surface and a specific threshold is satisfied, e.g., the rainfall intensity exceeds the infiltration capacity of the soil or rainfall occurs in an area with saturated soil. Precipitation in the form of snowfall is stored on the land surface and does not release water until atmospheric conditions reach a specific combined threshold and melting occurs. MR can result in flood events during the spring and summer [5,6]. These events complicate reservoir operation and flood control. The response of snow/glaciers to climate change (mainly changing temperature and precipitation) which affect the MR and the entire hydrological cycle is becoming more complicated [7,8]

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