The nonlinear hydro-climatic process in the Yarkand River, northwestern China

Based on the hydrologic and meteorological data in the Yarkand River Basin during 1957-2008, the nonlinear hydro-climatic process was analyzed by a comprehensive method, including the Mann-Kendall trend test, wavelet analysis, wavelet regression analysis and correlation dimension. The main findings are as following: (1) The annual runoff, annual average temperature and annual precipitation showed an increasing trend during the period of 1957-2008, and the average increase extent in runoff, temperature and precipitation was 2. 234 × 10⁸m³/10 year, 0. 223 °C/10 year, and 4. 453 mm/10 year, respectively. (2) The nonlinear pattern of runoff, temperature and precipitation was scale-dependent with time. In other words, the annual runoff, annual average temperature and annual precipitation at five time scales resulted in five patterns of nonlinear variations respectively. (3) Although annual runoff, annual average temperature and annual precipitation presented nonlinear variations at different time scales, the runoff has a linear correlation with the temperature and precipitation. (4) The hydro-climatic process of the Yarkand River is chaotic dynamic system, in which the correlation dimension of annual runoff, annual average temperature and annual precipitation is 3. 2118, 2. 999 and 2. 992 respectively. None of the correlation dimensions is an integer, and it indicates that the hydro-climatic process has the fractal characteristics.