Evaluation of MSDI bivariate drought index based on precipitation and runoff (Arazkouse and Galikesh stations of Golestan province)

A comprehensive index definition that provides a more complete interpretation of meteorological and hydrological drought is essential. Based on the multivariate drought index (MSDI) was defined in this study based on rainfall and runoff to diagnose meteorological and hydrological droughts. In this regard, two indices, SPI and SSI, were calculated seasonally in the Galikesh and Arazkouse regions in Golestan province. 50-year rainfall and runoff statistics were used for the calculations. The MSDI index was also calculated using joint functions based on flow and precipitation variables. To test the compatibility of the MSDI index with SPI and SSI, the degree of correlation, trend, and change points were checked using Mann-Kendall and Pettit tests. The results showed that while there was no perfect correlation between the SPI and SSI indices, the MSDI index had a high correlation with both of them. The degree of correlation varied in different seasons and stations. Even in the worst case where SPI and SSI had no significant correlation, the MSDI index created a 62% correlation with SPI in Galikesh. The trend and mutation results were in good agreement in the two stations. At Arazkouse station, SPI had no trend, SSI only in spring, and MSDI had a trend in spring and summer. At Galikesh station, MSDI didn’t have a trend in any season, SPI had a trend in autumn, and SSI in spring. The MSDI index was similar to SPI and SSI indices in cases where they showed the same dry conditions. Otherwise, it was consistent with the index that showed a drier condition. Additionally, the MSDI index had a tendency to show drier seasons. In conclusion, the MSDI index can be considered a suitable index for the simultaneous analysis of meteorology and hydrology drought.