Relationships between meteorological and hydrological drought in a young-glacial zone (north-western Poland)based on Standardised Precipitation Index (SPI) and Standardized Runoff Index (SRI)

This study aims to indicate the relationship between meteorological drought and hydrological drought on the example of a lakeland catchment in north-western Poland. The Standardised Precipitation Index (SPI) and Standardised Runoff Index (SRI) were used to identify drought during 1-, 3-, 6-, 9- and 12-month cumulation periods. In the study period 1971–2015, 13 to 62 meteorological droughts and 6 to 21 hydrological droughts were identified. The highest number of droughts occurred for the shortest cumulation period (1 month) and the lowest number for the longest cumulation period (12 months). The relationship between SPI and SRI coefficients over the annual course was strongest for the 9-month cumulation period. The highest correlation coefficient was obtained for February.

Assessment of hydrological drought based on nonstationary runoff data

A nonstationary standardized runoff index (NSRI) is proposed by using the GAMLSS framework to assess the hydrological drought under nonstationary conditions. The definition of the NSRI is similar to that of SRI, but using a nonstationary Gamma distribution by incorporating meteorological variables and antecedent runoff as covariates to describe the characteristics of runoff series. The new drought index is then applied to the upper reach of the Heihe River basin. Four models are developed, in which one is stationary, and the other three are nonstationary with one, two and three covariates, respectively. Results show that, for the nonstationary runoff series, the nonstationary models are more robust and reliable than the stationary one. Among these models, the model with two covariates performs the best. For the model with one covariate, the precipitation shows better in the fitting as a covariate in rainy seasons, and the antecedent runoff shows better in dry seasons. The NSRI identifies more drought events than SRI does, and the drought conditions in our case are mainly affected by precipitation. It is proved that the proposed new drought index is a more effective method for drought assessments under nonstationary conditions.

Regional drought assessment using a distributed hydrological model coupled with Standardized Runoff Index

Drought assessment is essential for coping with frequent droughts nowadays. Owing to the large spatio-temporal variations in hydrometeorology in most regions in China, it is very necessary to use a physically-based hydrological model to produce rational spatial and temporal distributions of hydro-meteorological variables for drought assessment. In this study, the large-scale distributed hydrological model Variable Infiltration Capacity (VIC) was coupled with a modified standardized runoff index (SRI) for drought assessment in the Weihe River basin, northwest China. The result indicates that the coupled model is capable of reasonably reproducing the spatial distribution of drought occurrence. It reflected the spatial heterogeneity of regional drought and improved the physical mechanism of SRI. This model also has potential for drought forecasting, early warning and mitigation, given that accurate meteorological forcing data are available.