Hydrological Extremes Increase during Past 50 years and Regional Climate Significantly Influences Extremes in Headwater of Tarim River

The Tarim River basin is the largest inland river basin in China. Several studies have detected the trends of hydroclimatic variables including annual precipitation, air temperature and runoff time series in the Tarim River basin. However, the hydrologic extremes and their teleconnection have not been studied. Identifying the affected circulation indices to streamflow is very important to predict the occurrence of the hydrologic extremes because of the complex regional terrain environment and atmospheric circulation structure in the arid region of China.

To detect the relations between hydrological extremes and circulation indices, variability and possible relationship between monthly 1-day maximum/minimum flow from headwater of Tarim River basin, climatic indices and regional climate were detected by Mann–Kendall test, continuous wavelet transform, cross-wavelet and wavelet coherence methods. The objectives of this study are to describe changes of hydrological extremes in the headwater of Tarim River, to select the circulation indices which may affect the hydrologic extremes, to apply cross-wavelet and coherence analysis for exploring possible changes in teleconnections as well as the dominant modes in terms of significant power between circulation indices and extremes, and to reveal the relationship between regional climate and hydrological extremes.

The results showed that hydrological extremes have increased during past 50 years, and the trends of 1-day minimum flow were larger than that of 1-day maximum flow. The most significant change occurred in winter. The hydrological extremes exhibited significant 1-year period and 0.5-year period along the whole hydrological series. Different circulation indices may influence the trends of hydrological extremes in different river. The area of polar vortex in North American (i25) and area of Northern Hemisphere polar vortex (i5) showed most significant correlation with 1-day maximum flow and 1-day minimum flow in Aksu River, respectively. In Hotan River, the most significant correlated climate indices with 1-day maximum and minimum flow were Southern oscillation index and area of Northern American Subtropical High (i15), respectively. The area of polar vortex in Atlantic and Europe Sector (i35) showed significant relationships with 1-day minimum flow in Yarkand River. Regions of shared power at 0.8–1.5 year mode were found between selected climate indices and the hydrological extremes, anti-phase relations were detected for most of the series. The fluctuations of temperature have strong effects on hydrological extremes, and significant coherence between regional climate and extremes was found at 0.7–1.5 year scale.

The results of the study provide valuable information for improving the long-term forecasting of the hydrological extremes using its relationship with climate indices. The study was published in Stochastic Environmental Research and Risk Assessment in February  2014.