Temporal and Spatial Distribution of Evapotranspiration in the Sanjiangyuan Region

doi:10.19657/j.geoscience.1000-8527.2020.075

Abstract

Abstract:

Located in the southern Qinghai Province in China, the Sanjiangyuan region contains the headwaters of the three great rivers of Yangtze, Yellow and Lancang. The Sanjiangyuan region is the highest natural wetland and the largest nature reserve in China, with fragile eco-environment. Groundwater evapotranspiration (ET) assessment is important for evaluating the water cycle and water resource in the region, which is crucial for eco-environmental protection. Based on MODIS data with moderate resolution in this study, the regional ET of the Sanjiangyuan region was estimated for the period of 2001-2017 with the Surface Energy Balance System. The Sen+Mann-Kendall method was used to analyze the temporal-spatial variation trends, and the influencing factors were discussed. The results show that in the Sanjiangyuan region: (1) ET increased from 2001 to 2017; (2) the areas (from highest to lowest annual average ET) are the Lancang River, Yellow River, and the Yangtze River headwaters; (3) over 62.62% of the region has a major ET increasing trend, while 28.03% of the region has a minor increasing trend, and areas with significant ET decrease barely exist; (4) ET variation is positively correlated with precipitation and air temperature, with the correlation coefficients of 0.80 and 0.89, respectively; (5) variation of ET is positively correlated with NDVI and soil moisture.

Key words: evapotranspiration (ET), Surface Energy Balance System, MODIS, Sen+Mann-Kendall, Sanjiangyuan region

CLC Number:

P641.69
X143

GAN Haihong, JIN Xiaomei, ZHANG Xucai, ZHU Xiaoqian. Temporal and Spatial Distribution of Evapotranspiration in the Sanjiangyuan Region[J]. Geoscience, 2021, 35(03): 665-674.

Figures/Tables 15

Fig.1 Geographic map of the study area

Fig.2 Annual variation of actual ET in the study area

Fig.3 Variation of the annual average ET in the study area

Fig.4 Spatial distribution of annual ET in the study area in 2017

Fig.5 Spatial ET variation trend in the study area

Fig.6 Classification of significant ET change in the study area

Table 1 Classification of variation trends

蒸散量变化趋势	程度
β<0且\|Z\|>1.96	显著减小
β<0且\|Z\|≤1.96	轻微减小
0≤β≤6	基本不变
β>6且\|Z\|≤1.96	轻微增长
β>6且\|Z\|>1.96	显著增长

Table 2 Area statistics of ET variation trends in the study area

变化趋势	三江源		长江源		黄河源		澜沧江源
变化趋势	面积/km²	面积占比/%	面积/km²	面积占比/%	面积/km²	面积占比/%	面积/km²	面积占比/%
显著减小	002.31	0	2.05	0	0.26	0	0	0
轻微减小	1 288.86	0.37	524.31	0.31	266.04	0.26	237.58	0.63
基本不变	31 630.46	8.99	13 946.15	8.22	8 421.82	8.32	2 872.81	7.63
轻微增长	98 654.14	28.03	47 847.31	28.21	33 108.50	32.69	8 795.04	23.37
显著增长	220 383.42	62.62	107 261.67	63.25	59 472.94	58.73	25 735.95	68.37

Fig.7 Annual variation of precipitation in the study area

Fig. 8 Effect of precipitation (a) and air temperature (b) on evapotranspiration

Fig.9 Annual (a) and monthly (b) variation of air temperature in the study area

Fig.10 Effect of NDVI on evapotranspiration

Fig.11 Histogram of ET of different land-use types in the study area

Fig.12 Annual variation of soil moisture and ET in the study area

Fig.13 Effect of soil moisture on evapotranspiration

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