Reconstruction of July-September standardized precipitation-evapotranspiration index (SPEI) for the Hindu Kush region of Northern Pakistan

The prolonged drought resulting from global warming is considered an important factor affecting West Asia's socioeconomic growth, with a significant impact on the dynamic forecasting of water supply and forest ecosystems. In such a scenario, understanding historical long-term drought changes is crucial for accurately forecasting regional drought shifts in the Hindukush region. In this study, a 517-year (1506-2022 C.E.) long tree-ring width chronology of the Himalayan Cedar (Cedrus deodara D. Don) from the eastern Hindukush has been developed. The July-September Standardized Precipitation-Evapotranspiration Index (SPEI) has revealed a positive and significant relationship (r = 0.633, p < 0.001) with tree growth, which leads to SPEI reconstruction from AD 1626 in the Hindu Kush region. Our reconstruction model has explained 40.1% of the climate variance during the instrumental period from C.E. 1965 to 2018. Fourteen wet periods (>= 3 years) were observed before the instrumental period, specifically in C.E. 1629-1635, 1638-1658, 1666-1674, 1680-1701, 1715-1724, 1770-1776, 1794-1797, 1802-1810, 1822-1846, 1850-1857, 1872-1881, 1883-1890, 1906-1914, and 1921-1937. Similarly, twelve dry summer periods were also observed in the past 339 years, such as C.E. 1659-1665, 1675-1679, 1702-1714, 1725-1769, 1777-1793, 1798-1801, 1811-1821, 1847-1849, 1858-1871, 1891-1905, 1915-1920, and 1938-1963. Nevertheless, AD 1663 was individually the wettest (with a value of 2.13), while AD 1754 was the driest (-0.99) year. The spatial correlation analysis and its comparisons with Karakoram-Himalayan drought and precipitation reconstructions have convincingly confirmed the reliability of our SPEI reconstruction. Consequently, this reconstruction can effectively serve as a proxy for large-scale drought variability in the Hindu Kush region of northern Pakistan. Our findings strongly suggest the considerable dendrochronological potential for further climatological studies in the western Hindu Kush Mountains System.