Similarity, difference and correlation of meteorological and hydrological drought indices in a humid climate region - the Poyang Lake catchment in China

Based on the estimation of standardized precipitation-evapotranspiration index (SPEI) and standardized runoff index (SRI), this study investigated the variability and correlation of hydrological drought and meteorological drought in a humid climate region - the Poyang Lake catchment in China. Results indicate that the occurrences of hydrological droughts in the catchment are different from those of meteorological drought on both a seasonal and annual basis. However, annual variability of both indices showed the same periodic variation characteristics during the study period. With comparison of the performance of SPEI and SRI time series at different timescales, our observation reveals that the two drought indices show a higher degree of similarity and correlation as timescales increased. In addition, SRI is found to be less variable than SPEI at shorter timescales and it shows an obvious hydrologic delay of about 1-2 months in response to SPEI at timescales > 12 months. Due to hydrologic detention of subsurface soil moisture, shallow groundwater and perhaps reservoir storage, a 2-month timescale of SPEI is found to be more appropriate for river discharge monitoring, especially for those rivers with similar drainage area, climate and geographical conditions as in this study region.