The global warming has triggered climate change, which has a certain impact on the redistribution of hydrology and water resources, and may even tilts the ecological balance. This paper sums up the trends of some climate and hydrological indices in several Chinese rivers, namely, temperature, precipitation and runoff, and examines how these indices vary with the time. Then, the wavelet analysis was introduced to disclose the hidden features of temperature, precipitation and runoff time series, revealing certain correlations between these series. As a result, the effect of temperature on precipitation was explored through correlation analysis, so was that of temperature and precipitation on runoff. Finally, the ecological water demands in the upstream, midstream and downstream of the target river were computed, and found to change in a similar way to temperature and precipitation. The research findings shed new light on the maintenance of hydrology and water resources in rivers and the handling of relevant problems.