Analysis of hydrological rhythm change based on IHA-RVA method in the upper and middle reaches of Datong River
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Abstract:
River hydrological rhythm reflects the dynamic changes in natural characteristics of water flow and is the key element of the river ecosystem. Recently, the rapid warming of the Qinghai Tibet Plateau has changed the hydrological rhythm of rivers to a certain extent. There is a national aquatic germplasm reserve in Datong River, and the Qilian Mountain area where it is located has an increase of 2.3 ℃ cumulative temperature. Therefore, exploring the changes in hydrological rhythm in the upper and middle reaches of Datong River under climate change has great significance and can play a supporting role in the ecological protection and water resources management of Datong River.There is evidence of the temperature rise rate on the Qinghai Tibet Plateau in the late 1990s. The data of meteorological stations around the upper and middle reaches of Datong River show that the average annual temperature increase rate after 1997 is 10 times before 1997. With the rapid increase in temperature, the relationship between frozen soil, glaciers, and rainfall runoff in Datong River basin has significantly changed. Based on the IHA-RVA method, the abrupt change time of rapid climate warming in the region in 1997 was selected as the dividing point. A total of 32 indicators were selected to analyze the runoff process in 1960-1996 and 1997-2016 for Gadatan / Qingshizui hydrological station. The principal component analysis method was used to remove redundant indicators, and 8 representative indicators were selected to calculate the overall hydrological change.The results show that: (1) April and October are the months of ice melting and freezing, which are directly affected by climate change. The change degree of median flow is 26.3% and 15.8%, respectively, belonging to slight change. The annual minimum flow of 30 d is representative of the annual minimum flow (1 d, 3 d, 7 d, and 90 d) and the median flow in dry season months. The change is significant, and the change degree reaches 100%. (2) The annual average maximum flow in 7 d is representative of the annual average multi-day maximum flow (1 d, 3 d, 30 d, and 90 d). The median value of the maximum flow in 7 d, and is unchanged, but the probability of falling increases between 25% and 75%, and the degree of change reaches 47%, which is a moderate change. The occurrence time of the annual maximum value, i.e. the occurrence time of the annual extreme flow, is averagely advanced by 7 to 9 d, which is a low change. (3) The number of low pulses is equivalent to the number of flow processes below 75% of the frequency, which is reduced from 2 to 1, and the duration is reduced from 49 d to 7 d. The change degree of the number and duration of low pulses is 29.8% and 50.1%, belonging to low and moderate change. The duration of a high pulse is equivalent to the duration of the flow process which is 25% higher than the frequency, increasing from an average of 5.8 d to 7 d, and the degree of change is 24.1%, which belongs to a low degree of change. The rising rate represents the change rate of flow change. The change rate slows down and low-degree changes occur. (4) The overall hydrological change degree of the upper and middle reaches of Datong River is 43%, indicating that the overall change degree of the upper and middle reaches under the influence of climate change has reached a medium level. With the expansion of the melting area, the transformation of water on the frozen layer and water in the frozen layer intensifies the change in the runoff process.
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