GROUNDWATER STORAGE IN WESTERN CHINA AND EASTERN TIBET OBSERVED FROM PRECIPITATION-DISCHARGE HYSTERESIS

The hydrological cycle is a crucial element of Earth’s surface processes. Unless we understand how Earth stores the water moving through it as part of the hydrological cycle we cannot determine the availability of this high demand resource.

The purpose of this study is to determine the transitive processes of precipitation to river discharge in western China, on the eastern margin of the Tibetan Plateau. This transfer of water produces a dynamic lag ‘hysteresis’ between the input of precipitation and discharge.

In this context, hysteresis refers to discharge that peaks after the peak precipitation; this is dependent on local conditions and the complicated transport processes inherent to groundwater movement. The relationship between precipitation-discharge hysteresis has important implications for potentially increasing demand for water, decreasing quality of water available, and decreasing availability of groundwater due to climate change. Andermann et al. (2012) analyzed precipitation and discharge data in the Nepali Himalayas, detected hysteresis, and concluded that groundwater storage in aquifers was the driving factor behind the hysteresis. They examined the contributions of precipitation, glacier melt, and snow fall to the annual water budget and found that there is a lag time of approximately 45 days, which suggests the existence of fractured basement aquifers. We applied their original study techniques to our study area in the eastern margin of the Tibetan Plateau by plotting discharge as a function of precipitation for 25 years of daily discharge data collected by the Chinese Hydrology Bureau in two small (<1400 km²) watersheds. The data exhibited a well-defined hysteresis loop and allowed us to infer that precipitation is slowed due to groundwater storage before reemerging as discharge.

Our ongoing analysis includes processing the 25 years of daily data, analyzing the results, and putting them into regional context. We are completing the quantitative analysis to accompany the hysteresis loops showing that groundwater storage occurs in the study area. Our next step will be to analyze and interpret the final results for quantitative confirmation of the hysteresis process. These results will help to better manage the water resources available now as well as plan for future strain on water resources.